Meeting Abstract
Evolution of nervous systems (NSs) has been an enigma. NS architectures vary widely across Metazoa. Such diversity relies on the developmental mechanisms controlling neurogenesis i.e. the generation of neurons from neural precursor cells (NPCs). Similar genes regulate neurogenesis in some ecdysozoans, deuterostomes, and cnidarians; however, there are similarities as well as differences in how certain neurogenic homologs are deployed across clades. For example, NPCs maintain their proliferative state via upregulation of SoxB1 factors in both vertebrates and insects. In contrast, proneural homologs (e.g. Achaete-Scute and Neurogenin) promote fate specification of NPCs in insects but induce cell-cycle exit and differentiation in vertebrates. Neurogenesis is largely unexplored in the third major bilaterian clade, Spiralia, and spiralian data would enable better reconstruction of NS evolution. We examined neurogenesis in the spiralian annelid Capitella teleta using fluorescent in situ hybridization and pulse-chase labeling with the thymidine analogs EdU and BrdU. In C. teleta, apical neuroectodermal cells express homologs of soxB1, neurogenin and ash while basal cells express neuronal markers like elav1 and synaptotagmin. We identified the spatial localization of proliferating cells within the developing neuroectoderm and correlated that with marker gene expression in order to better understand the progression of neurogenesis in C. teleta. Moreover, we also examined co-expression of neurogenic homologs to understand possible co-regulation within a gene regulatory network. Our data indicate a hierarchical regulation of these genes in a manner similar to that in insects and future gain- and loss-of-function studies will test these relationships.
