Cell Polarity Signaling in C. elegans Embryos

描述(申请人提供)：线虫最初的前后(a-p)极性是在受精时建立的。随之而来的是一系列不对称的细胞分裂，在此期间，细胞命运决定因素变得不同地定位于前部和后部细胞。随着发育的进行，Wnt信号，MoM-2，起到维持和传播共同AP细胞极性的作用。在4-细胞期，Wnt信号与酪氨酸激酶pp60Src介导的信号平行作用，控制内胚层前体细胞EMS中的细胞命运和细胞分裂方向。Wnt和Src通路聚集在几个共同的成分上，包括WRM-1(β-连环素相关蛋白)、LIT-1(Serfrhr Kinase)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主要的细胞周期调节因子CDK-1及其13kd结合伙伴CKS-1介导的信号转导。我们的发现提出了一个模型，在该模型中，CDK-1在有丝分裂过程中将WRM-1磷酸化，以揭示引导EMS纺锤体旋转到细胞a-p轴上的信号。然后，激活的WRM-1可以自由转导到EMS后部子体的核，称为E，在那里它起到下调和/或促进内胚层抑制物POP-1核输出的作用。拟议的研究将使用细胞生物学和生化方法来测试上述内胚层诱导模型。这些研究将集中于Wnt、Src和CDK-1信号通路对WRM-1的调控机制。蛋白质相互作用筛选、抑制子-遗传筛选和条件正向遗传筛选将识别每个信号通路的其他组成部分。WRM-1蛋白的定位将在野生型菌株和每个信号通路存在缺陷的菌株中进行检测，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类组织的发育和动态平衡是必不可少的，而这一过程中的缺陷与多种形式的癌症有关。这项工作的意义在于，它提供了在一个相对简单和特征明确的遗传模型系统中研究细胞极性的重要调节因素的机会。

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.