Department of Animal Biology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia 19104, USA.
The pancreas is a mixed exocrine and endocrine gland involved in the control of many homeostatic functions. During embryogenesis, the pancreas arises from dorsal and ventral evaginations of the foregut that will subsequently fuse into a single organ. The characterization of early genes expressed in the developing pancreas is critical to understand its specification and differentiation. Here we report the expression pattern of Sox9, a member of the Sox family of transcription factors, during development of the Xenopus pancreas and compare its expression to that of a well characterized pancreatic marker, Pdx1. By whole-mount in situ hybridization, Sox9 was first detected at stage 25 in the pancreatic anlagen--dorsally in the prospective foregut and ventrally on each side of the liver diverticulum. As development proceeds, Sox9 expression can be used to trace the development of the dorsal and ventral pancreatic buds and their repositioning associated with the dynamic movements of the gastrointestinal tract. Sox9 expression in the pancreatic rudiment was identical to that of Pdx1. However, while Pdx1 is expressed in both the pancreatic buds and the duodenum, Sox9 was restricted to ventral and dorsal pancreatic buds. Sox9 and Pdx1 are thus two of the earliest genes expressed in the presumptive pancreatic tissue.