Timpl R, Aumailley M
Department of Connective Tissue Research, Max-Planck-Institut für Biochemie, Martinsried/Munich, Federal Republic of Germany.
Adv Nephrol Necker Hosp. 1989;18:59-76.
Basement membranes are thin (20 to 300 nm) extracellular matrices with a ubiquitous occurrence in the body. They consist mainly of collagenous and noncollagenous glycoproteins, are formed early during embryonic development, and in mature tissues they compartmentalize various types of cells and tissue structures. The close apposition to cells is the most remarkable feature of basement membranes, which can either surround cells completely (muscle, fat, nerve axons) or separate them from underlying stroma in a polarized fashion (epithelium, endothelium). These cell contacts are mediated by cellular receptors and specific matrix components and have profound effects on polarization, differentiation, and proliferation of cells and on the control of their migratory behavior. In addition, basement membranes represent barriers regulating filtration of macromolecules and penetration by cells. The supramolecular organization of basement membranes is still insufficiently known. In transmission electron microscopy cross-sections show a two-layered morphology that includes an electron dense (lamina densa) and an electron lucent (lamina rara) zone, the latter being closer to the cells. Other specialized basement membranes such as those in renal glomeruli appear more complex and contain two laminae rarae. Here, presumably epithelial and invading endothelial cells each produce their own basement membrane, which then fuse together to form the filtration units of the glomerulus. Further structural and functional study of authentic basement membranes has been limited because these membranes comprise only a small fraction of tissues and most of their components are notoriously insoluble. Rodent tumors that produce large amounts of basement membrane material and the use of recombinant DNA technology in the past decade have paved the way for a more precise biochemical characterization of several basement membrane proteins. These components include collagen type IV, the cell-binding protein laminin, several proteoglycans, and other proteins. In the following pages we will briefly review the biochemical properties of the basement membranes and discuss their possible functions and contributions to supramolecular structures. For more extensive discussions, including certain biologic and pathologic aspects of basement membrane function, we refer the reader to several recent reviews.
基底膜是一种薄（20至300纳米）的细胞外基质，在体内广泛存在。它们主要由胶原和非胶原糖蛋白组成，在胚胎发育早期形成，在成熟组织中，它们将各种类型的细胞和组织结构分隔开来。与细胞紧密相邻是基底膜最显著的特征，基底膜既可以完全包围细胞（肌肉、脂肪、神经轴突），也可以以极化方式将它们与下方的基质分隔开（上皮、内皮）。这些细胞接触由细胞受体和特定的基质成分介导，对细胞的极化、分化和增殖以及对其迁移行为的控制具有深远影响。此外，基底膜是调节大分子过滤和细胞穿透的屏障。基底膜的超分子组织仍未得到充分了解。在透射电子显微镜下，横截面显示出两层形态，包括一个电子致密区（致密层）和一个电子透明区（疏松层），后者更靠近细胞。其他特殊的基底膜，如肾小球中的基底膜，看起来更复杂，包含两个疏松层。在这里，推测上皮细胞和侵入的内皮细胞各自产生自己的基底膜，然后融合在一起形成肾小球的过滤单位。对真实基底膜的进一步结构和功能研究受到限制，因为这些膜仅占组织的一小部分，而且它们的大多数成分都极难溶解。过去十年中，能产生大量基底膜物质的啮齿动物肿瘤以及重组DNA技术的应用，为更精确地生化鉴定几种基底膜蛋白铺平了道路。这些成分包括IV型胶原、细胞结合蛋白层粘连蛋白、几种蛋白聚糖和其他蛋白质。在接下来的几页中，我们将简要回顾基底膜的生化特性，并讨论它们可能的功能以及对超分子结构的贡献。如需更广泛的讨论，包括基底膜功能的某些生物学和病理学方面，我们建议读者参考最近的几篇综述。
