The evolution of nervous system centralization
The evolution of nervous system centralization
It is currently unknown when and in what form the central nervous system (CNS) in Bilateria first appeared, and how it further evolved in the different bilaterian phyla. To find out, a series of recent molecular studies has compared neurodevelopment in slow-evolving deuterostome and protostome invertebrates such as the enteropneust hemichordate Saccoglossus and the polychaete annelid Platynereis. These studies focus on the spatially different activation and, when accessible, function of genes that set up the molecular anatomy of the neuroectoderm, and specify neuron types that emerge from distinct molecular coordinates. Complex similarities are detected that reveal aspects of neurodevelopment that most likely already occurred in a similar manner in the last common ancestor of the bilaterians, Urbilateria. Using this approach, different aspects of the molecular architecture of the urbilaterian nervous system are being reconstructed and are yielding insight into the degree of centralization that was in place in the bilaterian ancestors.
Keywords: evo-devo, bmp signalling, dorsoventral axis inversion, Urbilateria, nervous system centralization
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