Fig. 4

The pattern of embryonic germ cell development is correlated to the process of first wave follicle growth and the time of puberty onset. a The vaginal opening ages of C57 and C3H strains, showing a significantly earlier vaginal opening in C3H compared to C57 (n = 19). b The age of first vaginal cornification in C57 and C3H, showing a significantly earlier onset of first vaginal cornification in the C3H compared to C57 (n = 19). c The age-related FOXO3 expressing profiles in embryonic germ cells of C57 and C3H females. The FOXO3⁺ germ cells (arrows) were observed in the C3H ovaries at 16.0 dpc, whereas the FOXO3⁺ germ cells started to appear in C57 ovaries at 18.0 dpc. FOXO3, green; DDX4, gray. d The ratio of activated germ cells at 16.0 dpc and 18.0 dpc showed a significant difference in C3H ovaries compared to that in C57 (n = 6). e Histological analysis of the ovarian development in C57 and C3H at 5 dpp, showing the secondary follicles with multi-layer of GCs (arrows) in C3H ovaries. f Follicle counting results showing a high proportion of secondary follicles in C3H ovaries compared to C57 at 5 dpp (n = 7). g Histological analysis of the ovarian development in C57 and C3H at 13 dpp, showing the antral follicles (arrow) existed at 13 dpp C3H ovaries. h, i Calculating results of the size and the GC layer number in 5 largest follicles per ovaries in C57 and C3H at 13 dpp. Showing a significantly larger size (h) and GC layer number (i) of pioneering follicles in C3H ovaries than that in C57 ovaries (n = 8). All experiments were repeated more than three times, and representative images are shown. Data are presented as the mean ± SD and analyzed by a two-tailed unpaired Student’s t-test, ***P < 0.001. Scale bars, 50 μm (c), 100 μm (e, g)