Molecular Mechanisms of Genomic Reprogramming during Germ Cell Specification

描述（由申请人提供）：生殖细胞的显著之处在于，在生物体中发现的所有细胞类型中，仅生殖细胞就保留了产生所有胚胎和胚胎外细胞类型的能力，这些细胞类型有助于生物体的形成。这种全能性的特性在原始生殖细胞（PGCs）中通过维持转录抑制的基因组而得到保护。在秀丽隐杆线虫中，两种时间上和生物化学上不同的机制实现了这一目标。最初，秀丽隐杆线虫特有的母体蛋白PIE-1，专门分割到种系卵裂球，抑制RNA聚合酶的激活。在PGCs诞生后不久，PIE-1被降解，并发生全基因组染色质重塑以维持转录抑制。然而，参与调节基因组整体重塑效应的途径仍然未知。这项提议的一个重要目标是揭示新生生殖细胞中各种“活性”染色质标记特异性丢失的分子机制。RNA聚合酶，组蛋白变异和翻译后修饰的作用将被询问在这些擦除事件的控制。初步实验还表明，在原始生殖细胞Z2和Z3出生时，组蛋白去乙酰化酶（HDAC）活性被特异性激活。在补充方法中，使用功能缺失突变体、RNA干扰和转基因错误表达，将阐明种系上持续组蛋白乙酰化的后果。最后，将利用遗传和生化方法探讨HDAC活性的翻译和翻译后控制。

DESCRIPTION (provided by applicant): Germ cells are remarkable in that, of all the cell types found in an organism they alone retain the ability to give rise to all the embryonic and extra-embryonic cell types that contribute to an organism. This property of totipotency is protected in primordial germ cells (PGCs) by their maintenance of a transcriptionally repressed genome. Two temporally and biochemically distinct mechanisms accomplish this objective in C. elegans. Initially, a C.elegans-specific maternal protein PIE-1, specifically partitioned to the germ line blastomeres, inhibits activation of RNA polymerase. Shortly, after the birth of the PGCs, PIE-1 is degraded and dramatic genome-wide chromatin remodeling occurs to sustain transcriptional repression. However, pathways involved in regulating effectors of global remodeling of the genome remain unknown. A significant goal of this proposal is to uncover molecular mechanisms underlying the specific loss of various marks of 'active' chromatin in newly bom germ cells. The role of RNA polymerase, histone variants and post-translational modifications will be interrogated in the control of these erasure events. Initial experiments also suggest specific activation of histone deacetylase (HDAC) activity at the birth of the primordial germ cells, Z2 and Z3. In complementary approaches, using loss-of-function mutants, RNA interference and transgenic misexpression, the consequence of persistent histone acetylation on the germ-line will be elucidated. Finally, translational and post-translational control of HDAC activity will be probed using genetic and biochemical approaches. Public Health Relevance: These studies address a fundamental question of biomedical relevance: how do embryonic cells, and for that matter, stem cells retain the ability to differentiate into all lineages of the adult animal? The answer to this question will undoubtedly have enormous ramifications for manipulating cells to generate tissue-specific progenitors that could ultimately be used to cure debilitating, degenerative illnesses such as Parkinson's. Additionally, since histone deacetylation has been implicated in aberrant gene silencing in cancerous cells and HDAC inhibitors are being developed as effective anti-cancer drugs, our long-term goal is to utilize our knowledge of histone deacetylation regulation to increase the specificity of next generation epigenetic therapies.