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 m yositis'' of the mouse (MDM, genotype mdm/mdm) is caused by a spontane ous recessive mutation on chromosome 2. Skeletal muscles of MDM mice d egenerate during the first few postnatal weeks and subsequently regene rate. 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 demon strate a transient increase of up to 4-fold in the satellite cell freq uency in both fast and slow muscles of affected animals. This differen ce from wildtype controls (+/+ or +/mdm) is also reflected in the yiel d of mononucleate myogenic cells upon dissociation of skeletal muscle and subsequent cell culture. Unlike the increase in satellite cell den sity in the myotonic ADR mouse, this phenomenon is not accompanied wit h a shift to more oxidative fibre types. It may however be related to the more profuse micro-vascularization of MDM muscle.