Distribution of extracellular matrix glycoproteins in the human mesonephros.

We analyzed the expression and distribution of collagen types IV and VI, laminin and fibronectin during the development and regression of the mesonephros in human embryos and fetuses ranging from 6 to 12 weeks of gestation by indirect immunoperoxidase methods. Type IV collagen, laminin and fibronectin were detected along the glomerular, tubular and capsular basement membranes of developing and mature nephrons. Only type IV collagen and fibronectin were found in the mesangium. Type VI collagen formed a delicate interstitial fibrillar network and a continuous basement membrane-like structure along the mesonephric nephrons. Basement membranes (GBM) of developing and mature glomeruli showed a distinct continuous staining for this collagen. The mesangial matrix was rich in type VI collagen. Mesonephric involution started during the 8th week of gestation and coincided with a moderate expansion of mesangial matrix and progressive collapse of the capillary walls, while the tubules became thinner and shorter. Staining for all extracellular matrix glycoproteins studied showed GBM wrinkling, gradual disintegration of some capillary loops and glomerulosclerosis. The sclerotic glomeruli were strongly positive for type IV collagen and less positive for type VI collagen and fibronectin. Laminin was absent. Our results indicate that collagen types IV, VI, laminin and fibronectin may be involved in the development and regression of the human mesonephros.