Gene Expression in the Development of the Little Skate, Leucoraja erinacea

The digestive tracts of vertebrates are structured differently based on diet and surrounding environment. The intestines of the skate, Leucoraja erinacea, a member of the Elasmobranch Family, has a unique shortened spiral valve structure.  This contrasts with the elongated intestines found in humans and other vertebrates. It is unknown whether the genetic patterning of this intestinal structure is also unique. In an effort to determine this, I focused on the expression of two key developmental homeotic genes, Hoxd12 and Cdx2. In order to observe the expression, the genes were amplified from the skate using PCR. The cloned PCR fragments were confirmed by DNA sequencing. Protein sequence alignment showed 60% and 52% identities between skate and chick Hoxd12 and Cdx2, respectively. RNA in situ hybridization revealed that the expression patterns for these genes in the skate are similar to that in chicken embryos. Cdx2 is expressed in the developing endoderm, and Hoxd12 in the pelvic fins of skate. These results show that although the skate is separated from the chicken through thousands of years of evolution, the function of these key developmental genes have remained conserved.