The dedicator of cytokinesis (DOCK) family proteins are known as one of guanine nucleotide exchange factors (GEFs), that contribute to cellular signaling processes by activating small G proteins. Although mammalian Zizimin is known to be a GEF for Cdc42 of Rho family small GTPase, its role in vivo is not well understood. Here we studied in vivo function of Drosophila Zizimin (Ziz). Knockdown of Ziz in eye imaginal discs induced the rough eye phenotype accompanied with fusion of ommatidia, loss of bristles and loss of pigments. Immunostaining analyses revealed that Ziz mainly localizes in the secondary pigment cells (SPCs) and tertiary pigment cells (TPCs) in pupal retinae. Ziz-knockdown induced SPC- and TPC-like cells with aberrant morphology in the pupal retina. Delta (Dl), a downstream target of EGFR signaling is known to regulate pigment cell differentiation. Loss-of-function mutation of Dl suppressed the rough eye phenotype and the defect in differentiation of SPCs and TPCs in Ziz-knockdown flies. Moreover, Ziz-knockdown increased Dl expression level especially in SPCs and TPCs. In addition, mutations of rhomboid-1 and roughoid that are activators of EGFR signaling pathway also suppressed both the rough eye phenotype and the defect in differentiation of SPCs and TPCs in Ziz-knockdown flies. Activation of EGFR signaling in Ziz-knockdown flies were further confirmed by immunostaining with anti-diphospho ERK IgG. These results indicate that Ziz negatively regulates the Dl expression in SPCs and TPCs to control differentiation of pigment cells and this regulation is mediated by EGFR signaling pathway.Key words: Zizimin, DOCK, EGFR signaling pathway, pigment cell, Drosophila.

中文翻译：

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果蝇DOCK家族蛋白Zizimin参与Pu视网膜中色素细胞的分化。

胞质分裂（DOCK）家族蛋白的专用剂被称为鸟嘌呤核苷酸交换因子（GEF）之一，它通过激活小G蛋白来促进细胞信号传导过程。尽管已知哺乳动物Zizimin是Rho家族小GTPase Cdc42的GEF，但其在体内的作用尚不清楚。在这里，我们研究了果蝇Zizimin（Ziz）的体内功能。Ziz击倒在眼球间盘中会引起粗糙的眼表型，并伴有眼球融合，硬毛损失和色素损失。免疫染色分析表明，Ziz主要位于p视网膜中的次级色素细胞（SPC）和第三色素细胞（TPC）中。Ziz-knockdown诱导S视网膜中形态异常的SPC和TPC样细胞。Delta（Dl），已知EGFR信号传导的下游靶标调节色素细胞分化。D1的功能丧失突变抑制了Ziz-knockdown果蝇的粗眼表型以及SPC和TPC的分化缺陷。此外，Ziz-knockdown增加了D1表达水平，尤其是在SPC和TPC中。此外，作为EGFR信号通路激活剂的菱形1和粗体突变也抑制了粗眼表型以及Ziz-knockdown蝇中SPC和TPC分化的缺陷。Ziz击倒果蝇中EGFR信号的激活通过抗二磷酸ERK IgG的免疫染色进一步证实。这些结果表明，Ziz负调节SPC和TPC中的D1表达以控制色素细胞的分化，并且这种调节是由EGFR信号通路介导的。