The factors that determine the precise antero-posterior (AP) position of the vertebrate limb are still unknown. This dissertation focuses on examining the roles of two classes of molecules in regulating the (AP) position of the pectoral fins in zebrafish. The pectoral fin is the fish homolog of the tetrapod forelimb. Retinoic acid (RA), one of the two molecules I investigate in this dissertation, must be carefully regulated in order for a fin bud to form and subsequently for it to establish normal AP polarity. RA is also required for the pectoral fin field to form, but the mechanistic role RA plays in development of the fin field is not clear. In this study, I describe the role for RA in regulating the precise location of the fin field. I also characterize the role that the Cdx family of transcription factors play in regulation of the pectoral fin field. I specifically examine two paralogs, Cdx4 and Cdx1a, that have never been studied in the context of pectoral fin development but are known to play a role in regulating cell fates along the AP axis. As I demonstrate, during gastrulation RA and the Cdx transcription factors play a parallel role in restricting the antero-posterior location where the pectoral fin field forms.



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