Fertilisation Flashcards
(38 cards)
How long can the sperm survive for in the female apparatus?
Sperm cells can survive in the female apparatus for up to 5 days.
How long does the egg last once ovulated?
When the oocyte is ovulated, if it’s not fertilised in 24 hours, it will no longer be fertilized.
Why is the age of the mother an important factor in fertilisation?
This is because after the age of 31, the fecundity rate decreases dramatically. When at age 42, there is a less than 0.2% chance of pregnancy. This is related to the fact that there is a limited set of oocytes.
What route does the sperm take to be ejaculated?
The sperm cells are produced at the level of the testes, released from the seminiferous tubules and move along the epididymis to reach the urethra to be ejaculated.
What is capacitation?
The sperm’s capability to fertilisation.
Why do sperm cells need to acquire capacitation?
Capacitation gives sperm cells hyperactivation.
What happens in the fast event for capacitation?
An influx of bicarbonate ions in the cytoplasm, which increases the pH.
Altogether this activates an adenylate cyclase which then increases the levels of cyclic AMP, a secondary messenger that activates protein kinase activities, leading to activation of sperm motility.
What happens in the slow event for capacitation?
A loss of cholesterol from the PM of sperm cells. BSA is added in vitro to capacitate sperm. This is because BSA is an acceptor of cholesterol, so can release from the PM, thus allowing hyperactivation of the spermatozoa.
Why is hyperactivity important?
Hyperactivity is important as sperm cells need to travel a very long path once released in the vagina.
Described the speculated ability of sperms for chemotaxis.
It was discovered that sperm cells present a olfactory receptor (hOR17-4), which is able to recognize the scent of bourgeonal.
This proves that sperm cells may have receptors that respond to specific molecules released by the oocyte, but this has not yet been proven in humans.
Described the speculated ability of sperms for thermotaxis.
Sperm cells may be able to sense temperature differences, preferring the higher one as the temperature is 2 degrees higher in the ampolla than the isthmus.
Described the speculated ability of sperms for rheotaxis.
Sperm cells have the ability to align against a flow and swim upstream.
How do sperm cells cross the cumulus oophorus?
The cells are maintained around the oocyte due to the deposition of a muculastic extracellular matrix particularly rich in hyaluronic acid.
This is a glycosaminoglycan able to make a mucus like extracellular matrix together with several proteins.
Sperm cells possess hyaluronidase activity. These activities contain several lytic enzymes, e.g. acrosin.
What is the zona pellucida made up of?
This is an envelope of glycoproteins. There are 4 in humans, ZP1, ZP2, ZP3 and ZP4.
How does sperm cross the zonal pellucida?
Only sperm cells of the same species are able to recognise and bind to particular sugar molecules present on the ZP proteins.
When the sperm cell binds to ZP3, there are several responses on the sperm cells which increases cAMP and activation of protein kinases as well as influx of Ca2+ resulting in a fusion of acrosomal membrane with the PM of the sperm cell.
This ends up in complete release of the contents of the acrosome in the environment. The sperm cell can penetrate the zona pellucida only after the acrosomal reaction has occurred.
What does the acrosomal reaction result in?
Results in a fusion between the outer membrane of the acrosome and the sperm PM. At the end of the process the original inner membrane of the acrosome will become the membrane of the sperm.
Which glycoprotein is considered the primary binding between the sperm and the oocyte?
ZP3 considered to be involved in primary sperm binding.
What is ZP2 thought to be involved in?
Once the sperm cell is bound to and goes across the zona pellucida, ZP2 is modified to prevent other sperm cells from binding.
Describe the evidence that the sperm may complete the acrosomal reaction before reaching pellucida.
Some studies demonstrate that there is an interaction between the cumulus and sperm cells, where the sperm cells release specific proteins to stimulate cumulus cells to release progesterone.
This may induce the acrosomal reaction. This might be needed to release the acrosomal hyaluronidases to help digest the hyaluronic acid of the extracellular matrix.
What is fertilin?
Fertilin (PH-30) belongs to the family of the ADAM proteins and can bind to integrins. They are present on the head of the sperm cells and can bind to a specific integrin expressed on the egg membrane.
Is fertilin indisposable to fertilisation?
Knockout studies (in mice) where expression of fertilin was completely abolished shows that the mice were still fertile.
Therefore fertilin is important to fertilisation, but not absolutely indispensable.
Where is IZUMO1 located?
IZUMO1 has been shown to locate on the inner side of the acrosome. Though after the sperm has undergone acrosomal reaction, there is a broader distribution of IZUMO on the head of the sperm cell, especially on the equatorial side.
Is the protein CD9 a confirmed partner of IZUMO?
Initially, the protein CD9 was identified as a partner to IZUMO. However if this expression is eliminated, the sperm cells can still bind but don’t fuse.
This shows that there may be another protein that interacts with IZUMO, but CD9 is still important for cell fusion.
How was JUNO discovered?
JUNO was originally identified when performing a screening of oocyte cDNA, identifying this as a folate receptor in the process.
