Meeting Abstract
Hemichordates are a key deuterostome phylum for understanding the evolution of the chordate CNS. Their nervous system is organized around two elements; a pervasive nerve plexus concentrated anteriorly, and two nerve cords; one dorsal and one ventral. Despite the major organizational differences between the nervous system of hemichordates and vertebrates, they share a well-conserved gene regulatory network for anterior-posterior patterning. It is still unclear whether any of this conserved pattern regulates any fundamental similarities in neural cell type specification. I will present data on the spatiotemporal expression of neural markers, including genes involved in neurotransmitter synthesis and transport by in situ hybridization, to determine the level of regional specialization of the neural plexus and nerve cords in juvenile S. kowalevskii. These data also facilitate more direct neural comparisons with chordates. I will also present data using a meganuclease, transposon – mediated approach, to generate transgenic animals expressing GPF in a small subset of neurons. These experiments facilitate an analysis of the identity and location of specific neural cell bodies, and also neuronal morphology and connectivity to better understand the structure and function of this nervous system. We have generated constructs to label neurons using pan-neural (synapsin, elaV, Syt1) and cell type specific markers (GAT, Nurr1, TH), and an endogenous synaptic vesicle protein, synaptotagmin, to label synapses. I will present a preliminary analysis of these data and their impact on our understanding of the comparative relevance of hemichordate nervous systems to broader questions of nervous system evolution. This work will give insights into the evolution of deuterostomes and the origins of the vertebrate brain, but also the evolution of bilaterian nervous systems.
