SANSTAD, E.A.; JARZAB, D.M.; LeCLAIR, E.E.: A cDNA catalog of turtle shell development

In turtles, the cranial and postcranial dermal bones are remarkably similar in structure, containing both sutures and plates. This leads to the question of how the vertebrate gene families that regulate mesodermal fate and intramembraneous bone formation have been co-opted to a different role in turtle shells. Using histological techniques we have cleared and stained the shells of developing turtle embryos (Chrysemys scripta) after 2 weeks, 3 weeks,5 weeks and 7 weeks of incubation. This allows us to study the progress of ossification as the shell develops. Next, we have created three tissue-specific cDNA libraries from the lateral carapace ridge (which initiates shell development), the 3-week embryonic shell (cartilaginous phase) and the 5-week embryonic shell (ossification phase). After reverse transcription and long-distance PCR amplification, all cDNAs were directionally cloned into the lTriplEx2 vector (Clontech) and packaged into phage. Preliminary analysis of the amplified libraries show that the titers exceed 4-8 million pfu/uL; randomly isolated phage were sequenced and found to contain mid-length (>700 bp) turtle-specific cDNAs, including the 3′ poly-A tail. These libraries are now being screened for genes involved in shell initiation (e.g. FGFs) and the regulation of growth at bony sutures (Msx, BMPs). Aliquots of these libraries are available to interested researchers. (Supported by the DePaul University Research Council and Sigma Xi.)