animal science 434

Animal Science 434Animal Science 434

Lecture 12: SpermatogenesisLecture 12: Spermatogenesis

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

Hormonal Regulation of the Testis

Hormonal Regulation of the Testis

LHLHLHLH LHLH

LHLH

GnRHGnRH

GnRHGnRHGnRHGnRH GnRHGnRH

FSHFSH FSH FSH

Time of Day (24 hr)

Pulses are important !Pulses are important !

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

SpermatogenesisSpermatogenesis

Myoid Cells

Sertoli Cell

Sertoli Cell

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

Spermatogonia(A, intermediate, B) Spermatogonia(A, intermediate, B)

Primary Spermatocyte

Primary Spermatocyte



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

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

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

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 !

Germ Cells / Sertoli CellGerm Cells / Sertoli Cell

Species Primary Round Max. PotentialSpermatocytes Spermatids 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

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


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

FSH

A4A4A3A3

A2A2

InInBB

PP

A1A1

SpermatogonialRenewal in the

Rat and Bull


Rat and Bull

PeriodicEntry of

Cells intoMitosis

PeriodicEntry of

Cells intoMitosis

Stem CellPool

Stem CellPool

FSH

ApAp

AdAd

BB

PP


Primate


PrimateStem CellPool

Stem CellPool

Stem Cell

SpermiogenesisSpermiogenesis

Golgi PhaseGolgi Phase

Development of Acrosome

Migration of Centrioles

Development of Acrosome

Migration of Centrioles

Cap PhaseCap Phase

Acrosome Development Continues

Flagellum Elongates

Acrosome Development Continues

Flagellum Elongates

Acrosomal PhaseAcrosomal Phase

Acrosome

Manchette

Elongation

Acrosome

Manchette

Elongation

Maturation PhaseMaturation Phase

Manchette disapears

Mitochondria migrate

Dense fibers form

Manchette disapears

Mitochondria migrate

Dense fibers form

SpermiationSpermiation

Bull SpermatogenesisBull Spermatogenesis

Stallion SpermatogenesisStallion Spermatogenesis

Bull SpermatogenesisBull Spermatogenesis

StagesStages

• Specific cellular associations within a small segment of a seminiferous tubule

• stages are not the same length in time



StagesStages

Cycles and StagesCycles and Stages

57 days

Stallion

CycleCycle

• progression through sequence of all stages

• progression through sequence of all stages


57 days(12.2 days/cycle) * (4.7 cycles) = 57 days

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


cycle (days) 13.5 10.4 8.3 12.2 16


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

Compartmentalization of Spermatogenesis

and theBlood Testis Barrier

Compartmentalization of Spermatogenesis

and theBlood Testis Barrier

Seminiferous Tubule

and

Interstitial Tissue

Seminiferous Tubule

and

Interstitial Tissue

Interstitial TissueInterstitial Tissue

Vascular System Provides• Nutrients• Oxygen• Growth Factors• Hormones

Vascular System Provides• Nutrients• Oxygen• Growth Factors• Hormones

Blood Vessel

Blood Vessel

Tight Junctions Myoid Cells

Luminal

Adluminal

Basal

CompartmentsCompartments

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

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

Tight Junctions Myoid Cells

Luminal

Adluminal

Basal

CompartmentsCompartments

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



Beef Bull 500 18 8

Ram 550 26 14

Boar 750 30 25

Stallion 165 18 3

Man 40 4 .045 - .2

Duration of SpermatogenesisDuration of Spermatogenesis


cycle (days) 13.5 10.4 8.3 12.2 16



cycle (days) 13.5 10.4 8.3 12.2 16


FSH

ApAp

AdAd

BB

PP


Primate


PrimateStem CellPool

Stem CellPool

Capacity for Sperm ProductionCapacity for Sperm Production



Beef Bull 500 18 8

Ram 550 26 14

Boar 750 30 25

Stallion 165 18 3

Man 40 4 .045 - .2



Beef Bull 500 18 8

Ram 550 26 14

Boar 750 30 25

Stallion 165 18 3

Man 40 4 .045 - .2

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

Apoptosis of Germ CellsApoptosis of Germ Cells

• Season

• Disease

• Trauma or heat

• Hormone levels


• Season

• Disease

• Trauma or heat

• Hormone levels


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

Animation of SpermatogenesisAnimation of Spermatogenesis

Spermatogenesis

animal science 434

Documents

seminiferous tubule

days sperm

small segment

daughter cellsall

pcytoplasmic bridges

spermatozoahormonal

stages57 daysstallioncycles

stages57 days12