Extraocular muscle is spared upon complete laminin α2 chain deficiency: Comparative expression of laminin and integrin isoforms

Mutations in the gene encoding laminin (LM) α2 chain cause congenital muscular dystrophy. Here, we show that extraocular muscle (EOM) is spared upon complete LMα2 chain absence. The major LM chains in limb muscle basement membranes are α2, β1, β2 and γ1 whereas α2, α4, β1, β2 and γ1 chains are expressed in EOM. Expression of LMα4 chain mRNA is further increased in LMα2 chain deficient EOM. Mainly integrin α7X1 subunit, which binds to laminin-411, is expressed in EOM and in contrast to dystrophic limb muscle, sustained integrin α7B expression is seen in LMα2 chain deficient EOM. We propose that LMα4 chain, possibly by binding to integrin α7BX1β1D, protects EOM in LMα2 chain deficient muscular dystrophy.