Embryonic neurogenesis in echinoderms

Abstract

The phylogenetic position of echinoderms is well suited to revealing shared features of deuterostomes that distinguish them from other bilaterians. Although echinoderm neurobiology remains understudied, genomic resources, molecular methods, and systems approaches have enabled progress in understanding mechanisms of embryonic neurogenesis. Even though the morphology of echinoderm larvae is diverse, larval nervous systems, which arise during gastrulation, have numerous similarities in their organization. Diverse neural subtypes and specialized sensory neurons have been identified and details of neuroanatomy using neuron-specific labels provide hypotheses for neural function. The early patterning of ectoderm and specification of axes has been well studied in several species and underlying gene regulatory networks have been established. The cells giving rise to central and peripheral neural components have been identified in urchins and sea stars. Neurogenesis includes typical metazoan features of asymmetric division of neural progenitors and in some cases limited proliferation of neural precursors. Delta/Notch signaling has been identified as having critical roles in regulating neural patterning and differentiation. Several transcription factors functioning in pro-neural phases of specification, neural differentiation, and sub-type specification have been identified and structural or functional components of neurons are used as differentiation markers. Several methods for altering expression in embryos have revealed aspects of a regulatory hierarchy of transcription factors in neurogenesis. Interfacing neurogenic gene regulatory networks to the networks regulating ectodermal domains and identifying the spatial and temporal inputs that pattern the larval nervous system is a major challenge that will contribute substantially to our understanding of the evolution of metazoan nervous systems. This article is categorized under: Comparative Development and Evolution > Model Systems Comparative Development and Evolution > Body Plan Evolution Early Embryonic Development > Gastrulation and Neurulation.

Neuropeptidergic Systems in Pluteus Larvae of the Sea Urchin Strongylocentrotus purpuratus: Neurochemical Complexity in a “Simple” Nervous System

“…The sea urchin larva, therefore, offers opportunities to observe the complete development and function of a nervous system in a small and tractable organism. The larval nervous system is the “product” of neurogenic processes that have been studied using immunostaining for neural markers and analysis of the expression of pro-neuronal genes, as reviewed in Hinman and Burke ( 4 ). However, the diversity of neuronal sub-types in sea urchin larvae has not been characterized in detail.…”

Neurogenesis in the sea urchin embryo is initiated uniquely in three domains

“…The bilaterally symmetrical larva of the sea urchin develops a nervous system that begins functioning when the larva begins to feed, which in Lytechinus variegatus occurs between 24 and 48 hours post fertilization (hpf ). By that time, 40-50 neurons constitute the nervous system composed of about four serotonergic, 30-35 cholinergic and five to ten dopaminergic neurons (Garner et al, 2016;Hinman and Burke, 2018;Slota and McClay, 2018). These neurons differentiate in three locations in the larva.…”

Neurons and Glia Cells in Marine Invertebrates: An Update

“…In the plexus and on the surface of the primary podia, epithelial (sensory) cells are responsible of axon supply. The distinct types of axons sometimes are not easily distinguishably, such is the case of the peripheral axons which can be confused with the processes of muscle and interstitial cells (Pentreath and Cobb, 1972;Byrne et al, 2018;Hinman and Burke, 2018).…”