PCNA/cyclin expression and BrdU uptake define proliferating myosatellite cells during hyperplastic muscle growth of...

The possibility of detecting in situ proliferating myosatellite cells during postlarval muscle growth in the carp (Cyprinus carpio, L.) by means of BrdU and PCNA (Cyclin) immunohistochemistry has been evaluated on paraffin embedded sections. Nine subadult stages were defined according to the body length and weight. The fish were injected intraperitoneally with BrdU and fixed one hour later. Adjacent cross sections mounted on glass slides were incubated with monoclonal antiBrdU (1:100) and antiPCNA (1:200) antibody. The proliferative rate, defined as the percentage of labelled cells for each stage, was correlated to the corresponding percentage of small fibers (area less than 200 microns 2) determined by morphometric analysis. Desmin expression, immunocytochemically detected, was aimed at discriminating between the postmitotic and stem myosatellite cells. A low myosatellite cell proliferative activity (2-7%) throughout the carp growth period considered was demonstrated. Quantitative analysis provided evidence that during growth stages in which small fibers are numerous, the myosatellite cell proliferative activity is low and it increases when the small fibers number decreases. It is suggested that an age dependence of myosatellite cell proliferative rate controls the recruitment of new fibers in the carp.