FGFR-dependent tissue separation in Hydra: the role of actomyosin interactions and cell polarity

淡水多毛类属于非双侧纲线虫，体型结构简单。两个细胞单层，外胚层和内胚层，形成管状体柱，并由双功能上皮-肌肉细胞组成。喂饱的息肉将组织横向输出到芽中，芽在4天后以一种未知的机制从父母那里分离出来。我们之前已经证明，花蕾的脱落受FGFR信号的控制，而FGFRa的靶标是肌动蛋白细胞骨架。我们现在将研究最近发现的依赖于Rho的候选通路在FGFR信号下游的作用，该通路可能改变肌动蛋白的收缩性能、流动性和肌动蛋白复合体的硬度，这些都是细胞与细胞和细胞与基质相互作用所必需的。我们的目标是a)阐明Hydra Rho的时空激活及其与细胞形状变化的关系，b)确定特定的肌动蛋白核仁和肌球蛋白II亚型的分布(和功能)，以及c)了解细胞的极性是否发生在脱离部位。在机械方面，有趣的问题是，除了细胞骨架肌动球蛋白复合体外，双功能上皮肌细胞是否还使用其基础收缩肌肉突起进行收缩。我们的项目将有助于阐明一种独特的组织分离过程。

The freshwater polyp Hydra belongs to the nonbilaterian phylum Cnidaria and displays a simple body architecture. Two cell monolayers, the ecto- and the entoderm, form the tubular body column and consist of bifunctional epithelio-muscular cells. Well fed polyps export tissue laterally into a bud, which detaches 4 days later from the parent by an unknown mechanism. We previously showed that bud detachment is under control of FGFR signaling and that FGFRa targets the actin cytoskeleton. We will now investigate the role of a recently identified Rho-dependent candidate pathway downstream of FGFR signaling, which likely alters actomyosin contractility, fluidity and stiffness of actomyosin complexes essential for cell-cell and cell-matrix interactions. Our goals are a) to elucidate the spatiotemporal activation of Hydra Rho and its connection to cell shape changes, b) to determine the distribution (and function) of specific actin nucleators and myosin II subtypes and c) to understand, whether cell polarity changes occur at the detachment site. Interesting under mechanistic aspects is the question, whether the bi-functional epitheliomuscular cells use their basal contractile muscle processes for constriction in addition to cytoskeletal actomyosin complexes. Our project will help to elucidate a unique process of tissue separation.