The present study examined the subcellular response of tumor suppressor p53 and inhibitor of DNA-binding/differentiation Id2 to muscle overload. Overload was induced by attaching a tube weight corresponding to 12% of the animal's bodyweight to one wing of young adult or old Japanese quails for 7 or 21 days. This approach induces muscle hypertrophy in fast patagialis (PAT) and slow anterior latissimus dorsi (ALD) wing muscles of the loaded side. The contralateral wing served as the intra-animal control. PAT muscle weight increased by 28% in young bird but no significant hypertrophy was found in aged birds following 7 days of loading. After 21 days of loading, PAT muscle weight increased by 49% and 29% in young and aged birds, respectively. ALD muscle weight increased by 96% in young bird whereas the gain in aged birds was not significant after 7 days of loading. Following 21 days of loading, ALD muscle weight increased by 179% and 102% in young and aged birds, respectively. Nuclear and cytosolic subcellular protein fractions were analyzed by Western immunoblots. The nuclear Id2 protein content was greater in PAT muscles from old and young birds that were loaded for 7 days relative to the contralateral control muscles. These changes were not found in PAT muscles after 21 days of loading. In ALD muscles, elevation of nuclear Id2 protein content was evident in both 7 and 21 day-loaded muscles relative to the contralateral control side in both young and aged birds. Nuclear p53 protein content was greater in all loaded PAT or ALD muscles when compared to the contralateral control muscles in all groups of birds. In contrast, no difference was found in either cytosolic Id2 or p53 protein content among all the loaded PAT or ALD muscles and the corresponding contralateral control muscles. These data suggest that nuclear, but not cytosolic Id2 and p53 are responsive to stretch-induced muscle overload. Moreover, the attenuated ability of the aged skeletal muscle to achieve hypertrophy is not explained by the subcellular changes of Id2 and p53 with overload.