2. What is capacitation?
• It is a process that allows the acrosome
reaction to occur, So the sperm can
penetrate the zona pellucida of the
oocyte.
• The physiological changes that confer on
the sperm the ability to fertilize are
called Capacitation.
3. Introduction
• After leaving the testis, mammalian
spermatozoa are morphologically
differentiated but have acquired neither
progressive motility nor the ability to
fertilize a metaphase II arrested egg.
• During epididymal transit, sperm
acquire the ability to move progressively;
but they are still fertilization
incompetent.
4. Int.Cont.
• Fertilization capacity is gained after
residence in the female tract for a finite
time.
• Capacitation is also correlated with
changes in sperm motility patterns,
designated as sperm hyperactivation.
• Capacitation causes head changes
(acrosome reaction) and tail changes
(motility changes).
5. Capacitation consists of at least two
components:
1- An initial membrane alteration, that allows
spermatozoa to undergo the second phase, which
is the fusion of plasma membrane with outer
acrosomal membrane.
-The first phase is referred to as capacitation.
- The second phase is referred to as acrosome
reaction(AR).
6.
7.
8. Original Models of Capacitation
Epididymal Capacitated
Female
Tract
+
Ejaculated
Seminal
Plasma
+
Decapacitation
Factors
10. What cause sperm capacitation?
• In vivo the oviduct and uterus fluids
capacitate the spermatozoa in different
animals.
• In vitro, both caudal or ejaculated sperm
capacitate when incubate under a variety
of conditions in defined madia.
11. In Vitro Sperm capacitation
The sperm cell is programmed to undergo
capacitation when it is incubated in the
appropriate medium.
1-Role of media constituents.
- Serum albumin.
- Calcium.
- Bicarbonate.
2- Effectors and intracellular messengers.
- Cyclic AMP metabolism.
- Protein tyrosine phosphrylation.
14. Initial Events in Capacitation
• Decapacitation factor removal
– Time dependent
– Induced by binding of a capacitating agent
• Glycosaminoglycans - heparin or heparan sulfate
– Components of extracellular matrix of uterine and
oviduct cells
– Induced by cholesterol removal
• Acceptor is albumin
– Sequence not clear
19. Role of media constituents
-Serum albumin ( usually bovine serum albumin)
BSA.
. BAS during in vitro capacitation remove
cholestrol from sperm plasma membrane.
BSA
A1 BSA-chol.
Sperm
plasma
membrane
Cholestrol efflux
20. Role of media constituents
-Calcium:increase in intracellular Ca during
capacitation.
Capacitate sperm with heparin requires
extracellular calcium.
When medium Ca decline the time required
for capacitation increases.
Sperm
plasma
membrane
Cholesterol efflux
BSA BSA-chol. Ca
Ca
A2
A1
26. ATP ADP
(+(
Decapacitation Factors
( Seminal Plasma) DF
Ca2+
•Ejaculated Sperm
•>> Active Ca2+ ATPase
•Removal DF
>> Decreased Ca2+-ATPase
Low Ca
(-)
Heparin and Cholesterol
Removal
Ca2+ Ca2+
Na+
Ca2+
H+
Increasing Ca
27. Role of media constituents
-Bicarbonate:Transmembrane movement of
HCO3 responsible for increase in intracellular pH
that is observed during capacitation.
SPM Cholesterol efflux
BSA BSA-chol.
A1 Ca
Ca
A2+
HCO3
HCO3
A3
AC
+ +
28. Intracellular second messengers
• Intracellular messenger mediating
capacitation will be considered from two
respective.
- The regulatory system that appear to
be common among different species.
- The regulatory process that may be
unique to one or more species.
29. Intracellular second messenger
cont.
-Cyclic AMP metabolism:The protein kinase A
(PK-A) activity increases during sperm capacitation as a
result of elevation intracellular cAMP.
- The mode of regulation of cAMP metabolism during
sperm capacitation may be integrated with changes in Ca
and HCO3 movement.
31. - Protein tyrosine phosphorylation
• Protein tyrosine phosphorylation mediates a
variety of cellular function .
• The increase in protein tyrosine
phosphorylation is dependent on the presence
of BSA, Ca and NaHCO3 in the medium.
• The role of protein tyrosine phosphorylation in
sperm capacitation is regulated through a PK-
A.
35. - Membrane potential
• Capacitation is accompanied by the
hyperpolarization of the sperm plasma
membrane.
• Membrane hyperpolarization is due to an
enhanced k permeability.
37. -Free radicals
• The free radicals has a role in sperm lipid
peroxidation and sperm viability.
• Superoxide anion cause capacitation and
hyperactivationof the spermatozoa.
• Reactive oxygen regulate protein tyrosine
phosphorelation of several protein.
39. -Heparin
• Bovine in vitro sperm capacitation can be
accomplished in media containing heparin.
• The active capacitating agent in the oviduct fluid
is though to be a heparin-like glycosaminoglycan.
• The glycosaminoglycan may promote capacitation
by binding to and removing seminal plasma
protein.
• Heparin increases cAMP synthesis,elevate pH and
regulate the capacitation-associated changes.
44. -Glucose
• Glucose has inhibitory or stimulatory
actions on capacitation is controversial and
is species dependent.
• In bovine glucose inhibits heparin-induced
capacitation in vitro.
• Capacitation medium for mouse sperm,
which contains glucose has no inhibatory
effects .
45. Cholesterol efflux
BSA
A1 BSA-chol.
+
HCO3
HCO3
A3
Ca
A2
Ca
+ +
AC
cAMP
PDE
+
PK-A
PTK
+
+
-
-
B1
B2
Rec
Ca
cAMP
pH
B3
heparin
KK
hyperpolarization
+
B4
Capacitation
5`AMP
Protein tyrosine phosphrylation
Ptyr-Ptase
O2
NO
B5a
B5b
+
B6
S.P.M.
glucose Gluc.
pyruvate
2ATP
2NADH
2H
-
B7
46. The Acrosome Reaction
Plasma Membrane
Acrosome
Fused Plasma
Membrane and
Outer Acrosomal
Membrane
Nucleus
Acrosin
Hyaluronidase
