Running Head: Satellite Cell Proliferation and Differentiation

Age-related changes in satellite cell proliferation and differentiation during rapid growth of porcine skeletal muscle were examined. Satellite cells were isolated from hindlimb muscles of pigs at 1, 7, 14, and 21 weeks of age (4 animals/age group). Satellite cells were separated from cellular debris using Percoll gradient centrifugation, and adsorbed to glass coverslips for fluorescent immunostaining. Positive staining for neural cell adhesion molecule (NCAM) distinguished satellite cells from non-myogenic cells. The proportion of NCAM-positive cells (satellite cells) in isolates decreased from 1 to 7 weeks of age. Greater than 77% of NCAMpositive cells were proliferating cell nuclear antigen (PCNA)-positive at all ages studied. Myogenin-positive satellite cells decreased from 30% at 1 week to 14% at 7 weeks of age and remained at constant levels thereafter. These data indicate that a high percentage of satellite cells remain proliferative during rapid postnatal muscle growth. The reduced proportion of myogenin-positive cells during growth may reflect a decrease in the proportion of differentiating satellite cells or accelerated incorporation of myogenin-positive cells into myofibers.