REGULATION OF FILAMENTOUS GROWTH IN YEAST

白色念珠菌是人类最常见的分离真菌病原体之一。它可以在出芽酵母、假菌丝和菌丝生长形式之间经历可逆的形态发生转变。其独特的能力，从酵母到菌丝生长响应各种环境信号的转换不仅是固有的致病性，但也提供了一个很好的范式来理解信号通路如何协调生长和发育。本研究的目的是了解各种信号通路如何整合以控制一组常见菌丝特异性基因的表达，以及信号通路与细胞形态发生之间的分子联系。主要有三个目的：1)鉴定白色念珠菌菌丝形态发生的丝化信号通路下游效应体。利用白色念珠菌DNA阵列进行差异基因表达研究，以确定与形态分化相关的基因表达变化以及受丝化信号通路的调节。将对从阵列实验中鉴定出的基因进行功能研究，以确定是否有任何新鉴定的基因负责菌丝形态发生。2)白色念珠菌菌丝特异性基因启动子的转录整合机制。结合DNA结合实验和功能分析，利用选择的菌丝特异性基因的启动子中的位点特异性突变，将用于确定MAP激酶途径和cAMP途径的末端转录因子是否直接作用于启动子，以及它们是否相互合作，还是与启动子上尚未确定的成分一起作用。此外，来自Aim 1的菌丝特异性基因的上游DNA序列将用于预测和鉴定新的顺式元件及其结合蛋白。3) Ste12在酿酒酵母中的调控及功能。Ste12是酿酒酵母交配、侵袭生长和假菌丝生长所需的MAP激酶通路的末端转录因子。提出了生物化学和遗传实验来鉴定Ste12的新调控因子。额外的DNA阵列实验将用于确定Ste12活化和细胞伸长之间的分子联系。

Candida albicans is one of the most frequently isolated fungal pathogens of humans. It can undergo reversible morphogenetic transitions among budding yeast, pseudohyphal, and hyphal growth forms. Its unique ability to switch from yeast to hyphal growth in response to various environmental signals not only is inherent to its pathogenicity, but also provides an excellent paradigm to understand how signaling pathways coordinate growth and development. The objectives of this research are to understand how various signaling pathways are integrated to control the expression of a common set of hypha- specific genes, and the molecular connection between the signaling pathways and cell morphogenesis. There are three Aims: 1) Identification of downstream effectors of filamentation signaling pathways that are responsible for hyphal morphogenesis in C. albicans. Differential gene expression studies with C. albicans DNA arrays will be performed to identify changes in gene expression associated with morphological differentiation as well as regulated by filamentation signaling pathways. Functional studies of the genes identified from the array experiments will be carried out to address whether any newly identified genes are responsible for hyphal morphogenesis. 2) Mechanisms of transcriptional integration at the promoters of hypha-specific genes in C. albicans. A combination of DNA binding experiments and functional assays using site-specific mutations in the promoter of a selected hypha-specific gene will be used to address whether the terminal transcription factors of a MAP kinase pathway and the cAMP pathway act directly on the promoter, and whether they act cooperatively with each other, or with yet unidentified components on the promoter. In addition, upstream DNA sequences of hypha-specific genes from Aim 1 will be used to predict and identify novel cis-elements and their binding proteins. 3) Regulation and function of Ste12 in S. cerevisiae. Ste12 is the terminal transcription factor of the MAP kinase pathways required for mating, invasive growth and pseudohyphal growth in S. cerevisiae. Both biochemical and genetic experiments are proposed to identify novel regulators of Ste12. Additional DNA array experiments will be used to determine the molecular connections between Ste12 activation and cell elongation.