Postnatal profiles of myogenic regulatory factors and the receptors of TGF-beta(2), LIF and IGF-I in the gastrocnemius and rectus femoris muscles of dy mouse

The dystrophin-deficient mdx mouse presents muscle fiber necrosis but activ e muscle regeneration, probably due to an extensive recruitment of myogenic regulatory factors (MRF), several growth factors and cytokines, and favora ble interaction of satellite cells. In contrast, the laminin alpha 2 (meros in)-deficient dy mouse shows progressive muscle fiber necrosis and ineffect ive muscle regeneration. Using Western blot and immunohistochemical analyse s, we investigated the adaptive changes in MRF, growth factors and cytokine s and their receptors in the muscles of dy mice during postnatal growth. Th e relative volume of MyoD, myogenin and Myf-5 proteins was markedly lower i n the gastrocnemius and rectus femoris muscles of dy mice. Transforming gro wth factor-beta 2, leukemia inhibitory factor (LIF) and basic fibroblast gr owth factor were not up-regulated in the muscles of dy mice. The levels of the LIF receptor and insulin-like growth factor-I receptor levels were mark edly decreased in the muscles of dy mice during the entire postnatal period observed in this study. Therefore, unlike the situation in mdx mice, the m ilieu of regeneration following repetitive damage seems to be degraded in t he muscles of dy mice.