From Bud to Organ: An In Depth Analysis of the Development of the Pancreas.

In this dissertation, a careful analysis of different aspects of pancreatic development was conducted in order to expand our understating of the biology of this organ. This thesis encompasses an in depth description of pancreas macro morphology throughout development as well as the analysis of the role of signaling molecules not previously studied in the pancreas. In brief, Chapter 2 presents a characterization of pancreatic branching and cellular polarization. It provides an anatomical model for branching of the pancreas and establishes the dynamics of cell polarity changes within the pancreatic epithelium throughout development. This chapter provides seminal work in an area that has received little attention in forwarding our understanding of how the epithelium reshapes itself to form a functional organ. Chapter 3 and Chapter 4 focus on the endocrine compartment of the pancreas. In Chapter 3, the expression of Neourogenin3, or Ngn3, a master gene regulator of endocrine fate was studied and a novel molecular correlation with the first and secondary transitions of pancreatic endocrine differentiation was demonstrated. In Chapter 4 it was shown that Rgs genes, specifically Rgs8 and Rgs16, are expressed in endocrine cells during pancreatic development and become quiescent during adulthood. Only under models of islet regeneration and pancreatic stress was a re-activation of Rgs8 and Rgs16 expression in endocrine cells observed. Our results suggest that Rgs16 and Rgs8 control aspects of islet progenitor cell activation, differentiation, and their actions might be required to compensate pancreatic metabolic stress. Finally, Chapter 5 analyzes the role Eph/ephrinB signaling in pancreatic development. Mice lacking signaling of EphB2 and EphB3 receptors showed fewer insulin-producing cells, abnormal islet distribution, anomalies in vasculogenesis and disrupted epithelial polarity and branching. In addition, they showed abnormal pancreatic function since the mutants are hypoglycemic after a glucose tolerance test. Studies in this chapter clearly reveal a role for Eph/ephrinB signaling during pancreatic morphogenesis, differentiation, and physiology. Moreover, since the ephrins (ligands) are expressed in the pancreatic mesoderm and blood vessels and the Eph (receptors) are expressed in the pancreatic endoderm; our results suggest that Eph/ephrinB-mediated tissue-cross-talk is required for proper pancreatic morphogenesis and islet formation. Overall, this thesis provides an in depth analysis of the biology of the developing pancreas