Developmental stages of Mus musculus

• oocyte MeSH primary oocyte (located in the ovarian follicle); for each primary oocyte that undergoes meiosis, only one functional oocyte is produced; the other two or three cells produced are called polar bodies; polar bodies have no function and eventually deteriorate
• unfertilized ovum secondary oocyte the primary oocyte turns into a secondary oocyte in mature ovarian follicles; unlike the sperm, the egg is arrested in the secondary stage of meiosis until fertilization; upon fertilization by sperm, the secondary oocyte continues the second part of meiosis and becomes a zygote
• prenatal
  • embryo MeSH the average gestation period is about 20-21 days
    • early gestation embryo
      • pre-implantation embryo
        • zygote MeSH fertilized egg, 1-cell embryo;
          0 dpc, Theiler 1;
        • cleavage MeSHdividing egg, 1-2 dpc, Theiler 2 dividing egg, 1-2 dpc, Theiler 2
          • early cleavage
            • 2-cell embryo
            • 4-cell embryo
          • morula MeSH 8-16-cell embryo,
            1-3.5 dpc, Theiler 3
        • blastocyst MeSH16-40-cell embryo,
          2-5.5 dpc, Theiler 4-5 16-40-cell embryo, 2-5.5 dpc, Theiler 4-5
    • post implantation embryo
      • egg cylinder 4.5-6.5 dpc, Theiler 7-10;
        stages of egg cylinder:
        implantation, formation,
        differentiation, and
        advanced egg cylinder
        (equivalent to Downs and Davies
        pre-streak and early streak)
      • mid-gestation embryo
        • gastrula MeSH 6.5+-8.0 dpc, Theiler 10abc
        • neurula 7.5-8.5 dpc, Theiler 11abcd
        • organogenesis MeSH 8.5-12 dpc, Theiler 12-19;
          stages of organogenesis:
          first 1-7 somite pairs,
          turning of the embryo;
          formation and closure of
          anterior and posterior
          neurospore;
          development of limb buds,
          olfactory pit,
          and optic vesicles
      • late gestation embryo
        • fetus MeSH 12-21 dpc, Theiler 20-26;
          embryo resembling mouse;
          stages: signs of fingers;
          anterior footplate indented,
          marked pinna;
          fingers and toes separate;
          reposition of umbilical hernia;
          skin wrinkles;
          long whiskers
• post natal
  • neonate 1-14 days of age; eyes closed
  • juvenile 14-35 days old; eyes are opening at 14 days of age; weaning at 21 days of age
  • adult reaching sexual maturity at 5-7 weeks; average life span is about 3 months in the wild and up to 3 years in captivity

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