Immunostaining of Oct-4 in 3-week postcultured OSE of different aged mice. The oocyte-like structures were developed in 3-week postcultured OSE of young (A) and aged mice (B) and they were positively stained for Oct-4. (C) The numbers of Oct-4-positive cells were counted under a microscope. Scale bar = 20 μm. N=3, 6 ovaries per age group.