Cellular and molecular mechanisms underlying the formation of sibling cell size asymmetry

项目摘要/摘要 人体含有约3.72 × 1013个细胞和200种不同的细胞类型。生成正确数量的 细胞和足够的专门细胞对于构建功能器官和组织至关重要。如何发展 生物体产生和维持具有专门功能和命运的细胞是一个基本问题， 生物学 不对称细胞分裂是一种进化上保守的机制，可以产生具有不同遗传特性的姐妹细胞。 命运细胞命运的差异可以通过形成大小不等的兄弟姐妹来实现。这种形式的 不对称的细胞分裂-这里也称为物理不对称-是发育控制的， 几种后生动物细胞类型主动诱导同胞细胞大小不对称或阻止同胞细胞的形成。 细胞大小不同。 物理不对称细胞分裂可以通过将分裂沟定位在细胞中心之外来诱导。 由于卵裂沟定位的主要机制来自有丝分裂纺锤体， 纺锤体错位或纺锤体不对称的产生导致细胞外卵裂沟的形成 中心或者，细胞皮质的动态行为-通过DNA衍生的，纺锤体- 依赖性或极性线索-可以导致不平等的皮质扩张，以创建不同大小的兄弟姐妹。 当然，这些机制可以根据发展背景以不同的组合应用 细胞类型。 在这里，我们建议使用果蝇幼虫成神经细胞来研究分子机制 在不对称细胞分裂期间调节细胞皮层的动态行为。果蝇成神经细胞 是果蝇中的神经干细胞，根据大小和命运不对称地分裂。我们将使用这个模型系统来 研究细胞内在极性线索如何与细胞周期协调作用，控制定位 和肌动球蛋白调节剂的活性来建立物理不对称细胞分裂。我们亦会研究 机械反馈回路如何影响纺锤体几何形状，从而影响卵裂沟定位线索。我们 我已经实施并开发了一套新颖的创新工具，以研究这些方面， 体内的发育背景。例如，我们正在利用果蝇极好的遗传 对于活细胞成像的易处理性和顺从性在其他体内系统中是不可用的。我们进一步利用 光遗传学方法来操纵具有高度时空控制的细胞皮层。 我们的长期目标是了解潜在的分子，细胞和生物物理机制 兄弟细胞大小不对称的产生。兄弟细胞的各自大小是严格 发育控制，并涉及调节细胞行为和命运。由于兄弟像元大小 不对称性是进化保守的，相关的成分也是进化保守的，这一提议将指导未来的研究。 其他phyla的研究。这项拟议中的研究在医学上也很重要; 研究已经涉及癌症和研究同胞细胞大小不对称如何促成 对于理解像小头畸形这样的神经发育障碍很重要。 这一建议也将对其他领域产生重大影响。组织形态发生，器官发生 和干细胞的行为都依赖于细胞皮层的正确时空调节。我们的研究 结合我们正在开发的工具和方法，将使我们处于有利地位， 对皮层驱动细胞形态发生的机制理解有重要贡献。

Project Abstract/Summary The human body contains ~ 3.72 x 1013 cells and 200 different cell types. Generating the right number of cells overall and enough specialized cells is vital for building functional organs and tissues. How developing organisms generate and maintain cells with specialized functions and fates is a fundamental problem in biology. Asymmetric cell division is an evolutionary conserved mechanism to create sister cells with different fate. Cell fate differences can be implemented through the formation of unequal sized siblings. This form of asymmetric cell division – here also referred to as physical asymmetry - is developmentally controlled since several metazoan cell types actively induce sibling cell size asymmetry or prevent the formation of sibling cells differing in their size. Physical asymmetric cell division can be induced by positioning the cleavage furrow off cell center. Since the predominant mechanism for cleavage furrow positioning originates from the mitotic spindle, spindle mispositioning or the generation of spindle asymmetry causes cleavage furrow formation off cell center. Alternatively, the dynamic behavior of the cell cortex – regulated through DNA-derived, spindle- dependent or polarity cues – can result in unequal cortical expansion to create different sized siblings. Naturally, these mechanisms can be applied in different combinations depending on developmental context and cell type. Here, we propose to use Drosophila larval neuroblasts to investigate molecular mechanisms regulating the dynamic behavior of the cell cortex during asymmetric cell division. Drosophila neuroblasts are neural stem cells in the fly, dividing asymmetrically by size and fate. We will use this model system to investigate how cell intrinsic polarity cues, acting in coordination with the cell cycle, control the localization and activity of actomyosin regulators to establish physical asymmetric cell division. We will also investigate how mechanical feedback loops influence spindle geometry and thus cleavage furrow positioning cues. We have implemented and developed a suite of novel and innovative tools to study these aspects in a developmental context in vivo. For instance, we are taking advantage of Drosophila’s superb genetic tractability and amenability for live cell imaging not available in other in vivo systems. We further utilize optogenetic approaches to manipulate the cell cortex with high spatiotemporal control. Our long-term goal is to understand the molecular, cellular and biophysical mechanisms underlying the generation of sibling cell size asymmetry. The respective size of sibling cells underlies stringent developmental control and has been implicated to regulate cell behavior and fate. Since sibling cell size asymmetry is – and involved components are – evolutionary conserved, this proposal will guide future studies in other phyla. The proposed research is also medically significant; several of the molecules under investigation have been implicated in cancer and investigating how sibling cell size asymmetry contributes to brain development is important to understand neurodevelopmental disorders such as microcephaly. This proposal will also have a strong impact in other fields. Tissue morphogenesis, organogenesis and stem cell behavior all depend on the correct spatiotemporal regulation of the cell cortex. Our research in conjunction with the tools and approaches we are developing will put us in a strong position to significantly contribute towards a mechanistic understanding of cortex-driven cell morphogenesis.