DISRUPTION OF THE LAMA2 GENE IN EMBRYONIC STEM-CELLS - LAMININ ALPHA-2 IS NECESSARY FOR SUSTENANCE OF MATURE MUSCLE-CELLS

Mutations in the gene coding for the alpha 2 chain of laminin-2 and -4 (merosin) cause a severe form of congenital muscular dystrophy in hum ans and mice. To establish a defined model for in vitro and in vivo st udies of the role of laminin alpha 2/merosin in development and cell a nd tissue function, we generated several lines of mutant embryonic ste m (ES) cell with disruption of the laminin alpha 2 chain gene. We find that homozygous mutant ES cells differentiate normally in vitro, givi ng rise to cardiomyocytes, myotubes, and smooth muscle cells in additi on to many other cell types. However, the myotubes that are formed are unstable. They detach, collapse, and degenerate, a process which is i nitiated at the appearance of the mature, contractile phenotype of the cells. We propose that the detachment and death of contracting myotub es in vitro has its counterpart in vivo and that contraction-induced m yofiber damage, along with the lack of survival cues provided by lamin in alpha 2/merosin, is a significant contribution to muscle degenerati on in merosin-deficient muscular dystrophy, (C) 1998 Academic Press.