| In the model amphibian, Xenopus laevis, the HMG box transcription factor, Sox17, is expressed throughout the vegetal region that forms the endoderm. It is both necessary and sufficient for the endoderm formation. In order to study endoderm formation in the direct developing frog, Eleutherodactylus coqui, its Sox17 orthologue EcSox17 was cloned by Sean Willamson. To look at the expression of EcSox17, I designed primers and did RT-PCR on whole embryos. EcSox17 was expressed from cleavage to hatching of free-living froglet. EcSox17 RNA was present in the ovaries, an expression which has not been reported in any other vertebrate. Whole mount and bisected in situ hybridizations were done to look at the location of the EcSox17 RNA. EcSox17 was expressed at the blastoporal lip at all times and was not expressed in the yolk-rich vegetal core. RT-PCR on dissected pieces of early gastrulae however, indicated that the vegetal core expressed EcSox17, suggesting its contribution to the developing endoderm. I conclude that EcSox17 expression is ovarian as well as zygotic throughout the embryonic development. The transcript location at the blastoporal lip and perhaps throughout the vegetal region in early gastrula suggests its contribution to the definitive endoderm. Further experimentation is required to assess the function and necessity of EcSox17 in endoderm formation. |
