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Nishida HY, Hamada K, Koshita M, Ohta Y, Nishida H. Ascidian gastrulation and blebbing activity of isolated endoderm blastomeres. Dev Biol 2023; 496:24-35. [PMID: 36702215 DOI: 10.1016/j.ydbio.2023.01.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2022] [Revised: 01/16/2023] [Accepted: 01/20/2023] [Indexed: 01/24/2023]
Abstract
Gastrulation is the first dynamic cell movement during embryogenesis. Endoderm and mesoderm cells are internalized into embryos during this process. Ascidian embryos provide a simple system for studying gastrulation in chordates. Gastrulation starts in spherical late 64-cell embryos with 10 endoderm blastomeres. The mechanisms of gastrulation in ascidians have been investigated, and a two-step model has been proposed. The first step involves apical constriction of endoderm cells, followed by apicobasal shortening in the second step. In this study, isolated ascidian endoderm progenitor cells displayed dynamic blebbing activity at the gastrula stage, although such a dynamic cell-shape change was not recognized in toto. Blebbing is often observed in migrating animal cells. In ascidians, endoderm cells displayed blebbing activity, while mesoderm and ectoderm cells did not. The timing of blebbing of isolated endoderm cells coincided with that of cell invagination. The constriction rate of apical surfaces correlated with the intensity of blebbing activity in each endoderm-lineage cell. Fibroblast growth factor (FGF) signaling was both necessary and sufficient for inducing blebbing activity, independent of cell fate specification. In contrast, the timing of initiation of blebbing and intensity of blebbing response to FGF signaling were controlled by intrinsic cellular factors. It is likely that the difference in intensity of blebbing activity between the anterior A-line and posterior B-line cells could account for the anteroposterior difference in the steepness of the archenteron wall. Inhibition of zygotic transcription, FGF signaling, and Rho kinase, all of which suppressed blebbing activity, resulted in incomplete apical constriction and failure of the eventual formation of cup-shaped gastrulae. Blebbing activity was involved in the progression and maintenance of apical constriction, but not in apicobasal shortening in whole embryos. Apical constriction is mediated by distinct blebbing-dependent and blebbing-independent mechanisms. Surface tension and consequent membrane contraction may not be the sole mechanical force for apical constriction and formation of cup-shaped gastrulae. The present study reveals the hidden cellular potential of endodermal cells during gastrulation and discusses the possible roles of blebbing in the invagination process.
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Affiliation(s)
- Haruka Y Nishida
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka, 560-0043, Japan
| | - Kaho Hamada
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka, 560-0043, Japan
| | - Mika Koshita
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka, 560-0043, Japan
| | - Yuki Ohta
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka, 560-0043, Japan
| | - Hiroki Nishida
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka, 560-0043, Japan.
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2
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Treen N, Konishi S, Nishida H, Onuma TA, Sasakura Y. Zic-r.b controls cell numbers in Ciona embryos by activating CDKN1B. Dev Biol 2023; 498:26-34. [PMID: 36965841 DOI: 10.1016/j.ydbio.2023.03.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2022] [Revised: 01/25/2023] [Accepted: 03/20/2023] [Indexed: 03/27/2023]
Abstract
The control of cell numbers and the establishment of cell types are two processes that are essential in early embryonic development. We have a reasonable understanding of how these processes occur individually, but we have considerably less sophisticated understanding of how these processes are linked. Tunicates have fixed cell lineages with predictable cell cycles, making them well suited to investigate these processes. In the ascidian Ciona, we show that the transcription factor Zic-r.b, known to be involved in establishing several cell types in early development also activates the expression of the cell cycle inhibitor CDKN1B. Zic-r.b is a major missing component of the cell division clock establishing specific cell numbers. We also show that a larvacean homolog of Zic-r.b is expressed one cell cycle earlier than its Ciona counterpart. The early expression in larvaceans may explain why they have half as many notochord cells as ascidians and may illustrate a general mechanism to evolve changes in morphology.
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Affiliation(s)
- Nicholas Treen
- Shimoda Marine Research Center, University of Tsukuba, 5-10-1, Shimoda, Shizuoka, 415-0025, Japan.
| | - Shohei Konishi
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka, 560-0043, Japan
| | - Hiroki Nishida
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka, 560-0043, Japan
| | - Takeshi A Onuma
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka, 560-0043, Japan
| | - Yasunori Sasakura
- Shimoda Marine Research Center, University of Tsukuba, 5-10-1, Shimoda, Shizuoka, 415-0025, Japan
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Song BP, Ragsac MF, Tellez K, Jindal GA, Grudzien JL, Le SH, Farley EK. Diverse logics and grammar encode notochord enhancers. Cell Rep 2023; 42:112052. [PMID: 36729834 PMCID: PMC10387507 DOI: 10.1016/j.celrep.2023.112052] [Citation(s) in RCA: 10] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2022] [Revised: 11/07/2022] [Accepted: 01/17/2023] [Indexed: 02/03/2023] Open
Abstract
The notochord is a defining feature of all chordates. The transcription factors Zic and ETS regulate enhancer activity within the notochord. We conduct high-throughput screens of genomic elements within developing Ciona embryos to understand how Zic and ETS sites encode notochord activity. Our screen discovers an enhancer located near Lama, a gene critical for notochord development. Reversing the orientation of an ETS site within this enhancer abolishes expression, indicating that enhancer grammar is critical for notochord activity. Similarly organized clusters of Zic and ETS sites occur within mouse and human Lama1 introns. Within a Brachyury (Bra) enhancer, FoxA and Bra, in combination with Zic and ETS binding sites, are necessary and sufficient for notochord expression. This binding site logic also occurs within other Ciona and vertebrate Bra enhancers. Collectively, this study uncovers the importance of grammar within notochord enhancers and discovers signatures of enhancer logic and grammar conserved across chordates.
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Affiliation(s)
- Benjamin P Song
- Department of Medicine, Health Sciences, University of California San Diego, La Jolla, CA 92093, USA; Department of Molecular Biology, Biological Sciences, University of California San Diego, La Jolla, CA 92093, USA; Biological Sciences Graduate Program, University of California San Diego, La Jolla, CA 92093, USA
| | - Michelle F Ragsac
- Department of Medicine, Health Sciences, University of California San Diego, La Jolla, CA 92093, USA; Department of Molecular Biology, Biological Sciences, University of California San Diego, La Jolla, CA 92093, USA; Bioinformatics and Systems Biology Graduate Program, University of California San Diego, La Jolla, CA 92093, USA
| | - Krissie Tellez
- Department of Medicine, Health Sciences, University of California San Diego, La Jolla, CA 92093, USA; Department of Molecular Biology, Biological Sciences, University of California San Diego, La Jolla, CA 92093, USA
| | - Granton A Jindal
- Department of Medicine, Health Sciences, University of California San Diego, La Jolla, CA 92093, USA; Department of Molecular Biology, Biological Sciences, University of California San Diego, La Jolla, CA 92093, USA
| | - Jessica L Grudzien
- Department of Medicine, Health Sciences, University of California San Diego, La Jolla, CA 92093, USA; Department of Molecular Biology, Biological Sciences, University of California San Diego, La Jolla, CA 92093, USA
| | - Sophia H Le
- Department of Medicine, Health Sciences, University of California San Diego, La Jolla, CA 92093, USA; Department of Molecular Biology, Biological Sciences, University of California San Diego, La Jolla, CA 92093, USA
| | - Emma K Farley
- Department of Medicine, Health Sciences, University of California San Diego, La Jolla, CA 92093, USA; Department of Molecular Biology, Biological Sciences, University of California San Diego, La Jolla, CA 92093, USA.
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Reeves WM, Shimai K, Winkley KM, Veeman MT. Brachyury controls Ciona notochord fate as part of a feed-forward network. Development 2021; 148:dev195230. [PMID: 33419874 PMCID: PMC7875503 DOI: 10.1242/dev.195230] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2020] [Accepted: 12/18/2020] [Indexed: 12/22/2022]
Abstract
The notochord is a defining feature of the chordates. The transcription factor Brachyury (Bra) is a key regulator of notochord fate but here we show that it is not a unitary master regulator in the model chordate Ciona Ectopic Bra expression only partially reprograms other cell types to a notochord-like transcriptional profile and a subset of notochord-enriched genes is unaffected by CRISPR Bra disruption. We identify Foxa.a and Mnx as potential co-regulators, and find that combinatorial cocktails are more effective at reprogramming other cell types than Bra alone. We reassess the network relationships between Bra, Foxa.a and other components of the notochord gene regulatory network, and find that Foxa.a expression in the notochord is regulated by vegetal FGF signaling. It is a direct activator of Bra expression and has a binding motif that is significantly enriched in the regulatory regions of notochord-enriched genes. These and other results indicate that Bra and Foxa.a act together in a regulatory network dominated by positive feed-forward interactions, with neither being a classically defined master regulator.
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Affiliation(s)
- Wendy M Reeves
- Division of Biology, Kansas State University, Manhattan, KS 66506, USA
| | - Kotaro Shimai
- Division of Biology, Kansas State University, Manhattan, KS 66506, USA
| | - Konner M Winkley
- Division of Biology, Kansas State University, Manhattan, KS 66506, USA
| | - Michael T Veeman
- Division of Biology, Kansas State University, Manhattan, KS 66506, USA
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Di Gregorio A. The notochord gene regulatory network in chordate evolution: Conservation and divergence from Ciona to vertebrates. Curr Top Dev Biol 2020; 139:325-374. [PMID: 32450965 DOI: 10.1016/bs.ctdb.2020.01.002] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The notochord is a structure required for support and patterning of all chordate embryos, from sea squirts to humans. An increasing amount of information on notochord development and on the molecular strategies that ensure its proper morphogenesis has been gleaned through studies in the sea squirt Ciona. This invertebrate chordate offers a fortunate combination of experimental advantages, ranging from translucent, fast-developing embryos to a compact genome and impressive biomolecular resources. These assets have enabled the rapid identification of numerous notochord genes and cis-regulatory regions, and provide a rather unique opportunity to reconstruct the gene regulatory network that controls the formation of this developmental and evolutionary chordate landmark. This chapter summarizes the morphogenetic milestones that punctuate notochord formation in Ciona, their molecular effectors, and the current knowledge of the gene regulatory network that ensures the accurate spatial and temporal orchestration of these processes.
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Affiliation(s)
- Anna Di Gregorio
- Department of Basic Science and Craniofacial Biology, New York University College of Dentistry, New York, NY, United States.
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Yamada S, Tanaka Y, Imai KS, Saigou M, Onuma TA, Nishida H. Wavy movements of epidermis monocilia drive the neurula rotation that determines left-right asymmetry in ascidian embryos. Dev Biol 2019; 448:173-182. [PMID: 30059669 DOI: 10.1016/j.ydbio.2018.07.023] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2018] [Revised: 06/19/2018] [Accepted: 07/26/2018] [Indexed: 12/22/2022]
Abstract
Tadpole larvae of the ascidian, Halocynthia roretzi, show morphological left-right asymmetry in the brain structures and the orientation of tail bending within the vitelline membrane. Neurula embryos rotate along the anterior-posterior axis in a counterclockwise direction, and then this rotation stops when the left side of the embryo is oriented downwards. Contact of the left-side epidermis with the vitelline membrane promotes nodal gene expression in the left-side epidermis. This is a novel mechanism in which rotation of whole embryos provides the initial cue for breaking left-right symmetry. Here we show that epidermal monocilia, which appear at the neurula rotation stage, generate the driving force for rotation. A ciliary protein, Arl13b, fused with Venus YFP was used for live imaging of ciliary movements. Although overexpression of wild-type Arl13b fusion protein resulted in aberrant movements of the cilia and abrogation of neurula rotation, mutant Arl13b fusion protein, in which the GTPase and coiled-coil domains were removed, did not affect the normal ciliary movements and neurula rotation. Epidermis cilia moved in a wavy and serpentine way like sperm flagella but not in a rotational way or beating way with effective stroke and recovery stroke. They moved very slowly, at 1/7 Hz, consistent with the low angular velocity of neurula rotation (ca. 43°/min). The tips of most cilia pointed in the opposite direction of embryonic rotation. Similar motility was also observed in Ciona robusta embryos. When embryos were treated with a dynein inhibitor, Ciliobrevin D, both ciliary movements and neurula rotation were abrogated, showing that ciliary movements drive neurula rotation in Halocynthia. The drug also inhibited Ciona neurula rotation. Our observations suggest that the driving force of rotation is generated using the vitelline membrane as a substrate but not by making a water current around the embryo. It is of evolutionary interest that ascidians use ciliary movements to break embryonic left-right symmetry, like in many vertebrates. Meanwhile, ascidian embryos rotate as a whole, similar to embryos of non-vertebrate deuterostomes, such as echinoderm, hemichordate, and amphioxus, while swimming.
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Affiliation(s)
- Shiori Yamada
- Department of Biological Sciences, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan
| | - Yuka Tanaka
- Department of Biological Sciences, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan
| | - Kaoru S Imai
- Department of Biological Sciences, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan
| | - Motohiko Saigou
- Department of Biological Sciences, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan
| | - Takeshi A Onuma
- Department of Biological Sciences, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan
| | - Hiroki Nishida
- Department of Biological Sciences, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan.
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7
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Evolution of the bilaterian mouth and anus. Nat Ecol Evol 2018; 2:1358-1376. [PMID: 30135501 DOI: 10.1038/s41559-018-0641-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2017] [Revised: 06/26/2018] [Accepted: 07/11/2018] [Indexed: 12/17/2022]
Abstract
It is widely held that the bilaterian tubular gut with mouth and anus evolved from a simple gut with one major gastric opening. However, there is no consensus on how this happened. Did the single gastric opening evolve into a mouth, with the anus forming elsewhere in the body (protostomy), or did it evolve into an anus, with the mouth forming elsewhere (deuterostomy), or did it evolve into both mouth and anus (amphistomy)? These questions are addressed by the comparison of developmental fates of the blastopore, the opening of the embryonic gut, in diverse animals that live today. Here we review comparative data on the identity and fate of blastoporal tissue, investigate how the formation of the through-gut relates to the major body axes, and discuss to what extent evolutionary scenarios are consistent with these data. Available evidence indicates that stem bilaterians had a slit-like gastric opening that was partially closed in subsequent evolution, leaving open the anus and most likely also the mouth, which would favour amphistomy. We discuss remaining difficulties, and outline directions for future research.
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8
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Abstract
Ascidians are tunicates, which constitute the sister group of vertebrates. The ascidian genome contains two Zic genes, called Zic-r.a (also called Macho-1) and Zic-r.b (ZicL). The latter is a multi-copy gene, and the precise copy number has not yet been determined. Zic-r.a is maternally expressed, and soon after fertilization Zic-r.a mRNA is localized in the posterior pole of the zygote. Zic-r.a protein is translated there and is involved in specification of posterior fate; in particular it is important for specification of muscle fate. Zic-r.a is also expressed zygotically in neural cells of the tailbud stage. On the other hand, Zic-r.b is first expressed in marginal cells of the vegetal hemisphere of 32-cell embryos and then in neural cells that contribute to the central nervous system during gastrulation. Zic-r.b is required first for specification of mesodermal tissues and then for specification of the central nervous system. Their upstream and downstream genetic pathways have been studied extensively by functional assays, which include gene knockdown and chromatin immunoprecipitation assays. Thus, ascidian Zic genes play central roles in specification of mesodermal and neural fates.
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Affiliation(s)
- Yutaka Satou
- Department of Zoology, Graduate School of Science, Kyoto University, Kyoto, Japan.
| | - Kaoru S Imai
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Japan
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Control of Pem protein level by localized maternal factors for transcriptional regulation in the germline of the ascidian, Halocynthia roretzi. PLoS One 2018; 13:e0196500. [PMID: 29709000 PMCID: PMC5927453 DOI: 10.1371/journal.pone.0196500] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2017] [Accepted: 04/13/2018] [Indexed: 12/04/2022] Open
Abstract
Localized maternal mRNAs play important roles in embryogenesis, e.g. the establishment of embryonic axes and the developmental cell fate specification, in various animal species. In ascidians, a group of maternal mRNAs, called postplasmic/PEM RNAs, is localized to a subcellular structure, called the Centrosome-Attracting Body (CAB), which contains the ascidian germ plasm, and is inherited by the germline cells during embryogenesis. Posterior end mark (Pem), a postplasmic/PEM RNAs member, represses somatic gene expression in the germline during cleavage stages by inhibition of RNA polymerase II activity. However, the functions of other postplasmic/ PEM RNAs members in germline formation are largely unknown. In this study, we analyzed the functions of two postplasmic/PEM RNAs, Popk-1 and Zf-1, in transcriptional regulation in the germline cells. We show that Popk-1 contributes to transcriptional quiescence by controlling the size of the CAB and amount of Pem protein translated at the CAB. Our studies also indicated that zygotic expression of a germline gene starts around the onset of gastrulation and that the decrease of Pem protein is necessary and sufficient for the zygotic germline gene expression. Finally, further studies showed that the decrease of the Pem protein level is facilitated by Zf-1. Taken together, we propose that postplasmic/PEM RNAs such as Popk-1 and Zf-1 control the protein level of the transcriptional repressor Pem and regulate its transcriptional state in the ascidian germline.
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Reporter Analyses Reveal Redundant Enhancers that Confer Robustness on Cis-Regulatory Mechanisms. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2018. [PMID: 29542081 DOI: 10.1007/978-981-10-7545-2_7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register]
Abstract
Reporter analyses of Hox1 and Brachyury (Bra) genes have revealed examples of redundant enhancers that provide regulatory robustness. Retinoic acid (RA) activates through an RA-response element the transcription of Hox1 in the nerve cord of the ascidian Ciona intestinalis. We also found a weak RA-independent neural enhancer within the second intron of Hox1. The Hox1 gene in the larvacean Oikopleura dioica is also expressed in the nerve cord. The O. dioica genome, however, does not contain the RA receptor-encoding gene, and the expression of Hox1 has become independent of RA. We have found that the upstream sequence of the O. dioica Hox1 was able to activate reporter gene expression in the nerve cord of the C. intestinalis embryo, suggesting that an RA-independent regulatory system in the nerve cord might be common in larvaceans and ascidians. This RA-independent redundant regulatory system may have facilitated the Oikopleura ancestor losing RA signaling without an apparent impact on Hox1 expression domains. On the other hand, vertebrate Bra is expressed in the ventral mesoderm and notochord, whereas its ascidian ortholog is exclusively expressed in the notochord. Fibroblast growth factor (FGF) induces Bra in the ventral mesoderm in vertebrates, whereas it induces Bra in the notochord in ascidians. Disruption of the FGF signal does not completely silence Bra expression in ascidians, suggesting that FGF-dependent and independent enhancers might comprise a redundant regulatory system in ascidians. The existence of redundant enhancers, therefore, provides regulatory robustness that may facilitate the acquisition of new expression domains.
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Maguire JE, Pandey A, Wu Y, Di Gregorio A. Investigating Evolutionarily Conserved Molecular Mechanisms Controlling Gene Expression in the Notochord. TRANSGENIC ASCIDIANS 2018. [DOI: 10.1007/978-981-10-7545-2_8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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12
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Abstract
Asymmetric cell division during embryogenesis contributes to cell diversity by generating daughter cells that adopt distinct developmental fates. In this chapter, we summarize current knowledge of three examples of asymmetric cell division occurring in ascidian early embryos: (1) Three successive cell divisions that are asymmetric in terms of cell fate and unequal in cell size in the germline lineage at the embryo posterior pole. A subcellular structure, the centrosome-attracting body (CAB), and maternal PEM mRNAs localized within it control both the positioning of the cell division planes and segregation of the germ cell fates. (2) Asymmetric cell divisions involving endoderm and mesoderm germ layer separation. Asymmetric partitioning of zygotically expressed mRNA for Not, a homeodomain transcription factor, promotes the mesoderm fate and suppresses the endoderm fate. This asymmetric partitioning is mediated by transient nuclear migration toward the mesodermal pole of the mother cell, where the mRNA is delivered. In this case, there is no special regulation of cleavage plane orientation. (3) Asymmetric cell divisions in the marginal region of the vegetal hemisphere. The directed extracellular FGF and ephrin signals polarize the mother cells, inducing distinct fates in a pair of daughter cells (nerve versus notochord and mesenchyme versus muscle). The directions of cell division are regulated and oriented but independently of FGF and ephrin signaling. In these examples, polarization of the mother cells is facilitated by localized maternal factors, by delivery of transcripts from the nucleus to one pole of each cell, and by directed extracellular signals. Two cellular processes-asymmetric fate allocation and orientation of the cell division plane-are coupled by a single factor in the first example, but these processes are regulated independently in the third example. Thus, various modes of asymmetric cell division operate even at the early developmental stages in this single type of organism.
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Affiliation(s)
- Takefumi Negishi
- Division of Morphogenesis, National Institute for Basic Biology, Nishigonaka 38, Myodaiji, Okazaki, Aichi, 444-8585, Japan
| | - Hiroki Nishida
- Department of Biological Sciences, Graduate School of Science, Osaka University, 1-1 Machikaneyama-Cho, Toyonaka, Osaka, 560-0043, Japan.
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Ikeda T, Satou Y. Differential temporal control of Foxa.a and Zic-r.b specifies brain versus notochord fate in the ascidian embryo. Development 2016; 144:38-43. [PMID: 27888196 DOI: 10.1242/dev.142174] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2016] [Accepted: 11/14/2016] [Indexed: 01/25/2023]
Abstract
In embryos of an invertebrate chordate, Ciona intestinalis, two transcription factors, Foxa.a and Zic-r.b, are required for specification of the brain and the notochord, which are derived from distinct cell lineages. In the brain lineage, Foxa.a and Zic-r.b are expressed with no temporal overlap. In the notochord lineage, Foxa.a and Zic-r.b are expressed simultaneously. In the present study, we found that the temporally non-overlapping expression of Foxa.a and Zic-r.b in the brain lineage was regulated by three repressors: Prdm1-r.a (formerly called BZ1), Prdm1-r.b (BZ2) and Hes.a. In morphant embryos of these three repressor genes, Foxa.a expression was not terminated at the normal time, and Zic-r.b was precociously expressed. Consequently, Foxa.a and Zic-r.b were expressed simultaneously, which led to ectopic activation of Brachyury and its downstream pathways for notochord differentiation. Thus, temporal controls by transcriptional repressors are essential for specification of the two distinct fates of brain and notochord by Foxa.a and Zic-r.b Such a mechanism might enable the repeated use of a limited repertoire of transcription factors in developmental gene regulatory networks.
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Affiliation(s)
- Tatsuro Ikeda
- Department of Zoology, Graduate School of Science, Kyoto University, Sakyo, Kyoto 606-8502, Japan
| | - Yutaka Satou
- Department of Zoology, Graduate School of Science, Kyoto University, Sakyo, Kyoto 606-8502, Japan
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14
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Hudson C, Sirour C, Yasuo H. Co-expression of Foxa.a, Foxd and Fgf9/16/20 defines a transient mesendoderm regulatory state in ascidian embryos. eLife 2016; 5. [PMID: 27351101 PMCID: PMC4945153 DOI: 10.7554/elife.14692] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2016] [Accepted: 06/24/2016] [Indexed: 12/12/2022] Open
Abstract
In many bilaterian embryos, nuclear β-catenin (nβ-catenin) promotes mesendoderm over ectoderm lineages. Although this is likely to represent an evolutionary ancient developmental process, the regulatory architecture of nβ-catenin-induced mesendoderm remains elusive in the majority of animals. Here, we show that, in ascidian embryos, three nβ-catenin transcriptional targets, Foxa.a, Foxd and Fgf9/16/20, are each required for the correct initiation of both the mesoderm and endoderm gene regulatory networks. Conversely, these three factors are sufficient, in combination, to produce a mesendoderm ground state that can be further programmed into mesoderm or endoderm lineages. Importantly, we show that the combinatorial activity of these three factors is sufficient to reprogramme developing ectoderm cells to mesendoderm. We conclude that in ascidian embryos, the transient mesendoderm regulatory state is defined by co-expression of Foxa.a, Foxd and Fgf9/16/20. DOI:http://dx.doi.org/10.7554/eLife.14692.001
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Affiliation(s)
- Clare Hudson
- Laboratoire de Biologie du Développement de Villefranche-sur-mer, Observatoire Océanologique, Sorbonne Universités, UPMC Univ Paris 06, CNRS, Villefranche-sur-Mer, France
| | - Cathy Sirour
- Laboratoire de Biologie du Développement de Villefranche-sur-mer, Observatoire Océanologique, Sorbonne Universités, UPMC Univ Paris 06, CNRS, Villefranche-sur-Mer, France
| | - Hitoyoshi Yasuo
- Laboratoire de Biologie du Développement de Villefranche-sur-mer, Observatoire Océanologique, Sorbonne Universités, UPMC Univ Paris 06, CNRS, Villefranche-sur-Mer, France
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15
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Kodama H, Miyata Y, Kuwajima M, Izuchi R, Kobayashi A, Gyoja F, Onuma TA, Kumano G, Nishida H. Redundant mechanisms are involved in suppression of default cell fates during embryonic mesenchyme and notochord induction in ascidians. Dev Biol 2016; 416:162-172. [PMID: 27265866 DOI: 10.1016/j.ydbio.2016.05.033] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2016] [Revised: 05/28/2016] [Accepted: 05/30/2016] [Indexed: 11/30/2022]
Abstract
During embryonic induction, the responding cells invoke an induced developmental program, whereas in the absence of an inducing signal, they assume a default uninduced cell fate. Suppression of the default fate during the inductive event is crucial for choice of the binary cell fate. In contrast to the mechanisms that promote an induced cell fate, those that suppress the default fate have been overlooked. Upon induction, intracellular signal transduction results in activation of genes encoding key transcription factors for induced tissue differentiation. It is elusive whether an induced key transcription factor has dual functions involving suppression of the default fates and promotion of the induced fate, or whether suppression of the default fate is independently regulated by other factors that are also downstream of the signaling cascade. We show that during ascidian embryonic induction, default fates were suppressed by multifold redundant mechanisms. The key transcription factor, Twist-related.a, which is required for mesenchyme differentiation, and another independent transcription factor, Lhx3, which is dispensable for mesenchyme differentiation, sequentially and redundantly suppress the default muscle fate in induced mesenchyme cells. Similarly in notochord induction, Brachyury, which is required for notochord differentiation, and other factors, Lhx3 and Mnx, are likely to suppress the default nerve cord fate redundantly. Lhx3 commonly suppresses the default fates in two kinds of induction. Mis-activation of the autonomously executed default program in induced cells is detrimental to choice of the binary cell fate. Multifold redundant mechanisms would be required for suppression of the default fate to be secure.
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Affiliation(s)
- Hitoshi Kodama
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
| | - Yoshimasa Miyata
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
| | - Mami Kuwajima
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
| | - Ryoichi Izuchi
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
| | - Ayumi Kobayashi
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
| | - Fuki Gyoja
- Marine Genomics Unit, Okinawa Institute of Science and Technology Graduate University, 1919-1 Tancha, Onna, Okinawa 904-0495, Japan
| | - Takeshi A Onuma
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
| | - Gaku Kumano
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
| | - Hiroki Nishida
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan.
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16
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Ricci L, Cabrera F, Lotito S, Tiozzo S. Redeployment of germ layers related TFs shows regionalized expression during two non-embryonic developments. Dev Biol 2016; 416:235-248. [PMID: 27208394 DOI: 10.1016/j.ydbio.2016.05.016] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2015] [Revised: 05/11/2016] [Accepted: 05/12/2016] [Indexed: 11/26/2022]
Abstract
In all non-vertebrate metazoan phyla, species that evolved non-embryonic developmental pathways as means of propagation or regeneration can be found. In this context, new bodies arise through asexual reproduction processes (such as budding) or whole body regeneration, that lack the familiar temporal and spatial cues classically associated with embryogenesis, like maternal determinants, or gastrulation. The molecular mechanisms underlying those non-embryonic developments (i.e., regeneration and asexual reproduction), and their relationship to those deployed during embryogenesis are poorly understood. We have addressed this question in the colonial ascidian Botryllus schlosseri, which undergoes an asexual reproductive process via palleal budding (PB), as well as a whole body regeneration by vascular budding (VB). We identified early regenerative structures during VB and then followed the fate of differentiating tissues during both non-embryonic developments (PB and VB) by monitoring the expression of genes known to play key functions in germ layer specification with well conserved expression patterns in solitary ascidian embryogenesis. The expression patterns of FoxA1, GATAa, GATAb, Otx, Bra, Gsc and Tbx2/3 were analysed during both PB and VB. We found that the majority of these transcription factors were expressed during both non-embryonic developmental processes, revealing a regionalization of the palleal and vascular buds. Knockdown of GATAa by siRNA in palleal buds confirmed that preventing the correct development of one of these regions blocks further tissue specification. Our results indicate that during both normal and injury-induced budding, a similar alternative developmental program operates via early commitment of epithelial regions.
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Affiliation(s)
- Lorenzo Ricci
- Sorbonne Universités, UPMC Univ. Paris 06, CNRS, Laboratoire de Biologie du Développement de Villefranche-sur-mer (LBDV), 06230 Villefranche sur-mer, France
| | - Fabien Cabrera
- Sorbonne Universités, UPMC Univ. Paris 06, CNRS, Laboratoire de Biologie du Développement de Villefranche-sur-mer (LBDV), 06230 Villefranche sur-mer, France
| | - Sonia Lotito
- Sorbonne Universités, UPMC Univ. Paris 06, CNRS, Laboratoire de Biologie du Développement de Villefranche-sur-mer (LBDV), 06230 Villefranche sur-mer, France
| | - Stefano Tiozzo
- Sorbonne Universités, UPMC Univ. Paris 06, CNRS, Laboratoire de Biologie du Développement de Villefranche-sur-mer (LBDV), 06230 Villefranche sur-mer, France.
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17
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Takatori N, Oonuma K, Nishida H, Saiga H. Polarization of PI3K Activity Initiated by Ooplasmic Segregation Guides Nuclear Migration in the Mesendoderm. Dev Cell 2016; 35:333-43. [PMID: 26555053 DOI: 10.1016/j.devcel.2015.10.012] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2015] [Revised: 09/16/2015] [Accepted: 10/15/2015] [Indexed: 11/29/2022]
Abstract
Asymmetric localization of RNA is a widely observed mechanism of cell polarization. Using embryos of the ascidian, Halocynthia roretzi, we previously showed that mesoderm and endoderm fates are separated by localization of mRNA encoding a transcription factor, Not, to the future mesoderm-side cytoplasm of the mesendoderm cell through asymmetric positioning of the nucleus. Here, we investigated the mechanism that defines the direction of the nuclear migration. We show that localization of PtdIns(3,4,5)P3 to the future mesoderm region determines the direction of nuclear migration. Localization of PtdIns(3,4,5)P3 was dependent on the localization of PI3Kα to the future mesoderm region. PI3Kα was first localized at the 1-cell stage by the ooplasmic movement. Activity of localized PI3Kα at the 4-cell stage was required for the localization of PI3Kα up to the nuclear migration. Our results provide the scaffold for understanding the chain of causality leading to the separation of germ layer fates.
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Affiliation(s)
- Naohito Takatori
- Department of Biological Sciences, Graduate School of Science and Engineering, Tokyo Metropolitan University, 1-1 Minamiohsawa, Hachioji, Tokyo 192-0397, Japan; Department of Biological Sciences, Graduate school of Science, Osaka University 1-1, Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan.
| | - Kouhei Oonuma
- Department of Biological Sciences, Graduate School of Science and Engineering, Tokyo Metropolitan University, 1-1 Minamiohsawa, Hachioji, Tokyo 192-0397, Japan
| | - Hiroki Nishida
- Department of Biological Sciences, Graduate school of Science, Osaka University 1-1, Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan
| | - Hidetoshi Saiga
- Department of Biological Sciences, Graduate School of Science and Engineering, Tokyo Metropolitan University, 1-1 Minamiohsawa, Hachioji, Tokyo 192-0397, Japan
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18
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Kim JE, Lee WY, Kim GJ. Expression of Hr-Erf Gene during Ascidian Embryogenesis. Dev Reprod 2015; 17:389-97. [PMID: 25949155 PMCID: PMC4382941 DOI: 10.12717/dr.2013.17.4.389] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2013] [Revised: 12/09/2013] [Accepted: 12/14/2013] [Indexed: 11/23/2022]
Abstract
FGF9/16/20 signaling pathway specify the developmental fates of notochord, mesenchyme, and neural cells in ascidian embryos. Although a conserved Ras/MEK/Erk/Ets pathway is known to be involved in this signaling, the detailed mechanisms of regulation of FGF signaling pathway have remained largely elusive. In this study, we have isolated Hr-Erf, an ascidian orthologue of vertebrate Erf, to elucidate interactions of transcription factors involved in FGF signaling of the ascidian embryo. The Hr-Erf cDNA encompassed 3110 nucleotides including sequence encoded a predicted polypeptide of 760 amino acids. The polypeptide had the Ets DNA-binding domain in its N-terminal region. In adult animals, Hr-Erf mRNA was predominantly detected in muscle, and at lower levels in ganglion, gills, gonad, hepatopancreas, and stomach by quantitative real-time PCR (QPCR) method. During embryogenesis, Hr-Erf mRNA was detected from eggs to early developmental stage embryos, whereas the transcript levels were decreased after neurula stage. Similar to the QPCR results, maternal transcripts of Hr-Erf was detected in the fertilized eggs by whole-mount in situ hybridization. Maternal mRNA of Hr-Erf was gradually lost from the neurula stage. Zygotic expression of Hr-Erf started in most blastomeres at the 8-cell stage. At gastrula stage, Hr-Erf was specifically expressed in the precursor cells of brain and mesenchyme. When MEK inhibitor was treated, embryos resulted in loss of Hr-Erf expression in mesenchyme cells, and in excess of Hr-Erf in a-line neural cells. These results suggest that zygotic Hr-Erf products are involved in specification of mesenchyme and neural cells.
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Affiliation(s)
- Jung Eun Kim
- Department of Marine Molecular Biotechnology, Gangneung-Wonju National University, Gangneung 210-702, Republic of Korea
| | - Won Young Lee
- Department of Marine Molecular Biotechnology, Gangneung-Wonju National University, Gangneung 210-702, Republic of Korea
| | - Gil Jung Kim
- Department of Marine Molecular Biotechnology, Gangneung-Wonju National University, Gangneung 210-702, Republic of Korea
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19
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Kumano G, Negoro N, Nishida H. Transcription factor Tbx6 plays a central role in fate determination between mesenchyme and muscle in embryos of the ascidian,Halocynthia roretzi. Dev Growth Differ 2014; 56:310-22. [DOI: 10.1111/dgd.12133] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2013] [Revised: 03/09/2014] [Accepted: 03/12/2014] [Indexed: 01/27/2023]
Affiliation(s)
- Gaku Kumano
- Asamushi Research Center for Marine Biology; Graduate School of Life Science; Tohoku University; 9 Sakamoto Asamushi Aomori 039-3501 Japan
| | - Nobue Negoro
- Department of Biological Sciences; Graduate School of Science; Osaka University; 1-1 Machikaneyama-cho Toyonaka Osaka 560-0043 Japan
| | - Hiroki Nishida
- Department of Biological Sciences; Graduate School of Science; Osaka University; 1-1 Machikaneyama-cho Toyonaka Osaka 560-0043 Japan
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20
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Kuwajima M, Kumano G, Nishida H. Regulation of the number of cell division rounds by tissue-specific transcription factors and Cdk inhibitor during ascidian embryogenesis. PLoS One 2014; 9:e90188. [PMID: 24608898 PMCID: PMC3946487 DOI: 10.1371/journal.pone.0090188] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2013] [Accepted: 01/31/2014] [Indexed: 02/06/2023] Open
Abstract
Mechanisms that regulate the number of cell division rounds during embryogenesis have remained largely elusive. To investigate this issue, we used the ascidian, which develops into a tadpole larva with a small number of cells. The embryonic cells divide 11.45 times on average from fertilization to hatching. The number of cell division rounds varies depending on embryonic lineages. Notochord and muscle consist of large postmitotic cells and stop dividing early in developing embryos. Here we show that conversion of mesenchyme to muscle cell fates by inhibition of inductive FGF signaling or mis-expression of a muscle-specific key transcription factor for muscle differentiation, Tbx6, changed the number of cell divisions in accordance with the altered fate. Tbx6 likely activates a putative mechanism to halt cell division at a specific stage. However, precocious expression of Tbx6 has no effect on progression of the developmental clock itself. Zygotic expression of a cyclin-dependent kinase inhibitor, CKI-b, is initiated in muscle and then in notochord precursors. CKI-b is possibly downstream of tissue-specific key transcription factors of notochord and muscle. In the two distinct muscle lineages, postmitotic muscle cells are generated after 9 and 8 rounds of cell division depending on lineage, but the final cell divisions occur at a similar developmental stage. CKI-b gene expression starts simultaneously in both muscle lineages at the 110-cell stage, suggesting that CKI-b protein accumulation halts cell division at a similar stage. The difference in the number of cell divisions would be due to the cumulative difference in cell cycle length. These results suggest that muscle cells do not count the number of cell division rounds, and that accumulation of CKI-b protein triggered by tissue-specific key transcription factors after cell fate determination might act as a kind of timer that measures elapsed time before cell division termination.
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Affiliation(s)
- Mami Kuwajima
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka, Japan
| | - Gaku Kumano
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka, Japan
| | - Hiroki Nishida
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka, Japan
- * E-mail:
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21
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Ikeda T, Matsuoka T, Satou Y. A time delay gene circuit is required for palp formation in the ascidian embryo. Development 2014; 140:4703-8. [PMID: 24255097 DOI: 10.1242/dev.100339] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
The ascidian larval brain and palps (a putative rudimentary placode) are specified by two transcription factor genes, ZicL and FoxC, respectively. FGF9/16/20 induces ZicL expression soon after the bi-potential ancestral cells divide into the brain and palp precursors at the early gastrula stage. FGF9/16/20 begins to be expressed at the 16-cell stage, and induces several target genes, including Otx, before the gastrula stage. Here, we show that ZicL expression in the brain lineage is transcriptionally repressed by Hes-a and two Blimp-1-like zinc finger proteins, BZ1 and BZ2, in the bi-potential ancestral cells. ZicL is precociously expressed in the bi-potential cells in embryos in which these repressors are knocked down. This precocious ZicL expression produces extra brain cells at the expense of palp cells. The expression of BZ1 and BZ2 is turned off by a negative auto-feedback loop. This auto-repression acts as a delay circuit that prevents ZicL from being expressed precociously before the brain and palp fates split, thereby making room within the neural plate for the palps to be specified. Addition of the BZ1/2 delay timer circuit to the gene regulatory network responsible for brain formation might represent a key event in the acquisition of the primitive palps/placodes in an ancestral animal.
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Affiliation(s)
- Tatsuro Ikeda
- Department of Zoology, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto, 606-8502, Japan
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22
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Ettensohn CA. Encoding anatomy: Developmental gene regulatory networks and morphogenesis. Genesis 2013; 51:383-409. [PMID: 23436627 DOI: 10.1002/dvg.22380] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2012] [Revised: 02/06/2013] [Accepted: 02/07/2013] [Indexed: 12/19/2022]
Affiliation(s)
- Charles A. Ettensohn
- Department of Biological Sciences; Carnegie Mellon University; Pittsburgh; Pennsylvania
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23
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Yoshida K, Ueno M, Niwano T, Saiga H. Transcription regulatory mechanism of Pitx in the papilla-forming region in the ascidian, Halocynthia roretzi, implies conserved involvement of Otx as the upstream gene in the adhesive organ development of chordates. Dev Growth Differ 2012; 54:649-59. [PMID: 22889275 DOI: 10.1111/j.1440-169x.2012.01366.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Pitx genes play important roles in a variety of developmental processes in vertebrates. In an ascidian species, Halocynthia roretzi, Hr-Pitx, the only Pitx gene of this species, has been reported to be expressed in the left epidermis at the tailbud stage. In the present study, first, we have shown that Hr-Pitx is also expressed in the papilla-forming region at the neurula to tailbud stages, and then we addressed transcription regulatory mechanisms for the expression of Hr-Pitx in the papilla-forming region. We have identified the genomic region ranging from 850 to 1211 bp upstream from the translation start site of the Hr-Pitx gene as an enhancer region that drives the transcription of Hr-Pitx in the papilla-forming region. Within the enhancer region, putative transcriptional factor binding sites for Otx as well as Fox were shown to be required for its activity. Finally, we carried out knocking down experiments of Hr-Otx function using an antisense morpholino oligonucleotide, in which the knocking down of Hr-Otx function resulted in reduction of the enhancer activity and loss of the expression of Hr-Pitx in the papilla-forming region. In Xenopus laevis, it has been reported that Pitx genes are expressed downstream of Otx function during development of the cement gland, an adhesive organ of its larva. Taken together, it is suggested that the expression regulatory mechanism of Pitx, involving Otx as the upstream gene, in the developing adhesive organ is conserved between ascidians and vertebrates.
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Affiliation(s)
- Keita Yoshida
- Department of Biological Sciences, Graduate School of Science and Engineering, Tokyo Metropolitan University, 1-1 Minamiohsawa, Hachiohji, Tokyo, 192-0397, Japan
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24
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Woznica A, Haeussler M, Starobinska E, Jemmett J, Li Y, Mount D, Davidson B. Initial deployment of the cardiogenic gene regulatory network in the basal chordate, Ciona intestinalis. Dev Biol 2012; 368:127-39. [PMID: 22595514 DOI: 10.1016/j.ydbio.2012.05.002] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2011] [Revised: 04/26/2012] [Accepted: 05/04/2012] [Indexed: 12/31/2022]
Abstract
The complex, partially redundant gene regulatory architecture underlying vertebrate heart formation has been difficult to characterize. Here, we dissect the primary cardiac gene regulatory network in the invertebrate chordate, Ciona intestinalis. The Ciona heart progenitor lineage is first specified by Fibroblast Growth Factor/Map Kinase (FGF/MapK) activation of the transcription factor Ets1/2 (Ets). Through microarray analysis of sorted heart progenitor cells, we identified the complete set of primary genes upregulated by FGF/Ets shortly after heart progenitor emergence. Combinatorial sequence analysis of these co-regulated genes generated a hypothetical regulatory code consisting of Ets binding sites associated with a specific co-motif, ATTA. Through extensive reporter analysis, we confirmed the functional importance of the ATTA co-motif in primary heart progenitor gene regulation. We then used the Ets/ATTA combination motif to successfully predict a number of additional heart progenitor gene regulatory elements, including an intronic element driving expression of the core conserved cardiac transcription factor, GATAa. This work significantly advances our understanding of the Ciona heart gene network. Furthermore, this work has begun to elucidate the precise regulatory architecture underlying the conserved, primary role of FGF/Ets in chordate heart lineage specification.
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Affiliation(s)
- Arielle Woznica
- Department of Molecular and Cellular Biology, Molecular Cardiovascular Research Program, University of Arizona, Arizona 85724, USA
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25
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Makabe KW, Nishida H. Cytoplasmic localization and reorganization in ascidian eggs: role of postplasmic/PEM RNAs in axis formation and fate determination. WILEY INTERDISCIPLINARY REVIEWS-DEVELOPMENTAL BIOLOGY 2012; 1:501-18. [PMID: 23801532 DOI: 10.1002/wdev.54] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Localization of maternal molecules in eggs and embryos and cytoplasmic movements to relocalize them are fundamental for the orderly cellular and genetic processes during early embryogenesis. Ascidian embryos have been known as 'mosaic eggs' because of their autonomous differentiation abilities based on localized cell fate determinants. This review gives a historical overview of the concept of cytoplasmic localization, and then explains the key features such as ooplasmic movements and cell lineages that are essential to grasp the process of ascidian development mediated by localized determinant activities. These activities are partly executed by localized molecules named postplasmic/PEM RNAs, originating from approximately 50 genes, of which the muscle determinant, macho-1, is an example. The cortical domain containing these RNAs is relocalized to the posterior-vegetal region of the egg by cytoskeletal movements after fertilization, and plays crucial roles in axis formation and cell fate determination. The cortical domain contains endoplasmic reticulum and characteristic granules, and gives rise to a subcellular structure called the centrosome-attracting body (CAB), in which postplasmic/PEM RNAs are highly concentrated. The CAB is responsible for a series of unequal partitionings of the posterior-vegetal cytoplasmic domain and the postplasmic/PEM RNAs at the posterior pole during cleavage. Some components of this domain, which is rich in granules, are eventually inherited by prospective germline cells with particular postplasmic/PEM RNAs such as vasa. The postplasmic/PEM RNAs are classified into two groups according to their final cellular destinations and localization pathways. Localization of these RNAs is regulated by specific nucleotide sequences in the 3' untranslated regions (3'UTRs).
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Affiliation(s)
- Kazuhiro W Makabe
- Institute of Socio-Arts and Sciences, University of Tokushima, Tokushima, Japan
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26
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Similarity and diversity in mechanisms of muscle fate induction between ascidian species. Biol Cell 2012; 100:265-77. [DOI: 10.1042/bc20070144] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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27
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Shirae-Kurabayashi M, Matsuda K, Nakamura A. Ci-Pem-1 localizes to the nucleus and represses somatic gene transcription in the germline of Ciona intestinalis embryos. Development 2011; 138:2871-81. [PMID: 21693510 DOI: 10.1242/dev.058131] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
In many animal embryos, germ-cell formation depends on maternal factors located in the germ plasm. To ensure the development of germ cells, germline progenitors must be prevented from differentiating inappropriately into somatic cells. A common mechanism for this appears to be the active repression of somatic gene transcription. Species-specific germ-plasm components, such as Pgc in Drosophila and PIE-1 in C. elegans, establish germline transcriptional quiescence by inhibiting general transcriptional machineries. In the ascidian Ciona intestinalis, although transcriptional repression in the germline has been proposed, the factors and mechanisms involved have been unknown. We found that the protein products of Ci-pem-1 RNA, which is an ascidian-specific component of the postplasm (the germ plasm equivalent in ascidians), localized to the nucleus of germline blastomeres, as well as to the postplasm. Morpholino oligonucleotide-mediated Ci-pem-1 knockdown resulted in the ectopic expression of several somatic genes that are usually silent in the germline. In the Ci-pem-1 knockdown embryos, the expression of both β-catenin- and GATAa-dependent genes was derepressed in the germline blastomeres, suggesting that Ci-Pem-1 broadly represses germline mRNA transcription. Immunoprecipitation assays showed that Ci-Pem-1 could interact with two C. intestinalis homologs of Groucho, which is a general co-repressor of mRNA transcription. These results suggest that Ci-pem-1 is the C. intestinalis version of a germ-plasm RNA whose protein product represses the transcription of somatic genes during specification of the germ-cell fate, and that this repression may be operated through interactions between Ci-Pem-1 and Groucho co-repressors.
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Affiliation(s)
- Maki Shirae-Kurabayashi
- Laboratory for Germline Development, RIKEN Center for Developmental Biology, Kobe, Hyogo, Japan.
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28
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Kumano G, Takatori N, Negishi T, Takada T, Nishida H. A maternal factor unique to ascidians silences the germline via binding to P-TEFb and RNAP II regulation. Curr Biol 2011; 21:1308-13. [PMID: 21782435 DOI: 10.1016/j.cub.2011.06.050] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2011] [Revised: 05/19/2011] [Accepted: 06/21/2011] [Indexed: 12/11/2022]
Abstract
Suppression of zygotic transcription in early embryonic germline cells is tightly linked to their separation from the somatic lineage. Many invertebrate embryos utilize localized maternal factors that are successively inherited by the germline cells for silencing the germline. Germline quiescence has also been associated with the underphosphorylation of Ser2 of the C-terminal domain (CTD-Ser2) of RNA polymerase II [1-3]. Here, using the ascidian Halocynthia roretzi, we identified a first deuterostome example of a maternally localized factor, posterior end mark (PEM), which globally represses germline transcription. PEM knockdown resulted in ectopic transcription and ectopic phosphorylation of CTD-Ser2 in the germline. Overexpression of PEM abolished all transcription and led to the underphosphorylation of CTD-Ser2 in the somatic cells. PEM protein was reiteratively detected in the nucleus of the germline cells and coimmunoprecipitated with CDK9, a component of posterior transcription elongation factor b (P-TEFb). These results suggest that nonhomologous proteins, PEM and Pgc of Drosophila [3-5] and PIE-1 of C. elegans [1, 6, 7], repress germline gene expression through analogous functions: by keeping CTD-Ser2 underphosphorylated through binding to the P-TEFb complex. The present study is an interesting example of evolutionary constraint on how a mechanism of germline silencing can evolve in diverse animals.
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Affiliation(s)
- Gaku Kumano
- Department of Biological Sciences, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan.
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29
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Hashimoto H, Enomoto T, Kumano G, Nishida H. The transcription factor FoxB mediates temporal loss of cellular competence for notochord induction in ascidian embryos. Development 2011; 138:2591-600. [DOI: 10.1242/dev.053082] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
In embryos of the ascidian Halocynthia roretzi, the competence of isolated presumptive notochord blastomeres to respond to fibroblast growth factor (FGF) for induction of the primary notochord decays by 1 hour after cleavage from the 32- to 64-cell stage. This study analyzes the molecular mechanisms responsible for this loss of competence and provides evidence for a novel mechanism. A forkhead family transcription factor, FoxB, plays a role in competence decay by preventing the induction of notochord-specific Brachyury (Bra) gene expression by the FGF/MAPK signaling pathway. Unlike the mechanisms reported previously in other animals, no component in the FGF signal transduction cascade appeared to be lost or inactivated at the time of competence loss. Knockdown of FoxB functions allowed the isolated cells to retain their competence for a longer period, and to respond to FGF with expression of Bra beyond the stage at which competence was normally lost. FoxB acts as a transcription repressor by directly binding to the cis-regulatory element of the Bra gene. Our results suggest that FoxB prevents ectopic induction of the notochord fate within the cells that assume a default nerve cord fate, after the stage when notochord induction has been completed. The merit of this system is that embryos can use the same FGF signaling cascade again for another purpose in the same cell lineage at later stages by keeping the signaling cascade itself available. Temporally and spatially regulated FoxB expression in nerve cord cells was promoted by the ZicN transcription factor and absence of FGF/MAPK signaling.
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Affiliation(s)
- Hidehiko Hashimoto
- Department of Biological Sciences, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka 560-0043, Osaka, Japan
| | - Takashi Enomoto
- Department of Biological Sciences, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka 560-0043, Osaka, Japan
| | - Gaku Kumano
- Department of Biological Sciences, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka 560-0043, Osaka, Japan
| | - Hiroki Nishida
- Department of Biological Sciences, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka 560-0043, Osaka, Japan
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30
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Fujikawa T, Takatori N, Kuwajima M, Kim GJ, Nishida H. Tissue-specific regulation of the number of cell division rounds by inductive cell interaction and transcription factors during ascidian embryogenesis. Dev Biol 2011; 355:313-23. [PMID: 21575623 DOI: 10.1016/j.ydbio.2011.04.033] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2010] [Revised: 04/06/2011] [Accepted: 04/28/2011] [Indexed: 11/16/2022]
Abstract
Mechanisms that regulate the number of cells constituting the body have remained largely elusive. We approached this issue in the ascidian, Halocynthia roretzi, which develops into a tadpole larva with a small number of cells. The embryonic cells divide 11 times on average from fertilization to hatching. The number of cell division rounds varies among tissue types. For example, notochord cells divide 9 times and give rise to large postmitotic cells in the tadpole. The number of cell division rounds in partial embryos derived from tissue-precursor blastomeres isolated at the 64-cell stage also varied between tissues and coincided with their counterparts in the intact whole embryos to some extent, suggesting tissue-autonomous regulation of cell division. Manipulation of cell fates in notochord, nerve cord, muscle, and mesenchyme lineage cells by inhibition or ectopic activation of the inductive FGF signal changed the number of cell divisions according to the altered fate. Knockdown and missexpression of Brachyury (Bra), an FGF-induced notochord-specific key transcription factor for notochord differentiation, indicated that Bra is also responsible for regulation of the number of cell division rounds, suggesting that Bra activates a putative mechanism to halt cell division at a specific stage. The outcome of precocious expression of Bra suggests that the mechanism involves a putative developmental clock that is likely shared in blastomeres other than those of notochord and functions to terminate cell division at three rounds after the 64-cell stage. Precocious expression of Bra has no effect on progression of the developmental clock itself.
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Affiliation(s)
- Tetsuya Fujikawa
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
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31
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The conserved role and divergent regulation of foxa, a pan-eumetazoan developmental regulatory gene. Dev Biol 2010; 357:21-6. [PMID: 21130759 DOI: 10.1016/j.ydbio.2010.11.027] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2010] [Revised: 11/15/2010] [Accepted: 11/24/2010] [Indexed: 11/23/2022]
Abstract
Foxa is a forkhead transcription factor that is expressed in the endoderm lineage across metazoans. Orthologs of foxa are expressed in cells that intercalate, polarize, and form tight junctions in the digestive tracts of the mouse, the sea urchin, and the nematode and in the chordate notochord. The loss of foxa expression eliminates these morphogenetic processes. The remarkable similarity in foxa phenotypes in these diverse organisms raises the following questions: why is the developmental role of Foxa so highly conserved? Is foxa transcriptional regulation as conserved as its developmental role? Comparison of the regulation of foxa orthologs in sea urchin and in Caenorhabditis elegans shows that foxa transcriptional regulation has diverged significantly between these two organisms, particularly in the cells that contribute to the C. elegans pharynx formation. We suggest that the similarity of foxa phenotype is due to its role in an ancestral gene regulatory network that controlled intercalation followed by mesenchymal-to-epithelial transition. foxa transcriptional regulation had evolved to support the developmental program in each species so foxa would play its role controlling morphogenesis at the necessary embryonic address.
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32
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Takatori N, Kumano G, Saiga H, Nishida H. Segregation of germ layer fates by nuclear migration-dependent localization of Not mRNA. Dev Cell 2010; 19:589-98. [PMID: 20951349 DOI: 10.1016/j.devcel.2010.09.003] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2010] [Revised: 08/25/2010] [Accepted: 08/26/2010] [Indexed: 10/18/2022]
Abstract
An important step in early embryonic development is the allocation and segregation of germ layer fates into distinct embryonic regions. However, the mechanism that segregates the mesendoderm into mesoderm and endoderm fates remains largely unknown in most animals. Here, using ascidians, a primitive chordate, we show that these fates are segregated by partitioning of asymmetrically localized Not mRNA from the mesendoderm cell to its mesodermal daughter. Migration of the mesendoderm cell nucleus to the future mesoderm-forming region, release of Not mRNA from the nucleus, Wnt5α-dependent local retention of the mRNA, and subsequent repositioning of the mitotic spindle to the center of the cell are each required for the asymmetric localization and partitioning of Not mRNA. Our results show that nuclear migration plays an unexpected role in asymmetric cell divisions that segregate germ layer fates in chordate embryos.
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Affiliation(s)
- Naohito Takatori
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan.
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33
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Kumano G, Kawai N, Nishida H. Macho-1 regulates unequal cell divisions independently of its function as a muscle determinant. Dev Biol 2010; 344:284-92. [PMID: 20478299 DOI: 10.1016/j.ydbio.2010.05.013] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2010] [Revised: 03/30/2010] [Accepted: 05/08/2010] [Indexed: 02/05/2023]
Abstract
The anterior-posterior (A-P) axis in ascidian embryos is established through the posteriorizing activities of a localized egg region known as the posterior vegetal cortex/cytoplasm (PVC). Here we describe a novel function of macho-1, a maternally-localized muscle determinant, in establishment of the A-P axis in the Halocynthia roretzi embryo. Macho-1, in addition to its known function in the formation of posterior tissue such as muscle and mesenchyme, and suppression of the anterior-derived notochord fate, acts independently of its transcriptional activity as a regulator of posterior-specific unequal cell divisions, in cooperation with beta-catenin. Our results suggest that macho-1 and beta-catenin regulate the formation of a microtubule bundle that shortens and pulls the centrosome toward a sub-cellular cortical structure known as centrosome-attracting body (CAB), which is located at the posterior pole of the embryo during unequal cell divisions, and act upstream of PEM, a recently-identified regulator of unequal cell divisions. We also present data that suggest that PEM localization to the CAB may not be required for unequal cleavage regulation. The present study provides an important and novel insight into the role of the zinc-finger-containing transcription factor and indicates that it constitutes a major part of the PVC activity.
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Affiliation(s)
- Gaku Kumano
- Department of Biological Sciences, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan.
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34
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Shimai K, Kitaura Y, Tamari Y, Nishikata T. Upstream Regulatory Sequences Required for Specific Gene Expression in the Ascidian Neural Tube. Zoolog Sci 2010; 27:76-83. [DOI: 10.2108/zsj.27.76] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Affiliation(s)
- Kotaro Shimai
- Graduate School of Natural Science, Konan University, Kobe 658-8501, Japan
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35
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Unfolding a chordate developmental program, one cell at a time: Invariant cell lineages, short-range inductions and evolutionary plasticity in ascidians. Dev Biol 2009; 332:48-60. [DOI: 10.1016/j.ydbio.2009.05.540] [Citation(s) in RCA: 104] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2009] [Revised: 04/27/2009] [Accepted: 05/03/2009] [Indexed: 12/25/2022]
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36
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Patterning of an ascidian embryo along the anterior–posterior axis through spatial regulation of competence and induction ability by maternally localized PEM. Dev Biol 2009; 331:78-88. [DOI: 10.1016/j.ydbio.2009.04.024] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2008] [Revised: 04/02/2009] [Accepted: 04/22/2009] [Indexed: 11/21/2022]
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37
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Chiba S, Jiang D, Satoh N, Smith WC. Brachyury null mutant-induced defects in juvenile ascidian endodermal organs. Development 2009; 136:35-9. [PMID: 19019990 PMCID: PMC2685961 DOI: 10.1242/dev.030981] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/28/2008] [Indexed: 11/20/2022]
Abstract
We report the isolation of a recessive ENU-induced short-tailed mutant in the ascidian Ciona intestinalis that is the product of a premature stop in the brachyury gene. Notochord differentiation and morphogenesis are severely disrupted in the mutant line. At the larval stage, variable degrees of ectopic endoderm staining were observed in the homozygous mutants, indicating that loss of brachyury results in stochastic fate transformation. In post-metamorphosis mutants, a uniform defect in tail resorption was observed, together with variable defects in digestive tract development. Some cells misdirected from the notochord lineage were found to be incorporated into definitive endodermal structures, such as stomach and intestine.
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Affiliation(s)
- Shota Chiba
- Department of Molecular, Cell and Developmental Biology, University of California Santa Barbara, Santa Barbara, CA 93106, USA
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38
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Abstract
Little is known about the ancient chordates that gave rise to the first vertebrates, but the descendants of other invertebrate chordates extant at the time still flourish in the ocean. These invertebrates include the cephalochordates and tunicates, whose larvae share with vertebrate embryos a common body plan with a central notochord and a dorsal nerve cord. Tunicates are now thought to be the sister group of vertebrates. However, research based on several species of ascidians, a diverse and wide-spread class of tunicates, revealed that the molecular strategies underlying their development appear to diverge greatly from those found in vertebrates. Furthermore, the adult body plan of most tunicates, which arises following an extensive post-larval metamorphosis, shows little resemblance to the body plan of any other chordate. In this review, we compare the developmental strategies of ascidians and vertebrates and argue that the very divergence of these strategies reveals the surprising level of plasticity of the chordate developmental program and is a rich resource to identify core regulatory mechanisms that are evolutionarily conserved in chordates. Further, we propose that the comparative analysis of the architecture of ascidian and vertebrate gene regulatory networks may provide critical insight into the origin of the chordate body plan.
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40
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Beh J, Shi W, Levine M, Davidson B, Christiaen L. FoxF is essential for FGF-induced migration of heart progenitor cells in the ascidian Ciona intestinalis. Development 2007; 134:3297-305. [PMID: 17720694 DOI: 10.1242/dev.010140] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Heart development requires precise coordination of morphogenetic movements with progressive cell fate specification and differentiation. In ascidian embryos, FGF/MAPK-mediated activation of the transcription factor Ets1/2 is required for heart tissue specification and cell migration. We found that FoxF is one of the first genes to be activated in heart precursors in response to FGF signaling. We identified the FoxF minimal heart enhancer and used a cis-trans complementation test to show that Ets1/2 can interact with the FoxF enhancer in vivo. Next, we found that FoxF function is required downstream and in parallel to the FGF/MAPK/Ets cascade for cell migration. In addition, we demonstrated that targeted expression of a dominant-negative form of FoxF inhibits cell migration but not heart differentiation, resulting in a striking phenotype: a beating heart at an ectopic location within the body cavity of juveniles. Taken together, our results indicate that FoxF is a direct target of FGF signaling and is predominantly involved in the regulation of heart cell migration.
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Affiliation(s)
- Jeni Beh
- Center for Integrative Genomics, Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, CA 94720, USA
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41
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Kawai N, Iida Y, Kumano G, Nishida H. Nuclear accumulation of β-catenin and transcription of downstream genes are regulated by zygotic Wnt5α and maternal Dsh in ascidian embryos. Dev Dyn 2007; 236:1570-82. [PMID: 17474118 DOI: 10.1002/dvdy.21169] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Nuclear beta-catenin plays crucial roles in the establishment of the embryonic axis and formation of mesendoderm tissues in ascidians and other animals. However, the cue responsible for nuclear accumulation of beta-catenin in the vegetal hemisphere is still unknown in ascidians. Here, we investigated the roles of Wnt5alpha and Dsh in the nuclear accumulation of beta-catenin and activation of its downstream genes in the ascidian Halocynthia roretzi. Wnt5alpha knockdown embryos lost nuclear accumulation of beta-catenin at the 64-cell stage but not at the 32-cell stage, and expression of Hr-lim, one of the targets of beta-catenin, was impaired in the anterior region of the embryo. Zygotic Wnt5alpha expression in the anterior-vegetal blastomeres was primarily responsible for these defects. Dsh knockdown showed no effect on nuclear localization of beta-catenin, but inhibited Hr-lim expression in the posterior region. These results suggest that maintenance of nuclear Hr-beta-catenin after the 64-cell stage is regulated by zygotic Hr-Wnt5alpha, and that expression of its target genes is modulated by both Hr-Wnt5alpha and Hr-Dsh. Our results also highlight the importance of nuclear accumulation of beta-catenin up to the 32-cell stage through a still unclarified mechanism.
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Affiliation(s)
- Narudo Kawai
- Department of Biological Sciences, Graduate School of Sciences, Osaka University, Osaka, Japan.
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42
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Tokuoka M, Kumano G, Nishida H. FGF9/16/20 and Wnt-5α signals are involved in specification of secondary muscle fate in embryos of the ascidian, Halocynthia roretzi. Dev Genes Evol 2007; 217:515-27. [PMID: 17534657 DOI: 10.1007/s00427-007-0160-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2006] [Accepted: 04/25/2007] [Indexed: 10/23/2022]
Abstract
The tail muscle cells of the ascidian tadpole larva originate from two different lineages, the B- (primary) and A- and b- (secondary) line blastomeres of the eight-cell stage embryo. The primary muscle cells assume muscle fate cell-autonomously with the involvement of a localized muscle determinant, macho-1. On the other hand, fate determination of secondary muscle cells is a non-cell-autonomous process that depends on cellular interactions. In this paper, we investigated the mechanisms underlying fate specification of secondary muscle cells in Halocynthia roretzi. We found that FGF and Wnt5 signals were required. In contrast, the Nodal signal, which is required for specification of A-line muscle cells in another ascidian, Ciona intestinalis, was not necessary for the formation of any secondary muscle cells in Halocynthia embryo. Therefore, Halocynthia and Ciona show distinctly different mechanisms for generation of the secondary lineages, despite the fact that embryogenesis appears very similar between these species. We also found that the mechanisms involved in specification of A- and b-line muscle cells were distinct in that the required timing of the FGF signal for the A-line muscle cells preceded that for the b-line. Moreover, the inducer blastomeres for specification of these two lineages were different.
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Affiliation(s)
- Miki Tokuoka
- Department of Biological Sciences, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan.
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43
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Matsumoto J, Kumano G, Nishida H. Direct activation by Ets and Zic is required for initial expression of the Brachyury gene in the ascidian notochord. Dev Biol 2007; 306:870-82. [PMID: 17459364 DOI: 10.1016/j.ydbio.2007.03.034] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2006] [Revised: 03/20/2007] [Accepted: 03/23/2007] [Indexed: 11/22/2022]
Abstract
Extrinsic fibroblast growth factor (FGF) signal and intrinsic factors that determine the response of the signal-receiving blastomeres to FGF regulate mesoderm patterning in embryos of the ascidian Halocynthia roretzi. To investigate how cells integrate information from extrinsic and intrinsic inputs, we examined Brachyury (Hr-Bra) promoter activity in the early embryo. Hr-Bra, which encodes a key transcription factor for notochord development, is expressed exclusively in notochord precursors in a manner dependent on the FGF-MEK-MAPK-Ets signaling pathway and on the intrinsic factors Zic and FoxA. Reporter gene expression driven by the 900-bp upstream region of the Hr-Bra promoter was detected as early as the 110-cell stage in notochord precursors by in situ hybridization with a LacZ probe. Deletion analysis combined with MEK inhibitor treatment demonstrated that the -598/-499 region carries FGF-responsiveness. Electrophoretic mobility shift assay identified three Ets-binding sites in this region that were required for promoter activity. Further deletion analysis conducted by injecting eggs with reporter constructs at higher concentration suggested that the -398/-289 region also has enhancer activity, although ectopic reporter expression was detected in nerve cord and endoderm precursors. The -398/-289 region has a Zic-binding site that was also essential for the enhancer activity. These results indicate that Ets- and Zic-binding sites are critical for the initiation of Hr-Bra expression. In conclusion, information from both extrinsic and intrinsic factors is integrated at the level of enhancer of the target gene by direct binding of the transcription factors to the enhancer region.
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Affiliation(s)
- Jun Matsumoto
- Department of Biological Sciences, Graduate School of Science, Osaka University, Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan.
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44
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Kim GJ, Kumano G, Nishida H. Cell fate polarization in ascidian mesenchyme/muscle precursors by directed FGF signaling and role for an additional ectodermal FGF antagonizing signal in notochord/nerve cord precursors. Development 2007; 134:1509-18. [PMID: 17360771 DOI: 10.1242/dev.02825] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Asymmetric cell division plays a fundamental role in generating various types of embryonic cell. In ascidian embryos, asymmetric cell divisions occur in the vegetal hemisphere in a manner similar to those found in Caenorhabditis elegans. Early divisions in embryos of both species involve inductive events on a single mother cell that result in production of daughters with different cell fates. Here we show in the ascidian Halocynthia roretzi that polarity of muscle/mesenchyme mother precursors is determined solely by the direction from which the FGF9/16/20 signal is presented, a role similar to that of Wnt signaling in the EMS and T cell divisions in C. elegans. However, polarity of nerve cord/notochord mother precursors is determined by possible antagonistic action between the FGF signal and a signal from anterior ectoderm, providing a new mechanism underlying asymmetric cell division. The ectoderm signal suppresses MAPK activation and expression of Hr-FoxA, which encodes an intrinsic competence factor for notochord induction, in the nerve cord lineage.
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Affiliation(s)
- Gil Jung Kim
- Faculty of Marine Bioscience and Technology, Kangnung National University, Gangneung Daehangno, Gangneung 210-702, Republic of Korea.
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45
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Miyazaki Y, Nishida H, Kumano G. Brain induction in ascidian embryos is dependent on juxtaposition of FGF9/16/20-producing and -receiving cells. Dev Genes Evol 2007; 217:177-88. [PMID: 17216525 DOI: 10.1007/s00427-006-0129-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2006] [Accepted: 11/30/2006] [Indexed: 10/23/2022]
Abstract
Coordinated regulation of inductive events, both spatially and temporally, during animal development ensures that tissues are induced at their specific positions within the embryo. The ascidian brain is induced in cells at the anterior edge of the animal hemisphere by fibroblast growth factor (FGF) signals secreted from vegetal cells. To clarify how this process is spatially regulated, we first identified the sources of the FGF signal by examining the expression of brain markers Hr-Otx and Hr-ETR-1 in embryos in which FGF signaling is locally inhibited by injecting individual blastomeres with morpholino oligonucleotide against Hr-FGF9/16/20, which encodes an endogenous brain inducer. The blastomeres identified as the inducing sources are A5.1 and A5.2 at the 16-cell stage and A6.2 and A6.4 at the 24-cell stage, which are juxtaposed with brain precursors at the anterior periphery of the embryo at the respective stages. We also showed that all the cells of the animal hemisphere are capable of expressing Hr-Otx in response to the FGF signal. These results suggest that the position of inducers, rather than competence, plays an important role in determining which animal cells are induced to become brain tissues during ascidian embryogenesis. This situation in brain induction contrasts with that in mesoderm induction, where the positions at which the notochord and mesenchyme are induced are determined mainly by intrinsic competence factors that are inherited by signal-receiving cells.
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Affiliation(s)
- Yuriko Miyazaki
- Department of Biological Sciences, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka, 560-0043, Japan
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46
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Kumano G, Nishida H. Ascidian embryonic development: An emerging model system for the study of cell fate specification in chordates. Dev Dyn 2007; 236:1732-47. [PMID: 17366575 DOI: 10.1002/dvdy.21108] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
The ascidian tadpole larva represents the basic body plan of all chordates in a relatively small number of cells and tissue types. Although it had been considered that ascidians develop largely in a determinative way, whereas vertebrates develop in an inductive way, recent studies at the molecular and cellular levels have uncovered several similarities in the way developmental fates are specified. In this review, we describe ascidian embryogenesis and its cell lineages, introduce several characteristics of ascidian embryos, describe recent advances in understanding of the mechanisms of cell fate specification, and discuss them in the context of what is known in vertebrates and other organisms.
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Affiliation(s)
- Gaku Kumano
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka, Japan.
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