Fertilisation, Subfertility, Subfertility Treatment and
Ptrimplantation Development and Diagnosis
Fertilisation:
• Fusion of male and female gametes > zygote
• Fertilisation occurs internally
• Sperm deposited in vagina > goes to
the oviduct by muscular movement
of the vaginal walls (sperm doesn’t
have to swim this bit) > in the
oviduct, capacitation of the sperm
occurs (Changes to sperm surface molecules and increased
motility - only sperm that have gone through these changes
can fertilise the egg) > Sperm then swim down the oviduct
towards the end. Where they have to go is controlled by
thermotaxis (the end of the oviduct is slightly warmer than
the entry side, sperm swim towards the higher temp) and
chemotaxis (Progesterone is released by the Cumulus cells
around the oocyte which attracts the sperm towards a higher
conc of progesterone) > Once the sperm
reaches the egg, it has to get through the
layers surrounding it - Cumulus cells
(Granulosa cells that were released
together with the oocyte) and Zona
Pellucida (Layer of glycoprotein that was
secreted by the granulosa cells and the
oocyte during follicle maturation)
• Cumulus cells are embedded in a matrix of hyaluronic acid,
the sperm cells contain an enzyme in
their membrane called Hyaluronidase
that can break down hyaluronic acid
• It then has to try and get through the
Zona Pellucida
◦ Experiment showing interactions between mouse sperm
and Zona pellucida: In mice, the Zona pellucida is made of 3
, glycoproteins (ZP1, ZP2, ZP3). ZP2 and ZP3 bind to each
other to form long chain proteins and ZP1 binds the chains
together (in humans this is very similar but there is also a
ZP4 protein which also connects the ZP2 and ZP3 chains).
There are also sugars associated
with the proteins. To find out how
the sperm interacted with the
Zona pellucida they did a
competition assay.
◦ They incubated groups of sperms
with different concentrations of ZP1, ZP2 or ZP3 and then
mixed them with eggs that had no cumulus layer (therefore
outer layer ‘ Zona pellucida)
◦ They then counted the number of sperm associated with
each egg
◦ If ZPX proteins bind to the sperm, they will occupy the
binding sites and the sperm will not bind to the Zona
pellucida on the egg.
◦ Higher ZPX protein binding > less egg binding
◦ They discovered: that the sperm binds to the ZP3
component of the Zona pellucida
because the binding of ZP3 interfered
with the Zona pellucida binding (and
it did this is a concentration affected
manner). ZP3 without carbohydrates
does not have the same affect which
shows the carbs are important for the
interaction of the sperm with the ZP3.
◦ Binding of the sperm induces the acrosome reaction:
◦ Sperm head contains an acrosome
membrane > during acrosome
reaction, the sperm cell membrane
and the outer acrosomal membrane
fuse which each other which releases
the acrosomal membrane contents
(including: enzymes that digest the
ZP3 glycoproteins of the Zona pellucida)
Ptrimplantation Development and Diagnosis
Fertilisation:
• Fusion of male and female gametes > zygote
• Fertilisation occurs internally
• Sperm deposited in vagina > goes to
the oviduct by muscular movement
of the vaginal walls (sperm doesn’t
have to swim this bit) > in the
oviduct, capacitation of the sperm
occurs (Changes to sperm surface molecules and increased
motility - only sperm that have gone through these changes
can fertilise the egg) > Sperm then swim down the oviduct
towards the end. Where they have to go is controlled by
thermotaxis (the end of the oviduct is slightly warmer than
the entry side, sperm swim towards the higher temp) and
chemotaxis (Progesterone is released by the Cumulus cells
around the oocyte which attracts the sperm towards a higher
conc of progesterone) > Once the sperm
reaches the egg, it has to get through the
layers surrounding it - Cumulus cells
(Granulosa cells that were released
together with the oocyte) and Zona
Pellucida (Layer of glycoprotein that was
secreted by the granulosa cells and the
oocyte during follicle maturation)
• Cumulus cells are embedded in a matrix of hyaluronic acid,
the sperm cells contain an enzyme in
their membrane called Hyaluronidase
that can break down hyaluronic acid
• It then has to try and get through the
Zona Pellucida
◦ Experiment showing interactions between mouse sperm
and Zona pellucida: In mice, the Zona pellucida is made of 3
, glycoproteins (ZP1, ZP2, ZP3). ZP2 and ZP3 bind to each
other to form long chain proteins and ZP1 binds the chains
together (in humans this is very similar but there is also a
ZP4 protein which also connects the ZP2 and ZP3 chains).
There are also sugars associated
with the proteins. To find out how
the sperm interacted with the
Zona pellucida they did a
competition assay.
◦ They incubated groups of sperms
with different concentrations of ZP1, ZP2 or ZP3 and then
mixed them with eggs that had no cumulus layer (therefore
outer layer ‘ Zona pellucida)
◦ They then counted the number of sperm associated with
each egg
◦ If ZPX proteins bind to the sperm, they will occupy the
binding sites and the sperm will not bind to the Zona
pellucida on the egg.
◦ Higher ZPX protein binding > less egg binding
◦ They discovered: that the sperm binds to the ZP3
component of the Zona pellucida
because the binding of ZP3 interfered
with the Zona pellucida binding (and
it did this is a concentration affected
manner). ZP3 without carbohydrates
does not have the same affect which
shows the carbs are important for the
interaction of the sperm with the ZP3.
◦ Binding of the sperm induces the acrosome reaction:
◦ Sperm head contains an acrosome
membrane > during acrosome
reaction, the sperm cell membrane
and the outer acrosomal membrane
fuse which each other which releases
the acrosomal membrane contents
(including: enzymes that digest the
ZP3 glycoproteins of the Zona pellucida)
