Control of epithelial cell layer spreading in zebrafish

上皮细胞层扩散是各种发育和疾病相关事件的共同和基本过程，如果蝇的背闭合和伤口愈合。在之前的资助期内，我们已经剖析了斑马鱼原肠胚形成过程中驱动上皮细胞层扩散的力产生机制。具体来说，我们发现在卵黄细胞的表观代谢过程中，包膜细胞层（EVL）在卵黄细胞上的扩散是由肌动球蛋白皮层的收缩触发的，在卵黄合胞层（YSL）内形成一个带状结构，这是卵黄细胞表面靠近EVL边缘的薄细胞质层。我们可以进一步证明，这个肌动球蛋白带通过两种不同的运动活动来拉动EVL的边缘——一种是索收缩运动，另一种是流动摩擦运动。电缆收缩马达通过肌动球蛋白带的周向收缩来运作，肌动球蛋白带与卵黄囊的球形几何形状相结合，拉动EVL边缘，很像钱包的绳子。流动摩擦马达通过YSL内的逆行肌动球蛋白流动运行。这些被相邻结构的摩擦所抵制，因此直接将EVL边缘拉向植物极。虽然这些发现为YSL肌动球蛋白带驱动EVL表观代谢运动的机制提供了新的见解，但关于YSL内肌动球蛋白带形成的起始以及EVL和YSL之间的机械联系使YSL能够拉动EVL的重要问题仍然存在。为了解决这些问题，我们已经开始分析EVL如何在其边缘与底层YSL建立接触，以及这种接触形成如何触发YSL内肌动球蛋白的带状积累。根据我们的初步观察，我们假设YSL内的微管（MTs）促进YSL和EVL之间紧密连接（TJ）的形成，这些连接的正确形成反过来指导EVL表观代谢运动所需的YSL内肌动球蛋白带的组装。我们将采用跨学科的方法和工具，从发育生物学、细胞生物学、生物物理学和理论建模来解决这一假设。我们的目的是阐明在EVL细胞层扩散过程中MTs、TJs和肌动球蛋白网络之间的相互作用。我们期望这种方法能够深入了解上皮细胞层扩散过程中力的产生、转导和机制。

Epithelial cell layer spreading is a common and fundamental process in various developmental and disease-related events, such as dorsal closure in Drosophila and wound healing. In the previous funding period, we have dissected the force-generating mechanisms driving epithelial cell layer spreading during zebrafish gastrulation. Specifically, we showed that spreading of the enveloping cell layer (EVL) over the yolk cell during epiboly is triggered by contraction of the actomyosin cortex forming a band-like structure within the yolk syncytial layer (YSL), a thin cytoplasmic layer on the yolk cell surface close to the margin of the EVL. We could further show that this actomyosin band pulls on the margin of the EVL by two distinct motor activities - a cable-constriction motor and a flow-friction motor. The cable-constriction motor operates via circumferential contraction of the actomyosin band, which couples to the spherical geometry of the yolk sac to pull on the EVL margin, much like a purse string. The flow-friction motor operates via retrograde actomyosin flows within the YSL. These are resisted by friction to adjacent structures and thus directly pull the EVL margin towards the vegetal pole. While these findings provided novel insight into the mechanisms by which the YSL actomyosin band drives EVL epiboly movements, important questions remain as to the initiation of actomyosin band formation within the YSL and the mechanical linkage between EVL and YSL allowing the YSL to pull on the EVL. To address these questions, we have begun to analyze how the EVL at its margin establishes contacts with the underlying YSL, and how this contact formation triggers the band-like accumulation of actomyosin within the YSL. Based on our preliminary observations, we hypothesize that microtubules (MTs) within the YSL promote tight junction (TJ) formation between the YSL and EVL, and that proper formation of these junctions in turn directs actomyosin band assembly within the YSL required for EVL epiboly movements. We will address this hypothesis by an interdisciplinary approach employing methods and tools from developmental biology, cell biology, biophysics and theoretical modeling. We aim to elucidate the interplay between MTs, TJs and the actomyosin network during EVL cell layer spreading. We expect that this approach will provide insight into the mechanisms of force-generation, transduction and mechansensation during epithelial cell layer spreading.