Figure 1

A method to quantitate satellite cell differentiation. Single fibres from EDL muscles of 2 month old mice were isolated and cultured for five days, switched to differentiation medium for two days and the fraction of desmin-positive (desmin⁺) cells expressing myosin heavy chain determined by immunofluorescence microscopy. A: Satellite cell cultures from myoD heterozygous (myoD ^+/-) and homozygous null (myoD ^-/-) animals. Essentially all cells (blue nuclei: DAPI) express desmin (red: Cy3) in both genotypes, but note the lack of multinucleate myotubes and cells expressing MyHC (green: FITC) in the myoD ^-/-. B-D: Quantification of satellite cell-derived myoblast growth and differentiation by genotype. Error bar = SD. Numbers above columns indicate number of wells counted (1 fibre/well) from 4 animals of myoD ^+/+, myoD ^+/-, and myoD ^-/- genotype, respectively. B: Differentiation of myoD ^-/- myoblasts is poor compared to littermates. C: Increase in cell number after the switch from plating to proliferation medium is independent from the genotype of the animals. myoD ^+/+, myoD ^+/- and myoD ^-/- cells proliferate to the same extent. D: The fraction of differentiated myogenic cells is unaffected by either the number of myogenic desmin⁺ cells or the number of non-myogenic desmin^- cells in each well. In all genotypes (myoD ^+/+, myoD ^+/-, and myoD ^-/-) all fibres yielded myogenic cells.