Browsing by Subject "Pancreas"
Now showing 1 - 7 of 7
- Results Per Page
- Sort Options
Item Afadin and RhoA Control Pancreatic Endocrine Mass via Lumen Morphogenesis(2018-04-12) Azizoglu, Dicle Berfin; Carroll, Thomas J.; Cleaver, Ondine; Johnson, Jane E.; Olson, Eric N.Pancreas is a vital organ responsible for digestion and blood glucose homeostasis in vertebrates. Pancreatic endocrine cells secrete hormones that regulate blood glucose levels, while exocrine cells secrete digestive enzymes. In mice, all pancreatic cell types derive from an early set of multipotent progenitors, cells of the early pancreatic bud. These progenitors complete differentiation by birth. Coincidental with differentiation, the bud epithelium forms and remodels lumens. Previous studies suggest that lumen morphogenesis is critical to endocrine and exocrine cell fate. Furthermore, recent studies show that a central network of lumens (termed core plexus) is the birthplace of most endocrine progenitors. To date, it remains unclear how pancreatic lumens form and remodel, and which aspects of lumen morphogenesis influence cell fate. Importantly, models testing the function of the central lumen network as an endocrine niche are lacking. My thesis work identifies mechanisms underlying lumen formation and remodeling, and shows that central lumen network morphogenesis impacts pancreatic endocrine mass. Through this work, I find that loss of the scaffolding protein Afadin disrupts de novo lumenogenesis and lumen continuity in the tip epithelium. Co-depletion of the actomyosin regulator RhoA and Afadin results in defects in the central lumens and arrests lumen remodeling. This arrest leads to prolonged perdurance of the central lumen network over developmental time, and expansion of the endocrine progenitor population and, eventually, endocrine mass. Thus, my thesis work uncovers essential roles of Afadin and RhoA in pancreatic central lumen morphogenesis, which subsequently determines endocrine cell mass.Item BMP Signaling through BMPR1A is Required for Establishment of Pancreatic Laterality(2009-09-04) Danesh, Shahab Malekpour; Cleaver, OndinePancreatic development begins in the mouse, at embryonic day 8.5, as two patches within the gut tube that are located between the stomach and the duodenum. These patches begin to bud, proliferate, and differentiate to become the dorsal and ventral pancreas. During pancreatic bud development several tissues that are adjacent to the gut tube provide important signals for pancreatic development. Various bone morphogenetic proteins (Bmps) and Bmp receptors (Bmprs) are expressed in the pancreas and in the tissues that flank the pancreatic bud during pancreatic development. Bmp7, BmpR1a, and BmpRII are expressed in the pancreatic endoderm during pancreatic bud development. Bmp2, Bmp4, BmpR1a and BmpRII are expressed in the dorsal aorta which transiently flanks the pancreatic bud. Bmp4, Bmp7, BmpR1a, BmpR1b, and BmpRII are expressed in the pre-pancreatic mesenchyme. Interestingly, Bmp4 is expressed asymmetrically along the gut in the mesogastrium, preceeding gut turning. Transgenic knock down of BMP signaling via the secreted BMP antagonist Noggin in the pre-pancreatic milieu results in reduced pancreas, spleen, stomach and in failure of pyloric sphincter formation. Interestingly, BMP knockdown also results in defects in lateral growth of the pancreas. Specifically, BMP knockdown prevents formation of the splanchnic mesodermal plate (SMP), the asymmetrically forming mesothelial structure that accompanies leftward growth of the pancreas. Conversely, over expression of Bmp2 in the pre-pancreatic milieu does not result in defects in SMP formation or lateral growth of the pancreas. However, overexpression of Bmp2 in the pancreas epithelium resulted in failure to differentiate into endocrine and exocrine cell lineages. Global knockout of BmpR1a, but not BmprII, prior to pancreatic bud development results in developmental defects in SMP formation and pancreatic laterality. Bmpr1a knockout results in reduced SMP expression of Bapx1, a gene required for SMP formation and lateral growth of the pancreas. Therefore, defects in lateral growth of the pancreas in Bmpr1a mutants are likely mediated by Bapx1 and, accordingly, Bmpr1a mutant pancreata exhibit misregulation of genes that require Bapx1, including Fgf9 and Fgf10. Additionally, deletion of Bmpr1a also leads to misregulation of Barx1, another gene with SMP restricted expression. Deletion of BmpR1a specifically from the pre-pancreatic endoderm or endothelial (aorta) cells did not show defects with respect to pancreatic growth, development, or differentiation. Finally, work herein shows that BMP-BMPR1A signaling to the endothelium specifically is required for vascularization of the pancreatic bud and SMP formation. This study presents the first evidence of a cell-cell signaling molecule playing a role in left-right patterning during organogenesis.Item Elucidating the Role of Cellular Architecture in the Developing Pancreas(2015-11-30) Marty Santos, Leilani Marie; MacDonald, Raymond J.; Johnson, Jane E.; Carroll, Thomas J.; Cleaver, OndineMany studies have focused on examining the intrinsic factors such as transcriptional regulators that instruct the step-wise acquisition of β-cell fate in the developing pancreas, with the intention of recapitulating the events necessary in order to generate these cells in vitro for replacement therapies. Directed differentiation protocols have improved upon transitioning from 2D to 3D cultures, indicating that the 3D microenvironment in which β cells are born is critical for the acquisition of their cell fate. However, little is known about the mechanisms through which the 3D architecture of the developing pancreas mediates cell fate specification and epithelial organization. In order to address some of the remaining gaps in the field, we proceeded to characterize the Pdx1-/- embryo, a mutant in which pancreatic cell fate and architecture had been reported to fail early in its development, to determine whether the developmental failure was related to defects in the epithelial architecture. After elucidating that Pdx1 is a transcriptional regulator of the cellular adhesion molecule E-cadherin, we then examined the effect that tissue-specific deletion of this molecule has on the developing pancreas. We determined that E-cadherin regulates both endocrine cell fate and isletogenesis, as we observe that there is a reduction in endocrine progenitors and total endocrine volume, in addition to a failure of the endocrine cells to coalesce into islets. Our findings also demonstrate that acinar cells are lost in the post-natal E-cadherinf/f;Pdx1Cre pancreas, due to an increase in cell death, suggesting that E-cadherin is capable of regulating cell survival. This body of work indicates that architectural molecules play a critical role in the regulation of cell fate specification and epithelial morphogenesis in the developing pancreas.Item From Bud to Organ: An In Depth Analysis of the Development of the Pancreas.(2009-09-04) Villasenor, Alethia; Cleaver, OndineIn 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 pancreasItem Pancreas and islet cell transplantation in diabetes(2003-08-21) Raskin, PhilipItem Screening and surveillance of pancreas neoplasia: Can we and should we?(2008-07-11) Lara, Luis F.Item [UT Southwestern Medical Center News](2009-09-17) Shear, Kristen Holland