The Larval Apical Organ in the Holothuroid Chiridota gigas (Apodida): Inferences on Evolution of the Ambulacrarian Larval Nervous System

2006 ◽  
Vol 211 (2) ◽  
pp. 95-100 ◽  
Author(s):  
Maria Byrne ◽  
Mary A. Sewell ◽  
Paulina Selvakumaraswamy ◽  
Thomas A. A. Prowse
Keyword(s):  
Nervous System ◽  
Apical Organ ◽  
Larval Nervous System

Structure and organization of the nervous system in the trochophore larva of spirobranchus

1984 ◽  
Vol 306 (1126) ◽  
pp. 79-135 ◽  
Keyword(s):  
Nervous System ◽  
Sensory Nerve ◽  
Cell Types ◽  
Nerve Cells ◽  
Cell Junctions ◽  
Apical Organ ◽  
Sensory Cells ◽  
Trochophore Larva ◽  
General Terms ◽  
Larval Nervous System

The trochophore larva of the polychaete Spirobranchus polycerus is described, based on ultrastructural surveys and three dimensional reconstructions, with emphasis on the structure and organization of the nervous system. A complete and detailed description is provided of the larval parts of the nervous system at the cellular level for the 48 h stage, by which time the larval system is fully developed in most respects. The adult nervous system, whose rudiments form a largely separate system of nerves and nerve cells, appears progressively during later development. Its principal structures, the brain, commissures and ventral cords, are briefly described based on an examination of the metatrochophore. The larval nervous system is entirely presegmental and is divisible into two parts: (1) a system of pretrochal cells and nerves arising from them that innervates the prototroch, linking it to the apical organ and the single larval eye, and (2) a system of intratrochal and intraepithelial nerves supplying the feeding apparatus of the larva. The latter consists of two nerves that encircle the pharynx and join basally beneath the cluster of cells that make up the basal pharyngeal complex. The pharyngeal nerves are then linked by means of a suboral complex of four sensory cells and their nerves to the nerves supplying the metatroch and neurotroch. The two parts of the larval system are anatomically separate and develop separately, each in association with its own organizational centres. These are: the apical organ and its central plexus in the case of the pretrochal system, and the suboral and pharyngeal complexes in the case of the oral and pharyngeal nerves. Like the larva itself, the larval nervous system is specialized and highly reduced. There are comparatively few cells, but a number of distinctive cell types. At 48 h, the larval system comprises 36 cells, including among these between 16 and 18 recognizably different types of sensory and non-sensory nerve cells and non-neural accessory cells. The majority of the cells are individually identifiable by morphology, ultrastructure and location, and are invariant or nearly so from larva to larva. The development of the system as a whole involves production of fibres by certain of these followed by fibre growth either along preestablished pathways, for example along the trochal bands or cells derived from these, or towards identifiable targets, for example, the apical plexus or pharyngeal complex. The resulting system varies little from larva to larva, and neurogenesis appears therefore to be a very precisely controlled developmental process. However, the individual cellular events that occur as parts of this process, do exhibit considerable diversity, both in terms of the cell types involved and of the types of interactions that occur between them, which raises the question of how the degree of developmental precision required by Spirobranchus is achieved. Cell lineage and lineage-dependent phenomena are clearly important, but it is not clear how concepts arising from linage studies in other organisms, e.g. in nematodes or other spiralia, should be applied in dealing with this particular case. Besides being anatomically separate, the two main parts of the larval nervous system evidently also have different evolutionary origins. Comparison of the Spirobranchus trochophore with the closely related M uller’s larva of polyclads supports the idea that the pretrochal system of the former is derived secondarily from the adult nervous system of some ancestral form despite the fact that it innervates a strictly larval organ, the protrotroch. Conversely, the nerves supplying the trochophore oral apparatus, which includes secondarily-derived adult structures like the pharynx, are of larval origin, probably derived by rearrangement from the nerves of a series of primitive trochal bands. The basic features of the oral apparatus in both Muller’s larva and the trochophore can be accounted for by assuming the existence of an ancestral larva with three circumferential trochal bands. Two of these would then be incorporated into the stomodeum as it evolved, with their nerves being retained as stomodeal structures in modern forms. This interpretation emphasizes (1) the evolutionary conservatism of the larval nervous system, i.e. larval nerves change less in organization and arrangement than the structures they innervate, which makes them important phylogenetic indicators, and (2) the importance of the evolutionary continuity of the mouth in protosomes as a justification for comparative studies of the oral apparatus in spiralian larvae that seek to establish homologies between them. In the case at hand, it is concluded that the oral apparatus of M uller’s larva and the trochopore, excluding the anus of the latter, are homologous. The functional operation of the larval nervous system in Spirobranchus is discussed briefly and in general terms. The larval nerve cells show a low degree of morphological differentiation, and specialized cell junctions (e.g., synapses) are largely absent, so only a rudimentary understanding of the circuitry of the larval system is possible. Further, it is not clear to what extent the morphological and ultrastructural differences between the various larval cell types and between larval and adult nerve cells reflect significant functional and physiological differences. It would be most interesting if such differences did exist: the trochophore would then have to be accorded independent status as an organism physiologically quite different from the adult polychaete with, in particular, a far more primitive nervous system.

scholarly journals Partitioning of N-Ethylmaleimide-Sensitive Fusion (NSF) Protein Function in Drosophila melanogaster: dNSF1 Is Required in the Nervous System, and dNSF2 Is Required in Mesoderm

Genetics ◽  
2001 ◽  
Vol 158 (1) ◽  
pp. 265-278
Author(s):  
Jessica A Golby ◽  
Leigh Anna Tolar ◽  
Leo Pallanck
Keyword(s):  
Nervous System ◽  
Protein Function ◽  
Ectopic Expression ◽  
Drosophila Genome ◽  
Loss Of Function ◽  
Stage Of Development ◽  
Expression Studies ◽  
Larval Nervous System ◽  
Constitutive Secretion ◽  
Temporal And Spatial

Abstract The N-ethylmaleimide-sensitive fusion protein (NSF) promotes the fusion of secretory vesicles with target membranes in both regulated and constitutive secretion. While it is thought that a single NSF may perform this function in many eukaryotes, previous work has shown that the Drosophila genome contains two distinct NSF genes, dNSF1 and dNSF2, raising the possibility that each plays a specific secretory role. To explore this possibility, we generated mutations in the dNSF2 gene and used these and novel dNSF1 loss-of-function mutations to analyze the temporal and spatial requirements and the degree of functional redundancy between dNSF1 and dNSF2. Results of this analysis indicate that dNSF1 function is required in the nervous system beginning at the adult stage of development and that dNSF2 function is required in mesoderm beginning at the first instar larval stage of development. Additional evidence suggests that dNSF1 and dNSF2 may play redundant roles during embryonic development and in the larval nervous system. Ectopic expression studies demonstrate that the dNSF1 and dNSF2 gene products can functionally substitute for one another. These results indicate that the Drosophila NSF proteins exhibit similar functional properties, but have evolved distinct tissue-specific roles.

Neurons of the ascidian larval nervous system inCiona intestinalis: II. Peripheral nervous system

2007 ◽  
Vol 501 (3) ◽  
pp. 335-352 ◽  
Author(s):  
Janice H. Imai ◽  
Ian A. Meinertzhagen
Keyword(s):  
Nervous System ◽  
Peripheral Nervous System ◽  
Larval Nervous System

The expression and role of a proneural gene, achaete, in the development of the larval nervous system of Drosophila.

1993 ◽  
Vol 12 (3) ◽  
pp. 1121-1130 ◽  
Author(s):  
M. Ruiz-Gómez ◽  
A. Ghysen
Keyword(s):  
Nervous System ◽  
Proneural Gene ◽  
Larval Nervous System

Bicuculline-insensitive GABA-gated Cl? channels in the larval nervous system of the moth Manduca sexta

2003 ◽  
Vol 5 (1) ◽  
pp. 37-43 ◽  
Author(s):  
David B. Sattelle ◽  
Donglin Bai ◽  
Hong Hong Chen ◽  
Jacqueline M. Skeer ◽  
Steven D. Buckingham ◽  
...  
Keyword(s):  
Nervous System ◽  
Manduca Sexta ◽  
Larval Nervous System ◽  
Cl Channels

Dif and cactus are colocalized in the larval nervous system ofDrosophila melanogaster

1999 ◽  
Vol 38 (1) ◽  
pp. 16-26 ◽  
Author(s):  
Rafael Cantera ◽  
Erik Roos ◽  
Ylva Engstr�m
Keyword(s):  
Nervous System ◽  
Larval Nervous System

The nervous system of a pilidium larva: evidence from electron microscope reconstructions

1985 ◽  
Vol 63 (8) ◽  
pp. 1909-1916 ◽  
Author(s):  
T. C. Lacalli ◽  
J. E. West
Keyword(s):  
Nervous System ◽  
Electron Microscope ◽  
Similar Type ◽  
Ciliary Band ◽  
Nerve Fibres ◽  
Larval Nervous System ◽  
Marginal Band ◽  
Friday Harbor ◽  
And Behavior ◽  
First Time

The principal ultrastructural features of a pilidium larva from Friday Harbor (pilidium A, unidentified as to species) are summarized and, based on electron microscope reconstructions, the larval nervous system is described for the first time. Ciliary effectors in the larva include the marginal ciliary band, which is drawn out to form a small accessory ridge at each of the junctions between lobes, and a pair of suboral (buccal) ridges, one on either side of the stomodeum, that run between the mouth and marginal band. The nervous system consists of a small intratrochal nerve supplying the marginal band, an oral nerve that encircles the mouth at the junction of stomodeum and stomach, and a pair of nerves connecting these that run beneath the suboral ridges. The nerve fibres appear to arise from uniciliate cells in the marginal band and the suboral region. The organization, innervation, and behavior of pilidium A are discussed briefly with reference to Müller's larva, a related larva with a similar type of trochal innervation.

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