Animal Science 434
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Transcript of Animal Science 434
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Animal Science 434Animal Science 434
SpermatogenesisSpermatogenesis
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Production of Fertile SpermProduction of Fertile Sperm
• hormonal regulation of the testis
• mitotic division of spermatogonia
• meiotic divisions of spermatocytes
• morphologic transformation of spermatids into spermatozoa
• hormonal regulation of the testis
• mitotic division of spermatogonia
• meiotic divisions of spermatocytes
• morphologic transformation of spermatids into spermatozoa
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Hormonal Regulation of the Testis
Hormonal Regulation of the Testis
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LHLHLHLH LHLH
LHLH
GnRHGnRH
GnRHGnRHGnRHGnRH GnRHGnRH
FSHFSH FSH FSH
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Time of Day (24 hr)
Pulses are important !Pulses are important !
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Hypothalamus
GnRHGnRH
E2E2
InhibinInhibin
ABPABP
SertoliCells
SertoliCells
LeydigCells
LeydigCells
SeminiferousTubule
SeminiferousTubule
Ant.Pituitary
FSH on Sertoli Cells• estradiol• inhibin• ABP• tight junctions
FSH on Sertoli Cells• estradiol• inhibin• ABP• tight junctions
FSHFSHLHLH
Negative Feedback ofEstradiol and Inhibin
GermCellsGermCells
TT
ABP+T
ABP+T
ToEpid.Negative
Feedback of Androgens
Negative Feedback of Androgens
TJTJ
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SpermatogenesisSpermatogenesis
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Myoid Cells
Sertoli Cell
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Sertoli CellSertoli Cell
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Every 13.5 Daysa new group of cellsinitiate the cycle
Every 13.5 Days sperm are released from this
point
Spermatozoa
SecondarySpermatocyte
PrimarySpermatocyte
RoundSpermatid
Spermatogonia
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Spermatogonia(A, intermediate, B) Spermatogonia(A, intermediate, B)
Primary Spermatocyte
Primary Spermatocyte
SecondarySpermatocyte
SecondarySpermatocyte
Round SpermatidRound Spermatid
SpermatozoaSpermatozoa
A
A A
I I
BB
P P
S S
RS RS
SP SP
Spermato-cytogenesisSpermato-cytogenesis
Spermio-genesisSpermio-genesis
MitosisMitosis
MeiosisMeiosis
Rete TestisRete Testis
SpermiationSpermiation
Typical Sequence of SpermatogenesisTypical Sequence of Spermatogenesis
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AA
AA AA
II II
BBBB
PP PP
SS SS
RSRS RSRS
SPSP SPSP
11
22
44
88
1616
3232
6464
Potential Sperm ProducedPotential Sperm Produced
Many Sperm are Produced Many Sperm are Produced
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Mitotic DivisionsMitotic Divisions• species dependent– between 2 and 6 divisions (4 to 64 potential
daughter cells produced)
• classifications vary among species and investigators– A1, A2, A3, A4, B 1, B2, P– Ad, Ap, B, P– As, A0, A1, A2, I, B, P
• cytoplasmic bridges form between daughter cells
• species dependent– between 2 and 6 divisions (4 to 64 potential
daughter cells produced)
• classifications vary among species and investigators– A1, A2, A3, A4, B 1, B2, P– Ad, Ap, B, P– As, A0, A1, A2, I, B, P
• cytoplasmic bridges form between daughter cells
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Degenerating Spermatogonia (Apoptosis, as high as 75%)Degenerating Spermatogonia (Apoptosis, as high as 75%)
Cytoplasmic Bridges Present Among Daughter CellsCytoplasmic Bridges Present Among Daughter Cells
All develop surrounded by 1
Sertoli cell !
All develop surrounded by 1
Sertoli cell !
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Germ Cells / Sertoli CellGerm Cells / Sertoli Cell
Species Primary Round Max. PotentialSpermatocytesSpermatids Spermatids
Equine 3.0 ± 0.2 10.9 ± 0.9 64
Bovine 1.2 ± 0.1 5.2 ± 0.6 64
Human 1.3 ± 0.1 4.2 ± 0.2 16
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Apoptosis of Germ CellsApoptosis of Germ Cells
• Season
• Disease
• Trauma or heat
• Hormone levels
• Normal part of spermatogenesis
• Season
• Disease
• Trauma or heat
• Hormone levels
• Normal part of spermatogenesis
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Stem Cell RenewalStem Cell Renewal
• To keep spermatogenesis going indefinitely
• Replenish testis incase of injury, trauma, or high heat
• To keep spermatogenesis going indefinitely
• Replenish testis incase of injury, trauma, or high heat
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FSH
A4A4A3A3
A2A2
InInBB
PP
A1A1
SpermatogonialRenewal in the
Rat and Bull
SpermatogonialRenewal in the
Rat and Bull
PeriodicEntry of
Cells intoMitosis
PeriodicEntry of
Cells intoMitosis
Stem CellPool
Stem CellPool
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FSH
ApAp
AdAd
BB
PP
SpermatogonialRenewal in the
Primate
SpermatogonialRenewal in the
PrimateStem CellPool
Stem CellPool
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Stem Cell
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SpermiogenesisSpermiogenesis
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Golgi PhaseGolgi Phase
Development of Acrosome
Migration of Centrioles
Development of Acrosome
Migration of Centrioles
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Cap PhaseCap Phase
Acrosome Development Continues
Flagellum Elongates
Acrosome Development Continues
Flagellum Elongates
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Acrosomal PhaseAcrosomal Phase
Acrosome
Manchette
Elongation
Acrosome
Manchette
Elongation
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ManchetteManchette
• A series of microtubules
• Associated with nuclear elongation
• A series of microtubules
• Associated with nuclear elongation
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Maturation PhaseMaturation Phase
Manchette disapears
Mitochondria migrate
Dense fibers form
Manchette disapears
Mitochondria migrate
Dense fibers form
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SpermiationSpermiation
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SpermiationSpermiationCytoplasmic
Droplet
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Temporal Relationships of Spermatogenesis
Temporal Relationships of Spermatogenesis
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SpermatogenesisSpermatogenesis
57 days
Stallion
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Multiple Generations of Germ CellsMultiple Generations of Germ Cells
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Bull SpermatogenesisBull Spermatogenesis
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StagesStages
• Specific cellular associations within a small segment of a seminiferous tubule
• stages are not the same length in time
• Specific cellular associations within a small segment of a seminiferous tubule
• stages are not the same length in time
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Bull Spermatogenesis - StagesBull Spermatogenesis - Stages
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StagesStages
• Specific cellular associations within a small segment of a seminiferous tubule
• stages are not the same length in time
• Specific cellular associations within a small segment of a seminiferous tubule
• stages are not the same length in time
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Bull SpermatogenesisBull Spermatogenesis
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CycleCycle
• progression through sequence of all stages
• progression through sequence of all stages
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Bull Spermatogenesis - CyclesBull Spermatogenesis - Cycles
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CycleCycle
• progression through sequence of all stages
• 4.5 cycles to form spermatozoa– some species variation
• progression through sequence of all stages
• 4.5 cycles to form spermatozoa– some species variation
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Duration of SpermatogenesisDuration of Spermatogenesis
Bull Ram Boar Stallion Man
cycle (days) 13.5 10.4 8.3 12.2 16
Spermatogenesis 61 47 39 57 75
Bull Ram Boar Stallion Man
cycle (days) 13.5 10.4 8.3 12.2 16
Spermatogenesis 61 47 39 57 75
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Coordination of Stages
Form Waves
Coordination of Stages
Form Waves
• some portion of seminiferous tubule is always releasing sperm
• some portion of seminiferous tubule is always releasing sperm
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Compartmentalization of Spermatogenesis
and theBlood Testis Barrier
Compartmentalization of Spermatogenesis
and theBlood Testis Barrier
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Seminiferous Tubule
and
Interstitial Tissue
Seminiferous Tubule
and
Interstitial Tissue
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Interstitial TissueInterstitial Tissue
Vascular System Provides• Nutrients• Oxygen• Growth Factors• Hormones
Vascular System Provides• Nutrients• Oxygen• Growth Factors• Hormones
Blood Vessel
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Blood Vessel
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Tight Junctions Myoid Cells
Luminal
Adluminal
Basal
CompartmentsCompartments
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Cycles and StagesCycles and Stages
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CompartmentalizationCompartmentalization• Basal
– mitosis• spermatogonia (A, I, B)• primary spermatocytes
• Adluminal– meiosis
• primary spermatocytes• secondary spermatocytes• spermatids
– spermiogenesis
• Lumen– spermiation
• Basal– mitosis
• spermatogonia (A, I, B)• primary spermatocytes
• Adluminal– meiosis
• primary spermatocytes• secondary spermatocytes• spermatids
– spermiogenesis
• Lumen– spermiation
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Blood Testis BarrierBlood Testis Barrier
• Sertoli cells and associated tight junctions
• first appears at puberty
• induced by FSH
• after puberty can be maintained by FSH and/or testosterone
• essential for meiosis
• Sertoli cells and associated tight junctions
• first appears at puberty
• induced by FSH
• after puberty can be maintained by FSH and/or testosterone
• essential for meiosis !!!!!!!!!!
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Tight Junction Role in MeiosisTight Junction Role in Meiosis
• Sertoli cells can manipulate environment around 1° spermatocyte– Enters meiosis– Completes meiosis
• Destruction of TJ causes impairment of meiosis– Heat, heavy metals, endocrine
disruptors, pesticides, lack of FSH or Testosterone
• Sertoli cells can manipulate environment around 1° spermatocyte– Enters meiosis– Completes meiosis
• Destruction of TJ causes impairment of meiosis– Heat, heavy metals, endocrine
disruptors, pesticides, lack of FSH or Testosterone
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Capacity for Sperm ProductionCapacity for Sperm Production
Species Testis Sperm/gm DSPWeight (gm) (X 106) (X 109)
Dairy Bull 650 18 10
Beef Bull 500 18 8
Ram 550 26 14
Boar 750 30 25
Stallion 165 18 3
Man 40 4 .045 - .2
Species Testis Sperm/gm DSPWeight (gm) (X 106) (X 109)
Dairy Bull 650 18 10
Beef Bull 500 18 8
Ram 550 26 14
Boar 750 30 25
Stallion 165 18 3
Man 40 4 .045 - .2
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Duration of SpermatogenesisDuration of Spermatogenesis
Bull Ram Boar Stallion Man
cycle (days) 13.5 10.4 8.3 12.2 16
Spermatogenesis 61 47 39 57 75
Bull Ram Boar Stallion Man
cycle (days) 13.5 10.4 8.3 12.2 16
Spermatogenesis 61 47 39 57 75
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FSH
ApAp
AdAd
BB
PP
SpermatogonialRenewal in the
Primate
SpermatogonialRenewal in the
PrimateStem CellPool
Stem CellPool
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Capacity for Sperm ProductionCapacity for Sperm Production
Species Testis Sperm/gm DSPWeight (gm) (X 106) (X 109)
Dairy Bull 650 18 10
Beef Bull 500 18 8
Ram 550 26 14
Boar 750 30 25
Stallion 165 18 3
Man 40 4 .045 - .2
Species Testis Sperm/gm DSPWeight (gm) (X 106) (X 109)
Dairy Bull 650 18 10
Beef Bull 500 18 8
Ram 550 26 14
Boar 750 30 25
Stallion 165 18 3
Man 40 4 .045 - .2
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Variation in Sperm ProductionVariation in Sperm Production
• Testis Size
• Efficiency of spermatogenesis–mitotic division– degeneration of germ cells
• Length of spermatogenesis
• Testis Size
• Efficiency of spermatogenesis–mitotic division– degeneration of germ cells
• Length of spermatogenesis
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Apoptosis of Germ CellsApoptosis of Germ Cells
• Season
• Disease
• Trauma or heat
• Hormone levels
• Normal part of spermatogenesis
• Season
• Disease
• Trauma or heat
• Hormone levels
• Normal part of spermatogenesis
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Over Population of SpermatogoniaOver Population of Spermatogonia
SGSGSGSG
SGSG SG SG SG
Basement Membrane
Sertoli Sertoli
Tight JunctionTight Junction
PS
PS
SGSG SG
Basement Membrane
SertoliSertoli
AP AP
AP AP
Normal Apoptosis Inhibited
SGSGSGSG
SGSG SG SG SG
Basement Membrane
Sertoli SertoliSG
SG