1Animal Science 434Lecture 12: SpermatogenesisProduction of Fertile Sperm• hormonal regulation of the testis• mitotic division of spermatogonia• meiotic divisions of spermatocytes• morphologic transformation ofspermatids into spermatozoaHormonal Regulationof the TestisLHLHLHLHGnRHGnRHGnRH GnRHFSHFSHFSHFSHTime of Day (24 hr)Pulses are important !HypothalamusGnRHE2InhibinABPSertoliCellsLeydigCellsSeminiferousTubuleAnt.PituitaryFSH on Sertoli Cells• estradiol• inhibin• ABP• tight junctionsFSHLHNegative Feedback ofEstradiol and InhibinGermCellsTABP+TToEpid.NegativeFeedback ofAndrogensTJ2SpermatogenesisMyoid CellsSertoli CellSertoli CellEvery 13.5 Daysa new group of cellsinitiate the cycle Every 13.5 Days spermare released from thispointSpermatozoaSecondarySpermatocytePrimarySpermatocyteRoundSpermatidSpermatogonia Spermatogonia(A, intermediate, B)Primary SpermatocyteSecondarySpermatocyteRound SpermatidSpermatozoaAAAI IBBP PS SRS RSSP SPSpermato-cytogenesisSpermio-genesisMitosisMeiosisRete TestisSpermiationTypical Sequence of SpermatogenesisAAAI IBBP PS SRS RSSP SP1248163264Potential Sperm ProducedMany Sperm are Produced3Mitotic Divisions• species dependent– between 2 and 6 divisions (4 to 64 potentialdaughter cells produced)• classifications vary among species andinvestigators– A1, A2, A3, A4, B 1, B2, P– Ad, Ap, B, P– As, A0, A1, A2, I, B, P• cytoplasmic bridges form betweendaughter cellsDegenerating Spermatogonia (Apoptosis, as high as 75%)Cytoplasmic Bridges Present Among Daughter CellsAll developsurrounded by 1Sertoli cell !Germ Cells / Sertoli CellSpecies Primary Round Max. PotentialSpermatocytes Spermatids SpermatidsEquine 3.0 ± 0.2 10.9 ± 0.9 64Bovine 1.2 ± 0.1 5.2 ± 0.6 64Human 1.3 ± 0.1 4.2 ± 0.2 16Apoptosis of Germ Cells• Season• Disease• Trauma or heat• Hormone levels• Normal part of spermatogenesisStem Cell Renewal• To keep spermatogenesis goingindefinitely• Replenish testis incase of injury,trauma, or high heatFSHA4A3A2InBPA1SpermatogonialRenewal in theRat and BullPeriodicEntry of Cells intoMitosisStem CellPool4FSHApAdBPSpermatogonialRenewal in thePrimateStem CellPoolStem CellSpermiogenesisGolgi PhaseDevelopment of AcrosomeMigration of CentriolesCap PhaseAcrosome Development ContinuesFlagellum ElongatesAcrosomal PhaseAcrosomeManchetteElongation5Maturation PhaseManchettedisapearsMitochondriamigrateDense fibersformSpermiationSpermiationTemporal Relationships ofSpermatogenesisSpermatogenesis57 daysStallionMultiple Generations of Germ Cells6Bull SpermatogenesisStages• Specific cellular associations withina small segment of a seminiferoustubule• stages are not the same length intimeBull Spermatogenesis - StagesStages• Specific cellular associations withina small segment of a seminiferoustubule• stages are not the same length intimeBull Spermatogenesis - Stages7Cycle• progression through sequence of allstagesBull Spermatogenesis - CyclesCycle• progression through sequence of allstages• 4.5 cycles to form spermatozoa– some species variationDuration of SpermatogenesisBull Ram Boar Stallion Mancycle (days) 13.5 10.4 8.3 12.2 16Spermatogenesis 61 47 39 57 75Coordinationof StagesForm Waves• some portion ofseminiferoustubule is alwaysreleasing spermCompartmentalization ofSpermatogenesisand theBlood Testis Barrier8SeminiferousTubuleandInterstitialTissueInterstitial TissueVascular System Provides• Nutrients• Oxygen• Growth Factors• HormonesBloodVesselBlood VesselTight JunctionsMyoid CellsLuminalAdluminalBasalCompartmentsCycles and StagesCompartmentalization• Basal– mitosis• spermatogonia (A, I, B)• primary spermatocytes• Adluminal– meiosis• primary spermatocytes• secondary spermatocytes• spermatids– spermiogenesis• Lumen– spermiation9Blood Testis Barrier• Sertoli cells and associated tightjunctions• first appears at puberty• induced by FSH• after puberty can be maintained byFSH and/or testosterone• essential for meiosis !!!!!Tight Junction Role in Meiosis• Sertoli cells can manipulateenvironment around 1° spermatocyte– Enters meiosis– Completes meiosis• Destruction of TJ causes impairmentof meiosis– Heat, heavy metals, pesticides, lack ofFSH or TestosteroneCapacity for Sperm ProductionSpecies Testis Sperm/gm DSPWeight (gm) (X 106) (X 109)Dairy Bull 650 18 10Beef Bull 500 18 8Ram 550 26 14Boar 750 30 25Stallion 165 18 3Man 40 4 .045 - .2Duration of SpermatogenesisBull Ram Boar Stallion Mancycle (days) 13.5 10.4 8.3 12.2 16Spermatogenesis 61 47 39 57 75FSHApAdBPSpermatogonialRenewal in thePrimateStem CellPoolCapacity for Sperm ProductionSpecies Testis Sperm/gm DSPWeight (gm) (X 106) (X 109)Dairy Bull 650 18 10Beef Bull 500 18 8Ram 550 26 14Boar 750 30 25Stallion 165 18 3Man 40 4 .045 - .210Variation in Sperm Production• Testis Size• Efficiency of spermatogenesis– mitotic division– degeneration of germ cells• Length of spermatogenesisApoptosis of Germ Cells• Season• Disease• Trauma or heat• Hormone levels• Normal part of spermatogenesisOver Population of SpermatogoniaSGSGSGSGSGSG SG SG SGBasement MembraneSertoliSertoliTight JunctionPSPSSGSG SGBasement MembraneSertoliSertoliAP APAP APNormalApoptosis InhibitedSGSGSGSGSGSG SG SG SGBasement MembraneSertoliSertoliSGSGAnimation of SpermatogenesisView the Animation of SpermatogenesisUsing the Link at the Bottom of the ScreenView the Animation of SpermatogenesisUsing the Link at the Bottom of the ScreenThe objective is to see how the process of spermatogenesistakes place over time and involves both stages and cycles.• In the animation, the timing of events is correct but wehave taken liberties in moving groups of cells from side toside to make room for development of other cells.• The animation begins with primordial germ cell migrationinto the primary sex chord and replication of gonocytes toform stem cell A-Type spermatogonia.The objective is to see how the process of spermatogenesistakes place over time and involves both stages and cycles.• In the animation, the timing of events is correct but wehave taken liberties in moving groups of cells from side toside to make room for development of other cells.• The animation begins with primordial germ cell migrationinto the primary sex chord and replication of gonocytes toform stem cell A-Type
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