Developmental Zoology
(ZOO 228.1.0)
Gametogenesis
1
What is Gametogenesis?
Production of Male and Female
gametes
2
What is Spermatogenesis?
•  Spermatogenesis is the process of germ
cells proliferation and differentiation within
the seminiferous tubules of the testes
leading to haploid, free swimming
spermatozoa
•  Spermatogonial stem cells (present in the
seminiferous tubules) form the basis of
spermatogenesis.
3
Fate of Spermatogonial Stem
Cells
Type A spermatogonia
Renewal
Differentiation
Apoptosis
4
Spermatogenesis
• Testes are comprised
of highly coiled tubes
surrounded by layers of
connective tissue
(tunica albugineo)
• Takes place in the
seminiferous tubules;
limited by a B.M.
• Other function of testes
are to secrete
androgens
5
Testes
•  Spermatogenesis takes
place in Seminiferous
tubules. These contain
2 types of cells
•  Spermatogenic cells
•  Spermatogonia,
spermatocyte,
spermatid
T.S. of a seminiferous
tubule
6
Seminiferous tubules
•  Contain
sustentacular/ Sertoli
cells
•  Sustain and
promote
development of
sperm
•  Interstitial cells of
Leydig
•  Exist outside
seminiferous
tubules. Secrete
testosterone
T.S. of a seminiferous
tubule
7
Mammalian spermatogenesis
Spermatogenesis
has 3 phases
• Mitotic
proliferation
• Meiotic divisions
• Remodeling
8
Mammalian spermatogenesis
9
spermatog
onium
(diploid)
part of the lumen of
a seminiferous
tubule
MITOSIS
MEIOSIS I
MEIOSIS II
Sertoli cell
secondary spermatocyte
primary
spermatocyte
IIry s cyte
early
spermatids
early
spermatids
late
spermatid
immature sperm
(haploid)
late
spermatids
mature sperm
(haploid)
10
Mammalian spermatogenesis
•  Two equal cytoplasmic meiotic divisions
•  Produces 4 equal sized gametes
•  Usually spermatozoa are motile
11
Mammalian spermatogenesis
• Duration of cytodifferentiation: 64 days
•  Spermatogenic cycle = period of initiation of
successive cycles: 16 days à displacement of
more advanced cells à 4 stages across the
g e r m i n a l e p i t h e l i u m . T h e s e s t a g e s a re
synchronized in wedges of the seminiferous
epithelium.
12
Mammalian spermatogenesis
Spermatogenic wave: phase-shifts between
adjacent segments along the length of the
seminiferous tubules to prevent fluctuations in
fertility; in men, such phase-shifts are also
present along the circumference of the
tubules.
rat
Hamster
54 days
35 days
13
Spermiogenesis
Spermatid
1. 
2. 
3. 
à
Spermatozoa
Nuclear changes: DNA
Nuclear changes: Morphology
Cellular changes: organelles
• 
• 
• 
• 
• 
Acrosome
Middle section
Axoneme formation
Cell surface
Cytoplasm reduction
14
Spermiogenesis
• Spermatozoa
then release into
the lumen by
•  Contraction
of contractile
muscles
• Infertile
• Then enters to
the epididymis
15
Epididedymes
•  Once mature, sperm released into lumen of
seminiferous tubules & carried to epididymis
where they mature fully & gain sustained
motility.
•  Free thiols oxidized into disulfide bonds to
give rigidity
•  Acquires protein binding receptor molecules
•  Monitors and adjusts fluid in seminiferous
tubules
•  Changes in the ion levels
16
Epididedymes
• Facilitates functional maturation of
spermatozoa
• Membrane changes to bind & fuse with
oolema
• Stores and protects sperm (glutathione)
• If not ejaculated, degenerates in about a
month and are absorbed by stereocilia
• Sperm stored in epididymis for 1 - 21 days.
17
Hormonal control of spermatogenesis
Sertoli
cells
5
T
∞
Redu ctase
Release ABP
Di hydro
T
18
Hormonal control of
spermatogenesis
• 
Hypothalamic production of GnRH and pituitary
production of LH are inhibited by high levels of
circulating testosterone.
• Inhibin, produced by Sertoli cells, inhibits GnRH and
FSH production
• In addition to ABP, Sertoli cells also produce; estrogen
19
Summary of spermatogenesis
• Two equal cytoplasmic meiotic divisions
• Produces 4 equal sized gametes
• Usually spermatozoa are motile
20
Mammalian Sperm
21
Mammalian Sperm
22