P.8.8 Basement membrane deposition during muscle development in the FKRP Deficient Mouse

Abstract

The defective glycosylation of <i>α</i>-dystroglycan is associated with a group of muscular dystrophies collectively referred to as the dystroglycanopathies. We previously generated a FKRP deficient mouse (FKRPKD) which recapitulates the severe end of the clinical spectrum and displays a muscle/eye/brain phenotype and dies soon after birth. In view of the well documented role of <i>α</i>-dystroglycan in basement membrane deposition we sought to determine if secondary myogenesis was altered in the FKRPKD mice. Here we show that the laminin binding epitope of <i>α</i>-dystroglycan is present from the earliest stages of secondary myotube formation at E15.5 in wild type mice. FKRPKD mice show a mild reduction in laminin <i>α</i>-2 at this time point. However, this reduction is not apparent using an antibody to pan laminin (identifies several laminin chains). However, at P0, a marked reduction of laminin <i>α</i>2 was noted in FKRPKD compared to wild type, together with a moderate reduction in the pan laminin, suggesting that the initial reduction in <i>α</i>2 subsequently alters the deposition of other laminin chains. In order to further examine this we have now examined the deposition of other laminin chains (<i>α</i>1, <i>α</i>4, <i>α</i>1, and ϒ1). There was no alteration in laminin <i>α</i>1, <i>α</i>4 and ϒ1 expression between wild type and mutant at either E15.5 or P0. Laminin <i>α</i>1 however, showed a subtle reduction in FKRPKD compared to wild type at E15.5 which became more apparent at P0. To determine the effect of these alterations on fibre formation we counted muscle fibres at E15.5 and P0 and showed that neither the number of primary myotubes (as indicated by slow myosin heavy chain expression) nor the total number of fibres at P0 was significantly different between FKRPKD and wild type mice. These observations suggest that alterations in basement membrane deposition during myogenesis do influence myoblast alignment and fusion.