Overshooting production of satellite cells in murine skeletal muscle affected by the mutation ''muscular dystrophy with myositis'' (mdm, Chr 2)

The hereditary degenerative muscle disease ''muscular dystrophy with myositis'' of the mouse (MDM, genotype mdm/mdm) is caused by a spontaneous recessive mutation on chromosome 2. Skeletal muscles of MDM mice degenerate during the first few postnatal weeks and subsequently regenerate. The cellular and molecular mechanisms of this muscle disease are not yet understood. An inflammatory component as implied by its name seems unlikely. By applying quantitative electron microscopy, we demonstrate a transient increase of up to 4-fold in the satellite cell frequency in both fast and slow muscles of affected animals. This difference from wildtype controls (+/+ or +/mdm) is also reflected in the yield of mononucleate myogenic cells upon dissociation of skeletal muscle and subsequent cell culture. Unlike the increase in satellite cell density in the myotonic ADR mouse, this phenomenon is not accompanied with a shift to more oxidative fibre types. It may however be related to the more profuse micro-vascularization of MDM muscle.