SATELLITE CELL CONTENT IN MUSCLES OF LARGE AND SMALL MICE

Quantitative analyses of the satellite cell content in the biceps brac hii muscle of mice genetically selected for high (QL) and low (QS) bod yweight showed that selection alters the total number of satellite cel l nuclei rather than the relative proportions of nuclei in the myofibr e and satellite cell populations. These findings are in accordance wit h those previously published for other tissues of these mice and suppo rt the hypothesis that regulatory mechanisms remain unaltered by selec tion pressure. Size at birth, however, is a reflection of nutritional status as well as genetic background, and comparisons between differen tly sized littermates within each of the lines showed a significant in crease in satellite cell density in larger compared with smaller indiv iduals. These differences between littermates were not accompanied by any alteration in myofibre nuclear density. It is therefore suggested that whilst both genetic and nutritional factors exert their effects o n muscle growth through an influence on satellite cell division, both do so at different stages during the programme of satellite cell diffe rentiation.