京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第18880号 / 医博第3991号 / 新制||医||1008(附属図書館) / 31831 / 京都大学大学院医学研究科医学専攻 / (主査)教授 山下 潤, 教授 篠原 隆司, 教授 斎藤 通紀 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

This thesis investigates the applicability of novel approaches designed to study the molecular mechanisms required for the initiation of organogenesis within the early endoderm. The endoderm is the germ layer that gives rise to the gut-tube and associated organs including the thyroid, lung, liver and pancreas. Our laboratory focuses on understanding the molecular mechanisms governing the developmental transition from endoderm to liver and pancreas. Several signaling pathways including Wnt, Retinoic Acid (RA), Bone Morphogenetic Protein (BMP) and Transforming Growth Factor-β (TGFβ) have been implicated in the emergence of the liver bud from the endoderm in the mouse or other vertebrate species. However, neither the exact signals nor the precise roles during budding process have been identified, due to the complexity of specifically altering these essential pathways using traditional genetic approaches during the earliest stages of endoderm organogenesis. These traditional techniques include transgenic, knockout or conditional knockouts strategies. To overcome the difficulties of genetic accessibility, our laboratory has optimized two complementary approaches, electroporation and addition of activators or inhibitors directly to the culture media, to study the earliest stages of organ formation using an ex vivo culture system (whole embryo culture), that allow us for normal embryonic development for up to two days. This ex-vivo technique also provides the opportunity to access and manipulate the endoderm, specifically the liver and pancreas precursor cells, prior to organ specification. Because the endoderm undergoes normal liver and pancreas specification in our ex vivo system by 24 hours after culture begin, we reason that it is possible to manipulate gene expression at the onset of culture. We then determine the effects of this manipulation on liver or pancreas development by molecular and morphological analysis after culture. The first approach we developed is the use of directional electroporation of nucleic acids to manipulate a specific region of the endoderm, particularly on liver and pancreas developmental processes. The second method is global inhibition or activation using inhibitors or growth factors activators, focusing on the TGFβ signaling pathway. These techniques will be performed prior to, or concurrent with, liver and pancreas specification, followed by embryo culture until after the onset of organogenesis. The combination of these techniques constitutes a practical approach to stage-manage the endoderm in a temporally and spatially distinct manner. In addition, it will allow us to alter specific signaling pathways without the labor-intensive generation of genetically modified animals. Indeed, establishment of these methodologies may provide a robust tool for rapid screening of candidate genes and signaling molecules underlying organogenesis in any endodermally derived organ in mouse embryos.