Testes were excised from 10- and 2-week-old mice (n = 10 each), minced with scissors in cold Hanks’ balanced salt solution (HBSS), and passed through a stainless steel mesh. TGCs were harvested by centrifugation at 400 G for 15 min, washed three times in cold Hanks’ balanced salt solution, and then adjusted to a concentration of 1 × 107 TGC/200 μl/mouse after determining cell viability by trypan blue dye exclusion. The TGC suspension contained more than 99% germ cells at various stages of spermatogenesis; the remaining <1% consisted of Sertoli and interstitial cells21. The ratio of prepared cells was determined by visual microscopic inspection using a hemocytometer. In addition, prepared cells have been confirmed by immunohistochemical method and real-time RT-PCR (Figure S1).