Induction of c- fos in WT and Msk1(-/-) ES cells. A – WT ES cells and three different Msk1(-/-) ES cell lines (No. 2, No. 4 and No. 5) were serum-starved for 24 h and stimulated with 15% FCS or 20 μM LPA for 30 min, followed by quantitative RT-PCR. Based on relative mRNA levels, fold inductions were calculated from five independent experiments. B – WT and Msk1(-/-) ES cells were serum-starved overnight and stimulated with 20 μM LPA for the times indicated. C-fos mRNA was amplified by semi-quantitative RT-PCR. PCR products were separated on agarose gels and stained with ethidium bromide (EtBr). EtBr intensities were used to calculate c-fos induction.