Rap1 為 Ras 超家族的小分子 G 蛋白，屬於。Rap1 已知在細胞遷移和胚胎發育中是必須的。在先前實驗室的實驗中發現，果蠅的邊境細胞遷移需要 Rap1。且肌動蛋白絲 (F-actin)，在無法遷移的邊境細胞周圍大量累積。為了探討 Rap1 藉由何種機制去調控肌動蛋白絲的動態變化，我的實驗在果蠅的 S2 細胞中表現不同活性的 Rap1: Rap1、 Rap1V12、 Rap1N17。發現 Rap1V12 細胞有 71% 伸出突觸。深入分析突觸長度，發現只有 Rap1V12 表現細胞突觸較長，有些細胞長度達18.8μm。進一步在表現融和綠螢光蛋白的肌動蛋白絲之 S2 細胞株 (S2-Mt-ActinGFP cell line) 中拍攝影像，觀察肌動蛋白絲動態變化上的差異。發現 Rap1V12 的表現細胞伸出較長或較多突觸，與固定細胞的實驗結果一致。且在分析突觸伸出或縮入的速度中發現 Rap1V12 表現細胞的速率較快。因此我們認為 Rap1 會調節突觸的動態。於是進一步假設 Rap1 影響突觸的動態是否藉由調控肌動蛋白絲的結合蛋白。結果發現 Rap1V12 表現細胞， WASP 和 SCAR 蛋白訊號增強，且訊號定量後達一倍之差。因此 Rap1 對細胞遷移的影響為恆定現象，藉由調節肌動蛋白絲結合蛋白調節細胞遷移過程中突觸變化的步驟。

Rap1 belongs to the Ras superfamily of small GTPase, which is essential for cell migration and the embryonic development. Previous study in our lab found that the Rap1 was required for border cell migration especially in regulation of asymmetrical distributions of actin at the leading edge of the migration cluster. To further examine the general mechanism of Rap1 in actin dynamics, we analyzed the cellular protrusions in Drosophila S2 cells by transfections of the Rap1, Rap1V12 or Rap1N17. Interestingly, we observed 71% of S2 cells in overexpression of Rap1V12 showing. Moreover, we also observed long protrusions that extended to 18.8 μm in length in expression of Rap1V12. In time lapse micrographs, we found that the Rap1V12 transfected S2 Mt-Actin::GFP cells could induce extended long protrusions and multiple protrusions, which was consistent with the results observed in fix samples. In our speed analysis, we found that the Rap1V12 transfected cell had more high displayed faster speed no matter in protrusion withdraw or extension. We further investigate several actin binding proteins to explore the role of Rap1 in actin dynamics. We found that the expression of WASP and SCAR was higher in Rap1V12 transfected cells. Taken together, our finding suggests that active form of Rap1 might regulate protrusion dynamics through SCAR and WASP.

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Zih-Min Liao, The role of Rap1 in regulation of actin dynamics during Drosophila border cell migration, National Cheng-Kung university Institute of Biotechnology Master thesis, 2013.