1Updated:11/13/07Lecture 18: Embryo DevelopmentAnimal Science 434John ParrishUpdated:11/13/07Timing of InseminationSpecies Time of Ovulation Optimal Insemination TimeCow 29 hr after start End of estrus (12 hr afterof estrus first seen in estrus)Ewe End of estrus End of 1st day or start of2nd day of estrusSow End of estrus End of 1st day or start of2nd day of estrusMare 1-2 days before Every other day beginningend of estrus day 3 of estrusUpdated:11/13/07Errors in Fertilization• Polyspermy - polyandry» Multiple sperm penetration» Invertebrates• excess sperm eliminated because sperm centriolecontributes to first embryonic cleavage spindle» Mammals• Sperm centriole not essential so developmentcontinues but fails early to midpregnancy due tomultiploidy• Occurs most often in aged oocytes due to failureof zona block to polyspermyUpdated:11/13/07Errors in Fertilization (cont.)• Polygyny» Multiple maternal pronuclei + 1 paternalpronuclei» Artificially created only• Suppress extrusion of the PBII• Androgenote» Union of 2 paternal pronuclei» Artificially created only• From pronuclear exchangeUpdated:11/13/07Errors in Fertilization (cont.)• Gynogenote» Union of 2 maternal pronuclei» Artificially created• Induced oocyte activation and supression of PBIIextrusion• Parthenogenesis» Activation of the oocyte without a sperm» Embryo is either haploid or gynogenesisoccurs to form diploid• Platties - sperm activates but then gynogenesisoccurs and sperm extruded from embryoUpdated:11/13/07Oocyte Development and FertilizationMPFMPFMPFMPFPrimary OocyteGV-IntactGVBD (8 hr)Metaphase IPB-1Secondary OocyteMetaphase II (21 hr)Ovulation(29 hr)LH Surge (0 hr)2Updated:11/13/07Zona PellucidaPerivitellineSpaceOocyteCa2+Sperm Penetration of theZona PellucidaandFusion with the Oocyte(30 hr)Updated:11/13/07Embryo Development in the Bovine2 cell (62 hr, day 2)4 cell (75 hr, day 3)8 cell (90 hr, day 3)16 cell (120 hr, day 4)32 cellMorula(day 5-6)Zygote(34 hr, day 1)TightMorula(day 6-7)Early Blastocyst(day 7-8)Blastocyst (day 7-9)ExpandedBlastocyst(day 8-10)HatchedBlastocyst(day 9-11)CompactionCompactionBlastocoelBlastocoelInner CellMassInner CellMassTrophectodermTrophectodermUpdated:11/13/07Fertilization to CleavagePolar BodyZona PellucidaPronucleiPerivitelline SpaceZygoteZygoteBlastomereUpdated:11/13/07Fertilization to Cleavage• Imprinting• Maternal Gene Control• Long Cell Cycle• Imprinting• Maternal Gene Control• Long Cell CycleUpdated:11/13/07ImprintingEgg PronucleusEgg PronucleusSperm PronucleusSperm PronucleusUpdated:11/13/07ImprintingEgg PronucleusEgg PronucleusSperm PronucleusSperm PronucleusAndrogenoteAndrogenoteGynogenoteGynogenote3Updated:11/13/07ImprintingControlsEgg PronucleusEgg PronucleusSperm PronucleusSperm PronucleusAndrogenoteAndrogenoteGynogenoteGynogenoteUpdated:11/13/07ImprintingAndrogenote GynogenoteControls• No Inner Cell Mass• Normal Placenta• Fails during embryodevelopment• Normal Fetus• Small Placenta• Fails Midpregnancy• Normal Fetus• Normal Placenta• Normal PregnancyMaternal and Paternal Genomes Are ExpressedDifferently in the Embryo and FetusMaternal and Paternal Genomes Are ExpressedDifferently in the Embryo and FetusUpdated:11/13/07Gene Control of DevelopmentOocyteGrowthLHSurgeFertilization Cleavage• Transciption• Translation• Transcription• Translation• Post-Translation• Translation• Post-Translation• No transcription• Translation• Post-TranslationMaternal Gene ControlMaternal Gene ControlEmbryonicGeneControlEmbryonicGeneControlUpdated:11/13/07Fertilization to CleavageMaternal Gene ControlMaternal Gene ControlUpdated:11/13/07Fertilization to Cleavage• Long Cell Cycle» Penetration to Cleavage• Long Cell Cycle» Penetration to Cleavage32 hour(Bovine)32 hour(Bovine)Updated:11/13/07Precompaction Cleavage• Cell size decreases• Cell cycle• Embryonic gene control• Asynchrony of cell divisions• Movement into Uterus• Early pregnancy factor• Cell size decreases• Cell cycle• Embryonic gene control• Asynchrony of cell divisions• Movement into Uterus• Early pregnancy factor4Updated:11/13/07Precompaction Cleavage• Cell size decreases• Cell cycle• Asynchrony of cell divisions• Embryonic gene control• Movement into Uterus• Early pregnancy factor• Cell size decreases• Cell cycle• Asynchrony of cell divisions• Embryonic gene control• Movement into Uterus• Early pregnancy factorUpdated:11/13/07Precompaction Cleavage• Cell size decreases• Cell cycle• Embryonic gene control• Asynchrony of cell divisions• Movement into Uterus• Early pregnancy factor• Cell size decreases• Cell cycle• Embryonic gene control• Asynchrony of cell divisions• Movement into Uterus• Early pregnancy factor13 hours13 hours15 hours15 hours30 hours30 hours32 hours32 hoursUpdated:11/13/07G1SG2 + MCell Cycle Lengths16 hr8 hr8 hr8 hr2 hr2 hr<1 hr<1 hrTotal = 32 hours Total = 13 hours1st Cell Cycle(zygote 2 cell)2nd Cell Cycle(2 cell 4 cell)Updated:11/13/07Precompaction Cleavage• Cell size decreases• Cell cycle• Embryonic gene control• Asynchrony of cell divisions• Movement into Uterus• Early pregnancy factor• Cell size decreases• Cell cycle• Embryonic gene control• Asynchrony of cell divisions• Movement into Uterus• Early pregnancy factor13 hours13 hours15 hours15 hours30 hours30 hours32 hours32 hoursShort G1 and G2Short G1 and G2Short G1 and G2Short G1 and G2Updated:11/13/07Precompaction Cleavage• Cell size decreases• Cell cycle• Asynchrony of cell divisions• Embryonic gene control• Movement into Uterus• Early pregnancy factor• Cell size decreases• Cell cycle• Asynchrony of cell divisions• Embryonic gene control• Movement into Uterus• Early pregnancy factorFaster dividingblastomeres go to center of embryoFaster dividingblastomeres go to center of embryoUpdated:11/13/07Asynchronous Cleavage - Inside Outside TheoryIf a marked blastomereis placed into the interiorof a 8-cell embryo, it andits progeny become partof the ICM.If a marked blastomere isplaced on the outside ofa 8-cell embryo, it and itsprogeny become part ofthe trophectoderm.TrophectodermTrophectodermInner Cell MassInner Cell Mass5Updated:11/13/07Asynchronous Cleavage Use• Create embryos from different species» Placenta from one species• Host mother» Embryo from some other species• Donor motherUpdated:11/13/07Precompaction Cleavage• Cell size
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