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种不同类型的细胞。生成适当数量的 完整的细胞和足够的特化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特殊功能和命运的细胞是生物界的一个基本问题 生物学。 不对称细胞分裂是一种进化保守的机制，可以创造出不同的姐妹细胞 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 不对称细胞分裂--在这里也称为物理不对称--是由发育控制的，因为 几种后生动物细胞类型主动诱导兄弟细胞大小不对称或阻止兄弟细胞的形成 大小不同的细胞。 通过将卵裂沟定位于细胞中心，可以诱导物理上的不对称细胞分裂。 由于卵裂沟定位的主要机制起源于有丝分裂纺锤体， 纺锤体错位或纺锤体不对称的产生导致细胞分裂沟的形成 中间。或者，细胞皮质的动态行为--通过DNA衍生的纺锤体--调节。 依赖或极性线索--可导致不同大小的兄弟姐妹的皮质扩张不相等。 当然，这些机制可以根据发展背景以不同的组合应用 和细胞类型。 在这里，我们建议使用果蝇幼虫的神经母细胞来研究分子机制 在细胞不对称分裂过程中调节细胞皮质的动态行为。果蝇神经母细胞 是果蝇中的神经干细胞，根据大小和命运进行不对称分裂。我们将使用这个模型系统来 研究细胞固有的极性信号如何与细胞周期协同作用，控制定位 以及肌动球蛋白调节剂的活性，以建立物理上的不对称细胞分裂。我们还将调查 机械反馈环如何影响主轴几何形状，从而影响裂沟定位线索。我们 实施并开发了一套新颖和创新的工具来研究这些方面 体内发育环境。例如，我们正在利用果蝇超凡的基因 活体细胞成像的易操纵性和适应性是其他活体系统所不具备的。我们进一步利用 光遗传学方法以高度时空控制来操纵细胞皮质。 我们的长期目标是了解潜在的分子、细胞和生物物理机制 同胞细胞大小不对称的产生。兄弟单元格的各自大小是严格的基础 发育控制，并已被牵连到调节细胞行为和命运。由于同级像元大小 不对称是进化保守的，而且涉及的成分是进化保守的，这一建议将指导未来 其他门类的研究。这项拟议的研究也具有重要的医学意义； 已有研究表明癌症与兄弟姐妹细胞大小不对称有关 对大脑发育的影响对于了解神经发育障碍，如小头畸形症非常重要。 这一提议还将在其他领域产生强烈影响。组织形态发生、器官发生 干细胞的行为都依赖于细胞皮质的正确时空调节。我们的研究 与我们正在开发的工具和方法相结合，将使我们处于有利地位 显著有助于从机制上理解皮质驱动的细胞形态发生。

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.