Basement Membrane Regulation of Sertoli Cells*

MOST vertebrate cells are in contact with an extracellular matrix (ECM) composed of both protein and carbohydrate in the form of glycoproteins and proteoglycans (1). The glycoproteins are defined by the attachment of relatively small carbohydrate moieties and include the major structural proteins laminin, fibronectin, collagen, and elastin. The proteoglycans, on the other hand, are characterized by a covalent linkage between a core protein and one or more glycosaminoglycans, which are large, negatively charged polymers of repeating disaccharide units such as heparan and chondroitin sulfate. In addition, many ECMs contain the glycosaminoglycan, hyaluronan, which does not appear to be covalently linked to protein. The various components of the ECM interact with each other in a complex fashion to form a meshwork-like structure. Some cell types, such as muscle cells and chondrocytes, are completely surrounded by ECM while others, such as simple epithelial cells and endothelial cells, are exposed to the ECM only on one surface. Because of its widespread distribution and strategic location, the ECM was originally believed to be an inert scaffolding for the support of cells and tissues. However, more recently, it has become increasingly clear that the ECM plays a fundamental role in the process of morphogenesis and differentiation and is essential in the development and maintenance of the differentiated state (2). During embryonic development an ECM is present from the two-cell stage.