Spatiotemporal Regulation of Liquid-like Condensates in the Germline

总结/摘要 液滴细胞器（也称为液体状冷凝物）是细胞内的细胞器的动态浓度。 通过液-液相从细胞质或核质自发结合的蛋白质和RNA 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。目前的模型认为液滴细胞器可能存在浓缩反应物 在空间和时间上以促进生物化学反应的方式结合在一起， 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、加工体、卡哈尔体和胚芽颗粒。胚芽中有胚芽颗粒 所有/大多数动物的细胞，认为它们有助于生殖细胞全能性。事实上， 蛋白质（如VASA）在许多不同种类的动物的生殖颗粒中发现，暗示某些方面 在所有动物中可能是保守的。 大多数表观遗传信息在动物的每一代开始时或接近开始时被删除，以确保 生殖系的全能性。在某些情况下，表观遗传信息逃脱了重新编程， 父母对子女表观遗传信息的遗传超过一代被称为反式遗传。 世代表观遗传（TEI）小的非编码RNA（例如siRNA、miRNA、piRNA和tRNA 片段）已经成为TEI（累积地，RNA指导的TEI）的重要介质。dsRNA介导的 基因沉默（RNAi）。线虫是RNA导向的TEI的一个强大而引人注目的例子。我的实验室正在使用RNA干扰技术 C.遗传作为一个模型系统来探索表观遗传信号是如何跨代传递的 在动物身上。我们最近对RNAi遗传因子进行了遗传筛选， RNA结合蛋白（RBP）。这些限制性商业惯例通过帮助维持遗产，直接有助于继承 在RNAi遗传过程中沉默RNA的世代表达。有趣的是，两种RBP都定位于 新猫栉头蚤一种线虫的生殖颗粒，其生物发生受发育调节，其位置相对于 其它种系浓缩物是高度有序的。最后，我们发现我们所拥有的两个RNAi遗传因子， 是维持生殖细胞永生所必需的。总之，我们的研究结果使我们提出， 液滴细胞器的时间和空间排序可能有助于生殖细胞组织和协调 基因调控系统的复杂RNA加工途径，如RNA介导的TEI和生殖系 仙该提案概述了我们为进一步了解类液体冷凝物在 发育，它们如何与其他生殖系浓缩物组装成复杂的结构，以及， 重要的是，他们为什么这样做。

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.