: The hypotheses will be addressed by the following specific aims: 1] To determine if myofibrillar mRNA abundance regulates skeletal muscle protein synthesis in the early postnatal period, and if variations in MRF expression in the early postnatal period modulate rates of myofibrillar protein synthesis, 2] a) To determine whether the enhanced skeletal muscle protein and DNA accretion induced by muscle-specific overexpression of IGF-I is impaired when MRF function is inhibited, b) To determine whether tissue IGF-I concentrations regulate skeletal muscle protein synthesis by increasing the sensitivity of muscle protein synthesis to insulin, 3] To compare the protein synthetic responses of immature versus mature skeletal muscle to nutritional rehabilitation in the presence of variable levels of MRF activity and muscle IGF-I abundance.