NSF Award
9876393
The goals of this project are to determine how the anterior of a vertebrate<br/>embryo becomes correctly positioned. The extreme anterior ectoderm in the frog<br/>Xenopus forms the cement gland, a mucus-secreting organ that is an excellent<br/>positional indicator. The focus of this project is to define ectodermal genes<br/>that regulate cement gland determination. One transcription factor expressed<br/>in the cement gland that is key for cement gland formation is the homeobox<br/>gene otx2. Ectopically expressed otx2 activates ectopic cement gland<br/>development, while ablation of otx2 activity using a dominant negative protein<br/>prevents cement gland formation. A hormone-inducible otx2 protein, otx2GR,<br/>activates the cement gland marker XAG1, however only with ongoing protein<br/>synthesis, suggesting that otx2 activates expression of downstream genes which<br/>in turn activate XAG1 expression. In this proposal, genes activated by otx2GR<br/>that may directly activate XAG1 expression will be isolated using a<br/>subtractive cloning strategy. In order to further analyze cement gland<br/>positioning, dissection of the XAG1 promoter has been carried out. A 200bp<br/>XAG1 fragment directs expression of a reporter to the cement gland. This<br/>fragment is also responsive to otx2GR, although it contains no otx2 binding<br/>sites. Further analysis of the XAG1 promoter will be performed to define<br/>promoter elements necessary for cement gland formation. Factors that interact<br/>with XAG1 regulatory sequences will be identified and characterized. Since the<br/>cement gland is an indicator of normal head development, and since genes and<br/>developmental strategies are evolutionarily conserved, what we learn in<br/>Xenopus is likely to have relevance for understanding normal and abnormal<br/>development of human embryos.
