Fig. 5. SKP1 is essential for maintenance of postnatal oocytes.

All the Skp1^cKO females used here were Skp1^f/− Ddx4-Cre females. The Ddx4-Cre was constitutively active in oocytes (20). (A) Western blot analysis of SKP1 in oocytes and preimplantation embryos. P13, postnatal day 13; GV, germinal vesicle stage; MII, metaphase II; 1C, one-cell embryos; 2C, two-cell embryos; 4C, four-cell embryos; M/B, morula/blastocyst. (B) Histological analysis of WT and Skp1^cKO ovaries at 2 and 4 months of age. Arrows indicate follicles. Scale bars, 200 μm. (C) Western blot analysis of WT and Skp1^cKO GV oocytes. (D) Morphology of GV oocytes collected from 2-month-old WT and Skp1^cKO mice. (E) Failure of preimplantation embryo development in Skp1^cKO females. IVF was performed with superovulated oocytes from 2-month-old females. One-cell embryos were cultured until morula/blastocyst stage and counted. WT, 228 one-cell embryos (5 females); Skp1^cKO, 40 one-cell embryos (13 females). (F) Analysis of chromosome alignment in MI oocytes. MI oocytes from WT and Skp1^cKO mice were fixed and stained for tubulin and DNA. Oocytes were divided into four categories (i to iv) based on chromosome alignment and spindle defects (χ² = 198, P = 0). Bottom right graph shows quantification of chromosome alignment in WT and Skp1-deficient MI oocytes (n = 25) as DNA density distribution along the spindle axes. Data are combined results from three independent experiments. Scale bar, 5 μm. A.U., arbitrary units.