Laminin chains in developing and adult human myotendinous junctions

Abstract

In addition to being the specialized site for transmission of force from the muscle to the tendon, the myotendinous junction (MTJ) also plays an important role in muscle splitting during morphogenesis. An early event in the formation of the MTJ is a regional deposition of basement membranes. We used immunocytochemistry to investigate the distribution of laminin chains during the development of MTJs in human limb muscle at 8-22 weeks of gestation (wg) and in adult MTJs. We used polyclonal antibodies and a new monoclonal antibody (MAb) against the human laminin α1 G4/G5 domains. At 8- 10 wg, laminin α1 and laminin α5 chains were specifically localized to the MTJ. Laminin α1 chain remained restricted to the MTJ at 22 wg as the laminin β2 chain had appeared, whereas the laminin α5 chain became deposited along the entire length of the myotubes from 12 wg. In the adult MTJ, only vestigial amounts of laminin α1 and laminin α5 chains could be detected. On the basis of co-distribution data, we speculate that laminin α1 chain in the forming MTJ undergoes an isoform switch from laminin 1 to laminin 3. Our data indicate a potentially important role for laminin α1 chain in skeletal muscle formation.