Myogenic cells are potential muscle cells which divide mitotically. Following their exit from the cell cycle at phase G1/G0 they enter the stage of post-mitotic myoblasts. Expression of regulatory proteins of MRF family (MyoD, Myf5, myogenin and MRF-4), which form heterodimers with E family proteins E (E12 and E47) aided by MEF family proteins, starts in their nuclei. The system activates muscle-specific genes. Before the fusion the myoblasts elongate, become linearly arranged, adhere to each other and fuse into an elongated myotube. Transmembrane proteins, e.g.