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Balasubramanian RN, Gao M, Umen J. Identification of cell-type specific alternative transcripts in the multicellular alga Volvox carteri. BMC Genomics 2023; 24:654. [PMID: 37904088 PMCID: PMC10617192 DOI: 10.1186/s12864-023-09558-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2023] [Accepted: 08/06/2023] [Indexed: 11/01/2023] Open
Abstract
BACKGROUND Cell type specialization is a hallmark of complex multicellular organisms and is usually established through implementation of cell-type-specific gene expression programs. The multicellular green alga Volvox carteri has just two cell types, germ and soma, that have previously been shown to have very different transcriptome compositions which match their specialized roles. Here we interrogated another potential mechanism for differentiation in V. carteri, cell type specific alternative transcript isoforms (CTSAI). METHODS We used pre-existing predictions of alternative transcripts and de novo transcript assembly with HISAT2 and Ballgown software to compile a list of loci with two or more transcript isoforms, identified a small subset that were candidates for CTSAI, and manually curated this subset of genes to remove false positives. We experimentally verified three candidates using semi-quantitative RT-PCR to assess relative isoform abundance in each cell type. RESULTS Of the 1978 loci with two or more predicted transcript isoforms 67 of these also showed cell type isoform expression biases. After curation 15 strong candidates for CTSAI were identified, three of which were experimentally verified, and their predicted gene product functions were evaluated in light of potential cell type specific roles. A comparison of genes with predicted alternative splicing from Chlamydomonas reinhardtii, a unicellular relative of V. carteri, identified little overlap between ortholog pairs with alternative splicing in both species. Finally, we interrogated cell type expression patterns of 126 V. carteri predicted RNA binding protein (RBP) encoding genes and found 40 that showed either somatic or germ cell expression bias. These RBPs are potential mediators of CTSAI in V. carteri and suggest possible pre-adaptation for cell type specific RNA processing and a potential path for generating CTSAI in the early ancestors of metazoans and plants. CONCLUSIONS We predicted numerous instances of alternative transcript isoforms in Volvox, only a small subset of which showed cell type specific isoform expression bias. However, the validated examples of CTSAI supported existing hypotheses about cell type specialization in V. carteri, and also suggested new hypotheses about mechanisms of functional specialization for their gene products. Our data imply that CTSAI operates as a minor but important component of V. carteri cellular differentiation and could be used as a model for how alternative isoforms emerge and co-evolve with cell type specialization.
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Affiliation(s)
| | - Minglu Gao
- Donald Danforth Plant Science Center, St. Louis, MO, USA
| | - James Umen
- Donald Danforth Plant Science Center, St. Louis, MO, USA.
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Geng S, Hamaji T, Ferris PJ, Gao M, Nishimura Y, Umen J. A conserved RWP-RK transcription factor VSR1 controls gametic differentiation in volvocine algae. Proc Natl Acad Sci U S A 2023; 120:e2305099120. [PMID: 37436957 PMCID: PMC10629530 DOI: 10.1073/pnas.2305099120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2023] [Accepted: 06/12/2023] [Indexed: 07/14/2023] Open
Abstract
Volvocine green algae are a model for understanding the evolution of mating types and sexes. They are facultatively sexual, with gametic differentiation occurring in response to nitrogen starvation (-N) in most genera and to sex inducer hormone in Volvox. The conserved RWP-RK family transcription factor (TF) MID is encoded by the minus mating-type locus or male sex-determining region of heterothallic volvocine species and dominantly determines minus or male gametic differentiation. However, the factor(s) responsible for establishing the default plus or female differentiation programs have remained elusive. We performed a phylo-transcriptomic screen for autosomal RWP-RK TFs induced during gametogenesis in unicellular isogamous Chlamydomonas reinhardtii (Chlamydomonas) and in multicellular oogamous Volvox carteri (Volvox) and identified a single conserved ortho-group we named Volvocine Sex Regulator 1 (VSR1). Chlamydomonas vsr1 mutants of either mating type failed to mate and could not induce expression of key mating-type-specific genes. Similarly, Volvox vsr1 mutants in either sex could initiate sexual embryogenesis, but the presumptive eggs or androgonidia (sperm packet precursors) were infertile and unable to express key sex-specific genes. Yeast two-hybrid assays identified a conserved domain in VSR1 capable of self-interaction or interaction with the conserved N terminal domain of MID. In vivo coimmunoprecipitation experiments demonstrated association of VSR1 and MID in both Chlamydomonas and Volvox. These data support a new model for volvocine sexual differentiation where VSR1 homodimers activate expression of plus/female gamete-specific-genes, but when MID is present, MID-VSR1 heterodimers are preferentially formed and activate minus/male gamete-specific-genes.
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Affiliation(s)
- Sa Geng
- Donald Danforth Plant Science Center, St Louis, MO63132
| | - Takashi Hamaji
- Donald Danforth Plant Science Center, St Louis, MO63132
- Department of Botany, Graduate School of Science, Kyoto University, Kyoto606-8502, Japan
- Research and Development Initiative, Chuo University, Bunkyo-ku, Tokyo112-8551, Japan
| | | | - Minglu Gao
- Donald Danforth Plant Science Center, St Louis, MO63132
| | - Yoshiki Nishimura
- Department of Botany, Graduate School of Science, Kyoto University, Kyoto606-8502, Japan
| | - James Umen
- Donald Danforth Plant Science Center, St Louis, MO63132
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Tanno A, Tokutsu R, Arakaki Y, Ueki N, Minagawa J, Yoshimura K, Hisabori T, Nozaki H, Wakabayashi KI. The four-celled Volvocales green alga Tetrabaena socialis exhibits weak photobehavior and high-photoprotection ability. PLoS One 2021; 16:e0259138. [PMID: 34699573 PMCID: PMC8547699 DOI: 10.1371/journal.pone.0259138] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2021] [Accepted: 10/13/2021] [Indexed: 11/28/2022] Open
Abstract
Photo-induced behavioral responses (photobehaviors) are crucial to the survival of motile phototrophic organisms in changing light conditions. Volvocine green algae are excellent model organisms for studying the regulatory mechanisms of photobehavior. We recently reported that unicellular Chlamydomonas reinhardtii and multicellular Volvox rousseletii exhibit similar photobehaviors, such as phototactic and photoshock responses, via different ciliary regulations. To clarify how the regulatory systems have changed during the evolution of multicellularity, we investigated the photobehaviors of four-celled Tetrabaena socialis. Surprisingly, unlike C. reinhardtii and V. rousseletii, T. socialis did not exhibit immediate photobehaviors after light illumination. Electrophysiological analysis revealed that the T. socialis eyespot does not function as a photoreceptor. Instead, T. socialis exhibited slow accumulation toward the light source in a photosynthesis-dependent manner. Our assessment of photosynthetic activities showed that T. socialis chloroplasts possess higher photoprotection abilities against strong light than C. reinhardtii. These data suggest that C. reinhardtii and T. socialis employ different strategies to avoid high-light stress (moving away rapidly and gaining photoprotection, respectively) despite their close phylogenetic relationship.
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Affiliation(s)
- Asuka Tanno
- Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, Yokohama, Japan
- School of Life Science and Technology, Tokyo Institute of Technology, Yokohama, Japan
| | - Ryutaro Tokutsu
- Division of Environmental Photobiology, National Institute for Basic Biology, Okazaki, Japan
- Faculty of Life Science, Department of Basic Biology, The Graduate University for Advanced Studies, SOKENDAI, Okazaki, Japan
| | - Yoko Arakaki
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Tokyo, Japan
| | - Noriko Ueki
- Science Research Center, Hosei University, Tokyo, Japan
| | - Jun Minagawa
- Division of Environmental Photobiology, National Institute for Basic Biology, Okazaki, Japan
- Faculty of Life Science, Department of Basic Biology, The Graduate University for Advanced Studies, SOKENDAI, Okazaki, Japan
| | - Kenjiro Yoshimura
- Department of Machinery and Control Systems, College of Systems Engineering and Science, Shibaura Institute of Technology, Saitama, Japan
| | - Toru Hisabori
- Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, Yokohama, Japan
- School of Life Science and Technology, Tokyo Institute of Technology, Yokohama, Japan
| | - Hisayoshi Nozaki
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Tokyo, Japan
- Biodiversity Division, National Institute for Environmental Studies, Tsukuba, Japan
| | - Ken-ichi Wakabayashi
- Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, Yokohama, Japan
- School of Life Science and Technology, Tokyo Institute of Technology, Yokohama, Japan
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König SG, Nedelcu AM. The genetic basis for the evolution of soma: mechanistic evidence for the co-option of a stress-induced gene into a developmental master regulator. Proc Biol Sci 2020; 287:20201414. [PMID: 33259762 DOI: 10.1098/rspb.2020.1414] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
In multicellular organisms with specialized cells, the most significant distinction among cell types is between reproductive (germ) cells and non-reproductive/somatic cells (soma). Although soma contributed to the marked increase in complexity of many multicellular lineages, little is known about its evolutionary origins. We have previously suggested that the evolution of genes responsible for the differentiation of somatic cells involved the co-option of life history trade-off genes that in unicellular organisms enhanced survival at a cost to immediate reproduction. In the multicellular green alga, Volvox carteri, cell fate is established early in development by the differential expression of a master regulatory gene known as regA. A closely related RegA-Like Sequence (RLS1) is present in its single-celled relative, Chlamydomonas reinhardtii. RLS1 is expressed in response to stress, and we proposed that an environmentally induced RLS1-like gene was co-opted into a developmental pathway in the lineage leading to V. carteri. However, the exact evolutionary scenario responsible for the postulated co-option event remains to be determined. Here, we show that in addition to being developmentally regulated, regA can also be induced by environmental cues, indicating that regA has maintained its ancestral regulation. We also found that the absence of a functional RegA protein confers increased sensitivity to stress, consistent with RegA having a direct or indirect role in stress responses. Overall, this study (i) provides mechanistic evidence for the co-option of an environmentally induced gene into a major developmental regulator, (ii) supports the view that major morphological innovations can evolve via regulatory changes and (iii) argues for the role of stress in the evolution of multicellular complexity.
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Affiliation(s)
- Stephan G König
- Department of Biology, University of New Brunswick, Fredericton, Canada E3B 5A3
| | - Aurora M Nedelcu
- Department of Biology, University of New Brunswick, Fredericton, Canada E3B 5A3
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Mahdavi S, Razeghi J, Pazhouhandeh M, Movafeghi A, Kosari-Nasab M, Kianianmomeni A. Characterization of two predicted DASH-related proteins from the green alga Volvox carteri provides new insights into their light-mediated transcript regulation and DNA repair activity. ALGAL RES 2020. [DOI: 10.1016/j.algal.2020.102116] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Abstract
The transition of life from single cells to more complex multicellular forms has occurred at least two dozen times among eukaryotes and is one of the major evolutionary transitions, but the early steps that enabled multicellular life to evolve and thrive remain poorly understood. Volvocine green algae are a taxonomic group that is uniquely suited to investigating the step-wise acquisition of multicellular organization. The multicellular volvocine species Volvox carteri exhibits many hallmarks of complex multicellularity including complete germ–soma division of labor, asymmetric cell divisions, coordinated tissue-level morphogenesis, and dimorphic sexes—none of which have obvious analogs in its closest unicellular relative, the model alga Chlamydomonas reinhardtii. Here, I summarize some of the key questions and areas of study that are being addressed with Volvox carteri and how increasing genomic information and methodologies for volvocine algae are opening up the entire group as an integrated experimental system for exploring the evolution of multicellularity and more.
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Affiliation(s)
- James G Umen
- Donald Danforth Plant Science Center, 975 N. Warson Rd, St. Louis, MO 63132 USA
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7
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Uppal G, Vural DC. Evolution of specialized microbial cooperation in dynamic fluids. J Evol Biol 2020; 33:256-269. [DOI: 10.1111/jeb.13593] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2019] [Revised: 01/16/2020] [Accepted: 01/20/2020] [Indexed: 12/28/2022]
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Embryogenesis of flattened colonies implies the innovation required for the evolution of spheroidal colonies in volvocine green algae. BMC Evol Biol 2019; 19:120. [PMID: 31185890 PMCID: PMC6560780 DOI: 10.1186/s12862-019-1452-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2019] [Accepted: 05/31/2019] [Indexed: 12/27/2022] Open
Abstract
Background Volvocine algae provide a suitable model for investigation of the evolution of multicellular organisms. Within this group, evolution of the body plan from flattened to spheroidal colonies is thought to have occurred independently in two different lineages, Volvocaceae and Astrephomene. Volvocacean species undergo inversion to form a spheroidal cell layer following successive cell divisions during embryogenesis. During inversion, the daughter protoplasts change their shape and develop acute chloroplast ends (opposite to basal bodies). By contrast, Astrephomene does not undergo inversion; rather, its daughter protoplasts rotate during successive cell divisions to form a spheroidal colony. However, the evolutionary pathways of these cellular events involved in the two tactics for formation of spheroidal colony are unclear, since the embryogenesis of extant volvocine genera with ancestral flattened colonies, such as Gonium and Tetrabaena, has not previously been investigated in detail. Results We conducted time-lapse imaging by light microscopy and indirect immunofluorescence microscopy with staining of basal bodies, nuclei, and microtubules to observe embryogenesis in G. pectorale and T. socialis, which form 16-celled or 4-celled flattened colonies, respectively. In G. pectorale, a cup-shaped cell layer of the 16-celled embryo underwent gradual expansion after successive cell divisions, with the apical ends (position of basal bodies) of the square embryo’s peripheral protoplasts separated from each other. In T. socialis, on the other hand, there was no apparent expansion of the daughter protoplasts in 4-celled embryos after successive cell divisions, however the two pairs of diagonally opposed daughter protoplasts shifted slightly and flattened after hatching. Neither of these two species exhibited rotation of daughter protoplasts during successive cell divisions as in Astrephomene or the formation of acute chloroplast ends of daughter protoplasts as in volvocacean inversion. Conclusions The present results indicate that the ancestor of Astrephomene might have newly acquired the rotation of daughter protoplasts after it diverged from the ancestor of Gonium, while the ancestor of Volvocaceae might have newly acquired the formation of acute chloroplast ends to complete inversion after divergence from the ancestor of Goniaceae (Gonium and Astrephomene). Electronic supplementary material The online version of this article (10.1186/s12862-019-1452-x) contains supplementary material, which is available to authorized users.
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Gaouda H, Hamaji T, Yamamoto K, Kawai-Toyooka H, Suzuki M, Noguchi H, Minakuchi Y, Toyoda A, Fujiyama A, Nozaki H, Smith DR. Exploring the Limits and Causes of Plastid Genome Expansion in Volvocine Green Algae. Genome Biol Evol 2018; 10:2248-2254. [PMID: 30102347 PMCID: PMC6128376 DOI: 10.1093/gbe/evy175] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/07/2018] [Indexed: 12/25/2022] Open
Abstract
Plastid genomes are not normally celebrated for being large. But researchers are steadily uncovering algal lineages with big and, in rare cases, enormous plastid DNAs (ptDNAs), such as volvocine green algae. Plastome sequencing of five different volvocine species has revealed some of the largest, most repeat-dense plastomes on record, including that of Volvox carteri (∼525 kb). Volvocine algae have also been used as models for testing leading hypotheses on organelle genome evolution (e.g., the mutational hazard hypothesis), and it has been suggested that ptDNA inflation within this group might be a consequence of low mutation rates and/or the transition from a unicellular to multicellular existence. Here, we further our understanding of plastome size variation in the volvocine line by examining the ptDNA sequences of the colonial species Yamagishiella unicocca and Eudorina sp. NIES-3984 and the multicellular Volvox africanus, which are phylogenetically situated between species with known ptDNA sizes. Although V. africanus is closely related and similar in multicellular organization to V. carteri, its ptDNA was much less inflated than that of V. carteri. Synonymous- and noncoding-site nucleotide substitution rate analyses of these two Volvox ptDNAs suggest that there are drastically different plastid mutation rates operating in the coding versus intergenic regions, supporting the idea that error-prone DNA repair in repeat-rich intergenic spacers is contributing to genome expansion. Our results reinforce the idea that the volvocine line harbors extremes in plastome size but ultimately shed doubt on some of the previously proposed hypotheses for ptDNA inflation within the lineage.
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Affiliation(s)
- Hager Gaouda
- Department of Biology, University of Western Ontario, London, Ontario, Canada
| | - Takashi Hamaji
- Department of Biological Sciences, Graduate School of Science, University of Tokyo, Japan
- Department of Biological Sciences, Graduate School of Science, Kyoto University, Japan
| | - Kayoko Yamamoto
- Department of Biological Sciences, Graduate School of Science, University of Tokyo, Japan
| | - Hiroko Kawai-Toyooka
- Department of Biological Sciences, Graduate School of Science, University of Tokyo, Japan
| | - Masahiro Suzuki
- Kobe University Research Center for Inland Seas, Awaji, Hyogo, Japan
| | - Hideki Noguchi
- Center for Genome Informatics, Joint Support-Center for Data Science Research, Research Organization of Information and Systems, Mishima, Shizuoka, Japan
- Advanced Genomics Center, National Institute of Genetics, Mishima, Shizuoka, Japan
| | - Yohei Minakuchi
- Center for Information Biology, National Institute of Genetics, Mishima, Shizuoka, Japan
| | - Atsushi Toyoda
- Advanced Genomics Center, National Institute of Genetics, Mishima, Shizuoka, Japan
- Center for Information Biology, National Institute of Genetics, Mishima, Shizuoka, Japan
| | - Asao Fujiyama
- Advanced Genomics Center, National Institute of Genetics, Mishima, Shizuoka, Japan
| | - Hisayoshi Nozaki
- Department of Biological Sciences, Graduate School of Science, University of Tokyo, Japan
| | - David Roy Smith
- Department of Biology, University of Western Ontario, London, Ontario, Canada
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Geng S, Miyagi A, Umen JG. Evolutionary divergence of the sex-determining gene MID uncoupled from the transition to anisogamy in volvocine algae. Development 2018; 145:dev.162537. [PMID: 29549112 DOI: 10.1242/dev.162537] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2017] [Accepted: 03/13/2018] [Indexed: 12/28/2022]
Abstract
Volvocine algae constitute a unique comparative model for investigating the evolution of oogamy from isogamous mating types. The sex- or mating type-determining gene MID encodes a conserved RWP-RK transcription factor found in either the MT- or male mating locus of dioecious volvocine species. We previously found that MID from the isogamous species Chlamydomonas reinhardtii (CrMID) could not induce ectopic spermatogenesis when expressed heterologously in Volvox carteri females, suggesting coevolution of Mid function with gamete dimorphism. Here we found that ectopic expression of MID from the anisogamous species Pleodorina starrii (PsMID) could efficiently induce spermatogenesis when expressed in V. carteri females and, unexpectedly, that GpMID from the isogamous species Gonium pectorale was also able to induce V. carteri spermatogenesis. Neither VcMID nor GpMID could complement a C. reinhardtii mid mutant, at least partly owing to instability of heterologous Mid proteins. Our data show that Mid divergence was not a major contributor to the transition between isogamy and anisogamy/oogamy in volvocine algae, and instead implicate changes in cis-regulatory interactions and/or trans-acting factors of the Mid network in the evolution of sexual dimorphism.
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Affiliation(s)
- Sa Geng
- Donald Danforth Plant Science Center, 975 N. Warson Rd., St. Louis, MO 63132, USA
| | - Ayano Miyagi
- Donald Danforth Plant Science Center, 975 N. Warson Rd., St. Louis, MO 63132, USA
| | - James G Umen
- Donald Danforth Plant Science Center, 975 N. Warson Rd., St. Louis, MO 63132, USA
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Hamaji T, Kawai-Toyooka H, Uchimura H, Suzuki M, Noguchi H, Minakuchi Y, Toyoda A, Fujiyama A, Miyagishima SY, Umen JG, Nozaki H. Anisogamy evolved with a reduced sex-determining region in volvocine green algae. Commun Biol 2018; 1:17. [PMID: 30271904 PMCID: PMC6123790 DOI: 10.1038/s42003-018-0019-5] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2017] [Accepted: 02/08/2018] [Indexed: 11/09/2022] Open
Abstract
Male and female gametes differing in size-anisogamy-emerged independently from isogamous ancestors in various eukaryotic lineages, although genetic bases of this emergence are still unknown. Volvocine green algae are a model lineage for investigating the transition from isogamy to anisogamy. Here we focus on two closely related volvocine genera that bracket this transition-isogamous Yamagishiella and anisogamous Eudorina. We generated de novo nuclear genome assemblies of both sexes of Yamagishiella and Eudorina to identify the dimorphic sex-determining chromosomal region or mating-type locus (MT) from each. In contrast to the large (>1 Mb) and complex MT of oogamous Volvox, Yamagishiella and Eudorina MT are smaller (7-268 kb) and simpler with only two sex-limited genes-the minus/male-limited MID and the plus/female-limited FUS1. No prominently dimorphic gametologs were identified in either species. Thus, the first step to anisogamy in volvocine algae presumably occurred without an increase in MT size and complexity.
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Affiliation(s)
- Takashi Hamaji
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Bunkyo-ku, Tokyo, 113-0033, Japan
- Department of Biological Sciences, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwakecho, Sakyo-ku, Kyoto, 606-8502, Japan
| | - Hiroko Kawai-Toyooka
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Bunkyo-ku, Tokyo, 113-0033, Japan.
| | - Haruka Uchimura
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Bunkyo-ku, Tokyo, 113-0033, Japan
| | - Masahiro Suzuki
- Kobe University Research Center for Inland Seas, Awaji, Hyogo, 656-2401, Japan
| | - Hideki Noguchi
- Center for Genome Informatics, Joint Support-Center for Data Science Research, Research Organization of Information and Systems, Mishima, Shizuoka, 411-8540, Japan
- Advanced Genomics Center, National Institute of Genetics, Mishima, Shizuoka, 411-8540, Japan
| | - Yohei Minakuchi
- Center for Information Biology, National Institute of Genetics, Mishima, Shizuoka, 411-8540, Japan
| | - Atsushi Toyoda
- Advanced Genomics Center, National Institute of Genetics, Mishima, Shizuoka, 411-8540, Japan
- Center for Information Biology, National Institute of Genetics, Mishima, Shizuoka, 411-8540, Japan
| | - Asao Fujiyama
- Advanced Genomics Center, National Institute of Genetics, Mishima, Shizuoka, 411-8540, Japan
| | - Shin-Ya Miyagishima
- Department of Cell Genetics, National Institute of Genetics, Mishima, Shizuoka, 411-8540, Japan
| | - James G Umen
- Donald Danforth Plant Science Center, 975 N Warson Rd, St. Louis, MO, 63132, USA
| | - Hisayoshi Nozaki
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Bunkyo-ku, Tokyo, 113-0033, Japan.
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Arakaki Y, Fujiwara T, Kawai-Toyooka H, Kawafune K, Featherston J, Durand PM, Miyagishima SY, Nozaki H. Evolution of cytokinesis-related protein localization during the emergence of multicellularity in volvocine green algae. BMC Evol Biol 2017; 17:243. [PMID: 29212441 PMCID: PMC5717801 DOI: 10.1186/s12862-017-1091-z] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2017] [Accepted: 11/24/2017] [Indexed: 01/27/2023] Open
Abstract
BACKGROUND The volvocine lineage, containing unicellular Chlamydomonas reinhardtii and differentiated multicellular Volvox carteri, is a powerful model for comparative studies aiming at understanding emergence of multicellularity. Tetrabaena socialis is the simplest multicellular volvocine alga and belongs to the family Tetrabaenaceae that is sister to more complex multicellular volvocine families, Goniaceae and Volvocaceae. Thus, T. socialis is a key species to elucidate the initial steps in the evolution of multicellularity. In the asexual life cycle of C. reinhardtii and multicellular volvocine species, reproductive cells form daughter cells/colonies by multiple fission. In embryogenesis of the multicellular species, daughter protoplasts are connected to one another by cytoplasmic bridges formed by incomplete cytokinesis during multiple fission. These bridges are important for arranging the daughter protoplasts in appropriate positions such that species-specific integrated multicellular individuals are shaped. Detailed comparative studies of cytokinesis between unicellular and simple multicellular volvocine species will help to elucidate the emergence of multicellularity from the unicellular ancestor. However, the cytokinesis-related genes between closely related unicellular and multicellular species have not been subjected to a comparative analysis. RESULTS Here we focused on dynamin-related protein 1 (DRP1), which is known for its role in cytokinesis in land plants. Immunofluorescence microscopy using an antibody against T. socialis DRP1 revealed that volvocine DRP1 was localized to division planes during cytokinesis in unicellular C. reinhardtii and two simple multicellular volvocine species T. socialis and Gonium pectorale. DRP1 signals were mainly observed in the newly formed division planes of unicellular C. reinhardtii during multiple fission, whereas in multicellular T. socialis and G. pectorale, DRP1 signals were observed in all division planes during embryogenesis. CONCLUSIONS These results indicate that the molecular mechanisms of cytokinesis may be different in unicellular and multicellular volvocine algae. The localization of DRP1 during multiple fission might have been modified in the common ancestor of multicellular volvocine algae. This modification may have been essential for the re-orientation of cells and shaping colonies during the emergence of multicellularity in this lineage.
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Affiliation(s)
- Yoko Arakaki
- Department of Biological Sciences, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
| | - Takayuki Fujiwara
- Department of Cell Genetics, National Institute of Genetics, 1111 Yata, Mishima, Shizuoka, 411-8540, Japan
| | - Hiroko Kawai-Toyooka
- Department of Biological Sciences, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
| | - Kaoru Kawafune
- Department of Biological Sciences, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan.,Department of Life Science and Technology, School of Life Science and Technology, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo, 152-8550, Japan
| | - Jonathan Featherston
- Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, 2000, South Africa.,Agricultural Research Council, Biotechnology Platform, Pretoria, 0040, South Africa
| | - Pierre M Durand
- Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, 2000, South Africa.,Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ, 85721, USA
| | - Shin-Ya Miyagishima
- Department of Cell Genetics, National Institute of Genetics, 1111 Yata, Mishima, Shizuoka, 411-8540, Japan
| | - Hisayoshi Nozaki
- Department of Biological Sciences, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan.
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13
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Klein B, Wibberg D, Hallmann A. Whole transcriptome RNA-Seq analysis reveals extensive cell type-specific compartmentalization in Volvox carteri. BMC Biol 2017; 15:111. [PMID: 29179763 PMCID: PMC5704591 DOI: 10.1186/s12915-017-0450-y] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2017] [Accepted: 10/30/2017] [Indexed: 12/20/2022] Open
Abstract
Background One of evolution’s most important achievements is the development and radiation of multicellular organisms with different types of cells. Complex multicellularity has evolved several times in eukaryotes; yet, in most lineages, an investigation of its molecular background is considerably challenging since the transition occurred too far in the past and, in addition, these lineages evolved a large number of cell types. However, for volvocine green algae, such as Volvox carteri, multicellularity is a relatively recent innovation. Furthermore, V. carteri shows a complete division of labor between only two cell types – small, flagellated somatic cells and large, immotile reproductive cells. Thus, V. carteri provides a unique opportunity to study multicellularity and cellular differentiation at the molecular level. Results This study provides a whole transcriptome RNA-Seq analysis of separated cell types of the multicellular green alga V. carteri f. nagariensis to reveal cell type-specific components and functions. To this end, 246 million quality filtered reads were mapped to the genome and valid expression data were obtained for 93% of the 14,247 gene loci. In the subsequent search for protein domains with assigned molecular function, we identified 9435 previously classified domains in 44% of all gene loci. Furthermore, in 43% of all gene loci we identified 15,254 domains that are involved in biological processes. All identified domains were investigated regarding cell type-specific expression. Moreover, we provide further insight into the expression pattern of previously described gene families (e.g., pherophorin, extracellular matrix metalloprotease, and VARL families). Our results demonstrate an extensive compartmentalization of the transcriptome between cell types: More than half of all genes show a clear difference in expression between somatic and reproductive cells. Conclusions This study constitutes the first transcriptome-wide RNA-Seq analysis of separated cell types of V. carteri focusing on gene expression. The high degree of differential expression indicates a strong differentiation of cell types despite the fact that V. carteri diverged relatively recently from its unicellular relatives. Our expression dataset and the bioinformatic analyses provide the opportunity to further investigate and understand the mechanisms of cell type-specific expression and its transcriptional regulation. Electronic supplementary material The online version of this article (doi:10.1186/s12915-017-0450-y) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Benjamin Klein
- Department of Cellular and Developmental Biology of Plants, University of Bielefeld, Universitätsstr. 25, 33615, Bielefeld, Germany
| | - Daniel Wibberg
- Center for Biotechnology (CeBiTec), University of Bielefeld, Bielefeld, Germany
| | - Armin Hallmann
- Department of Cellular and Developmental Biology of Plants, University of Bielefeld, Universitätsstr. 25, 33615, Bielefeld, Germany.
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14
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Koufopanou V, Bell G. DEVELOPMENTAL MUTANTS OF VOLVOX: DOES MUTATION RECREATE THE PATTERNS OF PHYLOGENETIC DIVERSITY? Evolution 2017; 45:1806-1822. [PMID: 28563961 DOI: 10.1111/j.1558-5646.1991.tb02689.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/1990] [Accepted: 04/19/1991] [Indexed: 11/29/2022]
Abstract
The nature of the variation which is created by mutation can show how the direction of evolution is constrained by internal biases arising from development and pre-existing design. We have attempted to quantify these biases by measuring eight life history characters in developmental mutants of Volvox carteri. Most of the mutants in our sample were inferior to the wild type, but deviated by less than tenfold from the wild-type mean. Characters differed in mutability, suggesting different levels of canalisation. Most correlations between life history characters among strains were positive, but there was a significant negative correlation between the size and the number of reproductive cells, suggesting an upper limit to the total quantity of germ produced by individuals. The most extreme phenotypes in our sample were very vigorous, showing that not all mutations of large effect are unconditionally deleterious. We investigated the effect of developmental constraints on the course of evolution by comparing the variance and covariance patterns among mutant strains with those among species in the family Volvocaceae. A close correspondence between patterns at these two levels would suggest that pre-existing design has a strong influence on evolution, while little or no correspondence shows the action of selection. The variance generated by mutation was equal to that generated by speciation in the family Volvocaceae, the genus Volvox, or the section Merillosphaera, depending on the character considered. We found that mutation changes the volume of somatic tissue independently of the quantity of germ tissue, so that the interspecific correlation between soma and germ can be attributed to selection. The negative correlation between size and number of germ cells among mutants of V. carteri is also seen among the larger members of the family (Volvox spp.), but not among the smaller members, suggesting a powerful design constraint that may be responsible for the absence of larger forms in the entire group.
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Affiliation(s)
- Vassiliki Koufopanou
- Department of Biology, McGill University, 1205 Avenue Dr. Penfield, Montreal, Quebec, H3A 1B1, CANADA
| | - Graham Bell
- Department of Biology, McGill University, 1205 Avenue Dr. Penfield, Montreal, Quebec, H3A 1B1, CANADA
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15
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Hamaji T, Kawai-Toyooka H, Toyoda A, Minakuchi Y, Suzuki M, Fujiyama A, Nozaki H, Smith DR. Multiple Independent Changes in Mitochondrial Genome Conformation in Chlamydomonadalean Algae. Genome Biol Evol 2017; 9:993-999. [PMID: 31972029 PMCID: PMC5398295 DOI: 10.1093/gbe/evx060] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/20/2017] [Indexed: 12/15/2022] Open
Abstract
Chlamydomonadalean green algae are no stranger to linear mitochondrial genomes, particularly members of the Reinhardtinia clade. At least nine different Reinhardtinia species are known to have linear mitochondrial DNAs (mtDNAs), including the model species Chlamydomonas reinhardtii. Thus, it is no surprise that some have suggested that the most recent common ancestor of the Reinhardtinia clade had a linear mtDNA. But the recent uncovering of circular-mapping mtDNAs in a range of Reinhardtinia algae, such as Volvox carteri and Tetrabaena socialis, has shed doubt on this hypothesis. Here, we explore mtDNA sequence and structure within the colonial Reinhardtinia algae Yamagishiella unicocca and Eudorina sp. NIES-3984, which occupy phylogenetically intermediate positions between species with opposing mtDNA mapping structures. Sequencing and gel electrophoresis data indicate that Y. unicocca has a linear monomeric mitochondrial genome with long (3 kb) palindromic telomeres. Conversely, the mtDNA of Eudorina sp., despite having an identical gene order to that of Y. unicocca, assembled as a circular-mapping molecule. Restriction digests of Eudorina sp. mtDNA supported its circular map, but also revealed a linear monomeric form with a matching architecture and gene order to the Y. unicocca mtDNA. Based on these data, we suggest that there have been at least three separate shifts in mtDNA conformation in the Reinhardtinia, and that the common ancestor of this clade had a linear monomeric mitochondrial genome with palindromic telomeres.
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Affiliation(s)
- Takashi Hamaji
- Department of Biological Sciences, Graduate School of Science, the University of Tokyo, Bunkyo-ku, Tokyo, Japan
| | - Hiroko Kawai-Toyooka
- Department of Biological Sciences, Graduate School of Science, the University of Tokyo, Bunkyo-ku, Tokyo, Japan
| | - Atsushi Toyoda
- Advanced Genomics Center, National Institute of Genetics, Mishima, Shizuoka, Japan.,Center for Information Biology, National Institute of Genetics, Mishima, Shizuoka, Japan
| | - Yohei Minakuchi
- Center for Information Biology, National Institute of Genetics, Mishima, Shizuoka, Japan
| | - Masahiro Suzuki
- Kobe University Research Center for Inland Seas, Awaji, Hyogo, Japan
| | - Asao Fujiyama
- Advanced Genomics Center, National Institute of Genetics, Mishima, Shizuoka, Japan
| | - Hisayoshi Nozaki
- Department of Biological Sciences, Graduate School of Science, the University of Tokyo, Bunkyo-ku, Tokyo, Japan
| | - David Roy Smith
- Department of Biology, University of Western Ontario, London, Ontario, Canada
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16
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Nishimura M, Nagashio R, Sato Y, Hasegawa T. Late Somatic Gene 2 disrupts parental spheroids cooperatively with Volvox hatching enzyme A in Volvox. PLANTA 2017; 245:183-192. [PMID: 27699488 DOI: 10.1007/s00425-016-2599-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2016] [Accepted: 09/27/2016] [Indexed: 06/06/2023]
Abstract
We identified LSG2 as a novel lytic enzyme that accumulates in the parental extracellular matrix and disrupts parental spheroids cooperatively with VheA secreted by juveniles in Volvox. Spatiotemporally restricted degradation of extracellular matrix (ECM) is essential for development and survival in multicellular organisms. In an asexual life cycle of green algae Volvox, juveniles are released from parental spheroids through holes made by restricted degradation of parental ECM at the proper timing. Lytic enzyme(s) should specifically degrade parental ECM upon Volvox hatching, but little is known about the mechanisms of spatiotemporally restricted parental degradation. Here, we identified a glycoprotein encoded by the Late Somatic Gene 2 (LSG2) as a novel lytic enzyme that accumulates in parental ECM during the prehatching stages. The dual action of LSG2 and Volvox hatching enzyme A (VheA), a serine protease secreted by juveniles, causes the degradation of ECM sheets at all stages and destroys even daughter spheroids, while VheA alone disrupts spheroids only in the prehatching stage when LSG2 is accumulated, suggesting that the combination of LSG2 and VheA is sufficient to cause the degradation of ECM sheet. In the prehatching stage, parental spheroids became susceptible to the proteolysis by a mixture of bacterial proteases applied externally, which could be facilitated by LSG2. These results suggest that LSG2 disrupts parental ECM cooperatively with VheA by modifying the parental ECM to make it fragile, and that the appropriate activity of these enzymes is crucial for the parent-specific ECM degradation at the proper timing.
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Affiliation(s)
- Mayuko Nishimura
- Section of Biology, College of Liberal Arts and Sciences, Kitasato University, Sagamihara, Kanagawa, 252-0373, Japan.
| | - Ryo Nagashio
- Department of Applied Tumor Pathology, Graduate School of Medical Sciences, Kitasato University, Kanagawa, 252-0373, Japan
- Department of Molecular Diagnostics, School of Allied Health Sciences, Kitasato University, Kanagawa, 252-0373, Japan
| | - Yuichi Sato
- Department of Applied Tumor Pathology, Graduate School of Medical Sciences, Kitasato University, Kanagawa, 252-0373, Japan
- Department of Molecular Diagnostics, School of Allied Health Sciences, Kitasato University, Kanagawa, 252-0373, Japan
| | - Takayuki Hasegawa
- Section of Biology, College of Liberal Arts and Sciences, Kitasato University, Sagamihara, Kanagawa, 252-0373, Japan
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17
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Matt G, Umen J. Volvox: A simple algal model for embryogenesis, morphogenesis and cellular differentiation. Dev Biol 2016; 419:99-113. [PMID: 27451296 PMCID: PMC5101179 DOI: 10.1016/j.ydbio.2016.07.014] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2016] [Revised: 07/15/2016] [Accepted: 07/15/2016] [Indexed: 11/20/2022]
Abstract
Patterning of a multicellular body plan involves a coordinated set of developmental processes that includes cell division, morphogenesis, and cellular differentiation. These processes have been most intensively studied in animals and land plants; however, deep insight can also be gained by studying development in simpler multicellular organisms. The multicellular green alga Volvox carteri (Volvox) is an excellent model for the investigation of developmental mechanisms and their evolutionary origins. Volvox has a streamlined body plan that contains only a few thousand cells and two distinct cell types: reproductive germ cells and terminally differentiated somatic cells. Patterning of the Volvox body plan is achieved through a stereotyped developmental program that includes embryonic cleavage with asymmetric cell division, morphogenesis, and cell-type differentiation. In this review we provide an overview of how these three developmental processes give rise to the adult form in Volvox and how developmental mutants have provided insights into the mechanisms behind these events. We highlight the accessibility and tractability of Volvox and its relatives that provide a unique opportunity for studying development.
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Affiliation(s)
- Gavriel Matt
- Donald Danforth Plant Science Center, 975 N Warson Rd, St. Louis, MO 63132, USA; Washington University in St. Louis, Division of Biology & Biomedical Science, Campus Box 8226, 660 South Euclid Ave, St. Louis, MO 63110, USA.
| | - James Umen
- Donald Danforth Plant Science Center, 975 N Warson Rd, St. Louis, MO 63132, USA.
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18
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Brumley DR, Polin M, Pedley TJ, Goldstein RE. Metachronal waves in the flagellar beating of Volvox and their hydrodynamic origin. J R Soc Interface 2016; 12:20141358. [PMID: 26040592 PMCID: PMC4528573 DOI: 10.1098/rsif.2014.1358] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Groups of eukaryotic cilia and flagella are capable of coordinating their beating over large scales, routinely exhibiting collective dynamics in the form of metachronal waves. The origin of this behaviour—possibly influenced by both mechanical interactions and direct biological regulation—is poorly understood, in large part due to a lack of quantitative experimental studies. Here we characterize in detail flagellar coordination on the surface of the multicellular alga Volvox carteri, an emerging model organism for flagellar dynamics. Our studies reveal for the first time that the average metachronal coordination observed is punctuated by periodic phase defects during which synchrony is partial and limited to specific groups of cells. A minimal model of hydrodynamically coupled oscillators can reproduce semi-quantitatively the characteristics of the average metachronal dynamics, and the emergence of defects. We systematically study the model's behaviour by assessing the effect of changing intrinsic rotor characteristics, including oscillator stiffness and the nature of their internal driving force, as well as their geometric properties and spatial arrangement. Our results suggest that metachronal coordination follows from deformations in the oscillators' limit cycles induced by hydrodynamic stresses, and that defects result from sufficiently steep local biases in the oscillators' intrinsic frequencies. Additionally, we find that random variations in the intrinsic rotor frequencies increase the robustness of the average properties of the emergent metachronal waves.
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Affiliation(s)
- Douglas R Brumley
- Department of Applied Mathematics and Theoretical Physics, Centre for Mathematical Sciences, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA, UK Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
| | - Marco Polin
- Physics Department, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
| | - Timothy J Pedley
- Department of Applied Mathematics and Theoretical Physics, Centre for Mathematical Sciences, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA, UK
| | - Raymond E Goldstein
- Department of Applied Mathematics and Theoretical Physics, Centre for Mathematical Sciences, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA, UK
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19
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Sugasawa M, Matsuzaki R, Kawafune K, Takahashi T, Kawachi M, Krienitz L, Nozaki H. Taxonomic Study of Pyrobotrys (Spondylomoraceae, Chlorophyceae) Based on Comparative Morphological and Molecular Analyses of Culture Strains Established Using Novel Methods. CYTOLOGIA 2015. [DOI: 10.1508/cytologia.80.513] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Affiliation(s)
- Mizuho Sugasawa
- Department of Biological Sciences, Graduate School of Science, University of Tokyo
| | - Ryo Matsuzaki
- Department of Biological Sciences, Graduate School of Science, University of Tokyo
- Micorobial Culture Collection, Center for Environmental Biology and Ecosystem Studies,
National Institute for Environmental Studies
| | - Kaoru Kawafune
- Department of Biological Sciences, Graduate School of Bioscience and Biotechnology,
Tokyo Institute of Technology
| | - Toshiyuki Takahashi
- Department of Biological Sciences, Graduate School of Science, University of Tokyo
| | - Masanobu Kawachi
- Micorobial Culture Collection, Center for Environmental Biology and Ecosystem Studies,
National Institute for Environmental Studies
| | - Lothar Krienitz
- Leibniz-Institute of Freshwater Ecology and Inland Fisheries
| | - Hisayoshi Nozaki
- Department of Biological Sciences, Graduate School of Science, University of Tokyo
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20
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Brumley DR, Wan KY, Polin M, Goldstein RE. Flagellar synchronization through direct hydrodynamic interactions. eLife 2014; 3:e02750. [PMID: 25073925 PMCID: PMC4113993 DOI: 10.7554/elife.02750] [Citation(s) in RCA: 120] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Flows generated by ensembles of flagella are crucial to development, motility and sensing, but the mechanisms behind this striking coordination remain unclear. We present novel experiments in which two micropipette-held somatic cells of Volvox carteri, with distinct intrinsic beating frequencies, are studied by high-speed imaging as a function of their separation and orientation. Analysis of time series shows that the interflagellar coupling, constrained by lack of connections between cells to be hydrodynamical, exhibits a spatial dependence consistent with theory. At close spacings it produces robust synchrony for thousands of beats, while at increasing separations synchrony is degraded by stochastic processes. Manipulation of the relative flagellar orientation reveals in-phase and antiphase states, consistent with dynamical theories. Flagellar tracking with exquisite precision reveals waveform changes that result from hydrodynamic coupling. This study proves unequivocally that flagella coupled solely through a fluid can achieve robust synchrony despite differences in their intrinsic properties.DOI: http://dx.doi.org/10.7554/eLife.02750.001.
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Affiliation(s)
- Douglas R Brumley
- Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge, United Kingdom Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, United States
| | - Kirsty Y Wan
- Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge, United Kingdom
| | - Marco Polin
- Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge, United Kingdom Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, United States
| | - Raymond E Goldstein
- Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge, United Kingdom
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21
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Desnitskiy AG. Ontogenetic diversity of colonies and intercellular cytoplasmic bridges in the algae of the genus Volvox. Russ J Dev Biol 2014. [DOI: 10.1134/s106236041404002x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
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22
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Arakaki Y, Kawai-Toyooka H, Hamamura Y, Higashiyama T, Noga A, Hirono M, Olson BJSC, Nozaki H. The simplest integrated multicellular organism unveiled. PLoS One 2013; 8:e81641. [PMID: 24349103 PMCID: PMC3859500 DOI: 10.1371/journal.pone.0081641] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2013] [Accepted: 10/15/2013] [Indexed: 11/18/2022] Open
Abstract
Volvocine green algae represent the "evolutionary time machine" model lineage for studying multicellularity, because they encompass the whole range of evolutionary transition of multicellularity from unicellular Chlamydomonas to >500-celled Volvox. Multicellular volvocalean species including Gonium pectorale and Volvox carteri generally have several common morphological features to survive as integrated multicellular organisms such as "rotational asymmetry of cells" so that the cells become components of the individual and "cytoplasmic bridges between protoplasts in developing embryos" to maintain the species-specific form of the multicellular individual before secretion of new extracellular matrix (ECM). However, these morphological features have not been studied in the four-celled colonial volvocine species Tetrabaena socialis that is positioned in the most basal lineage within the colonial or multicellular volvocine greens. Here we established synchronous cultures of T. socialis and carried out immunofluorescence microscopic and ultrastructural observations to elucidate these two morphological attributes. Based on immunofluorescence microscopy, four cells of the mature T. socialis colony were identical in morphology but had rotational asymmetry in arrangement of microtubular rootlets and separation of basal bodies like G. pectorale and V. carteri. Ultrastructural observations clearly confirmed the presence of cytoplasmic bridges between protoplasts in developing embryos of T. socialis even after the formation of new flagella in each daughter protoplast within the parental ECM. Therefore, these two morphological attributes might have evolved in the common four-celled ancestor of the colonial volvocine algae and contributed to the further increase in cell number and complexity of the multicellular individuals of this model lineage. T. socialis is one of the simplest integrated multicellular organisms in which four identical cells constitute the individual.
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Affiliation(s)
- Yoko Arakaki
- Department of Biological Sciences, Graduate School of Science, University of Tokyo, Bunkyo-ku, Tokyo, Japan
| | - Hiroko Kawai-Toyooka
- Department of Biological Sciences, Graduate School of Science, University of Tokyo, Bunkyo-ku, Tokyo, Japan
| | - Yuki Hamamura
- Division of Biological Science, Graduate School of Science, Nagoya University, Nagoya, Aichi, Japan
| | - Tetsuya Higashiyama
- Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Nagoya, Aichi, Japan
- JST ERATO Higashiyama Live-Holonics Project, Nagoya University, Nagoya, Aichi, Japan
| | - Akira Noga
- Department of Biological Sciences, Graduate School of Science, University of Tokyo, Bunkyo-ku, Tokyo, Japan
| | - Masafumi Hirono
- Department of Biological Sciences, Graduate School of Science, University of Tokyo, Bunkyo-ku, Tokyo, Japan
| | - Bradley J. S. C. Olson
- Division of Biology, Kansas State University, Chalmers, Manhattan, Kansas, United States of America
| | - Hisayoshi Nozaki
- Department of Biological Sciences, Graduate School of Science, University of Tokyo, Bunkyo-ku, Tokyo, Japan
- * E-mail:
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23
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Iida H, Ota S, Inouye I. Cleavage, incomplete inversion, and cytoplasmic bridges in Gonium pectorale (Volvocales, Chlorophyta). JOURNAL OF PLANT RESEARCH 2013; 126:699-707. [PMID: 23455615 DOI: 10.1007/s10265-013-0553-7] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/13/2012] [Accepted: 01/23/2013] [Indexed: 06/01/2023]
Abstract
Multicellularity arose several times in evolution of eukaryotes. The volvocine algae have full range of colonial organization from unicellular to colonies, and thus these algae are well-known models for examining the evolution and mechanisms of multicellularity. Gonium pectorale is a multicellular species of Volvocales and is thought to be one of the first small colonial organisms among the volvocine algae. In these algae, a cytoplasmic bridge is one of the key traits that arose during the evolution of multicellularity. Here, we observed the inversion process and the cytoplasmic bridges in G. pectorale using time-lapse, fluorescence, and electron microscopy. The cytoplasmic bridges were located in the middle region of the cell in 2-, 4-, 8-, and 16-celled stages and in inversion stages. However, there were no cytoplasmic bridges in the mature adult stage. Cytoplasmic bridges and cortical microtubules in G. pectorale suggest that a mechanism of kinesin-microtubule machinery similar to that in other volvocine algae is responsible for inversion in this species.
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Affiliation(s)
- Hitoshi Iida
- Takezono High School, 3-9-1 Takezono, Tsukuba, Ibaraki, Japan.
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24
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Brumley DR, Polin M, Pedley TJ, Goldstein RE. Hydrodynamic synchronization and metachronal waves on the surface of the colonial alga Volvox carteri. PHYSICAL REVIEW LETTERS 2012; 109:268102. [PMID: 23368623 DOI: 10.1103/physrevlett.109.268102] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/05/2012] [Indexed: 06/01/2023]
Abstract
From unicellular ciliates to the respiratory epithelium, carpets of cilia display metachronal waves, long-wavelength phase modulations of the beating cycles, which theory suggests may arise from hydrodynamic coupling. Experiments have been limited by a lack of organisms suitable for systematic study of flagella and the flows they create. Using time-resolved particle image velocimetry, we report the discovery of metachronal waves on the surface of the colonial alga Volvox carteri, whose large size and ease of visualization make it an ideal model organism for these studies. An elastohydrodynamic model of weakly coupled compliant oscillators, recast as interacting phase oscillators, reveals that orbit compliance can produce fast, robust synchronization in a manner essentially independent of boundary conditions, and offers an intuitive understanding of a possible mechanism leading to the emergence of metachronal waves.
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Affiliation(s)
- Douglas R Brumley
- Department of Applied Mathematics and Theoretical Physics, Centre for Mathematical Sciences, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA, United Kingdom
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25
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Solari CA, Drescher K, Goldstein RE. THE FLAGELLAR PHOTORESPONSE IN VOLVOX SPECIES (VOLVOCACEAE, CHLOROPHYCEAE) 1. JOURNAL OF PHYCOLOGY 2011; 47:580-583. [PMID: 27021987 DOI: 10.1111/j.1529-8817.2011.00983.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Steering their swimming direction toward the light is crucial for the viability of Volvox colonies, the larger members of the volvocine algae. While it is known that this phototactic steering is achieved by a difference in behavior of the flagella on the illuminated and shaded sides, conflicting reports suggest that this asymmetry arises either from a change in beating direction or a change in beating frequency. Here, we report direct observations of the flagellar behavior of various Volvox species with different phyletic origin in response to light intensity changes and thereby resolve this controversy: Volvox barberi W. Shaw from the section Volvox sensu Nozaki (2003) changes the direction of the flagellar beating plane, while species encompassed in the group Eudorina (Volvox carteri F. Stein, Volvox aureus Ehrenb., and Volvox tertius Art. Mey.) decrease the flagellar beating frequency, sometimes down to flagellar arrest.
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Affiliation(s)
- Cristian A Solari
- CONICET, Departamento de Biodiversidad y Biología Experimental (FCEyN), Laboratorio de Biología Comparada de Protistas, Universidad de Buenos Aires, Buenos Aires C1428EHA, ArgentinaDepartment of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge CB3 0WA, UK
| | - Knut Drescher
- CONICET, Departamento de Biodiversidad y Biología Experimental (FCEyN), Laboratorio de Biología Comparada de Protistas, Universidad de Buenos Aires, Buenos Aires C1428EHA, ArgentinaDepartment of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge CB3 0WA, UK
| | - Raymond E Goldstein
- CONICET, Departamento de Biodiversidad y Biología Experimental (FCEyN), Laboratorio de Biología Comparada de Protistas, Universidad de Buenos Aires, Buenos Aires C1428EHA, ArgentinaDepartment of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge CB3 0WA, UK
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26
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Solari CA, Drescher K, Ganguly S, Kessler JO, Michod RE, Goldstein RE. Flagellar phenotypic plasticity in volvocalean algae correlates with Péclet number. J R Soc Interface 2011; 8:1409-17. [PMID: 21367778 DOI: 10.1098/rsif.2011.0023] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Flagella-generated fluid stirring has been suggested to enhance nutrient uptake for sufficiently large micro-organisms, and to have played a role in evolutionary transitions to multicellularity. A corollary to this predicted size-dependent benefit is a propensity for phenotypic plasticity in the flow-generating mechanism to appear in large species under nutrient deprivation. We examined four species of volvocalean algae whose radii and flow speeds differ greatly, with Péclet numbers (Pe) separated by several orders of magnitude. Populations of unicellular Chlamydomonas reinhardtii and one- to eight-celled Gonium pectorale (Pe ∼ 0.1-1) and multicellular Volvox carteri and Volvox barberi (Pe ∼ 100) were grown in diluted and undiluted media. For C. reinhardtii and G. pectorale, decreasing the nutrient concentration resulted in smaller cells, but had no effect on flagellar length and propulsion force. In contrast, these conditions induced Volvox colonies to grow larger and increase their flagellar length, separating the somatic cells further. Detailed studies on V. carteri found that the opposing effects of increasing beating force and flagellar spacing balance, so the fluid speed across the colony surface remains unchanged between nutrient conditions. These results lend further support to the hypothesized link between the Péclet number, nutrient uptake and the evolution of biological complexity in the Volvocales.
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Affiliation(s)
- Cristian A Solari
- CONICET, Laboratorio de Biología Comparada de Protistas, Departamento de Biodiversidad y Biología Experimental (FCEN), Universidad de Buenos Aires, C1428EHA Buenos Aires, Argentina
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Rushkin I, Kantsler V, Goldstein RE. Fluid velocity fluctuations in a suspension of swimming protists. PHYSICAL REVIEW LETTERS 2010; 105:188101. [PMID: 21231140 DOI: 10.1103/physrevlett.105.188101] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/05/2010] [Indexed: 05/30/2023]
Abstract
In dilute suspensions of swimming microorganisms the local fluid velocity is a random superposition of the flow fields set up by the individual organisms, which in turn have multipole contributions decaying as inverse powers of distance from the organism. Here we show that the conditions under which the central limit theorem guarantees a Gaussian probability distribution function of velocities are satisfied when the leading force singularity is a Stokeslet, but are not when it is any higher multipole. These results are confirmed by numerical studies and by experiments on suspensions of the alga Volvox carteri, which show that deviations from Gaussianity arise from near-field effects.
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Affiliation(s)
- Ilia Rushkin
- Department of Applied Mathematics and Theoretical Physics, Centre for Mathematical Sciences, University of Cambridge, Wilberforce Raod, Cambridge CB3 0WA, United Kingdom
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Drescher K, Goldstein RE, Michel N, Polin M, Tuval I. Direct measurement of the flow field around swimming microorganisms. PHYSICAL REVIEW LETTERS 2010; 105:168101. [PMID: 21231017 DOI: 10.1103/physrevlett.105.168101] [Citation(s) in RCA: 174] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/03/2010] [Indexed: 05/30/2023]
Abstract
Swimming microorganisms create flows that influence their mutual interactions and modify the rheology of their suspensions. While extensively studied theoretically, these flows have not been measured in detail around any freely-swimming microorganism. We report such measurements for the microphytes Volvox carteri and Chlamydomonas reinhardtii. The minute (∼0.3%) density excess of V. carteri over water leads to a strongly dominant Stokeslet contribution, with the widely-assumed stresslet flow only a correction to the subleading source dipole term. This implies that suspensions of V. carteri have features similar to suspensions of sedimenting particles. The flow in the region around C. reinhardtii where significant hydrodynamic interaction is likely to occur differs qualitatively from a puller stresslet, and can be described by a simple three-Stokeslet model.
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Affiliation(s)
- Knut Drescher
- Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge CB3 0WA, United Kingdom
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Goldstein RE, Polin M, Tuval I. Noise and synchronization in pairs of beating eukaryotic flagella. PHYSICAL REVIEW LETTERS 2009; 103:168103. [PMID: 19905728 DOI: 10.1103/physrevlett.103.168103] [Citation(s) in RCA: 99] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/10/2009] [Indexed: 05/28/2023]
Abstract
It has long been conjectured that hydrodynamic interactions between beating eukaryotic flagella underlie their ubiquitous forms of synchronization; yet there has been no experimental test of this connection. The biflagellate alga Chlamydomonas is a simple model for such studies, as its two flagella are representative of those most commonly found in eukaryotes. Using micromanipulation and high-speed imaging, we show that the flagella of a C. reinhardtii cell present periods of synchronization interrupted by phase slips. The dynamics of slips and the statistics of phase-locked intervals are consistent with a low-dimensional stochastic model of hydrodynamically coupled oscillators, with a noise amplitude set by the intrinsic fluctuations of single flagellar beats.
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Affiliation(s)
- Raymond E Goldstein
- Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA, United Kingdom
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Drescher K, Leptos KC, Tuval I, Ishikawa T, Pedley TJ, Goldstein RE. Dancing volvox: hydrodynamic bound states of swimming algae. PHYSICAL REVIEW LETTERS 2009; 102:168101. [PMID: 19518757 PMCID: PMC4833199 DOI: 10.1103/physrevlett.102.168101] [Citation(s) in RCA: 157] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/14/2009] [Indexed: 05/19/2023]
Abstract
The spherical alga Volvox swims by means of flagella on thousands of surface somatic cells. This geometry and its large size make it a model organism for studying the fluid dynamics of multicellularity. Remarkably, when two nearby Volvox colonies swim close to a solid surface, they attract one another and can form stable bound states in which they "waltz" or "minuet" around each other. A surface-mediated hydrodynamic attraction combined with lubrication forces between spinning, bottom-heavy Volvox explains the formation, stability, and dynamics of the bound states. These phenomena are suggested to underlie observed clustering of Volvox at surfaces.
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Affiliation(s)
- Knut Drescher
- Department of Applied Mathematics, University of Cambridge, Cambridge CB3 0WA, United Kingdom
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Drescher K, Leptos KC, Goldstein RE. How to track protists in three dimensions. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2009; 80:014301. [PMID: 19191449 DOI: 10.1063/1.3053242] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
We present an apparatus optimized for tracking swimming micro-organisms in the size range of 10-1000 microm, in three dimensions (3Ds), far from surfaces, and with negligible background convective fluid motion. Charge coupled device cameras attached to two long working distance microscopes synchronously image the sample from two perpendicular directions, with narrow band dark-field or bright-field illumination chosen to avoid triggering a phototactic response. The images from the two cameras can be combined to yield 3D tracks of the organism. Using additional, highly directional broad-spectrum illumination with millisecond timing control the phototactic trajectories in 3D of organisms ranging from Chlamydomonas to Volvox can be studied in detail. Surface-mediated hydrodynamic interactions can also be investigated without convective interference. Minimal modifications to the apparatus allow for studies of chemotaxis and other taxes.
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Affiliation(s)
- Knut Drescher
- Department of Applied Mathematics and Theoretical Physics, Centre for Mathematical Sciences, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA, United Kingdom
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Solari CA, Michod RE, Goldstein RE. VOLVOX BARBERI, THE FASTEST SWIMMER OF THE VOLVOCALES (CHLOROPHYCEAE)(1). JOURNAL OF PHYCOLOGY 2008; 44:1395-1398. [PMID: 27039854 DOI: 10.1111/j.1529-8817.2008.00603.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Volvox barberi W. Shaw is a volvocalean green alga composed of biflagellated cells. Vovocales with 16 cells or more form spherical colonies, and their largest members have germ-soma separation (all species in the genus Volvox). V. barberi is the largest Volvox species recorded in terms of cell number (10,000-50,000 cells) and has the highest somatic to reproductive cell ratio (S/R). Since they are negatively buoyant, Volvocales need flagellar beating to avoid sinking and to reach light and nutrients. We measured V. barberi swimming speed and total swimming force. V. barberi swimming speeds are the highest recorded so far for volvocine algae (∼600 μm · s(-1) ). With this speed, V. barberi colonies have the potential to perform daily vertical migrations in the water column at speeds of 2-3 m · h(-1) , consistent with what has been reported about Volvox populations in the wild. Moreover, V. barberi data fit well in the scaling relationships derived with the other smaller Volvox species, namely, that the upward swimming speed Vup ∝N(0.28) and the total swimming force FS ∝N(0.77) (N = colony cell number). These allometric relationships have been important supporting evidence for reaching the conclusion that as size increases, colonies have to invest in cell specialization and increase their S/R to increase their motility capabilities to stay afloat and motile.
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Affiliation(s)
- Cristian A Solari
- CONICET Researcher, Laboratorio de Biología Comparada de Protistas, Departamento de Biodiversidad y Biología Experimental (FCEyN), Universidad de Buenos Aires, Buenos Aires, Argentina C1428EHADepartment of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona 85721, USADepartment of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge, CB3 0WA, UK
| | - Richard E Michod
- CONICET Researcher, Laboratorio de Biología Comparada de Protistas, Departamento de Biodiversidad y Biología Experimental (FCEyN), Universidad de Buenos Aires, Buenos Aires, Argentina C1428EHADepartment of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona 85721, USADepartment of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge, CB3 0WA, UK
| | - Raymond E Goldstein
- CONICET Researcher, Laboratorio de Biología Comparada de Protistas, Departamento de Biodiversidad y Biología Experimental (FCEyN), Universidad de Buenos Aires, Buenos Aires, Argentina C1428EHADepartment of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona 85721, USADepartment of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge, CB3 0WA, UK
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Idaten is a new cold-inducible transposon of Volvox carteri that can be used for tagging developmentally important genes. Genetics 2008; 180:1343-53. [PMID: 18791222 DOI: 10.1534/genetics.108.094672] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
A cold-inducible transposon called Jordan has previously been used to tag and recover genes controlling key aspects of Volvox development, including the process called inversion. In a search for additional genes, we isolated 17 new inversionless mutants from cultures grown at 24 degrees (the temperature that activates Jordan transposition). These mutants were stable at 32 degrees, but generated revertants at 24 degrees . DNA blots revealed that one mutant had a transposon unrelated to Jordan inserted in invA ("inversionless A"). This new transposon, which we named Idaten, has terminal inverted repeats (TIRs) beginning with CCCTA, and upon insertion it creates a 3-bp target-site duplication. It appears to belong to the CACTA superfamily of class II DNA transposons, which includes En/Spm. No significant open reading frames were in the Idaten sequence, but we retrieved another element with Idaten-type TIRs encoding a protein similar to the En/Spm transposase as a candidate for an Idaten-specific transposase. We found that in five of the new inversionless strains we could not find any Jordan insertions causing the phenotype to possess insertions of an Idaten family member in a single locus (invC). This clearly indicates that Idaten is a potentially powerful alternative to Jordan for tagging developmentally important genes in Volvox.
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Duncan L, Nishii I, Harryman A, Buckley S, Howard A, Friedman NR, Miller SM. The VARL gene family and the evolutionary origins of the master cell-type regulatory gene, regA, in Volvox carteri. J Mol Evol 2007; 65:1-11. [PMID: 17646893 DOI: 10.1007/s00239-006-0225-5] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2006] [Accepted: 04/02/2007] [Indexed: 10/23/2022]
Abstract
Chlamydomonas reinhardtii, Volvox carteri, and their relatives in the family Volvocaceae provide an excellent opportunity for studying how multicellular organisms with differentiated cell types evolved from unicellular ancestors. While C. reinhardtii is unicellular, V. carteri is multicellular with two cell types, one of which resembles C. reinhardtii cytologically but is terminally differentiated. Maintenance of this "somatic cell" fate is controlled by RegA, a putative transcription factor. We recently showed that RegA shares a conserved region with several predicted V. carteri and C. reinhardtii proteins and that this region, the VARL domain, is likely to include a DNA-binding SAND domain. As the next step toward understanding the evolutionary origins of the regA gene, we analyzed the genome sequences of C. reinhardtii and V. carteri to identify additional genes with the potential to encode VARL domain proteins. Here we report that the VARL gene family, which consists of 12 members in C. reinhardtii and 14 in V. carteri, has experienced a complex evolutionary history in which members of the family have been both gained and lost over time, although several pairs of potentially orthologous genes can still be identified. We find that regA is part of a tandem array of four VARL genes in V. carteri but that a similar array is absent in C. reinhardtii. Most importantly, our phylogenetic analysis suggests that a proto-regA gene was present in a common unicellular ancestor of V. carteri and C. reinhardtii and that this gene was lost in the latter lineage.
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Affiliation(s)
- Leonard Duncan
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
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Babinger P, Völkl R, Cakstina I, Maftei A, Schmitt R. Maintenance DNA methyltransferase (Met1) and silencing of CpG-methylated foreign DNA in Volvox carteri. PLANT MOLECULAR BIOLOGY 2007; 63:325-36. [PMID: 17033890 DOI: 10.1007/s11103-006-9091-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/07/2006] [Accepted: 09/10/2006] [Indexed: 05/12/2023]
Abstract
DNA methylation plays an important role in the gene-silencing network of higher eukaryotes. We have analyzed the 21.5-kb maintenance methyltransferase (M-MTase) gene, met1, of the multicellular green alga Volvox carteri. The met1 transcript was detected only during the period when DNA replication and cell division are taking place. It encodes a 238 kDa protein containing eight C-terminal activity domains typical of M-MTases, plus upstream DNA-binding domains including the ProDom domain PD003757, which experimental analyses in animal systems have indicated is required for targeting the enzyme to DNA-replication foci. Several insertions of unknown function make Volvox Met1 the largest known member of the Met1/Dnmt1 family. Here we also show that several endogenous transposon families are CpG-methylated in Volvox, which we think causes them to be inactive. This view is supported by the observation that an in vitro CpG-methylated gene introduced into Volvox was maintained in the methylated and silent state over >100 generations. Thus, we believe that Met1 recognizes and perpetuates the in vitro methylation signal, and that the silencing machinery is then able to transduce such a methylation-only signal into a stable heterochromatic (and silent) state.
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Affiliation(s)
- P Babinger
- Institute for Biochemistry, Genetics and Microbiology, University of Regensburg, 93040 Regensburg, Germany.
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Quantitative analysis of cell-type specific gene expression in the green alga Volvox carteri. BMC Genomics 2006; 7:321. [PMID: 17184518 PMCID: PMC1774577 DOI: 10.1186/1471-2164-7-321] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2006] [Accepted: 12/21/2006] [Indexed: 11/22/2022] Open
Abstract
Background The multicellular alga Volvox carteri possesses only two cell types: mortal, motile somatic cells and potentially immortal, immotile reproductive cells. It is therefore an attractive model system for studying how cell-autonomous cytodifferentiation is programmed within a genome. Moreover, there are ongoing genome projects both in Volvox carteri and in the closely related unicellular alga Chlamydomonas reinhardtii. However, gene sequencing is only the beginning. To identify cell-type specific expression and to determine relative expression rates, we evaluate the potential of real-time RT-PCR for quantifying gene transcript levels. Results Here we analyze a diversified pool of 39 target genes by real-time RT-PCR for each cell type. This gene pool contains previously known genes with unknown localization of cellular expression, 28 novel genes which are described in this study for the first time, and a few known, cell-type specific genes as a control. The respective gene products are, for instance, part of photosynthesis, cellular regulation, stress response, or transport processes. We provide expression data for all these genes. Conclusion The results show that quantitative real-time RT-PCR is a favorable approach to analyze cell-type specific gene expression in Volvox, which can be extended to a much larger number of genes or to developmental or metabolic mutants. Our expression data also provide a basis for a detailed analysis of individual, previously unknown, cell-type specifically expressed genes.
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Fukada K, Inoue T, Shiraishi H. A posttranslationally regulated protease, VheA, is involved in the liberation of juveniles from parental spheroids in Volvox carteri. THE PLANT CELL 2006; 18:2554-66. [PMID: 17028206 PMCID: PMC1626617 DOI: 10.1105/tpc.106.041343] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
The lineage of volvocine algae includes unicellular Chlamydomonas and multicellular Volvox in addition to their colonial relatives intermediate in size and cell number. In an asexual life cycle, daughter cells of Chlamydomonas hatch from parental cell walls soon after cell division, while Volvox juveniles are released from parental spheroids after the completion of various developmental events required for the survival of multicellular juveniles. Thus, heterochronic change in the timing of hatching is considered to have played an important role in the evolution of multicellularity in volvocine algae. To study the hatching process in Volvox carteri, we purified a 125-kD Volvox hatching enzyme (VheA) from a culture medium with enzymatic activity to degrade the parental spheroids. The coding region of vheA contains a prodomain with a transmembrane segment, a subtilisin-like Ser protease domain, and a functionally unknown domain, although purified 125-kD VheA does not contain a prodomain. While 143-kD VheA with a prodomain is synthesized long before the hatching stage, 125-kD VheA is released into the culture medium during hatching due to cleavage processing at the site between the prodomain and the subtilisin-like Ser protease domain, indicating that posttranslational regulation is involved in the determination of the timing of hatching.
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Affiliation(s)
- Kazutake Fukada
- Department of Gene Mechanisms, Graduate School of Biostudies, Kyoto University, Kyoto 606-8502, Japan
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Babinger K, Hallmann A, Schmitt R. Translational control of regA, a key gene controlling cell differentiation in Volvox carteri. Development 2006; 133:4045-51. [PMID: 16971469 DOI: 10.1242/dev.02582] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The complete division of labour between the reproductive and somatic cells of the green alga Volvox carteri is controlled by three types of genes. One of these is the regA gene, which controls terminal differentiation of the somatic cells. Here, we examined translational control elements located in the 5' UTR of regA, particularly the eight upstream start codons (AUGs) that have to be bypassed by the translation machinery before regA can be translated. The results of our systematic mutational, structural and functional analysis of the 5' UTR led us to conclude that a ribosome-shunting mechanism--rather than leaky scanning, ribosomal reinitiation, or internal ribosome entry site (IRES)-mediated initiation--controls the translation of regA mRNA. This mechanism, which involves dissociation of the 40S initiation complex from the message, followed by reattachment downstream, in order to bypass a secondary structure block in the mRNA, was validated by deleting the predicted ;landing site' (which prevented regA expression) and inserting a stable 64 nucleotide hairpin just upstream of this site (which did not prevent regA expression). We believe that this is the first report suggesting that translation of an mRNA in a green eukaryote is controlled by ribosome shunting.
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Affiliation(s)
- Karin Babinger
- Naturwissenschaftliche Fakultät III-Biologie und Vorklinische Medizin, University of Regensburg, D-93040 Regensburg, Germany
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Short MB, Solari CA, Ganguly S, Powers TR, Kessler JO, Goldstein RE. Flows driven by flagella of multicellular organisms enhance long-range molecular transport. Proc Natl Acad Sci U S A 2006; 103:8315-9. [PMID: 16707579 PMCID: PMC1482491 DOI: 10.1073/pnas.0600566103] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Evolution from unicellular organisms to larger multicellular ones requires matching their needs to the rate of exchange of molecular nutrients with the environment. This logistic problem poses a severe constraint on development. For organisms whose body plan is a spherical shell, such as the volvocine green algae, the current (molecules per second) of needed nutrients grows quadratically with radius, whereas the rate at which diffusion alone exchanges molecules grows linearly, leading to a bottleneck radius beyond which the diffusive current cannot meet metabolic demands. By using Volvox carteri, we examine the role that advection of fluid by the coordinated beating of surface-mounted flagella plays in enhancing nutrient uptake and show that it generates a boundary layer of concentration of the diffusing solute. That concentration gradient produces an exchange rate that is quadratic in the radius, as required, thus circumventing the bottleneck and facilitating evolutionary transitions to multicellularity and germ-soma differentiation in the volvocalean green algae.
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Affiliation(s)
| | | | | | - Thomas R. Powers
- Division of Engineering, Box D, Brown University, Providence, RI 02912
| | | | - Raymond E. Goldstein
- Departments of *Physics and
- Program in Applied Mathematics, and
- BIO5 Institute, University of Arizona, Tucson, AZ 85721; and
- To whom correspondence should be addressed. E-mail:
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Duncan L, Nishii I, Howard A, Kirk D, Miller SM. Orthologs and paralogs of regA, a master cell-type regulatory gene in Volvox carteri. Curr Genet 2006; 50:61-72. [PMID: 16622701 DOI: 10.1007/s00294-006-0071-4] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2006] [Revised: 03/17/2006] [Accepted: 03/20/2006] [Indexed: 10/24/2022]
Abstract
The multicellular green alga Volvox carteri forma nagariensis has only two cell types: terminally differentiated somatic cells and reproductive cells. The regA gene maintains the terminally differentiated state of the somatic cells, apparently by repressing transcription of genes required for chloroplast biogenesis and thereby preventing cell growth. Because the RegA protein sequence bore no obvious motifs, we are attempting to identify regions of functional importance by searching for strongly conserved domains in RegA orthologs. Here we report the cloning and characterization of regA from the most closely related known taxon, V. carteri f. kawasakiensis. Given the closeness of the relationship between these two formas, their regA genes are surprisingly different: they differ in the number of introns and by several lengthy indels, and they encode proteins that are only 80% identical. We also serendipitously discovered a paralogous gene immediately upstream of each regA locus. The two regA genes, both upstream paralogs and several genes in Chlamydomonas (the closest unicellular relative of Volvox) encode a conserved region (the VARL domain) that contains what appears to be a DNA-binding SAND domain. This discovery has opened up a new avenue for exploring how regA and the terminally differentiated state that it controls evolved.
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Affiliation(s)
- Leonard Duncan
- Department of Biology, Washington University, St. Louis, MO 63130, USA
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Aono N, Inoue T, Shiraishi H. Genes specifically expressed in sexually differentiated female spheroids of Volvox carteri. J Biochem 2006; 138:375-82. [PMID: 16272131 DOI: 10.1093/jb/mvi139] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Volvox carteri is a multicellular green alga with only two cell types, somatic cells and reproductive cells. Phylogenetic analysis suggests that this organism has evolved from a Chlamydomonas-like unicellular ancestor along with multicellularity, cellular differentiation, and a change in the mode of sexual reproduction from isogamy to oogamy. To examine the mechanism of sexual differentiation and the evolution of oogamy, we isolated 6 different cDNA sequences specifically expressed in sexually differentiated female spheroids. The genes for the cDNAs were designated SEF1 to SEF6. The time course of accumulation of each mRNA was shown to be distinct. The expression of some of these genes was not significantly affected when the sexual inducer was removed after the induction of sexual development. Sequence analysis indicates that SEF5 and SEF6 encode pherophorin-related proteins. Of these, SEF5 has the unique structural feature of a polyproline stretch in the C-terminal domain in addition to the one found in the central region.
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Affiliation(s)
- Naoki Aono
- Graduate School of Science and Graduate School of Biostudies, Kyoto University, Kitashirakawa Oiwake-cho, Kyoto 606-8502, Japan
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Solari CA, Kessler JO, Michod RE. A hydrodynamics approach to the evolution of multicellularity: flagellar motility and germ-soma differentiation in volvocalean green algae. Am Nat 2006; 167:537-54. [PMID: 16670996 DOI: 10.1086/501031] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2005] [Accepted: 01/06/2006] [Indexed: 11/03/2022]
Abstract
During the unicellular-multicellular transition, there are opportunities and costs associated with larger size. We argue that germ-soma separation evolved to counteract the increasing costs and requirements of larger multicellular colonies. Volvocalean green algae are uniquely suited for studying this transition because they range from unicells to multicellular individuals with germ-soma separation. Because Volvocales need flagellar beating for movement and to avoid sinking, their motility is modeled and analyzed experimentally using standard hydrodynamics. We provide comparative hydrodynamic data of an algal lineage composed of organisms of different sizes and degrees of complexity. In agreement with and extending the insights of Koufopanou, we show that the increase in cell specialization as colony size increases can be explained in terms of increased motility requirements. First, as colony size increases, soma must evolve, the somatic-to-reproductive cell ratio increasing to keep colonies buoyant and motile. Second, increased germ-soma specialization in larger colonies increases motility capabilities because internalization of nonflagellated germ cells decreases colony drag. Third, our analysis yields a limiting maximum size of the volvocalean spheroid that agrees with the sizes of the largest species known. Finally, the different colony designs in Volvocales reflect the trade-offs between reproduction, colony size, and motility.
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Affiliation(s)
- Cristian A Solari
- Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona 85721, USA.
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Solari CA, Ganguly S, Kessler JO, Michod RE, Goldstein RE. Multicellularity and the functional interdependence of motility and molecular transport. Proc Natl Acad Sci U S A 2006; 103:1353-8. [PMID: 16421211 PMCID: PMC1360517 DOI: 10.1073/pnas.0503810103] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2005] [Accepted: 12/04/2005] [Indexed: 11/18/2022] Open
Abstract
Benefits, costs, and requirements accompany the transition from motile totipotent unicellular organisms to multicellular organisms having cells specialized into reproductive (germ) and vegetative (sterile soma) functions such as motility. In flagellated colonial organisms such as the volvocalean green algae, organized beating by the somatic cells' flagella yields propulsion important in phototaxis and chemotaxis. It has not been generally appreciated that for the larger colonies flagellar stirring of boundary layers and remote transport are fundamental for maintaining a sufficient rate of metabolite turnover, one not attainable by diffusive transport alone. Here, we describe experiments that quantify the role of advective dynamics in enhancing productivity in germ soma-differentiated colonies. First, experiments with suspended deflagellated colonies of Volvox carteri show that forced advection improves productivity. Second, particle imaging velocimetry of fluid motion around colonies immobilized by micropipette aspiration reveals flow fields with very large characteristic velocities U extending to length scales exceeding the colony radius R. For a typical metabolite diffusion constant D, the associated Peclet number Pe = 2UR/D >> 1, indicative of the dominance of advection over diffusion, with striking augmentation at the cell division stage. Near the colony surface, flows generated by flagella can be chaotic, exhibiting mixing due to stretching and folding. These results imply that hydrodynamic transport external to colonies provides a crucial boundary condition, a source for supplying internal diffusional dynamics.
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Affiliation(s)
- Cristian A Solari
- Department of Ecology and Evolutionary Biology, Program in Applied Mathematics, University of Arizona, Tucson, AZ 85721, USA
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Kato-Minoura T, Okumura M, Hirono M, Kamiya R. A novel family of unconventional actins in volvocalean algae. J Mol Evol 2004; 57:555-61. [PMID: 14738314 DOI: 10.1007/s00239-003-2509-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2002] [Accepted: 06/03/2003] [Indexed: 10/26/2022]
Abstract
The unicellular green alga Chlamydomonas reinhardtii has two actin genes, one encoding a conventional actin (90% amino acid identity with mammalian actin), the other a highly divergent actin (64% identity) named novel actin-like protein (NAP). To see whether the presence of conventional and unconventional actins in a single organism is unique to C. reinhardtii, we searched for genomic sequences related to the NAP sequence in several other species of volvocalean algae. Here we show that Chlamydomonas moewusii and Volvox carteri also have, in addition to a conventional actin, an unconventional actin similar to the C. reinhardtii NAP. Analyses of the deduced protein sequences indicated that the NAP homologues form a distinct group derived from conventional actin.
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Affiliation(s)
- Takako Kato-Minoura
- Department of Cell Biology, National Institute for Basic Biology, Okazaki 444-8585, Japan.
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Affiliation(s)
- Marilyn M Kirk
- Department of Biology, Washington University, St. Louis, MO 63130, USA.
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Abstract
In Volvox carteri adults, reproductive cells called gonidia are enclosed within a spherical monolayer of biflagellate somatic cells. Embryos must "invert" (turn inside out) to achieve this configuration, however, because at the end of cleavage the gonidia are on the outside and the flagellar ends of all somatic cells point inward. Generation of a bend region adequate to turn the embryo inside out involves a dramatic change in cell shape, plus cell movements. Here, we cloned a gene called invA that is essential for inversion and found that it codes for a kinesin localized in the cytoplasmic bridges that link all cells to their neighbors. In invA null mutants, cells change shape normally, but are unable to move relative to the cytoplasmic bridges. A normal bend region cannot be formed and inversion stops. We conclude that the InvA kinesin provides the motile force that normally drives inversion to completion.
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Affiliation(s)
- Ichiro Nishii
- Department of Biology, Washington University, St Louis, MO 63130, USA
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Hallmann A. Extracellular matrix and sex-inducing pheromone in Volvox. INTERNATIONAL REVIEW OF CYTOLOGY 2003; 227:131-82. [PMID: 14518551 DOI: 10.1016/s0074-7696(03)01009-x] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
During evolution of multicellularity it was imperative to create a complex, multifunctional extracellular matrix (ECM) out of the simple cell wall of a unicellular ancestor. The green alga Volvox represents one of the simplest multicellular organisms, but even so, it already has a highly developed ECM. This ECM is mainly composed of an assortment of glycoproteins, many of which are hydroxyproline rich and extensively sulfated. Several ECM proteins are cross-linked and might have only structural functions. However, the ECM does not represent a static but rather a dynamic and multifunctional interface between a cell and its neighboring cells or its environment. It not only provides protection and structural support for the shape of each cell and the organism as a whole, but also plays a broad range of biological roles in growth, development, reproduction, and responses to environmental stress or wounding. The variety of functions of the ECM requires many glycoproteins to do the work. To attain a high flexibility and adaptability, almost all ECM glycoproteins from Volvox consist of modules, defined as functional subunits that form modular mosaic proteins with an outstanding combinatorial potential. The ECM's functions are not only extensive but also change under developmental control or by environmental incidents. The changing scope of duties necessitates a permanent ECM turnover and remodeling. In Volvox carteri one particularly challenging trigger of such ECM modifications is a sex-inducing pheromone, which is one of the most potent biological effector molecules known: the glycoprotein pheromone is fully effective for inducing sexual development in males and females at concentrations as low as 10(-16) M. The earliest detectable response to the pheromone is the synthesis of ECM glycoproteins.
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Affiliation(s)
- Armin Hallmann
- Department of Cellular and Developmental Biology of Plants, University of Bielefeld, D-33615 Bielefeld, Germany
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Duncan L, Bouckaert K, Yeh F, Kirk DL. kangaroo, a mobile element from Volvox carteri, is a member of a newly recognized third class of retrotransposons. Genetics 2002; 162:1617-30. [PMID: 12524337 PMCID: PMC1462361 DOI: 10.1093/genetics/162.4.1617] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Retrotransposons play an important role in the evolution of genomic structure and function. Here we report on the characterization of a novel retrotransposon called kangaroo from the multicellular green alga, Volvox carteri. kangaroo elements are highly mobile and their expression is developmentally regulated. They probably integrate via double-stranded, closed-circle DNA intermediates through the action of an encoded recombinase related to the lambda-site-specific integrase. Phylogenetic analysis indicates that kangaroo elements are closely related to other unorthodox retrotransposons including PAT (from a nematode), DIRS-1 (from Dictyostelium), and DrDIRS1 (from zebrafish). PAT and kangaroo both contain split direct repeat (SDR) termini, and here we show that DIRS-1 and DrDIRS1 elements contain terminal features structurally related to SDRs. Thus, these mobile elements appear to define a third class of retrotransposons (the DIRS1 group) that are unified by common structural features, genes, and integration mechanisms, all of which differ from those of LTR and conventional non-LTR retrotransposons.
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Affiliation(s)
- Leonard Duncan
- Department of Biology, Washington University, Saint Louis, Missouri 63130, USA.
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Shimizu T, Inoue T, Shiraishi H. Cloning and characterization of novel extensin-like cDNAs that are expressed during late somatic cell phase in the green alga Volvox carteri. Gene 2002; 284:179-87. [PMID: 11891059 DOI: 10.1016/s0378-1119(01)00899-x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Asexual individuals of the green alga Volvox carteri consist of two cell types, somatic and reproductive cells. The somatic cells are terminally differentiated post-mitotic cells which undergo gradual senescence leading to cell death in every generation. To understand the gene expression programs associated with senescence of somatic cells, we cloned two cDNAs, LSG1 and LSG2, that are preferentially expressed during this late developmental stage. These two cDNAs were deduced to encode Pro-rich motifs characteristic of extensin proteins that are components of the extracellular matrix. LSG1 also resembled genes encoding plant pathogenesis-related protein 1 (PR-1), while LSG2 showed similarities with genes encoding matrix metalloproteinases, including a gamete lytic enzyme of Chlamydomonas. We also found that S9, one of the late somatic cDNAs previously cloned by Tam and Kirk (Dev. Biol. 145 (1991) 51), was deduced to encode a protein with a composition similar to LSG2. The expression of PR-1 and a matrix-metalloproteinase-encoding gene has been shown to be induced during senescence in higher plants. These results indicate that some of the late somatic genes in V. carteri are related to the senescence-associated genes in higher plants.
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Affiliation(s)
- Toshinobu Shimizu
- Graduate School of Science, Kyoto University, 606-8502, Kyoto, Japan
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Abstract
Volvox carteri is a spherical green alga with a predominantly asexual mode of reproduction and a complete germ-soma division of labor. Its somatic cells are specialized for motility, incapable of dividing, and programmed to die when only a few days old, whereas its gonidia (asexual reproductive cells) are nonmotile, specialized for growth and reproduction, and potentially immortal. When a gonidium is less than 2 days old it divides to produce a juvenile spheroid containing all of the somatic cells and gonidia that will be present in an adult of the next generation. The first visible step in germ-soma differentiation is a set of asymmetric cleavage divisions in the embryo that set apart small somatic initials from their large gonidial-initial sister cells. Three types of genes have been found to play key roles in germ-soma specification. First a set of gls genes act in the embryos to shift cell-division planes, resulting in the asymmetric divisions that set apart the large-small sister-cell pairs. Then a set of lag genes act in the large cells to prevent somatic differentiation, while the regA gene acts in the small cells to prevent reproductive development. An inducible transposon was used to tag and recover some of these and other developmentally important genes. The glsA gene encodes a chaperone-like protein that, like another chaperone that is one of its putative binding partners, is associated with the cell division apparatus, although how this leads to asymmetric division remains to be elucidated. The regA gene encodes a somatic-cell-specific nuclear protein that appears to function by repressing genes required for chloroplast biogenesis, thereby preventing somatic cells from growing enough to reproduce. Somatic-cell-specific expression of regA is controlled by three intronic enhancers.
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Affiliation(s)
- D L Kirk
- Department of Biology, Washington University, St. Louis, Missouri 63130, USA.
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