Mice harboring an oocyte-specific knockout of the Ubc9-encoding gene (Ube2i-cKO) show infertility with complete failure of oocytes to extrude the polar bodies (but no aberrancy in spindle morphology) (Rodriguez et al., 2019), supporting the notion that SUMOylation is critical for regulation of molecules involved in the MI–MII transition (Wang et al., 2010; Yuan et al., 2014; Ding et al., 2018). This evidence concerns the gene UBE2I and Infertility.