Mice
Smc2 floxed and Gdf9-Cre mice were previously reported (Nishide & Hirano, 2014; Sun et al., 2008). All mouse strains had a C57B6 background. Wild-type C57B6 male mice were obtained from Speyford (Beijing) Biotechnology Co., Ltd. All mice care and handling were carried out under the guide of the Animal Care and Use Committee of the Institute of Zoology at the Chinese Academy of Sciences.