(A) The Stra8 transcript levels were analyzed in freshly isolated XX and XY germ cells at E11.5 ~ 15.5. Results were normalized to the β-actin mRNA expression. All expression values were calculated relative to control levels set at 1.0. Data represent the mean ± SEM (n = 3). * p < 0.05, ** p < 0.01, *** p < 0.001 vs. E11.5. (B) To determine whether RA activates MAPK (ERK1/2, p38 MAPK and JNK) and AKT pathways, isolated XX germ cells at E12.5 were incubated with 1 μM RA for 0, 0.5, 1 and 2h, then subjected to Western blotting. The fold changes were represented on the top of each band as numerical values that calculated based on the levels of germ cells without culture (0h).