Extrasynaptic localization of laminin β2 chain in developing and adult human skeletal muscle

We have investigated the distribution of the laminin β2 chain (previously s-laminin) in human fetal and adult skeletal muscle and compared it to the distribution of laminin β1. Immunoblotting and transfection assays were used to characterize a panel of monoclonal and polyclonal antibodies to the laminin β2 chain. We found that laminin β1 chain was detected at all times during development from 10 weeks of gestation. Laminin β2 chain was first detected in 15 to 22-week-old fetal skeletal muscle as distinct focal immunoreactivity in the sarcolemmal basement membrane area of some myofibers. In the adult skeletal muscle, laminin β2 chain immunoreactivity was found along the entire perimeter of each of the individual myofibers in a large series of different muscles studied. Laminin β2 chain was similarly found in the skeletal muscle basement membranes in patients with Duchenne and Becker muscular dystrophy. Immunoaffinity chromatography of muscle extracts with a monoclonal antibody to the laminin α2 chain followed by immunoblotting with various antibodies to the β2 chain demonstrated the presence of the laminin- 4 (α2-β2-γ1) isoform. Together the present results demonstrate a prominent extrasynaptic localization of laminin β2 in the human muscle, suggesting that it may have an important function in the sarcolemmal basement membrane.