Cobra,一個屬於Thij蛋白質家族的RNA附著蛋白調節因數，參與果蠅體軸極性決定蛋白的定位

Abstract

在果蠅卵發育過程中，生殖細胞(如卵及護衛細胞)與體細胞(如濾泡細胞)的分化與軸向決定是由果蠅的TGF-α, Gurken (grk)的定位與表現量所調控。濾泡細胞的前後及背腹軸向建立，是靠Grk啟動的EGFR訊息而建立。卵細胞的前後軸向極性建立，則早在卵母細胞不對稱分裂時就決定，至stage 7時，卵細胞接收由後端濾泡細胞所傳遞的Grk信號後，開始重組卵細胞內的微管系統(microtubule system)，而卵細胞核則藉由微管系統重組，由卵細胞後端移送至前端背側；stage 10之後，受Grk啟動EGFR訊息的背側濾泡細胞表現rhomboid,spitz,及argos回饋背腹極性的訊號給卵細胞，進一步決定未來胚胎的背腹極性。母源效應基因如spindle family,okra,aubergine, squid,f(s) k10及vasa等嚴密地調控grk的轉譯及蛋白質的運送與定位(localization)，使卵與胚胎的軸向決定能正確地完成。 在本次針對具母源效應之必須基因的突變搜尋中，找到一個參與果蠅卵發育的基因，cobra。在cobra突變卵巢中，呈現各種形態上及分子分佈上的異常。包括主導卵室及胚胎背腹極性的Grk蛋白質，生殖前驅細胞決定因數Vasa蛋白質以及負責胚胎後端和生殖細胞生成的Oskar的分佈都受到cobra突變的影響，故卵室與胚胎的背腹極性與前後極性都因cobra突變而錯亂。由於cobra突變影響的廣泛性，以及其在卵發育早期表現的特性，推測cobra作用在卵早期細胞分化及生長，並且影響多種體軸極性決定蛋白的定位。

In the early process of Drosophila oogenesis, the anterior-posterior and dorsal-ventral axes formation of oocyte and follicle cells are determined by Gurken (grk), a TGF-α homolog, mediated signaling between oocyte and nurse cells. Therefore, mutation in genes affecting grk distribution would cause defects in eggshell polarity and embryo pattern formation. Here, I report a novel marternal effect gene, cobra, recovered from my maternal effect gene screen, which involves in the proper localization of numerous ooplasm components and strongly influences eggshell polarity. Mutant egg chamber displays defects in nuclear position of oocyte and migration of follicle cells. Furthermore, the deposition pattern of grk, orb and stau in the oocyte revealed similar punctate accumulation. As a consequence, embryos lacking maternally provided cobra develop into various phenotypes, i.e. abdomen deletion, dorsalization, preblastoderm death, etc. The putative transcrip cobra interrupted encodes a member of Thij family. Among which, cobra resembles most to a RNA binding protein regulatory subunit, with the similarity of 51%. Since cobra mutant exhibits various abnormalties thoughout oogenesis, it is likely that cobra functions quite early in the developmental process. We speculate that cobra plays a role in proper protein localization and egg chamber patterning during previtellogenic stage.