P2.78  Saturday, Jan. 5  Identification of the LIM Homeobox gene family in the ctenophore Pleurobrachia bachei. SANFORD, R. S.*; KOHN, A.B.; SWALLA, B. J.; MOROR, L.L.; University of Florida; University of Florida, Whitney lab; University of Washington, Friday Harbor Labs; University of Florida, Whtiney lab rachelsusansanford@gmail.com

The LIM homeobox (Lhx) gene family is important for cell-fate specification in animals. In bilaterians and cnidarians there are six subfamilies of Lhx genes, Lhx1/5, Lhx2/9, Lhx3/4, Lhx6/8, Islet, and Lmx, which play a critical role in the development of the nervous system. In a search for genes controlling neural specification in early animals, we first screened the sequenced genome of Pleurobrachia bachei for the presence of Lhx-like gene homologs. From about 20,000 Pleurobrachia gene models, we identified four Lhx-like genes initially classified as Lhx1/5, Lhx3/4, Islet and Lmx but Lhx2/9 and Lhx6/8 were absent. This 4-gene Lhx-like complement is similar to another recently sequenced ctenophore Mnemiopsis leidyi while the sponge Amphimedon has only 3 suggesting that both sponges and ctenophores are among the most basally branched metazoan lineages. Our preliminary data (RT-PCR and in situ hybridization) suggest that in Pleurobrachia LIMs are predominantly expressed in embryonic stages with no detectable expression in adults supporting a hypothesis that even in ctenophores Lhx-like gene families can contribute to cell-fate specification. However, we were unable to confirm neuron-specific expression of Lhx-like genes in Pleurobrachia and further research is needed to understand the genomic bases of neurogenesis in ctenophores – the enigmatic early animal lineage with well-developed neural organization and a complex behavioral repertoire.