PCNA CYCLIN EXPRESSION AND BRDU UPTAKE DEFINE PROLIFERATING MYOSATELLITE CELLS DURING HYPERPLASTIC MUSCLE GROWTH OF FISH (CYPRINUS-CARPIO L)

The possibility of detecting in situ proliferating myosatellite cells during postlarval muscle growth in the carp (Cyprinus carpio, L.) by m eans of BrdU and PCNA (Cyclin) immunohistochemistry has been evaluated on paraffin embedded sections. Nine subadult stages were defined acco rding to the body length and weight. The fish were injected intraperit oneally with BrdU and fixed one hour later. Adjacent cross sections mo unted 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 cor responding percentage of small fibers (area less than 200 mum2) determ ined by morphometric analysis. Desmin expression, immunocytochemically detected, was aimed at discriminating between the postmitotic and ste m myosatellite cells. A low myosatellite cell proliferative activity ( 2-7%) throughout the carp growth period considered was demonstrated. Q uantitative analysis provided evidence that during growth stages in wh ich small fibers are numerous, the myosatellite cell proliferative act ivity is low and it increases when the small fibers number decreases. It is suggested that an age dependence of myosatellite cell proliferat ive rate controls the recruitment of new fibers in the carp.