Fertilisation Flashcards

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1
Q

How do sperm gain their fertilising capacity? (2)

A
  • Interactions with the female reproductive tract.
  • Sperm Capacitation
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2
Q

Define Sperm Capacitation (4)

A

Further and final maturation process which confers the following functional
characteristics on to sperm and ultimately renders them capable of fertilisation:

  1. A change to a state of hyperactivated motility.
  2. The ability to bind to the oocyte’s zona pellucida and afterwards undergo the acrosome reaction.
  3. The capacity to fuse with the oocyte
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3
Q

Name the 4 female tract Interaction mechanisms (4)

A

Chemotaxis
Thermotaxis
Rheotaxis
Boundary-following navigation

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4
Q

Define Chemotaxis (3)

A

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

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5
Q

Define Thermotaxis (3)

A

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

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6
Q

Define Rheotaxis (3)

A

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

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7
Q

Define Boundary-following navigation (4)

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

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8
Q

The Sperm Capacitation Puzzle

A

image

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9
Q

Sperm-oocyte interaction - 4 steps (6)

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 modulate the spermatozoa to initiate the process of sperm-oocyte interaction and subsequent fertilisation:
    — Penetration of the cumulus oophorus
    — Sperm-zona binding
    — Acrosome reaction
    — Sperm-oocyte fusion and oocyte activation
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10
Q

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) – the major
cementing factor between cells that constitute the cumulus oophorus cell mass.

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11
Q

Sperm-zona binding (3)

A
  • 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 show that human sperm bind to ZP2.
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12
Q

Acrosome Reaction (3)

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.
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13
Q

Sperm-oocyte fusion & oocyte activation (4)

A

Intracellular calcium spike + Cortical reaction =
1)Release from meiotic arrest and completion of meiosis II.
2)Incorporation of sperm DNA and pronuclear formation.
3)Embryo cleavage

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14
Q

How does the sperm trigger oocyte activation? (4)

A

Phospholipase C Zeta (PLC ζ). (PLC ζ + PIP2 = IP3 + DAG)
* Discovered in 2002 by Saunders et al. and widely accepted as the oocyte activation factor introduced by sperm.

  • Acts by activating 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
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15
Q

What 2 things do you look at for fertilisation? (2)

A

Pronuclei
Polar bodies

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16
Q

Fertilisation + Pronuclei (4)

A

PN: 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 fertilisation. Contains a haploid set of chromosomes. 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.

17
Q

Fertlisation + Polar Body (PB): (3)

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 fertilisation.

18
Q

Fertilisation + embro dev (9)

A

1) Fertilised egg ( 2PN)
2) 2 cell
3) 4 cell
4) 8 cell
5)Morula
6) Early blastocyst
7) expanded blastocyst
8) hatching blastocyst
9) Hatched Blastocyst