在果蠅的胚胎發育中,背部閉合 (dorsal closure) 主要藉由肌動凝蛋白 (actomyosin) 在不同細胞提供的兩種力來完成,一種是在最靠近背部的表皮細胞 (epidermal cells) 的先端 (leading edge) 形成 purse-string 提供縫合的拉力;另一 種是在 amnioserosa (AS) 細胞的周遭和中心提供縮小細胞的力量,又稱做 AS constriction。而細胞骨架 (cytoskeleton) 也在改變細胞的形狀上扮演很重要的角 色。 Echinoid (Ed) 是一個細胞黏著分子 (adhesion molecule) ,在正常情況下 AS 細胞的 Ed 在 stage 13 會被完全清掉,但先前有研究發現在同一個發育階段大 量表現 Ed 會造成細胞縮小,目前對肌動凝蛋白如何影響 AS 細胞的收縮仍不 清楚,而我們也發現在同一個發育階段表現不會被降解的 Ed (non-degrable Ed) 除了會造成細胞縮小外也會使 actin 大量累積,因此我們想藉由基因篩選 (genetic screen) 的方式來找出參與調控 AS 細胞收縮的肌動蛋白的調控因子 (actin regulator) ,在這個研究中,我們發現大部分在實驗中使用的調控因子都參 與了 Ed 調控的 AS 收縮 (Ed-mediated AS constriction) ,而較少的調控因子參 與了正常的 AS 收縮 (normal AS constriction) ,此外,我們也發現肌動蛋白 (actin) 和 微管 (microtubule) 參與了 Ed 調控或是正常狀況下的 AS 收縮現象。 根據這些結果,我們找出了在 Ed 調控或是正常狀況下調控 AS 收縮的肌動蛋 白調控因子,並推測會藉由影響細胞骨架去調控 AS 細胞收縮。

Dorsal closure is the last major process in Drosophila embryogenesis that mediated by two main forces, which provided by actomyosin in different cells. Actomyosin forms purse-string at leading edge of dorsal-most epidermal (DME) cells, which provide force for zippering, and the circumferential and cortical actomyosin coordinately reduce apical area by amnioserosa (AS) constriction. The cytoskeleton also participates in the cell remodeling process. Echinoid (Ed) is an adhesion molecule, which normally is completely removed at stage 13 in amnioserosa and causes premature AS constriction when ectopically expressed at same stage. However, how actomyosin regulates AS constriction remains unknown. In this study, we found that ectopically express non-degrable Ed cause premature AS constriction and extensively accumulation of actin. Therefore, we used genetic screen to investigate which actin regulator participates in AS constriction process. The results demonstrated that most of actin regulators, which we used in this study, participated in the Ed-mediated AS constriction but fewer involved in the normal AS constriction. We also found that actin and microtubule might participate in Ed-mediated or normal AS constriction event. Together, my thesis identified the specific actin regulators mediating AS constriction by affecting cytoskeleton in Ed-mediated or normal status.

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