Abnormal formation of sarcoplasmic reticulum networks and triads during early development of skeletal muscle cells in mitsugumin29-deficient mice.

Recently, we detected a novel membrane protein, mitsugumin29 (MG29), in the triads in rabbit skeletal muscle cells and suggested important roles for this membrane protein in the formation of the sarcoplasmic reticulum (SR) networks and triads in muscle cells. In the present study, we examined the development of skeletal muscle cells in MG29-deficient mice to try to determine the roles played by MG29 in the formation of the SR networks and triads. Ultrastructural observations revealed some morphological abnormalities in these mice, such as incomplete formation of the SR networks, an irregular running of the transverse tubule and a partial defect in the triads at the A-I junctional region. These ultrastructural abnormalities occurred during early myogenesis and were preserved until the adult stage. The possible roles for MG29 in the formation of SR networks and triads in skeletal muscle cells are discussed in the light of these observations.