Burdett I D
Division of Membrane Biology, National Institute for Medical Research, London, U.K.
Micron. 1998 Aug;29(4):309-28. doi: 10.1016/s0968-4328(98)00015-8.
Desmosomes are found principally in epithelial cells and consist of disc-like plaques, the extracellular face of which is paired with that of a neighbouring cell. There is increasing evidence that desmosomes are adhesive structures, and that two types of desmosomal glycoproteins, the desmogleins (Dsg) and desmocollins (Dsc) both Ca(2+)-binding cadherin-like molecules, perform this role in adhesion through interaction of their extracellular domains. A number of isoforms of Dsg and Dsc are present in specific tissues. The cytoplasmic side of the plaque is attached to intermediate filaments through desmoplakin, a major plaque protein. Also associated with desmosomes are plakoglobin and beta-catenin, suggesting that the adhesive function of desmosomes might be mediated by signal transduction. Formation of desmosomes can be studied by growing epithelial cells in low-Ca2+ medium (LCM, < 0.1 mM), where desmosomal proteins are either synthesized but not assembled, or form partially assembled but unstable half-desmosomes. Addition of Ca2+ (to about 2mM) initiates cell contact and, in the case of half-desmosomes, leads to stabilization by incorporation into membranes and formation of typical paired structures. In cases where such pre-assembled structures are not formed, recruitment of desmosomal proteins appears to occur by vesicular transport of desmocollins and desmogleins to the cell surface, where association is made with plakoglobin and later, with desmoplakin. Although much remains to be learned of the assembly process, specific interacting domains of the molecular components are being recognized. Desmosome assembly is part of a coordinated pattern of junction formation which accompanies the establishment of cell polarity, resulting in differentiation of apical and basolateral cell surfaces. Desmosomes are now being regarded, not as static and inert structures, but as membrane specializations linked to systems involved in cell-cell communication as well as adhesion.
桥粒主要存在于上皮细胞中，由盘状斑块组成，其细胞外表面与相邻细胞的外表面配对。越来越多的证据表明，桥粒是粘附结构，两种桥粒糖蛋白，桥粒芯糖蛋白（Dsg）和桥粒胶蛋白（Dsc）都是结合钙的钙粘蛋白样分子，通过其细胞外结构域的相互作用在粘附中发挥这一作用。Dsg和Dsc的多种同工型存在于特定组织中。斑块的细胞质侧通过主要的斑块蛋白桥粒斑蛋白附着于中间丝。与桥粒相关的还有桥粒斑珠蛋白和β-连环蛋白，这表明桥粒的粘附功能可能由信号转导介导。可以通过在低钙培养基（LCM，<0.1 mM）中培养上皮细胞来研究桥粒的形成，在这种培养基中，桥粒蛋白要么合成但未组装，要么形成部分组装但不稳定的半桥粒。添加钙（至约2 mM）会引发细胞接触，对于半桥粒而言，会通过整合到膜中并形成典型的配对结构而导致稳定。在未形成此类预组装结构的情况下，桥粒蛋白的募集似乎是通过桥粒胶蛋白和桥粒芯糖蛋白的囊泡运输到细胞表面来实现的，在细胞表面它们与桥粒斑珠蛋白结合，随后与桥粒斑蛋白结合。尽管关于组装过程仍有许多有待了解之处，但分子成分的特定相互作用结构域正在被识别。桥粒组装是伴随细胞极性建立的连接形成协调模式的一部分，导致顶端和基底外侧细胞表面的分化。现在，桥粒不再被视为静态和惰性结构，而是被视为与细胞间通讯以及粘附相关系统相连的膜特化结构。
