Gα_z, is a unique member of the G_i-family because it does not serve as a substrate of pertussis toxin. It is primarily expressed in neuronal tissues but it is also endogenously expressed in C2C12, a mouse myoblast cell line. However, the exact function of Gα_z, during muscle differentiation is unknown. The present study examined the role of Gα_z in regulating the differentiation of C2C12 myoblasts into myotubes. The expression of Gα_z was increased during differentiation but dropped suddenly towards the end of differentiation. Although Gα_z, was endogenously expressed in mouse myoblast C2C12 cells, the mRNA and protein of Gα_z cannot be detected in adult mouse skeletal muscle. These results hint that Gα_z functions during muscle differentiation predominantly in the stage of myoblast and diffe...[ Read more ]

Gα_z, is a unique member of the G_i-family because it does not serve as a substrate of pertussis toxin. It is primarily expressed in neuronal tissues but it is also endogenously expressed in C2C12, a mouse myoblast cell line. However, the exact function of Gα_z, during muscle differentiation is unknown. The present study examined the role of Gα_z in regulating the differentiation of C2C12 myoblasts into myotubes. The expression of Gα_z was increased during differentiation but dropped suddenly towards the end of differentiation. Although Gα_z, was endogenously expressed in mouse myoblast C2C12 cells, the mRNA and protein of Gα_z cannot be detected in adult mouse skeletal muscle. These results hint that Gα_z functions during muscle differentiation predominantly in the stage of myoblast and differentiation process, and is removed after the completion of differentiation. It was observed that C2C12 cells stably expressing Gα_z exhibited impaired ability to differentiate when compared with control cells. Gα_z-dependent inhibition of muscle differentiation was associated with the decreased expression of myogenin, an executor of muscle differentiation, even when the differentiation process was accelerated by the expression of constitutive active MKK6. Conversely, knock down of endogenous Gα_z in C2C12 cells by siRNA resulted in an increased expression of myogenin and suppression of myogenin expression was abolished upon knocking down the over-expressed Gα_z. The expression of other myogenic markers which emerge at different stages of terminal differentiation was also altered upon over-expressing or knocking down of Gα_z. Expression of a late myogenic marker MCK was decreased significantly upon over-expression of Gα_z, whereas the expression of MHC was increased when endogenous Gα_z was knocked down. The activity of early myogenic marker, MyoD and MEF2, which function co-operatively to control the transcription of myogenin (Molkentin et al, 1995), was increased for more than 35 folds when endogenous Gα_z was knocked down in C2C12. Collectively, these results provide strong indications that Gα_z serves as negative regulator of muscle differentiation.