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Steinmetz PRH. Development: Sea anemone segments polarise. Curr Biol 2023; 33:R717-R719. [PMID: 37433272 DOI: 10.1016/j.cub.2023.03.034] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/13/2023]
Abstract
The evolutionary origin of animal segmentation has been debated for centuries. A new study now reveals genetic similarities between the patterning of segmental pouches in a sea anemone, traditionally considered as unsegmented, and segmental structures of vertebrates and arthropods.
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Affiliation(s)
- Patrick R H Steinmetz
- Michael Sars Centre, University of Bergen, Thormøhlensgate 55, N-5008 Bergen, Norway.
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2
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Minelli A. Two-way exchanges between animal and plant biology, with focus on evo-devo. Front Ecol Evol 2022. [DOI: 10.3389/fevo.2022.1057355] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022] Open
Abstract
By definition, biology is the science of all living beings. However, horizons restricted to either plants or animals have characterized the development of life sciences well beyond the emergence of unified perspectives applying to all forms of life, such as the cell theory or the theory of evolution. Separation between botanical and zoological traditions is not destined to go extinct easily, or shortly. Disciplinary isolation is emphasized by institutional contexts such as scientific societies and their congresses, specialist journals, disciplines recognized as teaching subjects and legitimate and fundable research fields. By shaping the personal agendas of individual scientists, this has a strong impact on the development of biology. In some fields, botanical and zoological contributions have long being effectively intertwined, but in many others plant and animal biology have failed to progress beyond a marginal dialogue. Characteristically, the so-called “general biology” and the philosophy of biology are still zoocentric (and often vertebrato- or even anthropocentric). In this article, I discuss legitimacy and fruitfulness of some old lexical and conceptual exchanges between the two traditions (cell, tissue, and embryo). Finally, moving to recent developments, I compare the contributions of plant vs. animal biology to the establishment of evolutionary developmental biology. We cannot expect that stronger integration between the different strands of life sciences will soon emerge by self-organization, but highlighting this persisting imbalance between plant and animal biology will arguably foster progress.
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3
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Strausfeld NJ, Hou X, Sayre ME, Hirth F. The lower Cambrian lobopodian Cardiodictyon resolves the origin of euarthropod brains. Science 2022; 378:905-909. [PMID: 36423269 DOI: 10.1126/science.abn6264] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
For more than a century, the origin and evolution of the arthropod head and brain have eluded a unifying rationale reconciling divergent morphologies and phylogenetic relationships. Here, clarification is provided by the fossilized nervous system of the lower Cambrian lobopodian Cardiodictyon catenulum, which reveals an unsegmented head and brain comprising three cephalic domains, distinct from the metameric ventral nervous system serving its appendicular trunk. Each domain aligns with one of three components of the foregut and with a pair of head appendages. Morphological correspondences with stem group arthropods and alignments of homologous gene expression patterns with those of extant panarthropods demonstrate that cephalic domains of C. catenulum predate the evolution of the euarthropod head yet correspond to neuromeres defining brains of living chelicerates and mandibulates.
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Affiliation(s)
| | - Xianguang Hou
- Yunnan Key Laboratory for Palaeobiology, Institute of Palaeontology, Yunnan University, Kunming, China
| | - Marcel E Sayre
- Lund Vision Group, Department of Biology, Lund University, Lund, Sweden
- Department of Biological Sciences, Macquarie University, Sydney, NSW, Australia
| | - Frank Hirth
- Department of Basic and Clinical Neuroscience, Institute of Psychiatry, Psychology and Neuroscience, King's College London, London, UK
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4
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Mundaca-Escobar M, Cepeda RE, Sarrazin AF. The organizing role of Wnt signaling pathway during arthropod posterior growth. Front Cell Dev Biol 2022; 10:944673. [PMID: 35990604 PMCID: PMC9389326 DOI: 10.3389/fcell.2022.944673] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2022] [Accepted: 07/11/2022] [Indexed: 11/28/2022] Open
Abstract
Wnt signaling pathways are recognized for having major roles in tissue patterning and cell proliferation. In the last years, remarkable progress has been made in elucidating the molecular and cellular mechanisms that underlie sequential segmentation and axial elongation in various arthropods, and the canonical Wnt pathway has emerged as an essential factor in these processes. Here we review, with a comparative perspective, the current evidence concerning the participation of this pathway during posterior growth, its degree of conservation among the different subphyla within Arthropoda and its relationship with the rest of the gene regulatory network involved. Furthermore, we discuss how this signaling pathway could regulate segmentation to establish this repetitive pattern and, at the same time, probably modulate different cellular processes precisely coupled to axial elongation. Based on the information collected, we suggest that this pathway plays an organizing role in the formation of the body segments through the regulation of the dynamic expression of segmentation genes, via controlling the caudal gene, at the posterior region of the embryo/larva, that is necessary for the correct sequential formation of body segments in most arthropods and possibly in their common segmented ancestor. On the other hand, there is insufficient evidence to link this pathway to axial elongation by controlling its main cellular processes, such as convergent extension and cell proliferation. However, conclusions are premature until more studies incorporating diverse arthropods are carried out.
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Affiliation(s)
| | | | - Andres F. Sarrazin
- CoDe-Lab, Instituto de Química, Pontificia Universidad Católica de Valparaíso, Valparaíso, Chile
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5
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Evolutionarily conserved function of the even-skipped ortholog in insects revealed by gene knock-out analyses in Gryllus bimaculatus. Dev Biol 2022; 485:1-8. [DOI: 10.1016/j.ydbio.2022.02.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2021] [Revised: 02/10/2022] [Accepted: 02/11/2022] [Indexed: 11/18/2022]
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6
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Herranz M, Park T, Di Domenico M, Leander BS, Sørensen MV, Worsaae K. Revisiting kinorhynch segmentation: variation of segmental patterns in the nervous system of three aberrant species. Front Zool 2021; 18:54. [PMID: 34674731 PMCID: PMC8529749 DOI: 10.1186/s12983-021-00438-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2021] [Accepted: 10/05/2021] [Indexed: 11/16/2022] Open
Abstract
BACKGROUND Kinorhynch segmentation differs from the patterns found in Chordata, Arthropoda and Annelida which have coeloms and circulatory systems. Due to these differences and their obsolete status as 'Aschelminthes', the microscopic kinorhynchs are often not acknowledged as segmented bilaterians. Yet, morphological studies have shown a conserved segmental arrangement of ectodermal and mesodermal organ systems with spatial correspondence along the anterior-posterior axis. However, a few aberrant kinorhynch lineages present a worm-like body plan with thin cuticle and less distinct segmentation, and thus their study may aid to shed new light on the evolution of segmental patterns within Kinorhyncha. RESULTS Here we found the nervous system in the aberrant Cateria styx and Franciscideres kalenesos to be clearly segmental, and similar to those of non-aberrant kinorhynchs; hereby not mirroring their otherwise aberrant and posteriorly shifted myoanatomy. In Zelinkaderes yong, however, the segmental arrangement of the nervous system is also shifted posteriorly and misaligned with respect to the cuticular segmentation. CONCLUSIONS The morphological disparity together with the distant phylogenetic positions of F. kalenesos, C. styx and Z. yong support a convergent origin of aberrant appearances and segmental mismatches within Kinorhyncha.
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Affiliation(s)
- Maria Herranz
- Department of Biology, University of Copenhagen, Copenhagen, Denmark.
- Natural History Museum of Denmark, University of Copenhagen, Copenhagen, Denmark.
| | - Taeseo Park
- National Institute of Biological Resources, Incheon, South Korea
| | - Maikon Di Domenico
- Centro de Estudos do Mar, Universidade Federal do Paraná, Pontal do Paraná, Brazil
| | - Brian S Leander
- Departments of Zoology and Botany, University of British Columbia, Vancouver, Canada
| | - Martin V Sørensen
- Natural History Museum of Denmark, University of Copenhagen, Copenhagen, Denmark
| | - Katrine Worsaae
- Department of Biology, University of Copenhagen, Copenhagen, Denmark
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7
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Vujić V, Ilić B, Lučić L, Tomić V, Jovanović Z, Pavković-Lučić S, Makarov S. Morphological integration of the head capsule in the millipede Megaphyllum unilineatum (C. L. Koch, 1838) (Diplopoda: Julida): can different modules be recognized? ZOOLOGY 2021; 149:125970. [PMID: 34628210 DOI: 10.1016/j.zool.2021.125970] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Revised: 09/29/2021] [Accepted: 10/01/2021] [Indexed: 10/20/2022]
Abstract
Covariation of multiple morphological traits and modularity have been widely studied in the field of evolutionary developmental biology. Subunits of a morphological structure can evolve separately from each other in a modular fashion. The aims of our study therefore were: i) to test the hypothesis of modularity in the dorsal part of the head capsule and the gnathochilarium separately during late postembryogenesis in the julidan millipede Megaphyllum unilineatum (C. L. Koch, 1838) using geometric morphometrics; and ii) to investigate the influence of allometry on overall morphological integration in the dorsal part of the head capsule and the gnathochilarium in the mentioned species. Individuals from different ontogenetic stadia (stadium VI - stadium XI) were included in the analyses. Significant influence of fluctuating asymmetry on the dorsal part of the head capsule shape was detected by Procrustes ANOVA. Regressions were significant for the symmetric component of both analysed morphological traits, while non-significant regression was detected for the asymmetric component of the head capsule's dorsal part. Hypotheses of modularity for the dorsal part of the head capsule and the gnathochilarium are rejected because our results indicate that a small proportion of alternate partitions has higher covariation between subsets of structure than between the hypothesized modules. Contrary to our expectations, results of the present study show that allometry does not increase the level of morphological integration in the dorsal part of the head capsule and the gnathochilarium in M. unilineatum. Based on the obtained results, we conclude that the dorsal part of the head capsule and the gnathochilarium are not composed of independent modules and that in the case of the capsule's dorsal part, developmental processes affect morphological integration in different ways at different levels of shape variation.
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Affiliation(s)
- Vukica Vujić
- University of Belgrade, Faculty of Biology, Studentski Trg 16, 11000, Belgrade, Serbia.
| | - Bojan Ilić
- University of Belgrade, Faculty of Biology, Studentski Trg 16, 11000, Belgrade, Serbia.
| | - Luka Lučić
- University of Belgrade, Faculty of Biology, Studentski Trg 16, 11000, Belgrade, Serbia.
| | - Vladimir Tomić
- University of Belgrade, Faculty of Biology, Studentski Trg 16, 11000, Belgrade, Serbia.
| | - Zvezdana Jovanović
- University of Belgrade, Faculty of Biology, Studentski Trg 16, 11000, Belgrade, Serbia.
| | - Sofija Pavković-Lučić
- University of Belgrade, Faculty of Biology, Studentski Trg 16, 11000, Belgrade, Serbia.
| | - Slobodan Makarov
- University of Belgrade, Faculty of Biology, Studentski Trg 16, 11000, Belgrade, Serbia.
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8
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Evans SD, Gehling JG, Erwin DH, Droser ML. Ediacara growing pains: Modular addition and development in Dickinsonia costata. PALEOBIOLOGY 2021; 97:10.1017/pab.2021.31. [PMID: 35001986 PMCID: PMC8740542 DOI: 10.1017/pab.2021.31] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Constraining patterns of growth using directly observable and quantifiable characteristics can reveal a wealth of information regarding the biology of the Ediacara Biota - the oldest macroscopic, complex community forming organisms in the fossil record. However, these rely on individuals captured at an instant in time at various growth stages, and so different interpretations can be derived from the same material. Here we leverage newly discovered and well-preserved Dickinsonia costata Sprigg 1947 from South Australia, combined with hundreds of previously described specimens, to test competing hypotheses for the location of module addition. We find considerable variation in the relationship between the total number of modules and body size that cannot be explained solely by expansion and contraction of individuals. Patterns derived assuming new modules differentiated at the anterior result in numerous examples where the oldest module(s) must decrease in size with overall growth, potentially falsifying this hypothesis. Observed polarity as well as the consistent posterior location of defects and indentations support module formation at this end in D. costata. Regardless, changes in repeated units with growth share similarities with those regulated by morphogen gradients in metazoans today, suggesting that these genetic pathways were operating in Ediacaran animals.
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Affiliation(s)
- Scott D Evans
- Department of Geosciences, Virginia Tech, Blacksburg, VA, 24061, USA
| | - James G Gehling
- South Australia Museum, Adelaide, South Australia 5000, Australia
| | - Douglas H Erwin
- Department of Paleobiology MRC-121, National Museum of Natural History, Washington, DC 20013-7012, USA
| | - Mary L Droser
- Department of Earth and Planetary Sciences, University of California, Riverside, CA 92521, USA
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9
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Abstract
The Ediacara Biota preserves the oldest fossil evidence of abundant, complex metazoans. Despite their significance, assigning individual taxa to specific phylogenetic groups has proved problematic. To better understand these forms, we identify developmentally controlled characters in representative taxa from the Ediacaran White Sea assemblage and compare them with the regulatory tools underlying similar traits in modern organisms. This analysis demonstrates that the genetic pathways for multicellularity, axial polarity, musculature, and a nervous system were likely present in some of these early animals. Equally meaningful is the absence of evidence for major differentiation of macroscopic body units, including distinct organs, localized sensory machinery or appendages. Together these traits help to better constrain the phylogenetic position of several key Ediacara taxa and inform our views of early metazoan evolution. An apparent lack of heads with concentrated sensory machinery or ventral nerve cords in such taxa supports the hypothesis that these evolved independently in disparate bilaterian clades.
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Affiliation(s)
- Scott D Evans
- Department of Paleobiology MRC-121, National Museum of Natural History, Washington, DC 20013-7012, USA
| | - Mary L Droser
- Department of Earth and Planetary Sciences, University of California, Riverside, CA 92521, USA
| | - Douglas H Erwin
- Department of Paleobiology MRC-121, National Museum of Natural History, Washington, DC 20013-7012, USA
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10
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Fusco G, Minelli A. The Development of Arthropod Segmentation Across the Embryonic/Post-embryonic Divide – An Evolutionary Perspective. Front Ecol Evol 2021. [DOI: 10.3389/fevo.2021.622482] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
In many arthropods, the appearance of new segments and their differentiation are not completed by the end of embryogenesis but continue, in different form and degree, well after hatching, in some cases up to the last post-embryonic molt. Focusing on the segmentation process currently described as post-embryonic segment addition (or, anamorphosis), we revise here the current knowledge and discuss it in an evolutionary framework which involves data from fossils, comparative morphology of extant taxa and gene expression. We advise that for a better understanding of the developmental changes underlying the evolution of arthropod segmentation, some key concepts should be applied in a critical way. These include the notion of the segment as a body block and the idea that hatching represents a well-defined divide, shared by all arthropods, between two contrasting developmental phases, embryonic vs. post-embryonic. This eventually reveals the complexity of the developmental processes occurring across hatching, which can evolve in different directions and with a different pace, creating the observed vagueness of the embryonic/post-embryonic divide.
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11
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Okada K, Takada S. The second pharyngeal pouch is generated by dynamic remodeling of endodermal epithelium in zebrafish. Development 2020; 147:dev194738. [PMID: 33158927 DOI: 10.1242/dev.194738] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2020] [Accepted: 10/28/2020] [Indexed: 11/20/2022]
Abstract
Pharyngeal arches (PAs) are segmented by endodermal outpocketings called pharyngeal pouches (PPs). Anterior and posterior PAs appear to be generated by different mechanisms, but it is unclear how the anterior and posterior PAs combine. Here, we addressed this issue with precise live imaging of PP development and cell tracing of pharyngeal endoderm in zebrafish embryos. We found that two endodermal bulges are initially generated in the future second PP (PP2) region, which separates anterior and posterior PAs. Subsequently, epithelial remodeling causes contact between these two bulges, resulting in the formation of mature PP2 with a bilayered morphology. The rostral and caudal bulges develop into the operculum and gill, respectively. Development of the caudal PP2 and more posterior PPs is affected by impaired retinoic acid signaling or pax1a/b dysfunction, suggesting that the rostral front of posterior PA development corresponds to the caudal PP2. Our study clarifies an aspect of PA development that is essential for generation of a seamless array of PAs in zebrafish.
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Affiliation(s)
- Kazunori Okada
- Exploratory Research Center on Life and Living Systems, National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaijicho, Okazaki 444-8787, Japan
- National Institute for Basic Biology, National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaiji-cho, Okazaki 444-8787, Japan
| | - Shinji Takada
- Exploratory Research Center on Life and Living Systems, National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaijicho, Okazaki 444-8787, Japan
- National Institute for Basic Biology, National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaiji-cho, Okazaki 444-8787, Japan
- Department for Basic Biology, SOKENDAI (The Graduate University for Advanced Studies), 5-1 Higashiyama, Myodaiji-cho, Okazaki 444-8787, Japan
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12
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Naganathan S, Oates A. Patterning and mechanics of somite boundaries in zebrafish embryos. Semin Cell Dev Biol 2020; 107:170-178. [DOI: 10.1016/j.semcdb.2020.04.014] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2020] [Revised: 03/12/2020] [Accepted: 04/19/2020] [Indexed: 12/12/2022]
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13
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Abstract
ABSTRACT
There is now compelling evidence that many arthropods pattern their segments using a clock-and-wavefront mechanism, analogous to that operating during vertebrate somitogenesis. In this Review, we discuss how the arthropod segmentation clock generates a repeating sequence of pair-rule gene expression, and how this is converted into a segment-polarity pattern by ‘timing factor’ wavefronts associated with axial extension. We argue that the gene regulatory network that patterns segments may be relatively conserved, although the timing of segmentation varies widely, and double-segment periodicity appears to have evolved at least twice. Finally, we describe how the repeated evolution of a simultaneous (Drosophila-like) mode of segmentation within holometabolan insects can be explained by heterochronic shifts in timing factor expression plus extensive pre-patterning of the pair-rule genes.
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Affiliation(s)
- Erik Clark
- Department of Systems Biology, Harvard Medical School, Boston, MA 02115, USA
- Department of Zoology, University of Cambridge, Cambridge, CB2 3EJ, UK
| | - Andrew D. Peel
- School of Biology, Faculty of Biological Sciences, University of Leeds, Leeds, LS2 9JT, UK
| | - Michael Akam
- Department of Zoology, University of Cambridge, Cambridge, CB2 3EJ, UK
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14
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Carrillo-Baltodano AM, Boyle MJ, Rice ME, Meyer NP. Developmental architecture of the nervous system in Themiste lageniformis (Sipuncula): New evidence from confocal laser scanning microscopy and gene expression. J Morphol 2019; 280:1628-1650. [PMID: 31487090 DOI: 10.1002/jmor.21054] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2019] [Revised: 07/19/2019] [Accepted: 08/01/2019] [Indexed: 11/09/2022]
Abstract
Sipuncula is a clade of unsegmented marine worms that are currently placed among the basal radiation of conspicuously segmented Annelida. Their new location provides a unique opportunity to reinvestigate the evolution and development of segmented body plans. Neural segmentation is clearly evident during ganglionic ventral nerve cord (VNC) formation across Sedentaria and Errantia, which includes the majority of annelids. However, recent studies show that some annelid taxa outside of Sedentaria and Errantia have a medullary cord, without ganglia, as adults. Importantly, neural development in these taxa is understudied and interpretation can vary widely. For example, reports in sipunculans range from no evidence of segmentation to vestigial segmentation as inferred from a few pairs of serially repeated neuronal cell bodies along the VNC. We investigated patterns of pan-neuronal, neuronal subtype, and axonal markers using immunohistochemistry and whole mount in situ hybridization (WMISH) during neural development in an indirect-developing sipunculan, Themiste lageniformis. Confocal imaging revealed two clusters of 5HT+ neurons, two pairs of FMRF+ neurons, and Tubulin+ peripheral neurites that appear to be serially positioned along the VNC, similar to other sipunculans, to other annelids, and to spiralian taxa outside of Annelida. WMISH of a synaptotagmin1 ortholog in T. lageniformis (Tl-syt1) showed expression throughout the centralized nervous system (CNS), including the VNC where it appears to correlate with mature 5HT+ and FMRF+ neurons. An ortholog of elav1 (Tl-elav1) showed expression in differentiated neurons of the CNS with continuous expression in the VNC, supporting evidence of a medullary cord, and refuting evidence of ontogenetic segmentation during formation of the nervous system. Thus, we conclude that sipunculans do not exhibit any signs of morphological segmentation during development.
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Affiliation(s)
| | - Michael J Boyle
- Smithsonian Institution, Smithsonian Marine Station at Fort Pierce, Fort Pierce, Florida
| | - Mary E Rice
- Smithsonian Institution, Smithsonian Marine Station at Fort Pierce, Fort Pierce, Florida
| | - Néva P Meyer
- Biology Department, Clark University, Worcester, Massachusetts
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15
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Hemmi N, Akiyama-Oda Y, Fujimoto K, Oda H. A quantitative study of the diversity of stripe-forming processes in an arthropod cell-based field undergoing axis formation and growth. Dev Biol 2018; 437:84-104. [DOI: 10.1016/j.ydbio.2018.03.001] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2017] [Revised: 03/01/2018] [Accepted: 03/01/2018] [Indexed: 12/25/2022]
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16
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Evans SD, Droser ML, Gehling JG. Highly regulated growth and development of the Ediacara macrofossil Dickinsonia costata. PLoS One 2017; 12:e0176874. [PMID: 28520741 PMCID: PMC5435172 DOI: 10.1371/journal.pone.0176874] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2017] [Accepted: 04/18/2017] [Indexed: 11/21/2022] Open
Abstract
The Ediacara Biota represents the oldest fossil evidence for the appearance of animals but linking these taxa to specific clades has proved challenging. Dickinsonia is an abundant, apparently bilaterally symmetrical Ediacara fossil with uncertain affinities. We identified and measured key morphological features of over 900 specimens of Dickinsonia costata from the Ediacara Member, South Australia to characterize patterns in growth and morphology. Here we show that development in Dickinsonia costata was surprisingly highly regulated to maintain an ovoid shape via terminal addition and the predictable expansion of modules. This result, along with other characters found in Dickinsonia suggests that it does not belong within known animal groups, but that it utilized some of the developmental gene networks of bilaterians, a result predicted by gene sequencing of basal metazoans but previously unidentified in the fossil record. Dickinsonia thus represents an extinct clade located between sponges and the last common ancestor of Protostomes and Deuterostomes, and likely belongs within the Eumetazoa.
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Affiliation(s)
- Scott D. Evans
- Department of Earth Sciences, University of California at Riverside, Riverside, California, United States of America
- * E-mail:
| | - Mary L. Droser
- Department of Earth Sciences, University of California at Riverside, Riverside, California, United States of America
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17
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Smith FW, Goldstein B. Segmentation in Tardigrada and diversification of segmental patterns in Panarthropoda. ARTHROPOD STRUCTURE & DEVELOPMENT 2017; 46:328-340. [PMID: 27725256 DOI: 10.1016/j.asd.2016.10.005] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2016] [Revised: 08/11/2016] [Accepted: 10/03/2016] [Indexed: 05/03/2023]
Abstract
The origin and diversification of segmented metazoan body plans has fascinated biologists for over a century. The superphylum Panarthropoda includes three phyla of segmented animals-Euarthropoda, Onychophora, and Tardigrada. This superphylum includes representatives with relatively simple and representatives with relatively complex segmented body plans. At one extreme of this continuum, euarthropods exhibit an incredible diversity of serially homologous segments. Furthermore, distinct tagmosis patterns are exhibited by different classes of euarthropods. At the other extreme, all tardigrades share a simple segmented body plan that consists of a head and four leg-bearing segments. The modular body plans of panarthropods make them a tractable model for understanding diversification of animal body plans more generally. Here we review results of recent morphological and developmental studies of tardigrade segmentation. These results complement investigations of segmentation processes in other panarthropods and paleontological studies to illuminate the earliest steps in the evolution of panarthropod body plans.
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Affiliation(s)
- Frank W Smith
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
| | - Bob Goldstein
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
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18
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Minelli A. Introduction: The evolution of segmentation. ARTHROPOD STRUCTURE & DEVELOPMENT 2017; 46:323-327. [PMID: 28235577 DOI: 10.1016/j.asd.2017.02.002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2017] [Revised: 02/20/2017] [Accepted: 02/20/2017] [Indexed: 06/06/2023]
Affiliation(s)
- Alessandro Minelli
- Department of Biology, University of Padova, Via Ugo Bassi, 58 B, I 35131 Padova, Italy.
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19
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Martin C, Gross V, Pflüger HJ, Stevenson PA, Mayer G. Assessing segmental versus non-segmental features in the ventral nervous system of onychophorans (velvet worms). BMC Evol Biol 2017; 17:3. [PMID: 28049417 PMCID: PMC5209844 DOI: 10.1186/s12862-016-0853-3] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2016] [Accepted: 12/15/2016] [Indexed: 11/12/2022] Open
Abstract
Background Due to their phylogenetic position as one of the closest arthropod relatives, studies of the organisation of the nervous system in onychophorans play a key role for understanding the evolution of body segmentation in arthropods. Previous studies revealed that, in contrast to the arthropods, segmentally repeated ganglia are not present within the onychophoran ventral nerve cords, suggesting that segmentation is either reduced or might be incomplete in the onychophoran ventral nervous system. Results To assess segmental versus non-segmental features in the ventral nervous system of onychophorans, we screened the nerve cords for various markers, including synapsin, serotonin, gamma-aminobutyric acid, RFamide, dopamine, tyramine and octopamine. In addition, we performed retrograde fills of serially repeated commissures and leg nerves to localise the position of neuronal somata supplying those. Our data revealed a mixture of segmental and non-segmental elements within the onychophoran nervous system. Conclusions We suggest that the segmental ganglia of arthropods evolved by a gradual condensation of subsets of neurons either in the arthropod or the arthropod-tardigrade lineage. These findings are in line with the hypothesis of gradual evolution of segmentation in panarthropods and thus contradict a loss of ancestral segmentation within the onychophoran lineage. Electronic supplementary material The online version of this article (doi:10.1186/s12862-016-0853-3) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Christine Martin
- Department of Zoology, University of Kassel, Heinrich-Plett-Str. 40, D-34132, Kassel, Germany.
| | - Vladimir Gross
- Department of Zoology, University of Kassel, Heinrich-Plett-Str. 40, D-34132, Kassel, Germany
| | - Hans-Joachim Pflüger
- Institute of Biology, Neurobiology, Free University of Berlin, Königin-Luise-Str. 28-30, D-14195, Berlin, Germany
| | - Paul A Stevenson
- Physiology of Animals and Behaviour, Institute of Biology, University of Leipzig, Talstraße 33, D-04103, Leipzig, Germany
| | - Georg Mayer
- Department of Zoology, University of Kassel, Heinrich-Plett-Str. 40, D-34132, Kassel, Germany
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Altenburger A. The neuromuscular system of Pycnophyes kielensis (Kinorhyncha: Allomalorhagida) investigated by confocal laser scanning microscopy. EvoDevo 2016; 7:25. [PMID: 27933139 PMCID: PMC5126839 DOI: 10.1186/s13227-016-0062-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2016] [Accepted: 11/17/2016] [Indexed: 11/10/2022] Open
Abstract
Background Kinorhynchs are ecdysozoan animals with a phylogenetic position close to priapulids and loriciferans. To understand the nature of segmentation within Kinorhyncha and to infer a probable ancestry of segmentation within the last common ancestor of Ecdysozoa, the musculature and the nervous system of the allomalorhagid kinorhynch Pycnophyes kielensis were investigated by use of immunohistochemistry, confocal laser scanning microscopy, and 3D reconstruction software. Results The kinorhynch body plan comprises 11 trunk segments. Trunk musculature consists of paired ventral and dorsal longitudinal muscles in segments 1–10 as well as dorsoventral muscles in segments 1–11. Dorsal and ventral longitudinal muscles insert on apodemes of the cuticle inside the animal within each segment. Strands of longitudinal musculature extend over segment borders in segments 1–6. In segments 7–10, the trunk musculature is confined to the segments. Musculature of the digestive system comprises a strong pharyngeal bulb with attached mouth cone muscles as well as pharyngeal bulb protractors and retractors. The musculature of the digestive system shows no sign of segmentation. Judged by the size of the pharyngeal bulb protractors and retractors, the pharyngeal bulb, as well as the introvert, is moved passively by internal pressure caused by concerted action of the dorsoventral muscles. The nervous system comprises a neuropil ring anterior to the pharyngeal bulb. Associated with the neuropil ring are flask-shaped serotonergic somata extending anteriorly and posteriorly. A ventral nerve cord is connected to the neuropil ring and runs toward the anterior until an attachment point in segment 1, and from there toward the posterior with one ganglion in segment 6. Conclusions Segmentation within Kinorhyncha likely evolved from an unsegmented ancestor. This conclusion is supported by continuous trunk musculature in the anterior segments 1–6, continuous pharyngeal bulb protractors and retractors throughout the anterior segments, no sign of segmentation within the digestive system, and the absence of ganglia in most segments. The musculature shows evidence of segmentation that fit the definition of an anteroposteriorly repeated body unit only in segments 7–10. Electronic supplementary material The online version of this article (doi:10.1186/s13227-016-0062-6) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Andreas Altenburger
- Section for Evolutionary Genomics, Natural History Museum of Denmark, University of Copenhagen, Sølvgade 83, 1307 Copenhagen, Denmark
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21
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Clark E, Akam M. Odd-paired controls frequency doubling in Drosophila segmentation by altering the pair-rule gene regulatory network. eLife 2016; 5:e18215. [PMID: 27525481 PMCID: PMC5035143 DOI: 10.7554/elife.18215] [Citation(s) in RCA: 50] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2016] [Accepted: 08/14/2016] [Indexed: 01/08/2023] Open
Abstract
The Drosophila embryo transiently exhibits a double-segment periodicity, defined by the expression of seven 'pair-rule' genes, each in a pattern of seven stripes. At gastrulation, interactions between the pair-rule genes lead to frequency doubling and the patterning of 14 parasegment boundaries. In contrast to earlier stages of Drosophila anteroposterior patterning, this transition is not well understood. By carefully analysing the spatiotemporal dynamics of pair-rule gene expression, we demonstrate that frequency-doubling is precipitated by multiple coordinated changes to the network of regulatory interactions between the pair-rule genes. We identify the broadly expressed but temporally patterned transcription factor, Odd-paired (Opa/Zic), as the cause of these changes, and show that the patterning of the even-numbered parasegment boundaries relies on Opa-dependent regulatory interactions. Our findings indicate that the pair-rule gene regulatory network has a temporally modulated topology, permitting the pair-rule genes to play stage-specific patterning roles.
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Affiliation(s)
- Erik Clark
- Laboratory for Development and Evolution, Department of Zoology, University of Cambridge, Cambridge, United Kingdom
| | - Michael Akam
- Laboratory for Development and Evolution, Department of Zoology, University of Cambridge, Cambridge, United Kingdom
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22
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Leijnse JN, D'Herde K. Revisiting the segmental organization of the human spinal cord. J Anat 2016; 229:384-93. [PMID: 27173936 DOI: 10.1111/joa.12493] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/12/2016] [Indexed: 11/30/2022] Open
Abstract
In classic anatomic atlases, the spinal cord is standardly represented in its anatomical form with symmetrically emerging anterior and posterior roots, which at the level of the intervertebral foramen combine into the spinal nerves. The parts of the cord delimited by the boundaries of the roots are called segments or myelomeres. Associated with their regular repetitive appearance is the notion that the cord is segmentally organized. This segmental view is reinforced by clinical practice. Spinal cord roots innervate specific body parts. The level of cord trauma is diagnosed by the de-innervation symptoms of these parts. However, systemically, the case for a segmentally organized cord is not so clear. To date, developmental and genetic research points to a regionally rather than a segmentally organized cord. In the present study, to what degree the fila radicularia are segmentally implanted along the cord was investigated. The research hypothesis was that if the fila radicularia were non-segmentally implanted at the cord surface, it would be unlikely that the internal neuron stratum would be segmented. The visual segmented aspect of the myelomeres would then be the consequence of the necessary bundling of axons towards the vertebral foramen as the only exits of the vertebral canal, rather than of an underlying segment organization of the cord itself. To investigate the research hypothesis, the fila radicularia in the cervical-upper thoracic part of five spinal cords were detached from their spinal nerves and dissected in detail. The principal research question was if the fila radicularia are separated from their spinal nerves and dissected from their connective tissues up to the cord, would it be possible to reconstruct the original spinal segments from the morphology and interspaces of the fila? The dissections revealed that the anterior fila radicularia emerge from the cord at regular regionally modulated interspaces without systematic segmental delineations. The posterior fila radicularia are somewhat more segmentally implanted, but the pattern is individually inconsistent. The posterior and anterior roots have notable morphological differences, and hypotheses are presented to help explain these. The macroscopic observations are consistent with a regionally but not a segmentally organized cord. This conclusion was visually summarized in photographs of spinal cords with ipsilateral intact roots and contralateral individually dissected fila radicularia. It was suggested that this dual view of the spinal cord be added to the standard anatomic textbooks to counterbalance the current possibly biased view of a segmented cord.
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Affiliation(s)
- J N Leijnse
- Department of Anatomy and Embryology, University of Ghent, Ghent, Belgium
| | - K D'Herde
- Department of Anatomy and Embryology, University of Ghent, Ghent, Belgium
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Zhang H, Xiao S, Liu Y, Yuan X, Wan B, Muscente AD, Shao T, Gong H, Cao G. Armored kinorhynch-like scalidophoran animals from the early Cambrian. Sci Rep 2015; 5:16521. [PMID: 26610151 PMCID: PMC4660871 DOI: 10.1038/srep16521] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2015] [Accepted: 10/14/2015] [Indexed: 11/09/2022] Open
Abstract
Morphology-based phylogenetic analyses support the monophyly of the Scalidophora (Kinorhyncha, Loricifera, Priapulida) and Nematoida (Nematoda, Nematomorpha), together constituting the monophyletic Cycloneuralia that is the sister group of the Panarthropoda. Kinorhynchs are unique among living cycloneuralians in having a segmented body with repeated cuticular plates, longitudinal muscles, dorsoventral muscles, and ganglia. Molecular clock estimates suggest that kinorhynchs may have diverged in the Ediacaran Period. Remarkably, no kinorhynch fossils have been discovered, in sharp contrast to priapulids and loriciferans that are represented by numerous Cambrian fossils. Here we describe several early Cambrian (~535 million years old) kinorhynch-like fossils, including the new species Eokinorhynchus rarus and two unnamed but related forms. E. rarus has characteristic scalidophoran features, including an introvert with pentaradially arranged hollow scalids. Its trunk bears at least 20 annuli each consisting of numerous small rectangular plates, and is armored with five pairs of large and bilaterally placed sclerites. Its trunk annuli are reminiscent of the epidermis segments of kinorhynchs. A phylogenetic analysis resolves E. rarus as a stem-group kinorhynch. Thus, the fossil record confirms that all three scalidophoran phyla diverged no later than the Cambrian Period.
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Affiliation(s)
- Huaqiao Zhang
- Key Laboratory of Economic Stratigraphy and Palaeogeography, Chinese Academy of Sciences (Nanjing Institute of Geology and Palaeontology), Nanjing 210008, China
| | - Shuhai Xiao
- Department of Geosciences, Virginia Tech, Blacksburg, Virginia 24061, USA
| | - Yunhuan Liu
- College of Earth Science and Resources, Chang'an University, Xi'an 710054, China.,State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China
| | - Xunlai Yuan
- State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China
| | - Bin Wan
- State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China
| | - A D Muscente
- Department of Geosciences, Virginia Tech, Blacksburg, Virginia 24061, USA
| | - Tiequan Shao
- College of Earth Science and Resources, Chang'an University, Xi'an 710054, China
| | - Hao Gong
- Virginia Tech - Wake Forest University School of Biomedical Engineering and Sciences, Virginia Tech, Blacksburg, VA 24061, USA
| | - Guohua Cao
- Virginia Tech - Wake Forest University School of Biomedical Engineering and Sciences, Virginia Tech, Blacksburg, VA 24061, USA
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Franke FA, Mayer G. Controversies surrounding segments and parasegments in onychophora: insights from the expression patterns of four "segment polarity genes" in the peripatopsid Euperipatoides rowelli. PLoS One 2014; 9:e114383. [PMID: 25470738 PMCID: PMC4255022 DOI: 10.1371/journal.pone.0114383] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2014] [Accepted: 11/10/2014] [Indexed: 12/20/2022] Open
Abstract
Arthropods typically show two types of segmentation: the embryonic parasegments and the adult segments that lie out of register with each other. Such a dual nature of body segmentation has not been described from Onychophora, one of the closest arthropod relatives. Hence, it is unclear whether onychophorans have segments, parasegments, or both, and which of these features was present in the last common ancestor of Onychophora and Arthropoda. To address this issue, we analysed the expression patterns of the "segment polarity genes" engrailed, cubitus interruptus, wingless and hedgehog in embryos of the onychophoran Euperipatoides rowelli. Our data revealed that these genes are expressed in repeated sets with a specific anterior-to-posterior order along the body in embryos of E. rowelli. In contrast to arthropods, the expression occurs after the segmental boundaries have formed. Moreover, the initial segmental furrow retains its position within the engrailed domain throughout development, whereas no new furrow is formed posterior to this domain. This suggests that no re-segmentation of the embryo occurs in E. rowelli. Irrespective of whether or not there is a morphological or genetic manifestation of parasegments in Onychophora, our data clearly show that parasegments, even if present, cannot be regarded as the initial metameric units of the onychophoran embryo, because the expression of key genes that define the parasegmental boundaries in arthropods occurs after the segmental boundaries have formed. This is in contrast to arthropods, in which parasegments rather than segments are the initial metameric units of the embryo. Our data further revealed that the expression patterns of "segment polarity genes" correspond to organogenesis rather than segment formation. This is in line with the concept of segmentation as a result of concerted evolution of individual periodic structures rather than with the interpretation of 'segments' as holistic units.
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Affiliation(s)
- Franziska Anni Franke
- Animal Evolution & Development, Institute of Biology, University of Leipzig, Talstraße 33, D-04103 Leipzig, Germany
| | - Georg Mayer
- Animal Evolution & Development, Institute of Biology, University of Leipzig, Talstraße 33, D-04103 Leipzig, Germany
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Dunn CW, Giribet G, Edgecombe GD, Hejnol A. Animal Phylogeny and Its Evolutionary Implications. ANNUAL REVIEW OF ECOLOGY EVOLUTION AND SYSTEMATICS 2014. [DOI: 10.1146/annurev-ecolsys-120213-091627] [Citation(s) in RCA: 261] [Impact Index Per Article: 26.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Casey W. Dunn
- Department of Ecology and Evolutionary Biology, Brown University, Providence, Rhode Island 02912;
| | - Gonzalo Giribet
- Museum of Comparative Zoology, Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138;
| | - Gregory D. Edgecombe
- Department of Earth Sciences, The Natural History Museum, London SW7 5BD, United Kingdom;
| | - Andreas Hejnol
- Sars International Centre for Marine Molecular Biology, University of Bergen, 5008 Bergen, Norway;
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Graham A, Butts T, Lumsden A, Kiecker C. What can vertebrates tell us about segmentation? EvoDevo 2014; 5:24. [PMID: 25009737 PMCID: PMC4088296 DOI: 10.1186/2041-9139-5-24] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2014] [Accepted: 06/11/2014] [Indexed: 12/28/2022] Open
Abstract
Segmentation is a feature of the body plans of a number of diverse animal groupings, including the annelids, arthropods and chordates. However, it has been unclear whether or not these different manifestations of segmentation are independently derived or have a common origin. Central to this issue is whether or not there are common developmental mechanisms that establish segmentation and the evolutionary origins of these processes. A fruitful way to address this issue is to consider how segmentation in vertebrates is directed. During vertebrate development three different segmental systems are established: the somites, the rhombomeres and the pharyngeal arches. In each an iteration of parts along the long axis is established. However, it is clear that the formation of the somites, rhombomeres or pharyngeal arches have little in common, and as such there is no single segmentation process. These different segmental systems also have distinct evolutionary histories, thus highlighting the fact that segmentation can and does evolve independently at multiple points. We conclude that the term segmentation indicates nothing more than a morphological description and that it implies no mechanistic similarity. Thus it is probable that segmentation has arisen repeatedly during animal evolution.
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Affiliation(s)
- Anthony Graham
- MRC Centre for Developmental Neurobiology, King's College London, London SE1 1UL, UK
| | - Thomas Butts
- MRC Centre for Developmental Neurobiology, King's College London, London SE1 1UL, UK
| | - Andrew Lumsden
- MRC Centre for Developmental Neurobiology, King's College London, London SE1 1UL, UK
| | - Clemens Kiecker
- MRC Centre for Developmental Neurobiology, King's College London, London SE1 1UL, UK
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