Spatiotemporal Regulation of Liquid-like Condensates in the Germline

摘要/摘要 液滴细胞器(也称为类液体冷凝物)是动态浓缩的 蛋白质和核糖核酸通过液-液相从细胞质或核质自发结合 过渡。像油和水一样，这些液滴和它们周围的细胞质被认为是共存的 液体的不同状态。目前的模型假设液滴细胞器可能存在以浓缩反应物。 以促进生化反应的方式在空间和时间上聚集在一起，例如 这是基因调控的基础。真核细胞具有许多非膜封闭的液滴细胞器 包括核仁、突起小体、卡哈尔小体和胚泡。在细菌中发现了细菌颗粒 被认为对生殖细胞全能有贡献的所有/大多数动物的细胞。的确，是直系同源 在许多不同物种的动物的生殖粒中都发现了蛋白质(例如VASA)，这暗示着在某些方面 生殖器颗粒的功能在所有动物中都是保守的。 大多数表观遗传信息在动物每一代开始时或接近开始时被擦除，以确保 生殖系的全能。在某些情况下，表观遗传信息逃脱了重新编程，从 亲子之亲。表观遗传信息在一个世代以上的遗传称为反式遗传。 世代表观遗传(TEI)小的非编码RNA(例如siRNAs、miRNAs、piRNAs和tRNA 片段)已成为TEI(累积而言，RNA指导的TEI)的重要介体。DsRNA介导的 线虫中的基因沉默(RNAi)是RNA指导的TEI的一个强有力的和戏剧性的例子。我的实验室正在使用RNAi 线虫遗传作为探索表观遗传信号如何在世代间传递的模式系统 在动物身上。我们最近对RNAi遗传因子进行了遗传筛查，发现了两个保守的 RNA结合蛋白(RBPs)。这些RBP通过帮助维护 沉默RNA在RNAi遗传过程中的世代表达。有趣的是，这两个RBP都本地化为 一种新的线虫胚芽颗粒，其生物发生受发育调节，其相对定位 其他生殖系冷凝物是高度有序的。最后，我们发现我们拥有的两个RNAi遗传因素 已确定的是维持生殖系不朽所必需的。总而言之，我们的结果使我们提出， 液滴细胞器的时空有序性可能有助于生殖细胞组织和协调 基因调控系统下的复杂的RNA加工途径，如RNA指导的TEI和生殖系 永生。这项建议概述了我们为进一步了解在过程中形成类液体冷凝物所作的努力。 开发，它们如何与其他生殖系冷凝物组装成复杂的结构，以及大多数 重要的是，他们为什么要这样做。

SUMMARY/ABSTRACT Liquid droplet organelles (also referred to as liquid-like condensates) are dynamic concentrations of protein and RNA that coalesce spontaneously from the cytoplasm or nucleoplasm via liquid-liquid phase transition. Like oil and water, these liquid droplets and their surrounding cytoplasm are thought to co-exist as separate states of liquid. Current models posit that liquid droplet organelles may exist to concentrate reactants together in space and time in ways that facilitate biochemical reactions such as the complexes processes that underlie gene regulation. Eukaryotic cells possess many non-membrane-enclosed liquid droplet organelles including nucleoli, processing bodies, cajal bodies and germ granules. Germ granules are found in the germ cells of all/most animals where they are thought to contribute to germ cell totipotency. Indeed, orthologous proteins (e.g. VASA) are found in germ granules of many different species of animals, hinting that some aspects of germ granule function may be conserved in all animals. Most epigenetic information is erased at or near the start of each new generation in animals to ensure totipotency of the germline. In some cases, epigenetic information escapes reprogramming and is passed from parent to offspring. The inheritance of epigenetic information for more than one generation is termed trans- generational epigenetic inheritance (TEI). Small non-coding RNAs (e.g. siRNAs, miRNAs, piRNAs, and tRNA fragments) have emerged as important mediators of TEI (cumulatively, RNA-directed TEI). dsRNA-mediated gene silencing (RNAi) in C. elegans is a robust and dramatic example of RNA-directed TEI. My lab is using RNAi inheritance in C. elegans as a model system to explore how epigenetic signals are passed across generations in animals. We recently conducted a genetic screen for RNAi inheritance factors that identified two conserved RNA binding proteins (RBPs). These RBPs contribute directly to inheritance by helping to maintain the expression of silencing RNAs over generations during RNAi inheritance. Interestingly, both RBPs localize to a new C. elegans germ granule whose biogenesis is developmentally regulated and whose positioning relative to other germline condensates is highly ordered. Finally, we find that the two RNAi inheritance factors we have identified are required for maintaining germline immortality. Together, our results have led us to propose that the temporal and spatial ordering of liquid droplet organelles may help germ cells organize and coordinate the complex RNA processing pathways underlying gene regulatory systems, such as RNA-directed TEI and germline immortality. This proposal outlines our efforts to further understand how liquid-like condensates form during development, how they assemble into complex structures with other germline condensates, and, most importantly, why they do so.