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Wollesen T, Cummins SF, Degnan BM, Wanninger A. FMRFamide gene and peptide expression during central nervous system development of the cephalopod mollusk, Idiosepius notoides. Evol Dev 2010; 12:113-30. [DOI: 10.1111/j.1525-142x.2010.00398.x] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Kristof A, Klussmann-Kolb A. Neuromuscular development of Aeolidiella stephanieae Valdéz, 2005 (Mollusca, Gastropoda, Nudibranchia). Front Zool 2010; 7:5. [PMID: 20205753 PMCID: PMC2822759 DOI: 10.1186/1742-9994-7-5] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2009] [Accepted: 01/22/2010] [Indexed: 11/17/2022] Open
Abstract
Background Studies on the development of the nervous system and the musculature of invertebrates have become more sophisticated and numerous within the last decade and have proven to provide new insights into the evolutionary history of organisms. In order to provide new morphogenetic data on opisthobranch gastropods we investigated the neuromuscular development in the nudibranch Aeolidiella stephanieae Valdéz, 2005 using immunocytochemistry as well as F-actin labelling in conjunction with confocal laser scanning microscopy (cLSM). Results The ontogenetic development of Aeolidiella stephanieae can be subdivided into 8 stages, each recognisable by characteristic morphological and behavioural features as well as specific characters of the nervous system and the muscular system, respectively. The larval nervous system of A. stephanieae includes an apical organ, developing central ganglia, and peripheral neurons associated with the velum, foot and posterior, visceral part of the larva. The first serotonergic and FMRFamidergic neural structures appear in the apical organ that exhibits an array of three sensory, flask-shaped and two non-sensory, round neurons, which altogether disappear prior to metamorphosis. The postmetamorphic central nervous system (CNS) becomes concentrated, and the rhinophoral ganglia develop together with the anlage of the future rhinophores whereas oral tentacle ganglia are not found. The myogenesis in A. stephanieae begins with the larval retractor muscle followed by the accessory larval retractor muscle, the velar or prototroch muscles and the pedal retractors that all together degenerate during metamorphosis, and the adult muscle complex forms de novo. Conclusions Aeolidiella stephanieae comprises features of the larval and postmetamorphic nervous as well as muscular system that represent the ground plan of the Mollusca or even the Trochozoa (e. g. presence of the prototrochal or velar muscle ring). On the one hand, A. stephanieae shows some features shared by all nudibranchs like the postmetamorphic condensation of the CNS, the possession of rhinophoral ganglia and the lack of oral tentacle ganglia as well as the de novo formation of the adult muscle complex. On the other hand, the structure and arrangement of the serotonergic apical organ is similar to other caenogastropod and opisthobranch gastropods supporting their sister group relationship.
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Affiliation(s)
- Alen Kristof
- Research Group for Comparative Zoology, Department of Biology, University of Copenhagen, 2100 Copenhagen Ø, Denmark.
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Brinkmann N, Wanninger A. Neurogenesis suggests independent evolution of opercula in serpulid polychaetes. BMC Evol Biol 2009; 9:270. [PMID: 19930667 PMCID: PMC2785788 DOI: 10.1186/1471-2148-9-270] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2009] [Accepted: 11/23/2009] [Indexed: 11/20/2022] Open
Abstract
BACKGROUND The internal phylogenetic relationships of Annelida, one of the key lophotrochozoan lineages, are still heavily debated. Recent molecular analyses suggest that morphologically distinct groups, such as the polychaetes, are paraphyletic assemblages, thus questioning the homology of a number of polychaete morphological characters. Serpulid polychaetes are typically recognized by having fused anterior ends bearing a tentacular crown and an operculum. The latter is commonly viewed as a modified tentacle (= radiole) and is often used as an important diagnostic character in serpulid systematics. RESULTS By reconstructing the developmental neuroanatomy of the serpulid polychaete Spirorbis cf. spirorbis (Spirorbinae), we found striking differences in the overall neural architecture, the innervation pattern, and the ontogenetic establishment of the nervous supply of the operculum and the radioles in this species. Accordingly, the spirorbin operculum might not be homologous to the radioles or to the opercula of other serpulid taxa such as Serpula and Pomatoceros and is thus probably not a part of the tentacular crown. CONCLUSION We demonstrate that common morphological traits such as the prostomial appendages may have evolved independently in respective serpulid sublineages and therefore require reassessment before being used in phylogenetic analyses. Our findings corroborate recent molecular studies that argue for a revision of serpulid systematics. In addition, our data on Spirorbis neurogenesis provide a novel set of characters that highlight the developmental plasticity of the segmented annelid nervous system.
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Affiliation(s)
- Nora Brinkmann
- Department of Biology, Research Group for Comparative Zoology, University of Copenhagen, Universitetsparken 15, DK-2100 Copenhagen, Denmark
| | - Andreas Wanninger
- Department of Biology, Research Group for Comparative Zoology, University of Copenhagen, Universitetsparken 15, DK-2100 Copenhagen, Denmark
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Wanninger A. Shaping the things to come: ontogeny of lophotrochozoan neuromuscular systems and the tetraneuralia concept. THE BIOLOGICAL BULLETIN 2009; 216:293-306. [PMID: 19556595 DOI: 10.1086/bblv216n3p293] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Despite the large variation in adult bodyplan phenotypes, a worm-shaped morphology is considered plesiomorphic for both Lophotrochozoa and Bilateria. Although almost all larval and adult lophotrochozoan worms have serially arranged ring muscles in their body wall, a comparison of their ontogeny reveals no less than six different developmental pathways that lead to this homogenous arrangement of ring muscles. However, in all taxa, with the exception of chaetodermomorph molluscs and the segmented annelids, ring muscle development starts with synchronous formation of certain pioneer myocytes, which is thus considered basal for Lophotrochozoa. Recent studies on spiralian neurogenesis revealed remnants of ancestral segmentation in echiurans and sipunculans, thus confirming molecular phylogenetic studies that propose a close relationship of these three taxa. Larval entoprocts exhibit a mosaic of larval and adult molluscan characters and, among other apomorphies, share with polyplacophoran Mollusca a complex larval apical organ and a tetraneurous nervous system, strongly suggesting a monophyletic assemblage of Entoprocta and Mollusca. The term Tetraneuralia is proposed herein for this lophotrochozoan clade. Overall, formation of the lophotrochozoan neuromuscular bodyplan appears as a highly dynamic process on both the ontogenetic and the evolutionary timescales, highlighting the importance of insights into these processes for reconstructing ancestral bodyplan features and phylogenetic relationships.
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Affiliation(s)
- Andreas Wanninger
- University of Copenhagen, Department of Biology, Research Group for Comparative Zoology, Universitetsparken 15, DK-2100 Copenhagen, Denmark.
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Fine structure of the ventral nerve centre and interspecific identification of individual neurons in the enigmatic Chaetognatha. ZOOMORPHOLOGY 2008. [DOI: 10.1007/s00435-008-0074-4] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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58
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Isaeva VV, Yushin VV. Studies in developmental biology at the Institute of Marine Biology (Far Eastern Branch of the Russian Academy of Sciences). Russ J Dev Biol 2008. [DOI: 10.1134/s1062360408050093] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Santagata S. Evolutionary and structural diversification of the larval nervous system among marine bryozoans. THE BIOLOGICAL BULLETIN 2008; 215:3-23. [PMID: 18723633 DOI: 10.2307/25470679] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Regardless of the morphological divergence among larval forms of marine bryozoans, the larval nervous system and its major effector organs (musculature and ciliary fields) are largely molded on the basis of functional demands of feeding, ciliary propulsion, phototactic behaviors, and substrate exploration. Previously published ultrastructural information and immunohistochemical reconstructions presented here indicate that neuronal pathways are largely ipsilateral, with more complex synaptic connections localized within the nerve nodule. Multiciliated sensory-motor neurons diversify structurally and functionally on the basis of their position along the axis of swimming largely due to the functional demands of photoklinotaxis and substrate exploration. Vesiculariform, buguliform, and ascophoran coronate larvae all have patches of sensory neurons bordering the pyriform organ's ciliated groove (juxtapapillary cells and border cells) that are active during substrate selection. Despite their simplified form, cyclostome larvae maintain swimming and probing behaviors with sensory-motor systems functionally similar to those of some parenchymella and planula larval types. Considering the evolutionary relationships among the morphological grades of marine bryozoans, particular lineages within the gymnolaemates have independently evolved larval traits that convey a greater range of sensory abilities and increased propulsive capacity. The larval nervous system of bryozoans may be evolutionarily derived from the pretrochal region of a trochophore-like larval form.
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Affiliation(s)
- Scott Santagata
- Smithsonian Marine Station, 701 Seaway Drive, Fort Pierce, Florida 34949, USA.
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Voronezhskaya EE, Nezlin LP, Odintsova NA, Plummer JT, Croll RP. Neuronal development in larval mussel Mytilus trossulus (Mollusca: Bivalvia). ZOOMORPHOLOGY 2008. [DOI: 10.1007/s00435-007-0055-z] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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Haszprunar G, Wanninger A. On the fine structure of the creeping larva of Loxosomella murmanica: additional evidence for a clade of Kamptozoa (Entoprocta) and Mollusca. ACTA ZOOL-STOCKHOLM 2007. [DOI: 10.1111/j.1463-6395.2007.00301.x] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Tessmar-Raible K, Raible F, Christodoulou F, Guy K, Rembold M, Hausen H, Arendt D. Conserved sensory-neurosecretory cell types in annelid and fish forebrain: insights into hypothalamus evolution. Cell 2007; 129:1389-400. [PMID: 17604726 DOI: 10.1016/j.cell.2007.04.041] [Citation(s) in RCA: 249] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2006] [Revised: 01/12/2007] [Accepted: 04/26/2007] [Indexed: 10/23/2022]
Abstract
Neurosecretory control centers form part of the forebrain in many animal phyla, including vertebrates, insects, and annelids. The evolutionary origin of these centers is largely unknown. To identify conserved, and thus phylogenetically ancient, components of neurosecretory brain centers, we characterize and compare neurons that express the prohormone vasotocin (vasopressin/oxytocin)-neurophysin in the developing forebrain of the annelid Platynereis dumerilii and of the zebrafish. These neurons express the same tissue-restricted microRNA, miR-7, and conserved, cell-type-specific combinations of transcription factors (nk2.1, rx, and otp) that specify their identity, as evidenced by the specific requirement of zebrafish rx3 for vasotocin-neurophysin expression. MiR-7 also labels another shared population of neurons containing RFamides. Since the vasotocinergic and RFamidergic neurons appear to be directly sensory in annelid and fish, we propose that cell types with dual sensory-neurosecretory properties were the starting point for the evolution of neurosecretory brain centers in Bilateria.
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Affiliation(s)
- Kristin Tessmar-Raible
- Developmental Biology Unit, European Molecular Biology Laboratory, Meyerhofstrasse 1, D-69012 Heidelberg, Germany.
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Mayer G, Harzsch S. Immunolocalization of serotonin in Onychophora argues against segmental ganglia being an ancestral feature of arthropods. BMC Evol Biol 2007; 7:118. [PMID: 17629937 PMCID: PMC1933538 DOI: 10.1186/1471-2148-7-118] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2006] [Accepted: 07/15/2007] [Indexed: 11/10/2022] Open
Abstract
Background Onychophora (velvet worms) represent the most basal arthropod group and play a pivotal role in the current discussion on the evolution of nervous systems and segmentation in arthropods. Although there is a wealth of information on the immunolocalization of serotonin (5-hydroxytryptamine, 5-HT) in various euarthropods, as yet no comparable localization data are available for Onychophora. In order to understand how the onychophoran nervous system compares to that of other arthropods, we studied the distribution of serotonin-like immunoreactive neurons and histological characteristics of ventral nerve cords in Metaperipatus blainvillei (Onychophora, Peripatopsidae) and Epiperipatus biolleyi (Onychophora, Peripatidae). Results We demonstrate that paired leg nerves are the only segmental structures associated with the onychophoran nerve cord. Although the median commissures and peripheral nerves show a repeated pattern, their arrangement is independent from body segments characterized by the position of legs and associated structures. Moreover, the somata of serotonin-like immunoreactive neurons do not show any ordered arrangement in both species studied but are instead scattered throughout the entire length of each nerve cord. We observed neither a serially iterated nor a bilaterally symmetric pattern, which is in contrast to the strictly segmental arrangement of serotonergic neurons in other arthropods. Conclusion Our histological findings and immunolocalization experiments highlight the medullary organization of the onychophoran nerve cord and argue against segmental ganglia of the typical euarthropodan type being an ancestral feature of Onychophora. These results contradict a priori assumptions of segmental ganglia being an ancestral feature of arthropods and, thus, weaken the traditional Articulata hypothesis, which proposes a sistergroup relationship of Annelida and Arthropoda.
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Affiliation(s)
- Georg Mayer
- Department of Anatomy and Cell Biology, University of Melbourne, Victoria 3010, Australia
| | - Steffen Harzsch
- Department of Evolutionary Neuroethology, Max-Planck Institute for Chemical Ecology, Hans-Knöll-Straße 8, D-07745 Jena, Germany
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Harzsch S, Müller CHG. A new look at the ventral nerve centre of Sagitta: implications for the phylogenetic position of Chaetognatha (arrow worms) and the evolution of the bilaterian nervous system. Front Zool 2007; 4:14. [PMID: 17511857 PMCID: PMC1885248 DOI: 10.1186/1742-9994-4-14] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2007] [Accepted: 05/18/2007] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The Chaetognatha (arrow worms) are a group of marine carnivores whose phylogenetic relationships are still vigorously debated. Molecular studies have as yet failed to come up with a stable hypothesis on their phylogenetic position. In a wide range of metazoans, the nervous system has proven to provide a wealth of characters for analysing phylogenetic relationships (neurophylogeny). Therefore, in the present study we explored the structure of the ventral nerve centre ("ventral ganglion") in Sagitta setosa with a set of histochemical and immunohistochemical markers. RESULTS In specimens that were immunolabeled for acetylated-alpha tubulin the ventral nerve centre appeared to be a condensed continuation of the peripheral intraepidermal nerve plexus. Yet, synapsin immunolocalization showed that the ventral nerve centre is organized into a highly ordered array of ca. 80 serially arranged microcompartments. Immunohistochemistry against RFamide revealed a set of serially arranged individually identifiable neurons in the ventral nerve centre that we charted in detail. CONCLUSION The new information on the structure of the chaetognath nervous system is compared to previous descriptions of the ventral nerve centre which are critically evaluated. Our findings are discussed with regard to the debate on nervous system organisation in the last common bilaterian ancestor and with regard to the phylogenetic affinities of this Chaetognatha. We suggest to place the Chaetognatha within the Protostomia and argue against hypotheses which propose a deuterostome affinity of Chaetognatha or a sister-group relationship to all other Bilateria.
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Affiliation(s)
- Steffen Harzsch
- Max Planck Institute for Chemical Ecology, Department of Evolutionary Neuroethology, Beutenberg Campus, Hans-Knöll-Str. 8, 07745 Jena, Germany
| | - Carsten HG Müller
- Universität Rostock, Institut für Biowissenschaften, Allgemeine und Spezielle Zoologie, Universitätsplatz 2, 18051 Rostock, Germany
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Croll RP. Development of embryonic and larval cells containing serotonin, catecholamines, and FMRFamide-related peptides in the gastropod mollusc Phestilla sibogae. THE BIOLOGICAL BULLETIN 2006; 211:232-47. [PMID: 17179383 DOI: 10.2307/4134546] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
The present immunocytochemical study provides one of the first detailed descriptions of the development of cells containing a variety of neurotransmitters during much of the larval life of a nudibranch gastropod. Throughout much of early development, serotonergic cells were located only in the apical organ; as larvae approached metamorphosis, serotonergic cells were also detected in the cerebropleural and pedal ganglia. Cells exhibiting tyrosine hydroxylase immunoreactivity (indicative of catecholamine synthesis) were first located near the mouth but by late embryonic stages were also located in the apical organ and near the velum and eyes. By late larval stages, numerous catecholaminergic cells were found in the foot, with concentrations in the propodium. Finally, the first cells exhibiting FMRFamide immunoreactivity were detected posterior to the neuropil of the cerebropleural ganglia in the early embryo. Fibers that presumably originated from these cells subsequently invaded the cerebral and pedal ganglia and the apical organ. By early larval stages, a second pair of peptidergic neurons was located near the first pair, and additional peptidergic neurons were located in the apical organ and peripheral positions in the foot and medial and dorsal to the eyes. In addition to providing a unique phyletic perspective to our understanding of gastropod neural development, the present study also sets the stage for future studies into changes in the nervous system as this gastropod undergoes metamorphosis.
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Affiliation(s)
- Roger P Croll
- Department of Physiology & Biophysics, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4H7.
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Barucca M, Biscotti MA, Olmo E, Canapa A. All the three ParaHox genes are present inNuttallochiton mirandus (Mollusca: polyplacophora): evolutionary considerations. JOURNAL OF EXPERIMENTAL ZOOLOGY PART B-MOLECULAR AND DEVELOPMENTAL EVOLUTION 2006; 306:164-7. [PMID: 16331637 DOI: 10.1002/jez.b.21082] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The ParaHox gene cluster contains three homeobox genes, Gsx, Xlox and Cdx and has been demonstrated to be an evolutionary sister of the Hox gene cluster. Among deuterostomes the three genes are found in the majority of taxa, whereas among protostomes they have so far been isolated only in the phylum Sipuncula. We report the partial sequences of all three ParaHox genes in the polyplacophoran Nuttallochiton mirandus, the first species of the phylum Mollusca where all ParaHox genes have been isolated. This finding has phylogenetic implications for the phylum Mollusca and for its relationships with the other lophotrochozoan taxa.
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Affiliation(s)
- Marco Barucca
- Istituto di Biologia e Genetica, Università Politecnica delle Marche, Ancona, Italy
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Wanninger A. Immunocytochemistry of the nervous system and the musculature of the chordoid larva of Symbion pandora (Cycliophora). J Morphol 2005; 265:237-43. [PMID: 15986410 DOI: 10.1002/jmor.10354] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
To date, the phylum Cycliophora comprises only one described extant species of acoelomate marine invertebrates, Symbion pandora. Adult specimens live commensally on the mouthparts of the Norwegian lobster, Nephrops norvegicus. Its complicated life cycle includes an asexually produced Pandora larva and a sexually produced chordoid larva. Despite detailed TEM investigations and its inclusion in recent molecular phylogenetic analyses, cycliophoran relationships still remain enigmatic. In order to increase the morphological database, I investigated the anatomy of the nervous system and the musculature of the chordoid larva by applying fluorescence-coupled antibodies against the neurotransmitters serotonin and FMRFamide, as well as FITC-coupled phalloidin to label filamentous F-actin, in combination with confocal laser scanning microscopy. The FMRFamidergic nervous system shows a bilobed anterior ganglion and one pair of ventral nerve cords, while serotonin is distributed in a scattered pattern in the anterior ganglion. In addition, there are two pairs of ventral serotonergic nerves, of which the inner pair fuses with the outer nerve cords in the posterior third of the larva. The musculature comprises an outer layer of six units of circular body wall muscles, several helicoid muscle fibers, a set of paired longitudinal muscles that span the entire anterior-posterior axis of the larva, and a few oblique muscle strands. Furthermore, an anterior muscle complex and one pair of posterior muscles are present. The chordoid organ consists of a number of distinct subunits that are each formed by a dense layer of circular muscle fibers. The overall arrangement of the oblique and longitudinal muscles as well as the body wall musculature in the chordoid larva of Symbion pandora exhibits similarities with the condition found in certain rotifers. This is congruent with some recent phylogenies based on 18S rRNA sequences but additional morphological, developmental, and molecular data are needed to clarify the phylogenetic relationships of Cycliophora.
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Affiliation(s)
- Andreas Wanninger
- Department of Cell Biology and Comparative Zoology, University of Copenhagen, DK-2100 Copenhagen Ø, Denmark.
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Wanninger A, Koop D, Degnan BM. Immunocytochemistry and metamorphic fate of the larval nervous system of Triphyllozoon mucronatum (Ectoprocta: Gymnolaemata: Cheilostomata). ZOOMORPHOLOGY 2005. [DOI: 10.1007/s00435-005-0004-7] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Wanninger A, Koop D, Bromham L, Noonan E, Degnan BM. Nervous and muscle system development in Phascolion strombus (Sipuncula). Dev Genes Evol 2005; 215:509-18. [PMID: 16133569 DOI: 10.1007/s00427-005-0012-0] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2005] [Accepted: 06/03/2005] [Indexed: 11/28/2022]
Abstract
Recent interpretations of developmental gene expression patterns propose that the last common metazoan ancestor was segmented, although most animal phyla show no obvious signs of segmentation. Developmental studies of non-model system trochozoan taxa may shed light on this hypothesis by assessing possible cryptic segmentation patterns. In this paper, we present the first immunocytochemical data on the ontogeny of the nervous system and the musculature in the sipunculan Phascolion strombus. Myogenesis of the first anlagen of the body wall ring muscles occurs synchronously and not subsequently from anterior to posterior as in segmented spiralian taxa (i.e. annelids). The number of ring muscles remains constant during the initial stages of body axis elongation. In the anterior-posteriorly elongated larva, newly formed ring muscles originate along the entire body axis between existing myocytes, indicating that repeated muscle bands do not form from a posterior growth zone. During neurogenesis, the Phascolion larva expresses a non-metameric, paired, ventral nerve cord that fuses in the mid-body region in the late-stage elongated larva. Contrary to other trochozoans, Phascolion lacks any larval serotonergic structures. However, two to three FMRFamide-positive cells are found in the apical organ. In addition, late larvae show commissure-like neurones interconnecting the two ventral nerve cords, while early juveniles exhibit a third, medially placed FMRFamidergic ventral nerve. Although we did not find any indications for cryptic segmentation, certain neuro-developmental traits in Phascolion resemble the conditions found in polychaetes (including echiurans) and myzostomids and support a close relationship of Sipuncula and Annelida.
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Affiliation(s)
- Andreas Wanninger
- Department of Cell Biology and Comparative Zoology, Institute of Biology, University of Copenhagen, Universitetsparken 15, 2100, Copenhagen Ø, Denmark.
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CROLL ROGERP, DICKINSON AMANDAJ. Form and function of the larval nervous system in molluscs. INVERTEBR REPROD DEV 2004. [DOI: 10.1080/07924259.2004.9652620] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Nielsen C. Trochophora larvae: cell-lineages, ciliary bands, and body regions. 1. Annelida and Mollusca. JOURNAL OF EXPERIMENTAL ZOOLOGY PART B-MOLECULAR AND DEVELOPMENTAL EVOLUTION 2004; 302:35-68. [PMID: 14760653 DOI: 10.1002/jez.b.20001] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The trochophora concept and the literature on cleavage patterns and differentiation of ectodermal structures in annelids ("polychaetes") and molluscs are reviewed. The early development shows some variation within both phyla, and the cephalopods have a highly modified development. Nevertheless, there are conspicuous similarities between the early development of the two phyla, related to the highly conserved spiral cleavage pattern. Apical and cerebral ganglia have almost identical origin in the two phyla, and the cell-lineage of the prototroch is identical, except for minor variations between species. The cell-lineage of the metatrochs is almost unknown, but the telotroch of annelids and the "telotroch" of the gastropod Patella originate from the 2d-cell, as does the gastrotroch in the few species which have been studied. The segmented annelid body, i.e. the region behind the peristome, develops through addition of new ectoderm from a ring of 2d-cells just in front of the telotroch. This whole region is thus derived from 2d-cells. Conversely, the mollusc body is covered by descendants of cells from both the C and D quadrants and a growth zone is not apparent. This supports the notion that the molluscs are not segmented like the annelids, and that the repeated structures seen in polyplacophorans and monoplacophorans do not represent a segmentation homologous to that of the annelids.
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Affiliation(s)
- Claus Nielsen
- Zoological Museum (University of Copenhagen), Universitetsparken 15, DK-2100 Copenhagen, Denmark.
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Nezlin LP, Voronezhskaya EE. Novel, posterior sensory organ in the trochophore larva of Phyllodoce maculata (Polychaeta). Proc Biol Sci 2004; 270 Suppl 2:S159-62. [PMID: 14667369 PMCID: PMC1809934 DOI: 10.1098/rsbl.2003.0072] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
A new posterior sensory organ (PSO), located at the dorsal midline of the hyposphere, is described by immunocytochemical detection of acetylated alpha tubulin and serotonin (5-HT) in a laser-scanning microscope, as well as three-dimensional reconstructions after optical serial sectioning in the trochophore larva of the polychaete Phyllodoce maculata (Phyllodocidae). The unpaired PSO consists of five bipolar sensory cells, two of them being 5-HT immunopositive, which send axons to the cerebral ganglion and prototroch nerve. The dendrites of these cells project to the surface and bear one cilium each. A single neuronal fibre from the apical sensory organ innervates the PSO.
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Affiliation(s)
- L P Nezlin
- Institute of Developmental Biology, Russian Academy of Sciences, Moscow 117808, Russia.
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73
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Dickinson AJG, Croll RP. Development of the larval nervous system of the gastropod Ilyanassa obsoleta. J Comp Neurol 2003; 466:197-218. [PMID: 14528448 DOI: 10.1002/cne.10863] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Gastropods have been well studied in terms of early cell cleavage patterns and the neural basis of adult behaviors; however, much less is known about neural development in this taxon. Here we reveal a relatively sophisticated larval nervous system in a well-studied gastropod, Ilyanassa obsoleta. The present study employed immunocytochemical and histofluorescent techniques combined with confocal microscopy to examine the development of cells containing monoamines (serotonin and catecholamine), neuropeptides (FMRFamide and leu-enkephalin related peptides), and a substance(s) reactive to antibodies raised against dopamine beta-hydroxylase. Neurons were first observed in the apical organ and posterior regions during the embryonic trochophore stage. During later embryonic development neurons appeared in peripheral regions such as the foot, velum, and mantle and in the developing ganglia destined to become the adult central nervous system. In subsequent free-swimming veliger stages the larval nervous system became increasingly elaborate and by late larval stages there existed approximately 26-28 apical cells, 80-100 neurons in the central ganglia, and 200-300 peripherally located neurons. During metamorphosis some populations of neurons in the apical organ and in the periphery disappeared, while others were incorporated into the juvenile nervous system. Comparisons of neural elements in other molluscan larvae reveal several similarities such as comparable arrangements of cells in the apical organ and patterns of peripheral cells. This investigation reveals the most extensive larval nervous system described in any mollusc to date and information from this study will be useful for future experimental studies determining the role of larval neurons and investigations of the cellular and molecular mechanisms governing neural development in this taxon.
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Affiliation(s)
- Amanda J G Dickinson
- Department of Physiology and Biophysics, Faculty of Medicine, Dalhousie University, Halifax, B3H 4H7 Nova Scotia, Canada.
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74
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The development of the serotonergic and FMRF-amidergic nervous system in Antalis entalis (Mollusca, Scaphopoda). ZOOMORPHOLOGY 2003. [DOI: 10.1007/s00435-003-0071-6] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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75
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Buznikov GA, Nikitina LA, Voronezhskaya EE, Bezuglov VV, Dennis Willows AO, Nezlin LP. Localization of serotonin and its possible role in early embryos of Tritonia diomedea(Mollusca: Nudibranchia). Cell Tissue Res 2003; 311:259-66. [PMID: 12596045 DOI: 10.1007/s00441-002-0666-0] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2002] [Accepted: 10/28/2002] [Indexed: 10/25/2022]
Abstract
A classical neurotransmitter serotonin (5-HT) was detected immunochemically using laser scanning microscopy at the early stages of Tritonia diomedea development. At the one- to eight-cell stages, immunolabeling suggested the presence of 5-HT in the cytoplasm close to the animal pole. At the morula and blastula stages, a group of micromeres at the animal pole showed immunoreactivity. At the gastrula stage no immunoreactive cells were detected, but they arose again at the early veliger stage. Antagonists of 5-HT(2) receptors, ritanserin and cyproheptadine, as well as lipophilic derivatives of dopamine blocked cleavage divisions or distorted their normal pattern. These effects were prevented by 5-HT and its highly lipophilic derivates, serotoninamides of polyenoic fatty acids, but not by the hydrophilic (quaternary) analog of 5-HT, 5-HTQ. The results confirm our earlier suggestion that endogenous 5-HT in pre-nervous embryos acts as a regulator of cleavage divisions in nudibranch molluscs.
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Affiliation(s)
- Gennady A Buznikov
- Institute of Developmental Biology, Russian Academy of Sciences, Moscow, Russia
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76
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Voronezhskaya EE, Tsitrin EB, Nezlin LP. Neuronal development in larval polychaete Phyllodoce maculata (Phyllodocidae). J Comp Neurol 2003; 455:299-309. [PMID: 12483683 DOI: 10.1002/cne.10488] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The existing view on neuronal development in polychaetes, as undergoing neurogenesis beginning in the rudiments of central ganglia and then extending peripherally, has been contrasted with the latest findings in molluscs, their sister trochozoan group, which show a peripheral to central mode of neurogenesis. The current study addresses this issue by examining early neuronal development in the polychaete Phyllodoce maculata using immunolabeling against acetylated alpha-tubulin, serotonin, and the FMRFamide. The first nervous cell was detected 20 hours before hatching, at the early trochophore stage. A solitary serotonergic neuron was located at the posterior-dorsal extreme of the larva and issued anterior projecting fibers, which outline the future ventral nerve cords and prototroch nerve. Two more serotonergic dorsal peripheral cells and three peripheral FMRFamidergic cells appeared soon thereafter. The fibers of these early cells formed a scaffolding, which prefigured the future adult nervous system (cerebral ganglion, ventral cords, prototroch and esophageal nerve rings) in prehatched trochophores. Shortly before hatching, the larval nervous system developed, including the apical organ, meridianal nerves in the episphere, and posttrochal nerves that innervate the feeding apparatus. After hatching, the rudiments of the adult nervous system started to develop along the paths already established by the earliest peripheral neurons. Thus, the general strategy of neurogenesis in a representative polychaete trochophore appears to resemble that of molluscs. The first neuronal cells to appear are peripheral in origin, located near the posterior margins of the embryo. Their similar anatomical appearance suggests that they share a similar functional role in trochophore development and behavior.
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Affiliation(s)
- Elena E Voronezhskaya
- Institute of Developmental Biology, Russian Academy of Sciences, Moscow 117808, Russia
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