Functional analysis of mammalian midbody RNA in post-mitotic signaling functions

摘要 细胞分裂的最后一步，即脱落，依赖于一种叫做中体的暂时性结构，这种结构驻留在体内 新形成的子代细胞之间的细胞间桥。它由重叠的主轴中间区组成 覆盖有电子致密物质的微管称为中体基质。Long概念化为 这是一种结构残留物，在胞质分裂后容易降解，新出现的数据表明，中体发挥作用 有丝分裂后在确定细胞命运、增殖状态、组织极性、纤毛形成、神经元方面的指导性作用 功能和致癌作用。然而，人们对电子密度的功能意义知之甚少。 材料，因为它首先是迈克尔·穆林斯和迪克·麦金托什在20世纪70年代积极追求的，然后是 栗山良子在20世纪80年代。我的实验室为这种电子密度高的材料发现了一种令人惊讶的新功能 因为它是RNA存储部位，是一种具有独特复杂生命的新型主动翻译RNP颗粒 由无膜相和膜结合相组成的循环，我们称之为MB颗粒(用于 中体-颗粒)。在活细胞和固定细胞中使用定量、超分辨率方法，再加上 基因组学和基因操纵来解决我们的问题，我们发现翻译发生在 中体RNP颗粒周围的隔室，以及有丝分裂后的中体残留物(或MBR)， 和内在化的MBR(或MBSOM)。分离的哺乳动物中体的rna-seq数据显示了一种富集性。 致癌和干细胞转录因子都没有被描述在细胞分裂中的功能，但是 大概是有丝分裂后的行为。富含中体的转录本在脱落前立即启动翻译， 我们已经展示的一个步骤发生在G1早期，就在核膜完全重组之后。治疗 通常用于测定RNP相凝聚物揭示了中体基质的行为方式 KIF23/MKLP1可能是一种新的RNP 脚手架。MB颗粒是一种非常新颖的RNP颗粒，因为它具有翻译活性，具有膜- 更少的和膜结合的阶段，并在有丝分裂后在细胞命运和增殖决定中发挥作用。这里, 我们将集中精力确定MBR的细胞类型特定成分，即时空调节 以及MB颗粒RNA是否在吞噬它们的细胞中被释放。我们的 拟议的研究将揭示对保守和发散的MBome结构和功能的独特见解， 洞察这种独特的RNP凝聚体和细胞器如何作为细胞间的新形式 沟通。

SUMMARY The last step in cell division, abscission, relies on a transient structure called the midbody, which resides inside the intercellular bridge between newly forming daughter cells. It consists of overlapping spindle midzone microtubules which are coated with electron dense material called the midbody matrix. Long conceptualized as a structural remnant subject to degradation following cytokinesis, emerging data suggest that midbodies play instructive post-mitotic roles in establishing cell fate, proliferation state, tissue polarity, cilia formation, neuron function, and oncogenesis. However, very little is known about the functional significance of the electron dense material, since it was first actively pursued by Michael Mullins and Dick McIntosh in the 1970s, and then by Ryoko Kuriyama in the 1980s. My lab has uncovered a surprising novel function for this electron dense material in that it is a site of RNA storage and is a novel actively translating RNP granule with a uniquely complex life cycle comprised of both membrane-less and membrane-bound phases, that we are calling the MB-granule (for Midbody-granule). Employing quantitative, super-resolution approaches in live and fixed cells, coupled with genomics and genetic manipulations to address our questions, we discovered that translation occurs in a compartment surrounding the midbody RNP granule, as well as in post-mitotic midbody remnants (or MBRs), and internalized MBRs (or MBsomes). RNA-seq data of isolated mammalian midbodies revealed an enrichment of both oncogenic and stem cell transcription factors that have no described function in cell division, but presumably act post-mitotically. Midbody-enriched transcripts initiate translation immediately before abscission, a step that we have shown occurs in early G1, just after the nuclear envelope is fully reassembled. Treatments commonly used to determine RNP phase condensates revealed that the midbody matrix behaves as a novel type of RNP granule, and that the critical cytokinesis kinesin motor, Kif23/MKLP1, may serve as a novel RNP scaffold. The MB-granule is a very novel class of RNP granule in that it’s translationally active, has membrane- less and membrane-bound phases, and functions post-mitotically in cell fate and proliferative decisions. Here, we will focus our efforts to determine the cell-type specific components of MBRs, the spatiotemporal regulation of MBsome structure, and function, and if MB-granule RNAs are being liberated in cells that engulf them. Our proposed studies will uncover unique insights into conserved and divergent MBsome structure and function, offering insight into how this unique RNP condensate and organelle behaves as novel form of intercellular communication.