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BB20149 > Fertilisation 1 > Flashcards

Fertilisation 1 Flashcards

1
Q

What is fertilisation?

A

The union of male and female gametes to produce an embryo.

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2
Q

What are the stages involved in fertilisation?

A

Sperm capacitation, sperm acrosome reaction, sperm-egg binding and fusion, activation of development. Activation ends with mingling of paternal and maternal chromosomes in newly-formed one-cell embryo.

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3
Q

What is the zona glycoprotein recognised by the sperm in the mouse?

A

ZP2.

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4
Q

When is the acrosome reaction initiated?

A

Before the sperm reaches the zona - NOT triggered by zona binding.

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5
Q

What does cortical granule exocytosis contribute to?

A

The zona block to polyspermy, but NOT the plasma membrane block to polyspermy.

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6
Q

What is the cumulus oophorous?

A

The oocyte (centre) surrounded by a cloud of cumulus cells. It is approached by fertilising sperm.

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7
Q

What is sperm capacitation needed for?

A

Hyperactivated motility, acrosome reaction and ZP/plasma membrane binding.

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8
Q

What causes sperm capacitation?

A

The female reproductive tract.

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9
Q

What are some of the changes the sperm undergoes in capacitation?

A

Modification/removal of sperm surface compontents, redistribution of some antigens, conformational changes to intrinsic membrane proteins.

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10
Q

What happens to the charge and permeability of sperm during sperm capacitation?

A

There is a decrease in surface net negative charge and there are changes in permeability to ions such as Ca2+.

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11
Q

What are some of the features of the sperm head structure?

A

It has a plasma membrane, outer and inner acrosomal membrane, nuclear envelope, equatorial segment and post-acrosomal region.

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12
Q

What is the acrosome reaction essential for?

A

Sperm oocyte plasma membrane binding and fusion.

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13
Q

What is the acrosome reaction dependent on?

A

It is a Ca2+ dependent exocytosis event. The sperm membranes fuse. (fusion of the acrosomal membrane and the sperm membrane)

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14
Q

What thoughts have changed about the acrosomal reaction?

A

It used to be thought that it was triggered by zona binding but it is now thought it occurs pre-zona contact.

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15
Q

What is the modern idea for the acrosome reaction and how was this discovered?

A

It is induced during the approach through the cumulus oophorous. It was discovered using acrosin-GFP sperm, which visualised in which sperm the reaction had undergone.

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16
Q

What is the acrosome reaction needed for?

A

The reaction liberates hydrolytic enzymes from the acrosome which induces hyaluronidase and proteases that promotes the passage through the zona (which is also probably assisted by flagellar propulsion).

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17
Q

What is significant about the zona block to polyspermy?

A

It ensures that no subsequent sperm fertilise after the first.

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18
Q

What is required for the zona block?

A

Cortical granule exocytosis which causes ovastacin release to cleave ZP2 to the inactive form. As it is inactive another sperm cannot approach.

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19
Q

What is the oolemma?

A

The egg plasma membrane.

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20
Q

What is the perivitelline space?

A

The space between the cell membrane of of an oocyte and the zona pellucida.

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21
Q

What mediates the sperm binding to the egg plasma membrane?

A

Sperm IgG-like acrosomal protein Izumo.

22
Q

What is Izumo?

A

An acrosomal protein that moves to the equatorial segment during the acrosome reaction. It dimerizes on oocyte binding.

23
Q

What does the sperm-oocyte interaction involve?

A

Tetraspanin and CD9.

24
Q

What role does CD9 have?

A

It may organise protein complexes and plasma membrane topology that is required for fusion.

25
Q

What other protein mediates oolemma binding?

A

SPACA6 - a sperm plasma membrane protein.

26
Q

What is the Izumo receptor on eggs?

A

Juno.

27
Q

What happens if knockout females are created without Juno?

A

They cannot be fertilised.

28
Q

What is significant about the anchoring of juno?

A

It is GPI anchored.

29
Q

What does the plasma membrane block to polyspermy involve?

A

Juno.

30
Q

What happens after an egg has been fertilised?

A

Juno is rapidly depleted - it is undetectable after 40 minutes. This means there is nothing on the egg for the sperm to bind to.

31
Q

What are juno-containing vesicles used for?

A

Decoy eggs that sperm can bind to. These are extracellular vesicles that are released from the egg.

32
Q

What is sperm injection?

A

It causes the events of fertilisation.

33
Q

What is ICSI?

A

Intracytoplasmic sperm injection.

34
Q

Does the plasma membrane block occur after ICSI?

A

No - sperm fusion contributes somehow to the plasma membrane block but we are not sure how.

35
Q

What happens to Ca2+ levels after gamete fusion?

A

They increase significantly at the fusion point and increase throughout the entire egg.

36
Q

What does release of Ca2+ intracellularly do?

A

It initiates development.

37
Q

What is the sperm factor in mammals?

A

PLCz

38
Q

How can you measure Ca2+ release?

A

Ca2+ sensitive fluorophors such as FUra2 (Fura2-AM)

39
Q

What is the significance of PLCz?

A

It generates IP3 to release intracellular Ca2+.

40
Q

Why is Ca+ release important?

A

It is needed to stop metaphase ii arrest in the oocyte.

41
Q

What is the cytostatic factor?

A

Emi2 - an endogenous meiotic inhibitor 2.

42
Q

What is a cytostatic factor?

A

It arrests the oocyte in meiosis until fertilisation.

43
Q

How does Ca2+ cause meiosis to continue?

A

It activates CaMKII which removes EMi2 (the cytostatic factor) which prevents arrest of meiosis.

44
Q

What happens to sperm protamine during fertilisarion?

A

After around 30 minutes the protamine is removed and replaced by acidic, oocyte-specific protein nucleoplasmin.

45
Q

What is the significance of the sperm protamine being replaced?

A

It causes the sperm to decondense - become larger.

46
Q

What happens after the protamine has been replaced?

A

Maternally-derived histones are added so that sperm chromatin recondenses and becomes smaller. This forms pronucleus at the same time as maternal chromatin/

47
Q

What happens to histones of maternal and paternal chromatin?

A

They become modified - epigenetic modification.

48
Q

What happens to paternal genomic DNA?

A

It becomes demethylated.

49
Q

What is a zygote?

A

A 1-cell embryo with male and female pronuclei. Both pronuclei contain a haploid set of chromosomes so the embryo is diploid.

50
Q

What is syngamy?

A

When pronuclei converge, membranes breakdown and chromosomes mingle.

51
Q

What does totipotency mean?

A

The natural ability of a cell to give rise to an entire organism.

BB20149 (16 decks)

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