Meeting Abstract

13.1  Tuesday, Jan. 4  Genomic Basis of Neural Organization in a Hemichordate, Saccoglossus bromophenolosus: Do Hemichordate have a Central Nervous System? SWALLA, B.J.*; LUTTRELL, S.; BYRNE, A.; COLLIN, P.; MARDASHOVA, M.; LAVROVA, E.; SOPHER, K.; ANDRILENAS, K.; NIKITIN, M.; CITARELLA, M.; KOHN, A.B.; MOROZ, L.L.; FHL, Univ. of WA; FHL, Univ. of WA; FHL, Univ. of WA; FHL, Univ. of WA; FHL, Univ. of WA; FHL, Univ. of WA; FHL, Univ. of WA; FHL, Univ. of WA; FHL, Univ. of WA; Whitney Lab for Marine Biosciences, Univ. of FL; Whitney Lab for Marine Biosciences, Univ. of FL; Whitney Lab for Marine Biosciences, Univ. of FL bjswalla@uw.edu

Hemichordates are a crucial subject of study for understanding the deuterostome and chordate evolution and of the origin of chordate central nervous system (CNS) in particular. Morphological and developmental evidence suggests that hemichordates have cell populations homologous to subdivisions of chordate CNS, however, global expression of neural markers and genes involved in neural development have yet to be visualized at a cellular level. We held an undergraduate apprenticeship in the spring of 2010 at Friday Harbor Laboratories to perform molecular mapping of the neural system of hemichordates and ctenophores. Homologs to key neural and developmental genes have been found in the Saccoglossus kowalevskii genome; this available genomic information was used to clone specific genes, and make RNA probes for in-situ hybridization on the Pacific hemichordate species S. bromophenolosus. Results showed unusual molecular complexity in the hemichordate nervous system. We visualized a set of cells expressing vertebrate-specific neuronal markers surrounding the stomochord and heart/kidney complex. However, we also identified diversity of apparently non-neuronal cells expressing the same subset of vertebrate-specific neuronal gene homologs, questioning commonly used pan-neuronal marker genes among deuterostomes. In addition, we identified multiple neural cell populations that can not be interpreted as a single centralized nervous system although centralization was observed in collar, dorsal and ventral regions of S. bromophenolosus. Studies are ongoing to determine the origin and function(s) of these cells and reconstruct populations of ancestral cell lineages leading to the formation of complex nervous system organization and brains in chordates.