Browsing by Subject "Homeodomain Proteins"
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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 MEIS1: At the Crossroads Between Metabolic and Cell Cycle Regulation(2013-01-17) Kocabas, Fatih; Sadek, Hesham A.Stem cells undergo self-renewal, maintaining themselves in an undifferentiated state while generating differentiated cells that are required for the tissue homeostasis or repair. One intriguing feature of stem cells is their maintenance in their respective hypoxic niche. Survival in this low-oxygen microenvironment requires significant metabolic adaptation. However, little is known about stem cell metabolism, its regulation or its effect on stem cell function. We started our work by focusing on the most comprehensively characterized adult stem cell population, the hematopoietic stem cells (HSCs). We demonstrate that mouse and human HSCs utilize glycolysis instead of mitochondrial oxidative phosphorylation to meet their energy demands. Furthermore, we demonstrate that Meis1 and Hif-1α are markedly enriched in HSCs and that Meis1 functions upstream of the two master redox regulators Hif-1α and Hif-2α, where loss of Meis1 results in a metabolic shift from glycolysis to mitochondrial oxidative metabolism, and increased oxidative stress, and loss of HSC quiescence. These results underscore the critical link between metabolism and cell cycle regulation of HSCs. We then sought to determine whether other stem cell populations share these unique metabolic characteristics. This strategy enabled us to identify the epicardium and the subepicardium of the heart as the cardiac hypoxic stem cell niche, which houses a metabolically distinct, Hif-1α positive population of glycolytic cardiac progenitors. Moreover, our studies indicate that Meis1, which regulates HSC metabolism and quiescence, also induces post-natal cell cycle exit and quiescence of cardiomyocytes through induction of synergistic cyclin dependent kinase inhibitor families. We demonstrate that both embryonic and adult deletion of Meis1 in cardiomyocytes results in widespread cardiomyocyte proliferation in the adult heart. Overall, our studies identify Meis1 as a critical transcriptional regulator of cell cycle and metabolism.