Cell Polarity Signaling in C. elegans Embryos

描述（由申请人提供）：秀丽隐杆线虫的初始前后（a-p）极性在受精时建立。随后发生一组不对称的细胞分裂，细胞命运决定因素在前细胞和后细胞中发生不同的定位。随着发育的进行，Wnt信号mom2的作用是维持和传播共同的ap细胞极性。在4细胞阶段，Wnt信号传导与酪氨酸激酶pp60 Src介导的信号传导并行，控制内胚层前体细胞EMS的细胞命运和细胞分裂方向。Wnt和Src通路汇聚在几个共同的组分上，包括WRM-1 （β -连环蛋白相关蛋白）、lit1 （Serfrhr激酶）和POP-1 （hmg结构域转录因子）。最近的遗传学研究表明，细胞分裂轴与EMS细胞极化轴的协调依赖于细胞周期主要调控因子CDK-1及其13kd结合伙伴CKS-1介导的信号传导。我们的研究结果提出了一个模型，其中CDK-1在有丝分裂期间磷酸化WRM-1，以揭示指导EMS纺锤体旋转到细胞的a-p轴的线索。激活后的WRM-1可以自由地转导到后端EMS子代（称为E）的细胞核，在那里它的功能是下调和/或促进内胚层抑制因子POP-1的核输出。拟议的研究将使用细胞生物学和生化方法来测试上述模型的内胚层诱导。这些研究将重点关注Wnt、Src和CDK-1通路对WRM-1调控的机制。蛋白质相互作用筛选，抑制基因筛选和条件正向遗传筛选将确定每个信号通路的额外成分。WRM-1蛋白的定位将在野生型菌株和每种信号通路都有缺陷的菌株中进行研究，包括表达WRM-1自身特定突变形式的菌株。细胞极性的适当控制对人体组织的发育和稳态至关重要，而这一过程中的缺陷与许多形式的癌症有关。这项工作的意义在于它提供了在一个相对简单和特征良好的遗传模型系统中研究细胞极性的重要调节因子的机会。

DESCRIPTION (provided by applicant): Initial anterior-posterior (a-p) polarity in C. elegans is established at fertilization. A set of asymmetric cell divisions follow during which cell-fate determinants become localized differentially in anterior and posterior cells. As development proceeds a Wnt signal, MOM-2, functions to maintain and to propagate a common ap cellular polarity. At the 4-cell stage, Wnt signaling acts in parallel with signaling mediated by the tyrosine kinase pp60 Src to control both cell fate and cell division orientation in the endoderm precursor cell named EMS. The Wnt and Src pathways converge on several common components including WRM-1 (a beta-catenin related protein), LIT-1(a Serfrhr Kinase), and POP-1 an HMG-domain transcription factor. Recent genetic studies indicate that coordination of the cell-division axis with the polarized axis of the EMS cell depends on signaling mediated by the major cell-cycle regulator CDK-1 and its 13 kd binding partner CKS-1. Our findings suggest a model in which CDK-1 phosphorylates WRM-1 during mitosis to unmask cues that direct the rotation of the EMS spindle onto the a-p axis of the cell. The activated WRM-1 is then free to transduce to the nucleus of the posterior EMS daughter, called E, where it functions to down regulate and/or to promote nuclear export of the endoderm repressor, POP-1. The proposed studies will use cell-biological as well as biochemical methods to test the above model for endoderm induction. These studies will focus on the mechanisms of WRM-1 regulation by the Wnt, Src, and CDK-1 pathways. Protein interaction screens, suppressor-genetic screens, and conditional forward genetic screens will identify additional components of each signaling pathway. The localization of WRM-1 protein will be examined both in wild-type strains and in strains with defects in each signaling pathway, including strains that express specific mutant forms of WRM-1 itself. Proper control of cellular polarity is essential for the development and homeostasis of tissues in humans, and defects in this process are implicated in numerous forms of cancer. The significance of this work lies in the opportunity it provides to study important regulators of cellular polarity within a relatively simple and well characterized genetic model system.