Characterization of MEFs. (A) Mitogenic responsiveness of MEFs as measured by [3H]thymidine incorporation. Serum-deprived cells ("control") were treated with fetal calf serum (FCS; 10%), LPA (10 μM) or EGF (25 ng/ml). The response to FCS was set at 100%. Bars represent means ± SD (N = 3). (B) LPA receptor expression in MEFs. Expression levels were determined by qPCR using the GAPDH gene for normalization. Expression levels of LPA3 and LPA5 are negligible.