Abstract
achaete-scute homologs (ash) regulate neural development in all bilaterian model animals indicating that they represent a component of the ancestral neurogenic pathway. We test this by investigating four ash genes during development of a basal metazoan, the cnidarian sea anemone Nematostella vectensis. Spatiotemporal expression of ash genes in the early embryo and larval stages suggests that they regulate neurogenesis. More specifically, NvashA is co-expressed with neural genes in the embryonic ectoderm. Knockdown of NvashA results in decreased expression of eight neural markers, including the six novel neural targets identified here. Conversely, overexpression of NvashA induces increased expression of all eight genes, but only within their normal axial domains. Overexpression of NvashB-D differentially increases expression of NvashA targets. The expression patterns and differential ability of ash genes to regulate neural gene expression reveals surprising molecular complexity in these 'simple' animals. These data suggest that achaete-scute homologs functioned in the ancestral metazoan neurogenic pathway and provide a foundation to investigate further the evolution of neurogenesis and the origin of complex central nervous systems.