Meeting Abstract
The echinoderm central nervous system (CNS) has long been considered either “enigmatic” or “primitive”. Recent studies, however, resulted in a paradigm shift in our current understanding of echinoderm neurobiology and its phylogenetic significance. This study contributes to the growing body of evidence that the echinoderm CNS shares a number of general features with the chordate nervous system and is neither too primitive nor unusual. The main components of the brittle star CNS are the circumoral nerve ring and five radial nerve cords (RNCs) that supply each of the five appendages called arms. Traditionally, the echinoderm CNS has been thought to be composed of separate ectoneural and hyponeural components. Here we, show that they are extensively interconnected and form an anatomically continuous unit. The CNS is organized as a neuroepithelium, whose scaffold is composed of radial glial cells that share structural and functional similarities with the radial glia in chordates. This scaffold is also densely populated with neurons that show much diversity at the morphological and molecular level. The neuropil regions contain abundant chemical synapses, previously thought to be absent in echinoderms. The glial cells also show an unexpected level of diversity and comprise at least two distinct cell cohorts, which differ in terms of their ability to express the transcription factor Brn1/2/4, a marker of neuronal progenitors in the nervous system. Taken together, our data suggest that echinoderm CNS shares key structural features with the CNS of other Deuterostomes and is more complex in terms of its neuronal and glial architecture than previously thought.
