Dumstrei Karin, Wang Fay, Shy Diana, Tepass Ulrich, Hartenstein Volker
Department of Molecular Cell and Developmental Biology, University of California Los Angeles, 90095, USA.
Development. 2002 Sep;129(17):3983-94. doi: 10.1242/dev.129.17.3983.
Dynamically regulated cell adhesion plays an important role during animal morphogenesis. Here we use the formation of the visual system in Drosophila embryos as a model system to investigate the function of the Drosophila classic cadherin, DE-cadherin, which is encoded by the shotgun (shg) gene. The visual system is derived from the optic placode which normally invaginates from the surface ectoderm of the embryo and gives rise to two separate structures, the larval eye (Bolwig's organ) and the optic lobe. The optic placode dissociates and undergoes apoptotic cell death in the absence of DE-cadherin, whereas overexpression of DE-cadherin results in the failure of optic placode cells to invaginate and of Bolwig's organ precursors to separate from the placode. These findings indicate that dynamically regulated levels of DE-cadherin are essential for normal optic placode development. It was shown previously that overexpression of DE-cadherin can disrupt Wingless signaling through titration of Armadillo out of the cytoplasm to the membrane. However, the observed defects are likely the consequence of altered DE-cadherin mediated adhesion rather than a result of compromising Wingless signaling, as overexpression of a DE-cadherin-alpha-catenin fusion protein, which lacks Armadillo binding sites, causes similar defects as DE-cadherin overexpression. We further studied the genetic interaction between DE-cadherin and the Drosophila EGF receptor homolog, EGFR. If EGFR function is eliminated, optic placode defects resemble those following DE-cadherin overexpression, which suggests that loss of EGFR results in an increased adhesion of optic placode cells. An interaction between EGFR and DE-cadherin is further supported by the finding that expression of a constitutively active EGFR enhances the phenotype of a weak shg mutation, whereas a mutation in rhomboid (rho) (an activator of the EGFR ligand Spitz) partially suppresses the shg mutant phenotype. Finally, EGFR can be co-immunoprecipitated with anti-DE-cadherin and anti-Armadillo antibodies from embryonic protein extracts. We propose that EGFR signaling plays a role in morphogenesis by modulating cell adhesion.
动态调节的细胞黏附在动物形态发生过程中起着重要作用。在这里，我们以果蝇胚胎视觉系统的形成为模型系统，来研究果蝇经典钙黏蛋白DE-钙黏蛋白的功能，该蛋白由shotgun（shg）基因编码。视觉系统源自视板，视板通常从胚胎的表面外胚层内陷，并产生两个独立的结构，即幼虫眼（博尔维格氏器官）和视叶。在没有DE-钙黏蛋白的情况下，视板会解离并经历凋亡性细胞死亡，而DE-钙黏蛋白的过表达则导致视板细胞无法内陷，以及博尔维格氏器官前体无法与视板分离。这些发现表明，动态调节的DE-钙黏蛋白水平对于正常视板发育至关重要。先前的研究表明，DE-钙黏蛋白的过表达可通过将犰狳从细胞质滴定到细胞膜上而破坏无翅信号通路。然而，观察到的缺陷可能是DE-钙黏蛋白介导的黏附改变的结果，而不是无翅信号通路受损的结果，因为缺乏犰狳结合位点的DE-钙黏蛋白-α-连环蛋白融合蛋白的过表达会导致与DE-钙黏蛋白过表达类似的缺陷。我们进一步研究了DE-钙黏蛋白与果蝇表皮生长因子受体同源物EGFR之间的遗传相互作用。如果EGFR功能被消除，视板缺陷类似于DE-钙黏蛋白过表达后的缺陷，这表明EGFR的缺失导致视板细胞黏附增加。组成型活性EGFR的表达增强了弱shg突变的表型，而菱形（rho）（EGFR配体斯皮茨的激活剂）的突变部分抑制了shg突变体表型，这一发现进一步支持了EGFR与DE-钙黏蛋白之间的相互作用。最后，从胚胎蛋白提取物中，EGFR可以与抗DE-钙黏蛋白和抗犰狳抗体进行共免疫沉淀。我们提出，EGFR信号通路通过调节细胞黏附在形态发生中发挥作用。
