fertilisation Flashcards

1
Q

How do sperms gain their fertilising capacity?

A
  1. sperm capacitation
  2. interaction with the female reproductive tract
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Sperm capacitation

A
  • further and final maturation process in which sperms: happens in the female tract as the sperm get in.
    1. change to a state of hyperactivated
    motility.
    2. gain ability to bind to the oocyte’s zona pellucida and afterwards undergo the acrosome reaction.
    3. gain the capacity to fuse with the oocyte.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

female tract interaction mechanisms of sperm

A

-Chemotaxis
-Thermotaxis
-Rheotaxis
-Boundary-following navigation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Chemotaxis

A

— Chemical guiding mechanism.
— Sperm responding to a gradient of chemoattractant e.g. steroid hormones.
— Molecular and behavioural mechanisms yet to be fully understood.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Thermotaxis

A

— Temperature guiding mechanism.
— Female tract consists of different areas with marginal differences in temperature.
— Sperm responding to changes in the extracellular temperature gradient.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Rheotaxis

A

— Ability to respond to fluid currents in the female tract environment.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Boundry- following navigation

A

— Ability to turn corners in response to surface boundaries
— Human sperm with preference to follow boundaries on the left or right hand side have
been shown to possess higher DNA integrity than straight swimming sperm (Huang et

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What modulates the female tract interaction of sperms?

A

CatSper channels

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What are CatSper?

A
  • cation channel in sperms
  • located in the flagella region
  • responsible for calcium influx (calcium influx happens faster rate at body temp than room temp)
  • responds to diverse stumuli : Em, pH, progesterone, prostaglandins, small organic molecules
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the main change that occurs in sperm capacitation?

A

loss of cholesterol from cell membrane of sperm cells
=> Labs culture:
if you supplement culture media with substances that can take cholesterol away you see sperms switch to hyperactivity, which is a obvious sign they are undergoing cell capacitation.
- so female tract has cholesterol acceptors that takes away cholesterol from the sperm
- cholesterol leaving alters PL ratio in the cell membrane and also as a result affects the availability of soluble proteins in the membrane like soluble adenine cyclase become more available due to cholesterol loss further facilitating fertilisation.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What happens when progesterone(P4) binds to its receptors on cell membrane?

A

-P4 binds to ABHD2 receptor and stimulates CatSPer channels
-influx of Calcium allows for motility of sperm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What happens after capacitation?

A
  • Once a few capacitated sperm make it to the site of fertilisation, they come in contact with the cumulus-oocyte complex (COC) and a much higher concentration of follicular fluid (FF).
  • FF in addition to secretions from the COC e.g. progesterone further modulates
    the spermatozoa to initiate the process of sperm-oocyte interaction and subsequent fertilization.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are the events in Sperm- oocyte interaction?

A

Penetration of the cumulus oophorus
Sperm-zona binding
Acrosome reaction
Sperm-oocyte fusion and oocyte activation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q
  1. Penetration of the cumulus-oophorus
A

Once sperm come in contact with the
cumulus-oophorus cell mass surrounding the
oocyte, the enzyme hyaluronidase present on
the surface of the sperm head dissolves
hyaluronic acid (hyaluronan).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q
  1. Sperm-zona binding
A

ZP are located between the theca and granulosa in the oocyte , once the sperm penetrates through the cumulus it enters the oocyte :

  • Four zona pellucida (ZP) glycoproteins
    expressed – ZP1, ZP2, ZP3, ZP4.
  • Studies across mammalian species have
    shown that sperm bind to ZP2 and ZP3
    via receptors present on the sperm’s
    plasma membrane.
  • Recent studies by Yauger et al. (2011)
    and Baibakov et al. (2012) show that
    human sperm bind to ZP2.
    => transgenic mice used
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q
  1. Acrosome Reaction
A
  • Triggered in response to sperm-oocyte
    interaction
  • Fusion of the sperm’s plasma membrane
    with it’s outer acrosomal membrane.
  • Results in the release of hydrolytic and
    proteolytic enzymes e.g. hyaluronidase
    and acrosin.
    => the sperms that survive and make it through to the oocyte are the ones that undergo acrosome reaction, but some do undergo acrosomal reaction randomly, but the ones that succeed are the ones that are in the right place at the right time.
17
Q
  1. gain capacity to fuse with Oocyte : Sperm-oocyte fusion & oocyte activation
A
  • Juno-Izumo binding.
  • Intracellular calcium spike
  • Cortical reaction
  • Release from meiotic arrest and completion of meiosis II.
  • Incorporation of sperm DNA and pronuclear formation.
  • Embryo cleavage
18
Q

What is Juno?

A
  • juno is the egg Izumo receptor and is essential for mammanlian fertilisatuon
19
Q
  1. gain capacity to fuse with Oocyte : activation
A
  • Phospholipase C Zeta (PLC ζ) sperm introduces this and widely accepted as the oocyte activation factor introduced by sperm.
  • phospholipase C zeta activates inositol trisphosphate (IP3) production, leading to repetitive calcium release (oscillations) from the oocyte’s calcium stores.
  • Has been identified in all species studied so far, including human
20
Q

when looking at fertilisation the two key morphological features are :

A

presence of pronuclei = 2 pronuclei
presence of polar body = 2 polar body showing meiosis 2 is complete
identification of these two factors helps identify if fertilisation took place correctly
if there are <2 or >2 pronuclei of polar bodies something went wrong

21
Q

pro-nuclei

A

2PN - normal fertilisation.
Normally fertilised oocytes should contain two juxtaposed and centrally located PN, with distinctly clear membranes and nucleolar precursor bodies
(NPBs).

0PN - No fertilisation.

1PN - Abnormal fertilization. Contains a haploid
set of chromosomes, from only one parent.
There are cases where a 1PN zygote contains a diploid set of chromosomes, resulting from errors in the
synchrony of PN formation/fusion. Zygotes
in this category often have 2 polar bodies.

≥3PN -Abnormal fertilisation. Contains additional set(s) of chromosomes, which could be either digynic or diandric. Significantly linked
to the formation of aneuploid embryos.

22
Q

polar bodies

A

0PB- Oocyte at the Metaphase I
stage of meiosis.

1PB- Mature oocyte at the Metaphase II stage of meiosis with one polar body extruded.
No fertilisation.

2PB- Oocyte has completed second meiotic division and extruded second polar body in response
to fertilization.

23
Q

fertilisation and embryo development

A
  1. 8 cell
  2. morula = cells tightly packed, smaller gap junction , the precursor of early blastocyst formation
  3. early blastocysts
  4. expanded blastocysts
  5. hatching blastocysts
  6. hatched blastocysts

=> when blastocysts impants in the uterus depends on rate of development