Regulation of mediolateral cell polarity by PCP and notochord boundary signaling

描述（由申请人提供）：所有动物胚胎，开始为圆盘或球体，形成一个细长的身体轴，一端是头，另一端是尾巴。这种轴向伸长的基本过程是由胚胎组织的收敛和延伸（C&E）完成的，这一过程是由细胞极化行为驱动的，如原肠胚形成期间的细胞迁移和中外侧嵌入。虽然胚胎组织中ML细胞极性的分子调控主要归因于平面细胞极性（PCP）信号，但有证据表明来自脊索-体边界（NSB）的信号也参与其中。这种NSB信号的性质及其与PCP信号的关系尚不清楚。Solnica-Krezel实验室已经确定了染色质因子丑小鸭(Udu)/Gon4l是斑马鱼C&E的一种新的调节因子。母体合子（MZ） udu突变胚胎显示出非常短的前后轴，有趣的是，边界相邻细胞的NSB异常和ML极性降低。在PCP突变胚胎中，udu/gon4l功能的完全丧失增强了轴延长缺陷，而PCP依赖的细胞极性在MZudu胚胎中似乎不受影响，这表明udu/gon4l与PCP途径平行调节ML细胞极性。我们发现编码排斥性ECM配体的slit3的表达在MZudu胚胎中增加。Slit3及其Robo受体在WT胚胎轴向中胚层中的表达预测了Slit3 -Robo信号在正常轴向中胚层和NSB形成中的作用。此外，slit3的过表达破坏了斑马鱼胚胎中NSB的形成和C&E，加剧了PCP突变体的轴伸长缺陷。我假设udu/gon4l是NSB完整的Slit-Robo信号所必需的，NSB介导一种新的极性线索，与PCP平行作用，调节C&E基础上的ML细胞极性。表征这种新的极性信号及其与已知极性信号的关系，将进一步加深我们对脊椎动物胚胎发生过程中复杂的位置和形态发生信号如何协调的理解。

DESCRIPTION (provided by applicant): All animal embryos, which begin as a disc or sphere, form an elongated body axis with a head on one end and a tail on the other. This fundamental process of axial elongation is accomplished by convergence and extension (C&E) of embryonic tissues, a process driven by polarized cell behaviors such as cell migration and mediolateral (ML) intercalation during gastrulation. Although molecular regulation of ML cell polarity in embryonic tissues is largely attributed to planar cell polarity (PCP) signaling, there is evidence that signals from the notochord-somite boundary (NSB) are also involved. The nature of this NSB signal and its relationship to PCP signaling are not understood. The Solnica-Krezel lab has identified the chromatin factor Ugly duckling (Udu)/Gon4l as a novel regulator of C&E in zebrafish. Maternal zygotic (MZ) udu mutant embryos display an extremely short anterior-posterior axis, and interestingly, abnormal NSB and reduced ML polarity of boundary-adjacent cells. Complete loss of udu/gon4l function enhances axis elongation defects in PCP mutant embryos, and PCP-dependent cell polarity appears to be unaffected in MZudu embryos, suggesting that udu/gon4l regulates ML cell polarity in parallel to the PCP pathway. We found that expression of slit3, which encodes a repulsive ECM ligand, is increased in MZudu embryos. Expression of Slit3 and its Robo receptors in the axial mesoderm of WT embryos predict a role for Slit-Robo signaling in formation of normal axial mesoderm and the NSB. Furthermore, overexpression of slit3 disrupts NSB formation and C&E in zebrafish embryos, and exacerbates axis elongation defects in PCP mutants. I hypothesize that udu/gon4l is required for intact Slit-Robo signaling at the NSB, which mediates a novel polarity cue that acts in parallel to PCP to regulate ML cell polarity underlying C&E. Characterization of this novel polarity cue, and its relationship to known polarity signals, will further our understanding of how complex positional and morphogenetic cues are coordinated during vertebrate embryogenesis.