An Intercellular Connection in Endospore Development

描述（由申请人提供）：许多细菌构建专门的分化细胞，以便在环境损伤中生存，在环境中传播，并抵抗宿主防御，抗生素和消毒剂。这种类型的细胞分化的一个引人注目的例子是 许多重要的细菌病原体是内生孢子的形成（例如，炭疽杆菌、蜡状芽孢杆菌、艰难梭菌）。我们的总体目标是了解引导内生孢子发育的特殊分子机制，以确定破坏孢子发育的新靶点。我们将利用枯草芽孢杆菌内生孢子发育的模型系统，因为该系统易于分析，并且其研究已经导致发现了许多控制大多数细菌（包括病原体）中基因表达的机制。 在这个建议中，我们专注于蛋白质复合物的作用，连接两个细胞在内生孢子的发展。在内生孢子形成初期，细胞不对称分裂，产生两个不同的兄弟细胞。其中一个细胞（前孢子）发育成内生孢子，而另一个细胞（母细胞）则成为滋养发育中的内生孢子的终末分化细胞。值得注意的是，基因表达在前孢子和母细胞之间是协调的（例如，在随后的一组基因在前孢子中表达之前，需要在母细胞中表达特定的基因）。母细胞和前孢子之间的通讯依赖于几组蛋白质靶向母细胞和前孢子之间的界面。特定蛋白质的亚细胞定位机制在细胞生物学和发育中具有根本的重要性。在这个建议中要解决的中心问题是如何定位到母细胞和前孢子之间的界面的特定蛋白质，以及它们的功能是什么。本研究中的两个关键蛋白SpoIIQ和SpoIIIAH通过两个膜相互作用，以连接前孢子和母细胞。SpoIIQ-SpoIIIAH复合物作为标记前孢子和母细胞之间的膜界面的奠基者，用于将其他蛋白质募集到该亚细胞位置，包括在前孢子膜被母细胞膜吞噬样吞噬期间起作用的肽聚糖水解酶，从前孢子发出信号以激活母细胞基因表达所需的蛋白质，以及前孢子中基因表达所需的母细胞蛋白质。此外，SpoIIQ-SpoIIIAH复合物似乎形成了一种连接母细胞和前孢子细胞器的新型通道或转运蛋白。该提案的具体目标是确定哪些其他蛋白质以及如何招募到这种细胞间连接，以及这些蛋白质复合物如何发挥作用以协调两个细胞之间的基因表达。

DESCRIPTION (provided by applicant): Many bacteria build specialized differentiated cells in order to survive environmental insults, to disseminate in the environment, and to resist host defenses, antibiotics and disinfectants. A striking example of this type of cell differentiation by many important bacterial pathogens is the formation of endospores (e.g., Bacillus anthracis, Bacillus cereus, Clostridium difficile). Our overall goal is to understand the special molecular mechanisms that guide the development of endospores in order to identify novel targets for disrupting spore development. We will exploit the model system of endospore development in Bacillus subtilis because this system is amenable to analysis and its study has led to the discovery of many mechanisms that control gene expression in most bacteria, including pathogens. In this proposal we focus on the roles of a protein complex that connects two cells during endospore development. Early after the onset of endospore formation the cell divides asymmetrically giving rise to two dissimilar sibling cells. One of these cells (the forespore) develops into the endospore, while the other (the mother cell) becomes a terminally differentiated cell that nurtures the developing endospore. Remarkably, gene expression is coordinated between the forespore and mother cell (e.g., expression of specific genes in the mother cell is required before a subsequent set of genes is expressed in the forespore). The communication between the mother cell and forespore depends upon the targeting of several groups of proteins to the interface between the mother cell and forespore. The mechanisms for subcellular localization of specific proteins are of fundamental importance in cell biology and development. The central questions to be addressed in this proposal are how are specific proteins localized to the interface between the mother cell and forespore, and what are their functions. The two key proteins in this study, SpoIIQ and SpoIIIAH, interact through two membranes to connect the forespore and the mother cell. The SpoIIQ-SpoIIIAH complex serves as the founder that marks the membrane interface between the forespore and mother cell for the recruitment of other proteins to this subcellular location, including peptidoglycan hydrolases that function during the phagocytic-like engulfment of the forespore membrane by the mother cell membrane, proteins required for signaling from the forespore to the activate mother cell gene expression, and mother-cell proteins required for gene expression in the forespore. Moreover, the SpoIIQ-SpoIIIAH complex appears to form a new type of channel or transporter that connects the mother cell and forespore cytoplasms. The specific aims of this proposal are designed to identify which and how other proteins are recruited to this intercellular connection, and how these protein complexes function to coordinate gene expression between the two cells.