Meeting Abstract
21.6 Tuesday, Jan. 4 Different ways to build a backbone: Notch regulation of somitogenesis in the lizard Anolis carolinensis is highly divergent from birds and mammals ECKALBAR, WL; INFANTE, C; DENARDO, D; LOSOS, J; RAWLS, A; WILSON-RAWLS, J; KUSUMI, K*; Arizona State Univ.; Harvard Univ.; Univ. of Georgia; Arizona State Univ.; Harvard Univ.; Arizona State Univ.; Arizona State Univ.; Arizona State Univ. kenro.kusumi@asu.edu
In vertebrates, spinal segments are established through the formation of somites early in embryogenesis. The genetic regulation of somitogenesis in vertebrates can be divided into two major groups, based on how the Notch receptor is controlled. In teleosts such as zebrafish, Notch is cyclically activated by a delta ligand (deltaC). In contrast, in mammals and birds, activated Notch is regulated by cyclical inhibition by lunatic fringe, with constitutive expression of delta genes. Mammals further inhibit Notch signaling with Numb and Dll3 (an orthologue of zebrafish deltaC), which is not present in avian genomes. To better understand the evolutionary history of the switch in Notch regulation, we have undertaken a comparative analysis of a non-avian reptile. With the genomic sequencing of the first non-avian reptile, Anolis carolinensis, we have identified surprising divergence in the regulation of somitogenesis compared with other vertebrates. In Anolis, lunatic fringe is not expressed in the presomitic mesoderm and no evidence of cycling expression was observed in somites. Intriguingly, the Anolis dll1 orthologue displayed cycling expression within the presomitic mesoderm. We have identified a highly divergent delta gene in Anolis (orthologous to deltaC, Xenopus X-Delta-2 and Dll3) whose levels are dynamic in somitogenesis. Other somitogenesis genes such as tbx6, mesp, and hairy orthologues are comparable with other vertebrates. These findings suggest that the key regulatory Notch cycling gene in somitogenesis may have switched multiple times during vertebrate evolution. Further molecular analysis of chelonian and crocodilian reptiles and caudate amphibians will help address this hypothesis.
