Extraocular muscle is spared upon complete laminin alpha2 chain deficiency: comparative expression of laminin and integrin isoforms.

Mutations in the gene encoding laminin (LM) alpha2 chain cause congenital muscular dystrophy. Here, we show that extraocular muscle (EOM) is spared upon complete LMalpha2 chain absence. The major LM chains in limb muscle basement membranes are alpha2, beta1, beta2 and gamma1 whereas alpha2, alpha4, beta1, beta2 and gamma1 chains are expressed in EOM. Expression of LMalpha4 chain mRNA is further increased in LMalpha2 chain deficient EOM. Mainly integrin alpha7X1 subunit, which binds to laminin-411, is expressed in EOM and in contrast to dystrophic limb muscle, sustained integrin alpha7B expression is seen in LMalpha2 chain deficient EOM. We propose that LMalpha4 chain, possibly by binding to integrin alpha7BX1beta1D, protects EOM in LMalpha2 chain deficient muscular dystrophy.