Sources and consequences of phenotypic variation in complex regulatory networks

描述（由申请人提供）：复杂性状背后的分子系统通常知之甚少。个体之间的遗传和环境差异是如何转化为表型差异的，这一点更不为人所知。这种从基因型到表型的映射的一般特征是稳健性，或表型对遗传和环境变异的缓冲。复杂的人类疾病可以被视为强大系统的失败，表型变异表现为临床表现和疾病结果的个体差异。表型变异是形成调控网络的进化过程的产物，并提供了一个窗口。该项目的长期目标是在机制水平上了解复杂表型变异的来源和后果。具体而言，本项目将研究不同遗传背景下酿酒酵母单细胞形态的变化。酵母是了解基本细胞过程的一种已建立的模式生物，也是人类疾病，特别是与癌症相关的细胞周期缺陷和染色体不稳定性（CIN）的重要模型。具体目标1是确定缓冲复杂表型对抗环境变异和对抗遗传变异的机制之间的一致性。先前的实验确定了数百个缺失突变，这些突变增加了等基因细胞的形态变异。通过将这些突变的一个子集引入不同的酵母菌株，将环境差异的这种中断缓冲与遗传差异的缓冲进行比较。由于转录网络在稳健性中的重要性，将特别关注编码转录调节因子的基因突变。在染色体组织中起作用的基因也被发现不成比例地需要缓冲。其中一个基因HTZ1编码H2A。Z，一种组蛋白变体，需要适当的转录调节和适当的染色体分离。具体目标2是利用HTZ1中分离这两种变异源的工程突变，确定缓冲受损和CIN对表型变异的相对贡献。尽管癌症中伴随CIN的遗传变异性一直被认为是表型异质性的潜在来源，但调控网络的缓冲功能受损尚未得到证实。特异性目的3是测试必需基因的部分功能丧失突变是否损害缓冲。非必需基因与必需基因具有相同的特性，例如参与核心细胞过程和遗传网络中的高连通性。这一观察结果提出了一种可能性，即必需基因是健壮性的主要贡献者。在必要基因中含有亚形态突变的菌株的综合收集将用于确定这些基因缓冲形态表型的程度。该项目将测试关于健壮性遗传结构的关键假设，并可能揭示在人类疾病中产生异质性的未被充分认识的机制。

DESCRIPTION (provided by applicant): The molecular systems underlying complex traits are in general poorly understood. Even less well understood is how genetic and environmental differences between individuals translate into phenotypic differences. A general feature of this mapping from genotype to phenotype is robustness, or the buffering of the phenotype against genetic and environmental variation. Complex human diseases can be viewed as failures of robust systems, with phenotypic variation manifesting as individual differences in clinical presentation and in disease outcome. Phenotypic variation is a product of and provides a window into the evolutionary processes that have shaped regulatory networks. The long-term goal of this project is to understand at a mechanistic level the sources and the consequences of variation in complex phenotypes. Specifically, this project will study variation in single-cell morphology of the yeast Saccharomyces cerevisiae in different genetic backgrounds. Yeast is an established model organism for understanding basic cellular processes, and also an important model for human disease, particularly the cell-cycle defects and chromosome instability (CIN) associated with cancer. Specific Aim 1 is to determine the congruence between mechanisms that buffer complex phenotypes against environmental variation and against genetic variation. Previous experiments identified hundreds of deletion mutations that increase morphological variation in isogenic cells. This disrupted buffering of environmental differences will be compared to that of genetic differences by introducing a subset of these mutations into diverse yeast strains. Because of the importance of transcriptional networks in robustness, particular focus will be on mutations in genes that encode transcriptional regulators. Genes that act in chromosome organization are also disproportionately found to be required for buffering. One such gene, HTZ1, encodes H2A.Z, a histone variant that is required for proper transcriptional regulation and also proper chromosome segregation. Specific Aim 2 is to determine the relative contributions to phenotypic variation of impaired buffering and CIN, using engineered mutations in HTZ1 that separate these two sources of variation. Whereas the genetic variability that accompanies CIN in cancer has been a long-recognized potential source of phenotypic heterogeneity, impaired buffering of regulatory networks has not been. Specific Aim 3 is to test whether partial loss-of-function mutations in essential genes impair buffering. Nonessential genes that contribute to robustness share properties with essential genes, such as participation in core cellular processes and high connectivity in genetic networks. This observation raises the possibility that essential genes are major contributors to robustness. A comprehensive collection of strains containing hypomorphic mutations in essential genes will be used to determine the extent to which these genes buffer morphological phenotypes. The project will test key hypotheses about the genetic architecture of robustness and may reveal an underappreciated mechanism generating heterogeneity in human disease.