1
|
Martinez P, Bailly X, Sprecher SG, Hartenstein V. The Acoel nervous system: morphology and development. Neural Dev 2024; 19:9. [PMID: 38907301 PMCID: PMC11191258 DOI: 10.1186/s13064-024-00187-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2024] [Accepted: 06/15/2024] [Indexed: 06/23/2024] Open
Abstract
Acoel flatworms have played a relevant role in classical (and current) discussions on the evolutionary origin of bilaterian animals. This is mostly derived from the apparent simplicity of their body architectures. This tenet has been challenged over the last couple of decades, mostly because detailed studies of their morphology and the introduction of multiple genomic technologies have unveiled a complexity of cell types, tissular arrangements and patterning mechanisms that were hidden below this 'superficial' simplicity. One tissue that has received a particular attention has been the nervous system (NS). The combination of ultrastructural and single cell methodologies has revealed unique cellular diversity and developmental trajectories for most of their neurons and associated sensory systems. Moreover, the great diversity in NS architectures shown by different acoels offers us with a unique group of animals where to study key aspects of neurogenesis and diversification od neural systems over evolutionary time.In this review we revisit some recent developments in the characterization of the acoel nervous system structure and the regulatory mechanisms that contribute to their embryological development. We end up by suggesting some promising avenues to better understand how this tissue is organized in its finest cellular details and how to achieve a deeper knowledge of the functional roles that genes and gene networks play in its construction.
Collapse
Affiliation(s)
- Pedro Martinez
- Departament de Genètica, Microbiologia I Estadística, Universitat de Barcelona, Av. Diagonal 643, Barcelona, 08028, Spain.
- ICREA (Institut Català de Recerca I Estudis Avancats), Barcelona, Spain.
| | - Xavier Bailly
- Station Biologique de Roscoff, Multicellular Marine Models (M3) Team, FR2424, CNRS / Sorbonne Université - Place Georges Teissier, Roscoff, 29680, France
| | - Simon G Sprecher
- Department of Biology, University of Fribourg, 10, Ch. Du Musée, Fribourg, 1700, Switzerland
| | - Volker Hartenstein
- Department of Molecular, Cell and Developmental Biology, University of California, Los Angeles (UCLA), Los Angeles, CA, USA.
| |
Collapse
|
2
|
Mussini G, Dunn FS. Decline and fall of the Ediacarans: late-Neoproterozoic extinctions and the rise of the modern biosphere. Biol Rev Camb Philos Soc 2024; 99:110-130. [PMID: 37667585 DOI: 10.1111/brv.13014] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2023] [Revised: 08/22/2023] [Accepted: 08/25/2023] [Indexed: 09/06/2023]
Abstract
The end-Neoproterozoic transition marked a gradual but permanent shift between distinct configurations of Earth's biosphere. This interval witnessed the demise of the enigmatic Ediacaran Biota, ushering in the structured trophic webs and disparate animal body plans of Phanerozoic ecosystems. However, little consensus exists on the reality, drivers, and macroevolutionary implications of end-Neoproterozoic extinctions. Here we evaluate potential drivers of late-Neoproterozoic turnover by addressing recent findings on Ediacaran geochronology, the persistence of classical Ediacaran macrobionts into the Cambrian, and the existence of Ediacaran crown-group eumetazoans. Despite renewed interest in the possibility of Phanerozoic-style 'mass extinctions' in the latest Neoproterozoic, our synthesis of the available evidence does not support extinction models based on episodic geochemical triggers, nor does it validate simple ecological interpretations centred on direct competitive displacement. Instead, we argue that the protracted and indirect effects of early bilaterian innovations, including escalations in sediment engineering, predation, and the largely understudied impacts of reef-building, may best account for the temporal structure and possible selectivity of late-Neoproterozoic extinctions. We integrate these processes into a generalised model of early eumetazoan-dominated ecologies, charting the disruption of spatial and temporal isotropy on the Ediacaran benthos as a consequence of diversifying macrofaunal interactions. Given the nature of resource distribution in Ediacaran ecologies, the continuities among Ediacaran and Cambrian faunas, and the convergent origins of ecologically disruptive innovations among bilaterians we suggest that the rise of Phanerozoic-type biotas may have been unstoppable.
Collapse
Affiliation(s)
- Giovanni Mussini
- Department of Earth Sciences, Downing Street, University of Cambridge, Cambridge, CB2 3EQ, UK
| | - Frances S Dunn
- Oxford University Museum of Natural History, Parks Road, University of Oxford, Oxford, OX1 3PW, UK
| |
Collapse
|
3
|
Martinez P, Ustyantsev K, Biryukov M, Mouton S, Glasenburg L, Sprecher SG, Bailly X, Berezikov E. Genome assembly of the acoel flatworm Symsagittifera roscoffensis, a model for research on body plan evolution and photosymbiosis. G3 (BETHESDA, MD.) 2023; 13:jkac336. [PMID: 36542495 PMCID: PMC9911081 DOI: 10.1093/g3journal/jkac336] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/26/2022] [Revised: 12/16/2022] [Accepted: 12/17/2022] [Indexed: 12/24/2022]
Abstract
Symsagittifera roscoffensis is a well-known member of the order Acoela that lives in symbiosis with the algae Tetraselmis convolutae during its adult stage. Its natural habitat is the eastern coast of the Atlantic, where at specific locations thousands of individuals can be found, mostly, lying in large pools on the surface of sand at low tide. As a member of the Acoela it has been thought as a proxy for ancestral bilaterian animals; however, its phylogenetic position remains still debated. In order to understand the basic structural characteristics of the acoel genome, we sequenced and assembled the genome of aposymbiotic species S. roscoffensis. The size of this genome was measured to be in the range of 910-940 Mb. Sequencing of the genome was performed using PacBio Hi-Fi technology. Hi-C and RNA-seq data were also generated to scaffold and annotate it. The resulting assembly is 1.1 Gb large (covering 118% of the estimated genome size) and highly continuous, with N50 scaffold size of 1.04 Mb. The repetitive fraction of the genome is 61%, of which 85% (half of the genome) are LTR retrotransposons. Genome-guided transcriptome assembly identified 34,493 genes, of which 29,351 are protein coding (BUSCO score 97.6%), and 30.2% of genes are spliced leader trans-spliced. The completeness of this genome suggests that it can be used extensively to characterize gene families and conduct accurate phylogenomic reconstructions.
Collapse
Affiliation(s)
- Pedro Martinez
- Departament de Genètica, Microbiologia i Estadística, Universitat de Barcelona, Av. Diagonal 643, 08028 Barcelona, Spain
- Institut Català de Recerca i Estudis Avançats (ICREA), Barcelona 08193, Spain
| | - Kirill Ustyantsev
- European Research Institute for the Biology of Ageing, University Medical Center Groningen, University of Groningen, Groningen 9700AD, The Netherlands
| | - Mikhail Biryukov
- Institute of Cytology and Genetics SB RAS, Novosibirsk 630090, Russia
| | - Stijn Mouton
- European Research Institute for the Biology of Ageing, University Medical Center Groningen, University of Groningen, Groningen 9700AD, The Netherlands
| | - Liza Glasenburg
- European Research Institute for the Biology of Ageing, University Medical Center Groningen, University of Groningen, Groningen 9700AD, The Netherlands
| | - Simon G Sprecher
- Department of Biology, University of Fribourg, Chemin du Musee 10, 1700 Fribourg, Switzerland
| | - Xavier Bailly
- Station Biologique de Roscoff, Multicellular Marine Models (M3) team, FR2424, CNRS/Sorbonne Université—Place Georges Teissier, 29680 Roscoff, France
| | - Eugene Berezikov
- European Research Institute for the Biology of Ageing, University Medical Center Groningen, University of Groningen, Groningen 9700AD, The Netherlands
| |
Collapse
|
4
|
Nanglu K, Cole SR, Wright DF, Souto C. Worms and gills, plates and spines: the evolutionary origins and incredible disparity of deuterostomes revealed by fossils, genes, and development. Biol Rev Camb Philos Soc 2023; 98:316-351. [PMID: 36257784 DOI: 10.1111/brv.12908] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2022] [Revised: 09/23/2022] [Accepted: 09/28/2022] [Indexed: 01/12/2023]
Abstract
Deuterostomes are the major division of animal life which includes sea stars, acorn worms, and humans, among a wide variety of ecologically and morphologically disparate taxa. However, their early evolution is poorly understood, due in part to their disparity, which makes identifying commonalities difficult, as well as their relatively poor early fossil record. Here, we review the available morphological, palaeontological, developmental, and molecular data to establish a framework for exploring the origins of this important and enigmatic group. Recent fossil discoveries strongly support a vermiform ancestor to the group Hemichordata, and a fusiform active swimmer as ancestor to Chordata. The diverse and anatomically bewildering variety of forms among the early echinoderms show evidence of both bilateral and radial symmetry. We consider four characteristics most critical for understanding the form and function of the last common ancestor to Deuterostomia: Hox gene expression patterns, larval morphology, the capacity for biomineralization, and the morphology of the pharyngeal region. We posit a deuterostome last common ancestor with a similar antero-posterior gene regulatory system to that found in modern acorn worms and cephalochordates, a simple planktonic larval form, which was later elaborated in the ambulacrarian lineage, the ability to secrete calcium minerals in a limited fashion, and a pharyngeal respiratory region composed of simple pores. This animal was likely to be motile in adult form, as opposed to the sessile origins that have been historically suggested. Recent debates regarding deuterostome monophyly as well as the wide array of deuterostome-affiliated problematica further suggest the possibility that those features were not only present in the last common ancestor of Deuterostomia, but potentially in the ur-bilaterian. The morphology and development of the early deuterostomes, therefore, underpin some of the most significant questions in the study of metazoan evolution.
Collapse
Affiliation(s)
- Karma Nanglu
- Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA, 02138, USA
| | - Selina R Cole
- Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, 10th & Constitution Avenue NW, Washington, DC, 20560, USA.,Sam Noble Museum, University of Oklahoma, 2401 Chautauqua Avenue, Norman, OK, 73072, USA.,School of Geosciences, University of Oklahoma, 100 E Boyd Street, Norman, OK, 73019, USA
| | - David F Wright
- Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, 10th & Constitution Avenue NW, Washington, DC, 20560, USA.,Sam Noble Museum, University of Oklahoma, 2401 Chautauqua Avenue, Norman, OK, 73072, USA.,School of Geosciences, University of Oklahoma, 100 E Boyd Street, Norman, OK, 73019, USA
| | - Camilla Souto
- Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, 10th & Constitution Avenue NW, Washington, DC, 20560, USA.,School of Natural Sciences & Mathematics, Stockton University, 101 Vera King Farris Dr, Galloway, NJ, 08205, USA
| |
Collapse
|
5
|
Duruz J, Sprecher SG. Evolution and Origins of Nervous Systems. Neurogenetics 2023. [DOI: 10.1007/978-3-031-07793-7_8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
|
6
|
Zheng Y, Cong X, Liu H, Wang Y, Storey KB, Chen M. Nervous System Development and Neuropeptides Characterization in Embryo and Larva: Insights from a Non-Chordate Deuterostome, the Sea Cucumber Apostichopus japonicus. BIOLOGY 2022; 11:biology11101538. [PMID: 36290441 PMCID: PMC9598280 DOI: 10.3390/biology11101538] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/26/2022] [Revised: 10/17/2022] [Accepted: 10/18/2022] [Indexed: 11/16/2022]
Abstract
Here, we described the complex nervous system at five early developmental stages (blastula, gastrula, auricularia, doliolaria and pentactula) of a holothurian species with highly economic value, Apostichopus japonicus. The results revealed that the nervous system of embryos and larvae is mainly distributed in the anterior apical region, ciliary bands or rings, and the feeding and attachment organs, and that serotonergic immunoreactivity was not observed until the embryo developed into the late gastrula; these are evolutionarily conserved features of echinoderm, hemichordate and protostome larvae. Furthermore, based on available transcriptome data, we reported the neuropeptide precursors profile at different embryonic and larval developmental stages. This analysis showed that 40 neuropeptide precursors present in adult sea cucumbers were also identified at different developmental stages of embryos and larvae, and only four neuropeptide precursors (SWYG precursor 2, GYWKDLDNYVKAHKT precursor, Neuropeptide precursor 14-like precursor, GLRFAmprecursor-like precursor) predicted in adults were absent in embryos and larvae. Combining the quantitative expression of ten specific neuropeptide precursor genes (NPs) by qRT-PCR, we revealed the potential important roles of neuropeptides in embryo development, feeding and attachment in A. japonicus larvae. In conclusion, this work provides novel perspectives on the diverse physiological functions of neuropeptides and contributes to understanding the evolution of neuropeptidergic systems in echinoderm embryos and larvae.
Collapse
Affiliation(s)
- Yingqiu Zheng
- The Key Laboratory of Mariculture, Ministry of Education, Ocean University of China, Qingdao 266003, China
| | - Xiao Cong
- The Key Laboratory of Mariculture, Ministry of Education, Ocean University of China, Qingdao 266003, China
| | - Huachen Liu
- The Key Laboratory of Mariculture, Ministry of Education, Ocean University of China, Qingdao 266003, China
| | - Yixin Wang
- The Key Laboratory of Mariculture, Ministry of Education, Ocean University of China, Qingdao 266003, China
| | - Kenneth B. Storey
- Institute of Biochemistry, Carleton University, 1125 Colonel By Drive, Ottawa, ON K1S 5B6, Canada
| | - Muyan Chen
- The Key Laboratory of Mariculture, Ministry of Education, Ocean University of China, Qingdao 266003, China
- Correspondence:
| |
Collapse
|
7
|
Duruz J, Kaltenrieder C, Ladurner P, Bruggmann R, Martìnez P, Sprecher SG. Acoel Single-Cell Transcriptomics: Cell Type Analysis of a Deep Branching Bilaterian. Mol Biol Evol 2021; 38:1888-1904. [PMID: 33355655 PMCID: PMC8097308 DOI: 10.1093/molbev/msaa333] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Bilaterian animals display a wide variety of cell types, organized into defined anatomical structures and organ systems, which are mostly absent in prebilaterian animals. Xenacoelomorpha are an early-branching bilaterian phylum displaying an apparently relatively simple anatomical organization that have greatly diverged from other bilaterian clades. In this study, we use whole-body single-cell transcriptomics on the acoel Isodiametra pulchra to identify and characterize different cell types. Our analysis identifies the existence of ten major cell type categories in acoels all contributing to main biological functions of the organism: metabolism, locomotion and movements, behavior, defense, and development. Interestingly, although most cell clusters express core fate markers shared with other animal clades, we also describe a surprisingly large number of clade-specific marker genes, suggesting the emergence of clade-specific common molecular machineries functioning in distinct cell types. Together, these results provide novel insight into the evolution of bilaterian cell types and open the door to a better understanding of the origins of the bilaterian body plan and their constitutive cell types.
Collapse
Affiliation(s)
- Jules Duruz
- Department of Biology, Institute of Zoology, University of Fribourg, Fribourg, Switzerland
| | - Cyrielle Kaltenrieder
- Department of Biology, Institute of Zoology, University of Fribourg, Fribourg, Switzerland
| | - Peter Ladurner
- Institute of Zoology and Center of Molecular Bioscience Innsbruck, University of Innsbruck, Innsbruck, Austria
| | - Rémy Bruggmann
- Institute of Cell Biology, University of Bern, Bern, Switzerland.,Interfaculty Bioinformatics Unit, University of Bern, Bern, Switzerland
| | - Pedro Martìnez
- Departament de Genètica, Universitat de Barcelona, Barcelona, Catalonia, Spain.,Institut Català de Recerca i Estudis Avancats (ICREA), Passeig de Lluís Companys, Barcelona, Spain
| | - Simon G Sprecher
- Department of Biology, Institute of Zoology, University of Fribourg, Fribourg, Switzerland
| |
Collapse
|
8
|
Structural analysis of the statocyst and nervous system of Praesagittifera naikaiensis, an acoel flatworm, during development after hatching. ZOOMORPHOLOGY 2021. [DOI: 10.1007/s00435-021-00521-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
|
9
|
Formery L, Orange F, Formery A, Yaguchi S, Lowe CJ, Schubert M, Croce JC. Neural anatomy of echinoid early juveniles and comparison of nervous system organization in echinoderms. J Comp Neurol 2020; 529:1135-1156. [PMID: 32841380 DOI: 10.1002/cne.25012] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2020] [Revised: 07/07/2020] [Accepted: 07/24/2020] [Indexed: 12/12/2022]
Abstract
The echinoderms are a phylum of marine deuterostomes characterized by the pentaradial (five fold) symmetry of their adult bodies. Due to this unusual body plan, adult echinoderms have long been excluded from comparative analyses aimed at understanding the origin and evolution of deuterostome nervous systems. Here, we investigated the neural anatomy of early juveniles of representatives of three of the five echinoderm classes: the echinoid Paracentrotus lividus, the asteroid Patiria miniata, and the holothuroid Parastichopus parvimensis. Using whole mount immunohistochemistry and confocal microscopy, we found that the nervous system of echinoid early juveniles is composed of three main structures: a basiepidermal nerve plexus, five radial nerve cords connected by a circumoral nerve ring, and peripheral nerves innervating the appendages. Our whole mount preparations further allowed us to obtain thorough descriptions of these structures and of several innervation patterns, in particular at the level of the appendages. Detailed comparisons of the echinoid juvenile nervous system with those of asteroid and holothuroid juveniles moreover supported a general conservation of the main neural structures in all three species, including at the level of the appendages. Our results support the previously proposed hypotheses for the existence of two neural units in echinoderms: one consisting of the basiepidermal nerve plexus to process sensory stimuli locally and one composed of the radial nerve cords and the peripheral nerves constituting a centralized control system. This study provides the basis for more in-depth comparisons of the echinoderm adult nervous system with those of other animals, in particular hemichordates and chordates, to address the long-standing controversies about deuterostome nervous system evolution.
Collapse
Affiliation(s)
- Laurent Formery
- Laboratoire de Biologie du Développement de Villefranche-sur-Mer (LBDV), Evolution of Intracellular Signaling in Development (EvoInSiDe), Sorbonne Université, CNRS, Villefranche-sur-Mer, France
| | - François Orange
- Centre Commun de Microscopie Appliquée (CCMA), Université Côte d'Azur, Nice, France
| | | | - Shunsuke Yaguchi
- Shimoda Marine Research Center, University of Tsukuba, Shizuoka, Japan
| | - Christopher J Lowe
- Department of Biology, Hopkins Marine Station, Stanford University, Pacific Grove, California, USA
| | - Michael Schubert
- Laboratoire de Biologie du Développement de Villefranche-sur-Mer (LBDV), Evolution of Intracellular Signaling in Development (EvoInSiDe), Sorbonne Université, CNRS, Villefranche-sur-Mer, France
| | - Jenifer C Croce
- Laboratoire de Biologie du Développement de Villefranche-sur-Mer (LBDV), Evolution of Intracellular Signaling in Development (EvoInSiDe), Sorbonne Université, CNRS, Villefranche-sur-Mer, France
| |
Collapse
|
10
|
Hulett RE, Potter D, Srivastava M. Neural architecture and regeneration in the acoel Hofstenia miamia. Proc Biol Sci 2020; 287:20201198. [PMID: 32693729 PMCID: PMC7423668 DOI: 10.1098/rspb.2020.1198] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
The origin of bilateral symmetry, a major transition in animal evolution, coincided with the evolution of organized nervous systems that show regionalization along major body axes. Studies of Xenacoelomorpha, the likely outgroup lineage to all other animals with bilateral symmetry, can inform the evolutionary history of animal nervous systems. Here, we characterized the neural anatomy of the acoel Hofstenia miamia. Our analysis of transcriptomic data uncovered orthologues of enzymes for all major neurotransmitter synthesis pathways. Expression patterns of these enzymes revealed the presence of a nerve net and an anterior condensation of neural cells. The anterior condensation was layered, containing several cell types with distinct molecular identities organized in spatially distinct territories. Using these anterior cell types and structures as landmarks, we obtained a detailed timeline for regeneration of the H. miamia nervous system, showing that the anterior condensation is restored by eight days after amputation. Our work detailing neural anatomy in H. miamia will enable mechanistic studies of neural cell type diversity and regeneration and provide insight into the evolution of these processes.
Collapse
Affiliation(s)
- Ryan E Hulett
- Department of Organismic and Evolutionary Biology, Museum of Comparative Zoology, Harvard University, Cambridge, MA, USA
| | - Deirdre Potter
- Department of Stem Cell and Regenerative Biology, Harvard University, Cambridge, MA, USA
| | - Mansi Srivastava
- Department of Organismic and Evolutionary Biology, Museum of Comparative Zoology, Harvard University, Cambridge, MA, USA
| |
Collapse
|
11
|
Martinez P, Sprecher SG. Of Circuits and Brains: The Origin and Diversification of Neural Architectures. Front Ecol Evol 2020. [DOI: 10.3389/fevo.2020.00082] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
|
12
|
Fields C, Levin M. Does regeneration recapitulate phylogeny? Planaria as a model of body-axis specification in ancestral eumetazoa. Commun Integr Biol 2020; 13:27-38. [PMID: 32128026 PMCID: PMC7039665 DOI: 10.1080/19420889.2020.1729601] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2019] [Revised: 02/07/2020] [Accepted: 02/09/2020] [Indexed: 12/31/2022] Open
Abstract
Metazoan body plans combine well-defined primary, secondary, and in many bilaterians, tertiary body axes with structural asymmetries at multiple scales. Despite decades of study, how axis-defining symmetries and system-defining asymmetries co-emerge during both evolution and development remain open questions. Regeneration studies in asexual planaria have demonstrated an array of viable forms with symmetrized and, in some cases, duplicated body axes. We suggest that such forms may point toward an ancestral eumetazoan form with characteristics of both cnidarians and placazoa.
Collapse
Affiliation(s)
| | - Michael Levin
- Allen Discovery Center, Tufts University, Medford, MA, USA
| |
Collapse
|
13
|
Fields C, Bischof J, Levin M. Morphological Coordination: A Common Ancestral Function Unifying Neural and Non-Neural Signaling. Physiology (Bethesda) 2020; 35:16-30. [DOI: 10.1152/physiol.00027.2019] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Nervous systems are traditionally thought of as providing sensing and behavioral coordination functions at the level of the whole organism. What is the evolutionary origin of the mechanisms enabling the nervous systems’ information processing ability? Here, we review evidence from evolutionary, developmental, and regenerative biology suggesting a deeper, ancestral function of both pre-neural and neural cell-cell communication systems: the long-distance coordination of cell division and differentiation required to create and maintain body-axis symmetries. This conceptualization of the function of nervous system activity sheds new light on the evolutionary transition from the morphologically rudimentary, non-neural Porifera and Placazoa to the complex morphologies of Ctenophores, Cnidarians, and Bilaterians. It further allows a sharp formulation of the distinction between long-distance axis-symmetry coordination based on external coordinates, e.g., by whole-organism scale trophisms as employed by plants and sessile animals, and coordination based on body-centered coordinates as employed by motile animals. Thus we suggest that the systems that control animal behavior evolved from ancient mechanisms adapting preexisting ionic and neurotransmitter mechanisms to regulate individual cell behaviors during morphogenesis. An appreciation of the ancient, non-neural origins of bioelectrically mediated computation suggests new approaches to the study of embryological development, including embryological dysregulation, cancer, regenerative medicine, and synthetic bioengineering.
Collapse
Affiliation(s)
- Chris Fields
- 23 Rue des Lavandières, Caunes Minervois, France
| | - Johanna Bischof
- Allen Discovery Center at Tufts University, Medford, Massachusetts
| | - Michael Levin
- Allen Discovery Center at Tufts University, Medford, Massachusetts
| |
Collapse
|
14
|
Mitigating Anticipated Effects of Systematic Errors Supports Sister-Group Relationship between Xenacoelomorpha and Ambulacraria. Curr Biol 2019; 29:1818-1826.e6. [PMID: 31104936 DOI: 10.1016/j.cub.2019.04.009] [Citation(s) in RCA: 78] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2019] [Revised: 03/19/2019] [Accepted: 04/03/2019] [Indexed: 01/21/2023]
Abstract
Xenoturbella and the acoelomorph worms (Xenacoelomorpha) are simple marine animals with controversial affinities. They have been placed as the sister group of all other bilaterian animals (Nephrozoa hypothesis), implying their simplicity is an ancient characteristic [1, 2]; alternatively, they have been linked to the complex Ambulacraria (echinoderms and hemichordates) in a clade called the Xenambulacraria [3-5], suggesting their simplicity evolved by reduction from a complex ancestor. The difficulty resolving this problem implies the phylogenetic signal supporting the correct solution is weak and affected by inadequate modeling, creating a misleading non-phylogenetic signal. The idea that the Nephrozoa hypothesis might be an artifact is prompted by the faster molecular evolutionary rate observed within the Acoelomorpha. Unequal rates of evolution are known to result in the systematic artifact of long branch attraction, which would be predicted to result in an attraction between long-branch acoelomorphs and the outgroup, pulling them toward the root [6]. Other biases inadequately accommodated by the models used can also have strong effects, exacerbated in the context of short internal branches and long terminal branches [7]. We have assembled a large and informative dataset to address this problem. Analyses designed to reduce or to emphasize misleading signals show the Nephrozoa hypothesis is supported under conditions expected to exacerbate errors, and the Xenambulacraria hypothesis is preferred in conditions designed to reduce errors. Our reanalyses of two other recently published datasets [1, 2] produce the same result. We conclude that the Xenacoelomorpha are simplified relatives of the Ambulacraria.
Collapse
|
15
|
Brauchle M, Bilican A, Eyer C, Bailly X, Martínez P, Ladurner P, Bruggmann R, Sprecher SG. Xenacoelomorpha Survey Reveals That All 11 Animal Homeobox Gene Classes Were Present in the First Bilaterians. Genome Biol Evol 2018; 10:2205-2217. [PMID: 30102357 PMCID: PMC6125248 DOI: 10.1093/gbe/evy170] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/07/2018] [Indexed: 11/13/2022] Open
Abstract
Homeodomain transcription factors are involved in many developmental processes across animals and have been linked to body plan evolution. Detailed classifications of these proteins identified 11 distinct classes of homeodomain proteins in animal genomes, each harboring specific sequence composition and protein domains. Although humans contain the full set of classes, Drosophila melanogaster and Caenorhabditis elegans each lack one specific class. Furthermore, representative previous analyses in sponges, ctenophores, and cnidarians could not identify several classes in those nonbilaterian metazoan taxa. Consequently, it is currently unknown when certain homeodomain protein classes first evolved during animal evolution. Here, we investigate representatives of the sister group to all remaining bilaterians, the Xenacoelomorpha. We analyzed three acoel, one nemertodermatid, and one Xenoturbella transcriptomes and identified their expressed homeodomain protein content. We report the identification of representatives of all 11 classes of animal homeodomain transcription factors in Xenacoelomorpha and we describe and classify their homeobox genes relative to the established animal homeodomain protein families. Our findings suggest that the genome of the last common ancestor of bilateria contained the full set of these gene classes, supporting the subsequent diversification of bilaterians.
Collapse
Affiliation(s)
- Michael Brauchle
- Department of Biology, Institute of Zoology, University of Fribourg, Switzerland.,Department of Biology, Institute of Cell Biology, University of Bern, Switzerland.,These authors contributed equally to this work
| | - Adem Bilican
- Department of Biology, Interfaculty Bioinformatics Unit, University of Bern, Switzerland.,These authors contributed equally to this work
| | - Claudia Eyer
- Department of Biology, Interfaculty Bioinformatics Unit, University of Bern, Switzerland
| | - Xavier Bailly
- UPMC-CNRS FR2424, Station Biologique de Roscoff, Roscoff, France
| | - Pedro Martínez
- Departament de Genètica, Universitat de Barcelona, Catalonia, Spain.,Institut Català de Recerca i Estudis Avancats (ICREA), Barcelona, Spain
| | - Peter Ladurner
- Institute of Zoology and Center of Molecular Bioscience Innsbruck, University of Innsbruck, Austria
| | - Rémy Bruggmann
- Department of Biology, Interfaculty Bioinformatics Unit, University of Bern, Switzerland
| | - Simon G Sprecher
- Department of Biology, Institute of Zoology, University of Fribourg, Switzerland
| |
Collapse
|
16
|
Arboleda E, Hartenstein V, Martinez P, Reichert H, Sen S, Sprecher S, Bailly X. An Emerging System to Study Photosymbiosis, Brain Regeneration, Chronobiology, and Behavior: The Marine Acoel Symsagittifera roscoffensis. Bioessays 2018; 40:e1800107. [PMID: 30151860 DOI: 10.1002/bies.201800107] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2018] [Revised: 07/23/2018] [Indexed: 01/23/2023]
Abstract
The acoel worm Symsagittifera roscoffensis, an early offshoot of the Bilateria and the only well-studied marine acoel that lives in a photosymbiotic relationship, exhibits a centralized nervous system, brain regeneration, and a wide repertoire of complex behaviors such as circatidal rhythmicity, photo/geotaxis, and social interactions. While this animal can be collected by the thousands and is studied historically, significant progress is made over the last decade to develop it as an emerging marine model. The authors here present the feasibility of culturing it in the laboratory and describe the progress made on different areas, including genomic and tissue architectures, highlighting the associated challenges. In light of these developments, and on the ability to access abundant synchronized embryos, the authors put forward S. roscoffensis as a marine system to revisit questions in the areas of photosymbiosis, regeneration, chronobiology, and the study of complex behaviors from a molecular and evolutionary perspective.
Collapse
Affiliation(s)
- Enrique Arboleda
- Station Biologique de Roscoff, Place Georges Teissier, 29680 Roscoff, France
| | | | - Pedro Martinez
- Institut Català de Recerca i EstudisAvancats (ICREA), Passeig de Lluís Companys, 23, 08010 Barcelona, Spain
| | - Heinrich Reichert
- Departement de Biologie Universite de Fribourg, 1700 Fribourg, Switzerland
| | - Sonia Sen
- Institute of Neuroscience, Institute of Molecular Biology, Howard Hughes Medical Institute, Eugene, OR 97403
| | | | - Xavier Bailly
- CNRS, Station Biologique de Roscoff, 29680 Roscoff, France
| |
Collapse
|
17
|
Thiel D, Franz-Wachtel M, Aguilera F, Hejnol A. Xenacoelomorph Neuropeptidomes Reveal a Major Expansion of Neuropeptide Systems during Early Bilaterian Evolution. Mol Biol Evol 2018. [PMCID: PMC6188537 DOI: 10.1093/molbev/msy160] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Neuropeptides are neurosecretory signaling molecules in protostomes and deuterostomes (together Nephrozoa). Little, however, is known about the neuropeptide complement of the sister group of Nephrozoa, the Xenacoelomorpha, which together form the Bilateria. Because members of the xenacoelomorph clades Xenoturbella, Nemertodermatida, and Acoela differ extensively in their central nervous system anatomy, the reconstruction of the xenacoelomorph and bilaterian neuropeptide complements may provide insights into the relationship between nervous system evolution and peptidergic signaling. Here, we analyzed transcriptomes of seven acoels, four nemertodermatids, and two Xenoturbella species using motif searches, similarity searches, mass spectrometry and phylogenetic analyses to characterize neuropeptide precursors and neuropeptide receptors. Our comparison of these repertoires with previously reported nephrozoan and cnidarian sequences shows that the majority of annotated neuropeptide GPCRs in cnidarians are not orthologs of specific bilaterian neuropeptide receptors, which suggests that most of the bilaterian neuropeptide systems evolved after the cnidarian–bilaterian evolutionary split. This expansion of more than 20 peptidergic systems in the stem leading to the Bilateria predates the evolution of complex nephrozoan organs and nervous system architectures. From this ancient set of neuropeptides, acoels show frequent losses that correlate with their divergent central nervous system anatomy. We furthermore detected the emergence of novel neuropeptides in xenacoelomorphs and their expansion along the nemertodermatid and acoel lineages, the two clades that evolved nervous system condensations. Together, our study provides fundamental insights into the early evolution of the bilaterian peptidergic systems, which will guide future functional and comparative studies of bilaterian nervous systems.
Collapse
Affiliation(s)
- Daniel Thiel
- Sars International Centre for Marine Molecular Biology, University of Bergen, Bergen, Norway
| | | | - Felipe Aguilera
- Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile
- Sars International Centre for Marine Molecular Biology, University of Bergen, Bergen, Norway
| | - Andreas Hejnol
- Sars International Centre for Marine Molecular Biology, University of Bergen, Bergen, Norway
| |
Collapse
|
18
|
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.
Collapse
|
19
|
Dittmann IL, Zauchner T, Nevard LM, Telford MJ, Egger B. SALMFamide2 and serotonin immunoreactivity in the nervous system of some acoels (Xenacoelomorpha). J Morphol 2018; 279:589-597. [PMID: 29388261 PMCID: PMC5947262 DOI: 10.1002/jmor.20794] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2017] [Revised: 12/20/2017] [Accepted: 12/31/2017] [Indexed: 11/06/2022]
Abstract
Acoel worms are simple, often microscopic animals with direct development, a multiciliated epidermis, a statocyst, and a digestive parenchyma instead of a gut epithelium. Morphological characters of acoels have been notoriously difficult to interpret due to their relative scarcity. The nervous system is one of the most accessible and widely used comparative features in acoels, which have a so-called commissural brain without capsule and several major longitudinal neurite bundles. Here, we use the selective binding properties of a neuropeptide antibody raised in echinoderms (SALMFamide2, or S2), and a commercial antibody against serotonin (5-HT) to provide additional characters of the acoel nervous system. We have prepared whole-mount immunofluorescent stainings of three acoel species: Symsagittifera psammophila (Convolutidae), Aphanostoma pisae, and the model acoel Isodiametra pulchra (both Isodiametridae). The commissural brain of all three acoels is delimited anteriorly by the ventral anterior commissure, and posteriorly by the dorsal posterior commissure. The dorsal anterior commissure is situated between the ventral anterior commissure and the dorsal posterior commissure, while the statocyst lies between dorsal anterior and dorsal posterior commissure. S2 and serotonin do not co-localise, and they follow similar patterns to each other within an animal. In particular, S2, but not 5-HT, stains a prominent commissure posterior to the main (dorsal) posterior commissure. We have for the first time observed a closed posterior loop of the main neurite bundles in S. psammophila for both the amidergic and the serotonergic nervous system. In I. pulchra, the lateral neurite bundles also form a posterior loop in our serotonergic nervous system stainings.
Collapse
Affiliation(s)
- Isabel L. Dittmann
- Research unit Evolutionary Developmental BiologyInstitute of Zoology, University of Innsbruck, Technikerstr. 25Innsbruck6020Austria
| | - Thomas Zauchner
- Research unit Evolutionary Developmental BiologyInstitute of Zoology, University of Innsbruck, Technikerstr. 25Innsbruck6020Austria
- Department of Genetics, Evolution and EnvironmentUniversity College London, Darwin Building, Gower StreetLondonWC1E 6BTUnited Kingdom
| | - Lucy M. Nevard
- Department of Genetics, Evolution and EnvironmentUniversity College London, Darwin Building, Gower StreetLondonWC1E 6BTUnited Kingdom
| | - Maximilian J. Telford
- Department of Genetics, Evolution and EnvironmentUniversity College London, Darwin Building, Gower StreetLondonWC1E 6BTUnited Kingdom
| | - Bernhard Egger
- Research unit Evolutionary Developmental BiologyInstitute of Zoology, University of Innsbruck, Technikerstr. 25Innsbruck6020Austria
- Department of Genetics, Evolution and EnvironmentUniversity College London, Darwin Building, Gower StreetLondonWC1E 6BTUnited Kingdom
| |
Collapse
|
20
|
Perea-Atienza E, Sprecher SG, Martínez P. Characterization of the bHLH family of transcriptional regulators in the acoel S. roscoffensis and their putative role in neurogenesis. EvoDevo 2018; 9:8. [PMID: 29610658 PMCID: PMC5875013 DOI: 10.1186/s13227-018-0097-y] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2018] [Accepted: 03/22/2018] [Indexed: 12/27/2022] Open
Abstract
Background The basic helix-loop-helix (bHLH) family of transcription factors is one of the largest superfamilies of regulatory transcription factors and is widely used in eukaryotic organisms. They play an essential role in a range of metabolic, physiological, and developmental processes, including the development of the nervous system (NS). These transcription factors have been studied in many metazoans, especially in vertebrates but also in early branching metazoan clades such as the cnidarians and sponges. However, currently very little is known about their expression in the most basally branching bilaterian group, the xenacoelomorphs. Recently, our laboratory has characterized the full complement of bHLH in the genome of two members of the Xenacoelomorpha, the xenoturbellid Xenoturbella bocki and the acoel Symsagittifera roscoffensis. Understanding the patterns of bHLH gene expression in members of this phylum (in space and time) provides critical new insights into the conserved roles of the bHLH and their putative specificities in this group. Our focus is on deciphering the specific roles that these genes have in the process of neurogenesis. Results Here, we analyze the developmental expression of the whole complement of bHLH genes identified in the acoel S. roscoffensis. Based on their expression patterns, several members of bHLH class A appear to have specific conserved roles in neurogenesis, while other class A genes (as well as members of other classes) have likely taken on more generalized functions. All gene expression patterns are described in embryos and early juveniles. Conclusion Our results suggest that the main roles of the bHLH genes of S. roscoffensis are evolutionarily conserved, with a specific subset dedicated to patterning the nervous system: SrAscA, SrAscB, SrHes/Hey, SrNscl, SrSrebp, SrE12/E47 and SrOlig. Electronic supplementary material The online version of this article (10.1186/s13227-018-0097-y) contains supplementary material, which is available to authorized users.
Collapse
Affiliation(s)
- E Perea-Atienza
- 1Departament de Genètica, Universitat de Barcelona, Av. Diagonal 643, 08028 Barcelona, Spain
| | - S G Sprecher
- 3Department of Biology, University of Fribourg, 10, ch. Du Musée, 1700 Fribourg, Switzerland
| | - P Martínez
- 1Departament de Genètica, Universitat de Barcelona, Av. Diagonal 643, 08028 Barcelona, Spain.,2Institut Català de Recerca i Estudis Avancats (ICREA), Barcelona, Spain
| |
Collapse
|
21
|
Nakano H, Miyazawa H, Maeno A, Shiroishi T, Kakui K, Koyanagi R, Kanda M, Satoh N, Omori A, Kohtsuka H. A new species of Xenoturbella from the western Pacific Ocean and the evolution of Xenoturbella. BMC Evol Biol 2017; 17:245. [PMID: 29249199 PMCID: PMC5733810 DOI: 10.1186/s12862-017-1080-2] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2017] [Accepted: 11/16/2017] [Indexed: 12/13/2022] Open
Abstract
BACKGROUND Xenoturbella is a group of marine benthic animals lacking an anus and a centralized nervous system. Molecular phylogenetic analyses group the animal together with the Acoelomorpha, forming the Xenacoelomorpha. This group has been suggested to be either a sister group to the Nephrozoa or a deuterostome, and therefore it may provide important insights into origins of bilaterian traits such as an anus, the nephron, feeding larvae and centralized nervous systems. However, only five Xenoturbella species have been reported and the evolutionary history of xenoturbellids and Xenacoelomorpha remains obscure. RESULTS Here we describe a new Xenoturbella species from the western Pacific Ocean, and report a new xenoturbellid structure - the frontal pore. Non-destructive microCT was used to investigate the internal morphology of this soft-bodied animal. This revealed the presence of a frontal pore that is continuous with the ventral glandular network and which exhibits similarities with the frontal organ in acoelomorphs. CONCLUSIONS Our results suggest that large size, oval mouth, frontal pore and ventral glandular network may be ancestral features for Xenoturbella. Further studies will clarify the evolutionary relationship of the frontal pore and ventral glandular network of xenoturbellids and the acoelomorph frontal organ. One of the habitats of the newly identified species is easily accessible from a marine station and so this species promises to be valuable for research on bilaterian and deuterostome evolution.
Collapse
Affiliation(s)
- Hiroaki Nakano
- Shimoda Marine Research Center, University of Tsukuba, 5-10-1, Shimoda, Shizuoka, 415-0025, Japan.
| | - Hideyuki Miyazawa
- Shimoda Marine Research Center, University of Tsukuba, 5-10-1, Shimoda, Shizuoka, 415-0025, Japan
| | - Akiteru Maeno
- Mammalian Genetics Laboratory, National Institute of Genetics, 1111 Yata, Mishima, Shizuoka, 411-8540, Japan
| | - Toshihiko Shiroishi
- Mammalian Genetics Laboratory, National Institute of Genetics, 1111 Yata, Mishima, Shizuoka, 411-8540, Japan
| | - Keiichi Kakui
- Faculty of Science, Hokkaido University, N10 W8, Kita-ku, Sapporo, Hokkaido, 060-0810, Japan
| | - Ryo Koyanagi
- DNA Sequencing Section, Okinawa Institute of Science and Technology Graduate University, Onna, Okinawa, 904-0495, Japan
| | - Miyuki Kanda
- DNA Sequencing Section, Okinawa Institute of Science and Technology Graduate University, Onna, Okinawa, 904-0495, Japan
| | - Noriyuki Satoh
- Marine Genomics Unit, Okinawa Institute of Science and Technology Graduate University, Onna, Okinawa, 904-0495, Japan
| | - Akihito Omori
- Misaki Marine Biological Station, The University of Tokyo, 1024 Koajiro, Misaki, Miura, Kanagawa, 238-0225, Japan.,Present address: Sado Marine Biological Station, Faculty of Science, Niigata University, Sado, Niigata, 952-2135, Japan
| | - Hisanori Kohtsuka
- Misaki Marine Biological Station, The University of Tokyo, 1024 Koajiro, Misaki, Miura, Kanagawa, 238-0225, Japan
| |
Collapse
|
22
|
Strausfeld NJ, Hirth F. Introduction to 'Homology and convergence in nervous system evolution'. Philos Trans R Soc Lond B Biol Sci 2016; 371:20150034. [PMID: 26598720 DOI: 10.1098/rstb.2015.0034] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
The origin of brains and central nervous systems (CNSs) is thought to have occurred before the Palaeozoic era 540 Ma. Yet in the absence of tangible evidence, there has been continued debate whether today's brains and nervous systems derive from one ancestral origin or whether similarities among them are due to convergent evolution. With the advent of molecular developmental genetics and genomics, it has become clear that homology is a concept that applies not only to morphologies, but also to genes, developmental processes, as well as to behaviours. Comparative studies in phyla ranging from annelids and arthropods to mammals are providing evidence that corresponding developmental genetic mechanisms act not only in dorso-ventral and anterior-posterior axis specification but also in segmentation, neurogenesis, axogenesis and eye/photoreceptor cell formation that appear to be conserved throughout the animal kingdom. These data are supported by recent studies which identified Mid-Cambrian fossils with preserved soft body parts that present segmental arrangements in brains typical of modern arthropods, and similarly organized brain centres and circuits across phyla that may reflect genealogical correspondence and control similar behavioural manifestations. Moreover, congruence between genetic and geological fossil records support the notion that by the 'Cambrian explosion' arthropods and chordates shared similarities in brain and nervous system organization. However, these similarities are strikingly absent in several sister- and outgroups of arthropods and chordates which raises several questions, foremost among them: what kind of natural laws and mechanisms underlie the convergent evolution of such similarities? And, vice versa: what are the selection pressures and genetic mechanisms underlying the possible loss or reduction of brains and CNSs in multiple lineages during the course of evolution? These questions were addressed at a Royal Society meeting to discuss homology and convergence in nervous system evolution. By integrating knowledge ranging from evolutionary theory and palaeontology to comparative developmental genetics and phylogenomics, the meeting covered disparities in nervous system origins as well as correspondences of neural circuit organization and behaviours, all of which allow evidence-based debates for and against the proposition that the nervous systems and brains of animals might derive from a common ancestor.
Collapse
Affiliation(s)
| | - Frank Hirth
- Department of Basic and Clinical Neuroscience, Institute of Psychiatry, Psychology and Neuroscience, King's College London, London SE5 8AF, UK
| |
Collapse
|