細胞遷移在胚胎發育以及細胞內的動態平衡中都扮演著關鍵角色。在過去十年，單細胞移動機制研究相當完整。反之，對於群體細胞 (border cells) 之間，細胞與細胞之間是如何協調進而調整細胞骨架進行移動的機制並不清楚。所以本論文將利用果蠅卵巢發育過程中的邊境細胞作為模式系統來研究群體細胞遷移，我們發現Rap1是Ras家族中的small GTPase，並參與調控邊境細胞骨架的過程。在Rap1失去功能的邊境細胞中，發現高達94%的邊境細胞移動失常。另外，大量表現持續活化的Rap1V12不僅造成100% 的細胞移動失常，且有42%的邊境細胞呈現散開的現象，同時也發現F-actin大量累積在邊境細胞的邊緣。故此，利用Actin::GFP在活體即時影像中觀察Rap1在細胞移動中如何調控細胞骨架。在正常狀況下，Actin會聚集在前端且伸出突出往前移動。當大量表現Rap1V12，會破壞肌動蛋白聚集在邊境細胞前端伸出延展現象的極性，Actin::GFP也大量表現在邊境細胞中，造成邊境細胞產生多方向的極性。此外，在Rap1失去功能的邊境細胞中，同時發現會降低F-actin量 。總結所有實驗，Rap1主要是調控邊境細胞的細胞骨架形成方向性的突出來進行移動。

Cell migration plays a critical role in normal embryo development and homeostasis. Abnormal cell migration is detrimental that causes not only growth defects but also dissemination of cancers. There are two types of cell migration, until now, the research at the single-cell level has been studied over decades but the collective cell migration, how cells form a cluster and coordinate cytoskeleton during movement, which is still unclear. Here we apply a group of migratory cells called border cells in Drosophila oogenesis as a model to examine the molecular mechanism by which the collective cell migration is regulated in vivo. Here, we report Rap1, a small GTPase that belongs to a member of Ras superfamily, which is involved in actin dynamics during border cell migration. When the mutant clones of Rap11B were generated in border cells, nearly 94% of border cells did not arrive at oocyte. Moreover, 75% of border cells fail to detach in overexpression of UAS-Rap1V12, a constitutive-active form of Rap1, and overall displayed 100% migration defects. Interestingly, in overexpress Rap1V12, we observed highly accumulated F-actin in border cells and 42% of cell clusters were scattered in fixed-sample analysis. To further elucidate the actin dynamics in overexpression of UAS-Rap1V12, we performed live imaging analysis and recorded the dynamics in expression of Actin::GFP fusion protein in border cells. In wild type border cells, Actin::GFP was asymmetrically enriched in the leading cells and especially at the extended protrusions. However, in border cell cluster with UAS-Rap1V12 overexpression, Actin::GFP was overall elevated in whole cluster, which caused multiple protrusions projecting to different directions. By contrast, we observed reduced phalloidin staining in Rap11B clone generated in border cell. Taken together our observations suggest that Rap1 regulates directional protrusions during border cell migration by coordinating asymmetrical distributions of actin.

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