Meeting Abstract
Recent phylogenomic studies have suggested that ctenophores are basal in Metazoa, leading to two hypotheses on the evolution of the nervous system: either sponges, a phylum of nerveless animals, lost a nervous system or ctenophores independently gained one. This is difficult to test, but understanding the function of neurodevelopmental genes in an aneural animal is informative. An intriguing suite of neurodevelopmental genes have been discovered in sponges. A tentative regulatory network consisting of an atonal-related bHLH, Notch and Delta orthologs was found to underlie the differentiation of a distinct cell type in the larvae of Amphimedon queenslandica. Orthologs of Six, Pax, Elav and Msi are expressed in another sponge, Sycon ciliatum. And multiple Sox genes are differentially expressed during development of the larvae and juvenile of S. ciliatum. Moreover, adult sponges can sense a disruption of flow in its canal system and respond with a choreographed inflation-contraction behavior to flush out obstructions. Though the underlying genetic basis of this behavior remains obscure, sensory abilities and initiation of the inflation-contraction behavior can be traced to primary cilia in the osculum, the excurrent canal of the sponge. This suggests that the osculum may act as a sensory and coordinating hub. Since transcriptomes of various life stages and body regions are available from Sycon, this hypothesis can be tested by searching for expression of these neural genes during development of the osculum and in the region proximal to the osculum. I will present the findings of these analyses, a first step towards using the sensitive osculum as the basis of functional experiments to explore the neural heritage of sponges.
