MYOD1 and infection: Moreover, as shown in Supplementary Fig. 4c–e, retrovirus-mediated expression of exogenous MyoD in murine C3H/10T1/2 fibroblasts, a well described model of myogenic-like differentiation26, resulted in increased mRNA and protein expression of SKP2 24 h post-infection in growth/proliferation medium (GM, supplemented with 10% serum) that was maintained 24 h upon shifting to differentiation medium (DM, serum-free medium).