An Intercellular Connection in Endospore Development

描述(申请人提供)：许多细菌建立专门的分化细胞，以便在环境侮辱中生存，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显著例子是 许多重要的细菌病原体是内孢子的形成(例如，炭疽芽孢杆菌、蜡状芽孢杆菌、艰难梭菌)。我们的总体目标是了解指导内孢子发育的特殊分子机制，以便确定干扰孢子发育的新靶点。我们将开发枯草杆菌内孢子发育的模型系统，因为这个系统易于分析，它的研究已经发现了许多控制大多数细菌(包括病原体)基因表达的机制。在这项建议中，我们重点关注在内孢子发育过程中连接两个细胞的蛋白质复合体的作用。在内孢子形成初期，细胞不对称分裂，形成两个不同的同胞细胞。其中一个细胞(前孢子)发育成内孢子，而另一个(母细胞)成为终末分化的细胞，滋养发育中的内孢子。值得注意的是，前孔和母细胞之间的基因表达是协调的(例如，在前孔中表达随后的一组基因之前，需要在母细胞中表达特定的基因)。母细胞和前孔之间的通讯依赖于几组蛋白质靶向到母细胞和前孔之间的界面。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重要意义。这项提议要解决的中心问题是，特定的蛋白质如何定位于母细胞和前孔之间的界面，以及它们的功能是什么。这项研究中的两个关键蛋白质SpoIIQ和SpoIIIAH通过两个膜相互作用，连接前孔和母细胞。SpoIIQ-SpoIIIAH复合体是标记前孔和母细胞之间的膜界面的创建者，用于将其他蛋白质招募到这一亚细胞位置，包括在母细胞膜吞噬前孔膜的吞噬样吞噬过程中起作用的肽聚糖水解酶，从前孔向激活的母细胞基因表达发出信号所需的蛋白质，以及在前孔中基因表达所需的母细胞蛋白。此外，SpoIIQ-SpoIIIAH复合体似乎形成了一种连接母细胞和前孔细胞质的新型通道或转运蛋白。这项提案的具体目的是确定哪些蛋白质以及如何招募到这种细胞间连接中，以及这些蛋白质复合体如何发挥功能来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.