I, MyoD activates muscle-specific gene expression myoD p21/af/cip I activates MVOD p2l/ waf/cipl→+CDKs… cell cycle activates cyclin dependent kinase) muscle specific arrest gene expression at the gl-phase Cell differentiationmyoD p21/waf/cip1 activates MyoD p21/waf/cip1 CDKs cell cycle activates ( cyclin dependent kinase) muscle specific arrest gene expression at the G1-phase. Cell differentiation 1、MyoD activates muscle-specific gene expression *