SATELLITE CELL MITOTIC-ACTIVITY IN POSTHATCH TURKEY SKELETAL-MUSCLE GROWTH

The relationship between satellite cell mitotic activity and skeletal myofiber growth was examined in Pectoralis thoracicus and Biceps femor is muscles of Large White tom turkeys (Nicholas strain) at 3,6,9,18, a nd 26 wk of age. Mitotically active satellite cells were labeled with 5-bromo-2'-deoxyuridine (BrdU). Labeled satellite cells were identifie d on enzymatically isolated myofiber segments using mouse anti-BrdU fo llowed by fluorescein-5-isothiocyanate FITC) conjugated goat anti-mous e IgG secondary antibodies. Myofiber nuclei (satellite cell nuclei + m yonuclei) were counterstained with propidium iodide (PI). Myofiber seg ment diameter, myofiber segment length, and number of FITC- and PI-lab eled nuclei were determined for each segment. At each age interval the re was an increase in myofiber diameter, suggesting that the myofibers were growing during the entire experimental period. There was an age- related (P < .001) decrease in satellite cell mitotic activity and an age-related increase (P < .001) in the cytoplasmic volume to nucleus r atio (CNR) from 3 to 26 wk of age. An early phase of myofiber growth, between 3 and 6 wk of age, was characterized by a high level of satell ite cell mitotic activity and increased CNR. Between 6 and 9 wk of age , satellite cell mitotic activity decreased, but the CNR showed no cha nge (P > .05). During a late phase of myofiber growth, beyond 9 wk of age, satellite cell mitotic activity continued to decrease and myofibe r growth occurred by an increased CNR. This study demonstrated that bo th Pectoralis thoracicus and Biceps femoris undergo a significant late phase of growth without appreciable production of myonuclei by satell ite cell proliferation.