Small GTPases of the Rab family are important in the stage of vesicle tethering, and SNAREs might mediate membrane fusion . and GLUT4 in C2C12 myoblasts is assessed by surface biotinylation and Western blotting. Results Overexpression or knockdown of Stx4 enhances or inhibits myogenic differentiation, respectively. Stx4 binds to the cytoplasmic tail of Cdo, and this interaction seems to be critical for induction of p38MAPK activation and myotube formation. Stx4 depletion decreases specifically the cell surface localization of Cdo without changes in surface N-Cadherin levels. Interestingly, Cdo depletion reduces the level of GLUT4 and Stx4 at cell surface. Consistently, overexpression of Cdo in C2C12 myoblasts generally increases glucose uptake, while Cdo depletion reduces it. Conclusions Stx4 promotes myoblast differentiation through interaction with Cdo and stimulation of its surface translocation. Both Cdo and Stx4 are required for GLUT4 translocation to cell surface and glucose uptake in myoblast differentiation. Electronic supplementary material The online version of this article (doi:10.1186/s13395-015-0052-8) contains supplementary material, which is available to authorized users. or mice. Previously, we have shown that Cdo-deficient primary myoblasts display defects in myoblast differentiation and p38MAPK activation . or myoblasts at high cell density (D0) were induced to differentiate by removal of basic fibroblast growth factor (bFGF) for 2?days. The expression of Stx4 in myoblasts was substantially increased at D2 compared to that of myoblasts, whereas there was only slight or no difference at D0 and D1 (Fig.?1c). In addition, the qRT-PCR analysis showed that Stx4 transcript levels were increased at D1 in Cdo-deficient myoblasts, but no difference in cells at D0 or D2 (Fig.?1d). These data suggest that the Stx4 expression level alone may not be sufficient to induce myoblast Indolelactic acid differentiation when Cdo is deficient. Open in a separate window Fig. 1 Stx4 is expressed in skeletal muscles and induced in myoblast differentiation. a RT-PCR analysis of hindlimb muscles EDC3 from E15.5 embryos and P1, P5, P7, P14, and P30 mice for the expression of Stx4, Cdo, MyoD, Myogenin, and 18S rRNA serves as a loading control. b Immunoblot analysis of C2C12 cells from various differentiation days (and primary myoblasts during differentiation, and pan-Cadherin serves as a loading control. d qRT-PCR analysis Indolelactic acid for Stx4 mRNA expression in and primary myoblasts during differentiation Overexpression of Stx4 enhances myogenic differentiation To investigate the function of Stx4 in myogenesis, C2C12 cells were stably transfected with control or Stx4 expression vectors and induced to differentiate. Overexpression of Stx4 in C2C12 cells generally resulted in a twofold increase of Stx4 protein (Fig.?2a) and the expression of muscle-specific genes including MHC; Myogenin and Troponin T were significantly enhanced in Stx4-overexpressing C2C12 cells, compared to that of control cells, while MyoD levels were not altered (Fig.?2b). Next, we examined the effect of Stx4 overexpression on myotube formation. Control (pcDNA) and Stx4-overexpressing C2C12 cells were induced to differentiate for 2?days, fixed, and immunostained with anti-MHC antibody followed by DAPI staining. Stx4-overexpressing C2C12 cells formed larger myotubes than the control (pcDNA) cells (Fig.?2c, d). MHC-positive cells were scored as mononucleate, containing two to five nuclei, containing six to nine nuclei, or containing ten or Indolelactic acid more nuclei. Stx4-overexpressing cells formed more larger myotubes containing six to nine nuclei (18?%) and ten or more nuclei (15?%), compared to control cells with 10 and 3?%, respectively. In contrast, the percentile of mononucleate cells decreased to 38?%, compared to 53?% of control cells (Fig.?2d). These data suggest that Stx4 promotes myoblast differentiation. Open in a separate window Fig. 2 Overexpression or knockdown.