Type VI collagen in the rat testis: monoclonal antibody, isolation, and localization during development

To investigate the components of the seminiferous tubule extracellular matrix (ST-ECM), monoclonal antibodies were raised against ST-ECM. One of these (15B6) recognized the nonreduced form of type VI collagen. With this antibody as a probe, type VI collagen was isolated from an SDS-urea extract of ST-ECM. It took a tetrameric form, and upon reduction dissociated into a major 140-kDa band and two bands at 190 and 210 kDa. Developmental changes in the distribution of type VI collagen were investigated by immunofluorescence microscopy. In 16-day rat embryos when myoid cells began to differentiate, type VI, collagen was seen in the urogenital mesentery, and it had begun to surround the gonad and, in some embryos, the seminiferous cords. In newborn rats, it was found throughout the extracellular spaces between the cords, being localized in the interstitium. In adults, however, it was confined to two parallel lines around the seminiferous tubules and to filamentous structures in the adventitia of vascular systems. Immunoelectron microscopy showed that this collagen was distributed in the interstitium independently from collagenous fibrils, but was excluded from the basal lamina of Sertoli cells. These observations indicate that type VI collagen is a major component of the ST-ECM and that it may be important in the organization of the matrix and in the differentiation of peritubular cells.