Cavβ1a/YFP overexpression in undifferentiated C2C12 myoblasts was observed primarily in the cytoplasm and weakly in the nucleus (A, C, and C′). Endogenous TnT3 was detected by immunfluorescence in mononucleated, elongated cells in both cytoplasm and nucleus (B, D, and D′). In the elongated C2C12 cells at an early stage of differentiation and co-expressed with Cavβ1a/YFP, both TnT3 and Cavβ1a/YFP were observed in the nucleus; the latter was greatly enriched (D, D′) compared to the case when it only was expressed in undifferentiated myoblasts (A, C, and C′).