Miller J R, McClay D R
Developmental, Cellular and Molecular Biology Group, Duke University, Durham, North Carolina 27708, USA.
Dev Biol. 1997 Dec 15;192(2):323-39. doi: 10.1006/dbio.1997.8740.
During development, the modulation of cadherin adhesive function is proposed to control various morphogenetic events including epithelial-mesenchymal conversions and tubulogenesis, although the mechanisms responsible for regulating cadherin activity during these events remain unclear. In order to gain insights into the regulation of cadherin function during morphogenesis, we utilized the sea urchin embryo as a model system to study the regulation of cadherin localization during epithelial-mesenchymal conversion and convergent-extension movements. Polyclonal antibodies raised against the cytoplasmic domain of a cloned sea urchin cadherin recognize three major polypeptides of M(r) 320, 140, and 125 kDa and specifically stain adherens junctions, and to a lesser extent, lateral membrane domains in all epithelial tissues of the embryo. Analysis of embryos during gastrulation demonstrates that changes in cadherin localization are observed in cells undergoing an epithelial-mesenchymal conversion. Ingression of primary mesenchyme cells is accompanied by the rapid loss of junctional cadherin staining and the coincident accumulation of cadherin in intracellular organelles. These data are consistent with the idea that the deadhesion of mesenchymal cells from neighboring epithelial cells involves the regulated endocytosis of cell surface cadherin molecules. Conversely, neither cadherin abundance nor localization is altered in cells of the gut which undergo convergent-extension movements during the formation of the archenteron. This observation indicates that these movements do not require the loss of junctional cadherin molecules. Instead, the necessary balance between adhesion and motility may be achieved by regulating the expression of different subtypes of cadherin molecules or modifying interactions between cadherins and catenins, proteins that bind the cytoplasmic domain of cadherin and are necessary for cadherin adhesive function. To address cadherin function at the molecular level, we used a partial cDNA representing the conserved cytoplasmic domain to identify a novel cadherin molecule in the sea urchin Lytechinus variegatus. The deduced amino acid sequence of LvG-cadherin (for Goliath-cadherin) predicts that it is a transmembrane protein with an apparent relative molecular mass of 303 kDa. The cytoplasmic domain shows significant sequence identity to that of vertebrate classic cadherins. However, the extracellular domain is distinguished from its vertebrate counterparts by both an increased number of cadherin-specific repeats and the presence of four EGF-like repeats proximal to the transmembrane domain. Taken together, these data are consistent with the hypothesis that the sea urchin possesses several cadherins, including a novel member of the cadherin family, and that the dynamic regulation of cadherin localization plays a role in epithelial to mesenchymal conversions during gastrulation.
在发育过程中，有人提出钙黏蛋白黏附功能的调节可控制包括上皮 - 间充质转化和管状发生在内的各种形态发生事件，尽管在这些事件中负责调节钙黏蛋白活性的机制仍不清楚。为了深入了解形态发生过程中钙黏蛋白功能的调节，我们利用海胆胚胎作为模型系统，研究上皮 - 间充质转化和汇聚延伸运动过程中钙黏蛋白定位的调节。针对克隆的海胆钙黏蛋白细胞质结构域产生的多克隆抗体识别出三种主要多肽，分子量分别为320、140和125 kDa，并特异性地标记黏着连接，在较小程度上也标记胚胎所有上皮组织中的侧膜结构域。对原肠胚形成过程中的胚胎进行分析表明，在经历上皮 - 间充质转化的细胞中观察到钙黏蛋白定位的变化。初级间充质细胞的内陷伴随着连接性钙黏蛋白染色的快速丧失以及钙黏蛋白在细胞内细胞器中的同时积累。这些数据与以下观点一致，即间充质细胞与相邻上皮细胞的去黏附涉及细胞表面钙黏蛋白分子的调节性内吞作用。相反，在原肠形成过程中经历汇聚延伸运动的肠道细胞中，钙黏蛋白的丰度和定位均未改变。这一观察结果表明，这些运动不需要连接性钙黏蛋白分子的丧失。相反，黏附与运动之间的必要平衡可能通过调节钙黏蛋白分子不同亚型的表达或改变钙黏蛋白与连环蛋白之间的相互作用来实现，连环蛋白是结合钙黏蛋白细胞质结构域且对钙黏蛋白黏附功能必不可少的蛋白质。为了在分子水平上研究钙黏蛋白的功能，我们使用了代表保守细胞质结构域的部分cDNA，在海胆多疣荔枝海胆中鉴定出一种新的钙黏蛋白分子。LvG - 钙黏蛋白（巨人钙黏蛋白）推导的氨基酸序列预测它是一种跨膜蛋白，表观相对分子质量为303 kDa。细胞质结构域与脊椎动物经典钙黏蛋白的细胞质结构域具有显著的序列同一性。然而，其细胞外结构域与脊椎动物的对应物不同，钙黏蛋白特异性重复序列数量增加，并且在跨膜结构域附近存在四个表皮生长因子样重复序列。综上所述，这些数据与以下假设一致，即海胆拥有几种钙黏蛋白，包括钙黏蛋白家族的一个新成员，并且钙黏蛋白定位的动态调节在原肠胚形成过程中的上皮向间充质转化中起作用。
