HANDRIGAN, Gregory R.*; WASSERSUG, Richard J.; Dalhousie University, Halifax, NS, Canada; Dalhousie University, Halifax, NS, Canada: A role for Gdf11 in patterning the anuran vertebral column

The hallmark of vertebrates is their vertebral column. This string of skeletal elements protects the spinal cord and provides a rigid core against which axial muscles work. Terrestrial vertebrates typically have 40-50 vertebrae, derived from a corresponding number of somites. Anurans (frogs and toads) start off with a comparable number of somites, but only the most anterior of these (~20) develop vertebrae. The remaining somites are lost as the tadpole tail is resorbed during metamorphosis. It has been suggested that an anterior shift of the trunk-tail boundary in anurans could confer a caudal identity to prospective trunk somites; these new caudal somites do not contribute to the vertebral column. Such a shift in axial patterning likely occurs via a plethora of morphogenetic factors, including the Hox genes, retinoic acid, and various fibroblast growth factors. Our research focuses on one of the more dramatic players to affect vertebrate axial patterning, growth/differentiation factor 11 (Gdf11). Gene targeting experiments in mice have determined that Gdf11 functions as a posteriorising signal in vertebral column patterning by defining the expression boundaries of various HoxC genes. Thus, Gdf11-deficient mice have 6-8 more trunk�and fewer caudal�vertebrae than their wild-type littermates. Given the conservation of the Hox program across the vertebrates, Gdf11 likely plays a role in shaping the anuran skeleton. We are applying molecular techniques to the frog Xenopus laevis to elucidate the function of a presumptive Gdf11 homolog (XGdf11). Preliminary in situ hybridization studies indicate that XGdf11 is expressed in a similar fashion as its mammalian homologs. The function of this gene in patterning the anuran vertebral column will be explored using transgenic and morpholino techniques.