siRNA transfection

Passage 1 primary MEFs were grown to 40-50 % confluency and transfected with 20 μM siRNAs against mouse Cdkn1a, Mdm2 or a negative control (ON TARGETplus SMARTpool, Dharmacon) using Lipofectamine RNAiMAX (Thermo Fisher) according to manufacturer instructions. siRNAs and Lipofectamine were initially diluted in Opti-MEM Medium and mixed after 5 min incubation. After an additional 15 min, the transfection mix was directly added to the cells. 48 h later, cells were lysed for Western blot or incubated with CldU and IdU for fiber stretching assay.