Cellular Control of Endoplasmic Reticulum Biogenesis

真核细胞由一组基本的细胞器“构建块”组成，所述细胞器“构建块”包括（除其他外）细胞核、内质网（ER）、高尔基体、溶酶体、线粒体、过氧化物酶体以及光合生物中的叶绿体。 这种相对较少的独立细胞成分掩盖了真核生物中存在的细胞结构和功能的惊人多样性。 在每种情况下，细胞结构和功能的专门化都反映在细胞器组成的变化上。 因此，细胞生物学的一个关键特征是亚细胞组织的调节，即调节细胞器的存在及其大小，组成，位置，数量和寿命。 令人惊讶的是，考虑到这种调节的重要性，还没有一个例子，其中这种调节的分子本质是很好地理解的实验，将进行探索这个问题，通过集中在调节内质网的结构和功能的酵母，酿酒酵母。 正如在所有其他细胞类型的检查，组织的ER在酵母是敏感的ER蛋白的一个子集的水平。 这些蛋白质之一，HMG-CoA还原酶，催化甾醇和异戊二烯生物合成的第一个关键步骤。 在酵母中，HMG-CoA还原酶水平增加的表达诱导ER的专门区域的组装，称为karmament，由与细胞核密切相关的成对光滑膜堆叠组成。 通过仅仅改变单个蛋白质的水平来控制Karmella组装的能力提供了一个独特的机会来探索细胞在生理需求支配时增加特定ER结构域的生物合成的分子机制。 为了揭示这些机制，Wright博士将使用遗传学方法，利用酵母基因组计划完成后的新资源。 具体来说，她将使用群体遗传学方法来识别缺失突变体，这些突变体在组装业力时显示出生长速度缺陷。 再加上从双杂交方法来确定与HMG-CoA还原酶相互作用的基因产物的信息，这种方法应该揭示在装配业力中具有重要作用的基因。 Karmella装配突变体的分析将通过Karmella装配的体内延时光学显微镜和电子显微镜分析来指导。 这些实验的完成应该揭示通信网络的基本特征，该通信网络报告和调节ER功能与不断变化的生理需求相协调。 这些知识将有具体的应用，以了解ER结构和功能的细胞调节，但也应该提供有关细胞器生物发生的细胞调节的一般见解。

Eukaryotic cells are composed of a basic set of organelle "building blocks" that include (among others) the nucleus, endoplasmic reticulum (ER), Golgi apparatus, lysosomes, mitochondria, peroxisomes and, in photosynthetic organisms, chloroplasts. This relatively small number of separate cellular components belies the amazing diversity of cell structure and function that exists in eukaryotic organisms. In each case, the specialization of cell structure and function is mirrored by changes in organelle composition. Thus, a key feature of cell biology is the regulation of subcellular organization, that is, the regulation of which organelles are present and their size, composition, location, number, and life spans. Surprisingly, given the importance of this regulation, there is not yet a single example in which the molecular nature of this regulation is well understood.The experiments that will be performed explore this question by focusing on the regulation of endoplasmic reticulum structure and function in the yeast, Saccharomyces cerevisiae. As in all other cell-types examined, the organization of the ER in yeast is sensitive to the levels of a subset of ER proteins. One of these proteins, HMG-CoA reductase, catalyzes the first committed step in sterol and isoprene biosynthesis. In yeast, expression of increased levels of HMG-CoA reductase induces assembly of specialized regions of ER termed karmellae, consisting of stacks of paired smooth membranes that are closely associated with the nucleus. The ability to control karmella assembly by merely changing the levels of a single protein provides a unique opportunity to explore the molecular mechanisms by which cells increase biogenesis of a particular ER domain when dictated by physiological demands. To uncover these mechanisms, Dr. Wright will use a genetic approach that takes advantage of new resources available as a result of completion of the Yeast Genome Project. Specifically, she will use a population genetic approach to identify deletion mutants that display defects in growth rate when they assemble karmellae. Coupled with information from a Two-Hybrid approach to identify gene products that interact with HMG-CoA reductase, this approach should reveal genes that have important roles in assembly of karmellae. The analysis of karmella assembly mutants will be guided by in vivo time-lapse light microscopy and electron microscopic analysis of karmella assembly. Completion of these experiments should uncover basic features of the communication network that reports and regulates ER function coordinately with changing physiological demands. Such knowledge will have specific application to understanding the cellular regulation of ER structure and function, but should also provide general insights concerning the cellular regulation of organelle biogenesis.