Satellite cell content in muscles of large and small mice.

Quantitative analyses of the satellite cell content in the biceps brachii muscle of mice genetically selected for high (QL) and low (QS) bodyweight showed that selection alters the total number of satellite cell nuclei rather than the relative proportions of nuclei in the myofibre and satellite cell populations. These findings are in accordance with those previously published for other tissues of these mice and support the hypothesis that regulatory mechanisms remain unaltered by selection pressure. Size at birth, however, is a reflection of nutritional status as well as genetic background, and comparisons between differently sized littermates within each of the lines showed a significant increase in satellite cell density in larger compared with smaller individuals. 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 on muscle growth through an influence on satellite cell division, both do so at different stages during the programme of satellite cell differentiation.