Sources and consequences of phenotypic variation in complex regulatory networks

描述(申请人提供)：复杂性状背后的分子系统通常知之甚少。更不清楚的是，个体之间的遗传和环境差异如何转化为表型差异。这种从基因型到表型的映射的一个一般特征是稳健性，即表型对遗传和环境变化的缓冲。复杂的人类疾病可被视为强健系统的故障，表型差异表现为临床表现和疾病结局的个体差异。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械学水平上理解复杂表型变异的来源和后果。具体地说，这个项目将研究不同遗传背景下酿酒酵母单细胞形态的变化。酵母是理解基本细胞过程的模式生物，也是研究人类疾病，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的机制之间的一致性，以抵御环境变异和遗传变异。此前的实验发现，数百种缺失突变会增加同基因细胞的形态变异。通过将这些突变的子集引入不同的酵母菌株，这种对环境差异的干扰缓冲将与遗传差异进行比较。由于转录网络在稳健性方面的重要性，将特别关注编码转录调控因子的基因突变。在染色体组织中起作用的基因也不成比例地被发现需要缓冲。其中一个名为HTZ1的基因编码H_2A.Z，这是一种组蛋白变体，对适当的转录调控和适当的染色体分离都是必需的。具体目标2是利用HTZ1中分离这两个变异来源的工程突变，确定缓冲受损和CIN的表型变异的相对贡献。虽然在癌症中伴随CIN的遗传变异性一直被认为是表型异质性的潜在来源，但调节网络的缓冲受损并不是。具体目标3是测试必要基因的部分功能丧失突变是否会损害缓冲。有助于稳健性的非必需基因与必需基因具有共同的特性，例如参与核心细胞过程和遗传网络中的高度连通性。这一观察结果提出了基本基因是健壮性的主要贡献者的可能性。包含基本基因亚型突变的菌株的综合集合将被用来确定这些基因缓冲形态表型的程度。该项目将测试关于稳健性遗传架构的关键假设，并可能揭示人类疾病中一种未被认识到的产生异质性的机制。 公共卫生相关性：复杂的人类疾病，如癌症，受到大量环境和遗传因素的影响，使其难以诊断、治疗和预防。我们将通过实验室实验来了解这些因素的变异如何导致复杂性状的变异。这将促进我们对健康和疾病状态背后的分子机制的理解。

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. PUBLIC HEALTH RELEVANCE: Complex human diseases, such as cancer, are affected by a large number of environmental and genetic factors, making them difficult to diagnose, treat and prevent. We will use laboratory experiments to understand how variation in these factors produces variability in complex traits. This will advance our understanding of the molecular mechanisms underlying healthy and diseased states.