Animal Science 434

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Animal Science 434

• Lecture 12 Spermatogenesis

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Production of Fertile Sperm

• 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
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FSH
FSH
FSH
FSH
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Time of Day (24 hr)
Pulses are important !
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• FSH on Sertoli Cells
• estradiol
• inhibin
• ABP
• tight junctions

Hypothalamus
GnRH
Ant. Pituitary
Leydig Cells
Sertoli Cells
Germ Cells
Seminiferous Tubule
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Spermatogenesis
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Sertoli Cell
Myoid Cells
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Sertoli Cell
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Every 13.5 Days sperm are released from this point
Spermatozoa
Round Spermatid
Secondary Spermatocyte
Primary Spermatocyte
Every 13.5 Days a new group of cells initiate the
cycle
Spermatogonia
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Typical Sequence of Spermatogenesis
A
Spermatogonia (A, intermediate, B)
A
A
Spermato-cytogenesis
I
I
B
B
Primary Spermatocyte
Mitosis
P
P
Meiosis
S
S
SecondarySpermatocyte
RS
RS
Round Spermatid
Spermio-genesis
Spermatozoa
SP
SP
Spermiation
Rete Testis
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Many Sperm are Produced
Potential Sperm Produced
1
A
2
A
A
4
I
I
8
B
B
16
P
P
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S
S
64
RS
RS
SP
SP
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Mitotic 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

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Cytoplasmic Bridges Present Among Daughter Cells
All develop surrounded by 1 Sertoli cell !
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Germ Cells / Sertoli Cell
Species Primary Round Max. Potential Spermatocyte
s 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
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Apoptosis of Germ Cells

• Season
• Disease
• Trauma or heat
• Hormone levels
• Normal part of spermatogenesis

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Stem Cell Renewal

• To keep spermatogenesis going indefinitely
• Replenish testis incase of injury, trauma, or
  high heat

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Periodic Entry of Cells into Mitosis
A2
Spermatogonial Renewal in the Rat and Bull
A1
Stem Cell Pool
A3
A4
In
B
P
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Ap
Spermatogonial Renewal in the Primate
Ad
Stem Cell Pool
B
P
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Stem Cell
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Spermiogenesis
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Golgi Phase
Development of Acrosome Migration of Centrioles
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Cap Phase
Acrosome Development Continues Flagellum Elongates
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Acrosomal Phase
Acrosome Manchette Elongation
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Maturation Phase
Manchette disapears Mitochondria migrate Dense
fibers form
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Spermiation
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Spermiation
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Temporal Relationships of Spermatogenesis
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Spermatogenesis
57 days
Stallion
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Multiple Generations of Germ Cells
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Bull Spermatogenesis
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(No Transcript)
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Stages

• 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 - Stages
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Stages

• 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 - Stages
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Cycle

• progression through sequence of all stages

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Bull Spermatogenesis - Cycles
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Cycle

• progression through sequence of all stages
• 4.5 cycles to form spermatozoa
• some species variation

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Duration of Spermatogenesis
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Coordination of Stages Form Waves

• some portion of seminiferous tubule is always
  releasing sperm

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Compartmentalization of Spermatogenesisand
theBlood Testis Barrier
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Seminiferous Tubule andInterstitial Tissue
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Interstitial Tissue

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

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Blood Vessel
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Compartments
Luminal
Adluminal
Basal
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Cycles and Stages
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Compartmentalization

• Basal
• mitosis
• spermatogonia (A, I, B)
• primary spermatocytes
• Adluminal
• meiosis
• primary spermatocytes
• secondary spermatocytes
• spermatids
• spermiogenesis
• Lumen
• spermiation

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Blood 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

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Tight 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, pesticides, lack of FSH or
  Testosterone

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Capacity for Sperm Production
Species Testis Sperm/gm DSP Weight (gm) (X
106) (X 109) Dairy Bull 650 18 10 Beef
Bull 500 18 8 Ram 550 26 14 Boar 750 30 25 Stallio
n 165 18 3 Man 40 4 .045 - .2
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Duration of Spermatogenesis
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Ap
Spermatogonial Renewal in the Primate
Ad
Stem Cell Pool
B
P
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Capacity for Sperm Production
Species Testis Sperm/gm DSP Weight (gm) (X
106) (X 109) Dairy Bull 650 18 10 Beef
Bull 500 18 8 Ram 550 26 14 Boar 750 30 25 Stallio
n 165 18 3 Man 40 4 .045 - .2
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Variation in Sperm Production

• Testis Size
• Efficiency of spermatogenesis
• mitotic division
• degeneration of germ cells
• Length of spermatogenesis

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Apoptosis of Germ Cells

• Season
• Disease
• Trauma or heat
• Hormone levels
• Normal part of spermatogenesis

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Over Population of Spermatogonia
Tight Junction
Sertoli
Sertoli
SG
SG
SG
SG
SG
SG
SG
SG
SG
Basement Membrane
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Animation of Spermatogenesis
View the Animation of SpermatogenesisUsing the
Link at the Bottom of the Screen

• The objective is to see how the process of
  spermatogenesis takes place over time and
  involves both stages and cycles.
• In the animation, the timing of events is correct
  but we have taken liberties in moving groups of
  cells from side to side to make room for
  development of other cells.
• The animation begins with primordial germ cell
  migration into the primary sex chord and
  replication of gonocytes to form stem cell A-Type
  spermatogonia.