Examining cytokinesis in reductive cell divisions

细胞质分裂是细胞分裂的最后阶段，在此期间，单个细胞围绕两组最近分离的姐妹染色单体分裂成两个子细胞。胚胎是一种球形微生物，在4-5天的时间里，从一个单细胞发育成一个约100个细胞的囊胚，在此期间，细胞的大小随着每次细胞分裂而逐渐缩小一半，并且出现了最初的两个细胞系。因此，它是一个高度易于处理的系统，用于在复杂的多细胞环境中检查细胞分裂的各个方面，这在其他哺乳动物系统中是无法实现的。在这里，我们将使用活细胞和固定细胞成像方法，遗传操作和微操作，对早期小鼠胚胎的细胞分裂进行首次机制分析。我们将把重点放在两个独立但相互关联的子项目上。首先，我们将确定沟速是由细胞大小还是细胞分化决定的。我们的初步数据表明，与秀丽隐杆线虫形成鲜明对比的是，小鼠的沟槽侵入速度与细胞大小成正比，而小鼠的沟槽侵入并不与细胞大小成正比。我们将使用各种操作来彻底测试这个概念。相反，我们发现胚胎内的沟槽速度在16个细胞阶段出现分歧，并且有理由相信这可归因于该阶段外细胞的几种形态发生影响之一，包括细胞形状的改变、细胞-细胞粘附、细胞极性的出现和转录水平的细胞命运决定。我们将探索在早期发育期间的沟入，并确定哪些发育事件影响沟入机制。其次，我们将确定分裂细胞脱落延迟的原因和后果。我们已经证实了一个经典但未被探索的观察结果，即在早期小鼠胚胎中，脱落被大大延迟，导致姐妹细胞之间形成“细胞质桥”，通过这种桥可以共享大分子。我们将研究这些稳定的细胞质桥是如何形成的，重点是TEX14，这是一种负责在生殖细胞中形成稳定桥的分子，我们发现它也在胚胎中表达。我们将解决早期胚胎细胞质桥允许姐妹细胞同步细胞周期的可能性，从而影响细胞分裂时间和细胞分化事件。我们期望发现早期小鼠胚胎作为部分合胞体存在，用于调节早期细胞周期和细胞命运决定。总的来说，我们期望这个项目能够建立小鼠胚胎作为细胞质分裂研究的有价值的模型，并在哺乳动物环境中提供细胞质分裂与细胞大小和谱系分化有关的一些最初的信息。

Cytokinesis is the final stage of cell division, during which a single cell is divided into two daughter cells around the two sets of recently separated sister chromatids. The embryo is a spherical micro-organism that develops from a single cell into a ~100 cell blastocyst over the course of 4-5 days, during which time cells progressively halve in size with each cell division, and the first two cell lineages arise. It is thus a highly tractable system for examining aspects of cytokinesis in a complex multicellular context that are inaccessible in other mammalian systems. Here we will use live and fixed cell imaging approaches, genetic manipulations, and micro-manipulation, to perform the first mechanistic analysis of cytokinesis in the early mouse embryo. We will focus on separate two separate but inter-related sub-projects. First, we will determine whether furrowing speed is determined by cell size or cell differentiation. Our preliminary data suggests that, in stark contrast to C elegans where the speed of furrow ingression furrowing scales as a function of cell size, in mouse furrow ingression does not scale to cell size. We will use a variety of manipulations to test this notion thoroughly. Rather, we have found that furrowing speeds within the embryo diverge at the 16 cell stage, and have reason to believe this is attributable to one of several morphogenetic influences upon the outer cells at that stage, including changing cell shape, cell-cell adhesion, emergence of cellular polarity, and transcriptional-level cell fate decisions. We will explore furrow ingression during early development, and determine which of these developmental events impacts furrow ingression mechanisms. Second, we will determine the cause and consequence of abscission delay in dividing cells. We have confirmed a classic but unexplored observation that abscission is greatly delayed in the early mouse embryos, causing the formation of `cytoplasmic bridges' between sister cells through which large molecules can be shared. We will examine how these stable cytoplasmic bridges are formed, focussing on TEX14, the molecule responsible for the formation of stable bridges in germ cells, which we have found is also expressed in embryos. We will address the possibility that cytoplasmic bridges in the early embryo allow sister-cells to synchronise cell cycles, and thereby impact cell-division timing and cell-differentiation events. We expect to find that the early mouse embryo exists as a partial syncytium that serves to regulate early cell cycles and cell fate decisions. Overall, we expect this programme to establish the mouse embryo as a valuable model for the study of cytokinesis, and provide some of the very first information relating cytokinesis to cell size and lineage differentiation in a mammalian setting.