Cytoplasmic Retention as a Regulatory Mechanism in Embryogenesis

许多核蛋白的功能受选择性核定位的调控。爪蟾核因子7 （Xenopus nuclear factor 7, xnf7）是一种新的锌指基因家族的成员，其成员主要由转录因子和原癌基因组成。Xnf7首先在卵母细胞细胞核中被检测到，并保留在细胞质中，直到囊胚发育中期才重新进入细胞核。最近的证据表明，xnf7中有一个22个氨基酸的序列，称为细胞质保留域（CRD），是囊胚中期之前细胞质保留所必需的，并且该蛋白中两个位点的磷酸化对于正常的CRD功能是必要的。Etkin博士的实验室已经证明，xnf7通过一种锚定机制保留在细胞质中，这种机制很可能与细胞质锚定蛋白的拴系有关。本项目正在验证的假设是，磷酸化诱导xnf7的结构变化，导致CRD序列与锚定蛋白结合。Etkin博士将通过完成以下具体目标来验证这一假设：(1)他将进一步确定磷酸化在细胞质中xnf7保留中的作用。(2)他将分析和鉴定与CRD序列相互作用并在xnf7细胞质保留中起作用的蛋白质，并克隆这些蛋白质的cdna。除了深入了解两栖动物发育过程中的重要调控过程外，对xnf7选择性核定位机制的分析将为理解其他系统中的这种现象提供必要的信息。＊＊＊

9319178 Etkin The function of many nuclear proteins is regulated by selective nuclear localization. Xenopus nuclear factor 7 (xnf7), a putative transcription factor, is a member of a novel zinc finger gene family whose members consist primarily of transcription factors and protooncogenes. Xnf7 is first detected in the oocyte nucleus and is retained in the cytoplasm until the mid blastula stage of development when it reenters the nucleus. Recent evidence showed that a 22 amino acid sequence in xnf7 called the cytoplasmic retention domain (CRD) is required for cytoplasmic retention prior to the mid blastula stage and that phosphorylation of two sites within the protein is necessary for proper CRD function. Dr. Etkin's laboratory has shown that xnf7 is retained in the cytoplasm through an anchor mechanism most likely involving the tethering to a ctyoplasmic anchor protein. The hypothesis being tested in this project is that phosphorylation induces a structural change in xnf7 resulting in the binding of the CRD sequence to an anchor protein. Dr. Etkin will test this hypothesis by accomplishing the following specific aims: (1) He will further determine the role of phosphorylation in the retention of xnf7 in the cytoplasm. (2) He will analyze and identify the proteins that interact with the CRD sequence and function in cytoplasmic retention of xnf7 and will clone the cDNAs for these proteins. In addition to gaining an insight into an important regulatory process during amphibian development, the analysis of the mechanism of selective nuclear localization of xnf7 will provide information necessary to understand this phenomenon in other systems. ***