Developmental stages of preimplantation embryos obtained from mHR6A+/− (A, B, E, and F) and mHR6A−/− (C, D, G, and H) female mice fertilized by wild-type males. Images obtained with confocal laser scanning microscopy (A to D) show embryos from an mHR6A+/− heterozygous mother (A and B) and an mHR6A−/− knockout mother (C and D) approximately 8 h after fertilization. Two planes are displayed for the fertilized egg, one showing the paternal pronucleus (P in panels A and C) and one showing the maternal pronucleus (M in panels B and D). Phase-contrast microscopy shows examples of embryos obtained from mHR6A+/− (E and F) and mHR6A−/− (G and H) female mice at 1.5 dpc (E and G) and cultured for 3 days (F and H). (E) Embryos at various stages of development, obtained from an mHR6A+/− female. (F) Hatching (left) and hatched (upper right) embryos and an empty zona pellucida (lower right). (G) Embryos obtained from an mHR6A−/− female. (H) One-cell (left), two-cell (upper right), and fragmented (lower right) embryos. Scale bar, 20 μm.