Fertilisation and contraception

Question 1

What membrane changes occur during sperm maturation?

Answer 1

transfer of proteins into and onto the sperm plasma membrane
increase in membrane fluidity
essential for acrosome reaction

Question 2

What flagellum changes occur during sperm maturation?

Answer 2

become more rigid
cAMP content of tail increases

Question 3

When does capacitation begin?

Answer 3

predominantly within the female tract
due to proteolytic enzymes, cholesterol sinks and higher ionic strength

Question 4

What characteristics do fully capacitated sperm exhibit?

Answer 4

hyperactivated motility
changes in membrane properties that subsequently allow the acrosome reaction to happen

Question 5

Why is capacitation necessary?

Answer 5

they become more responsive to signals from oocyte
able to undergo acrosome reaction essential for fertilisation

Question 6

What processes occur in capacitation?

Answer 6

stripping or modification of surface glycoproteins
changes in surface charge
reduction in membrane stability through loss of cholesterol and formation of lipid rafts

Question 7

Hyperactivated sperm motility

Answer 7

involved high amplitude asymmetrical beating of the flagellum
helps sperm meet target
aids sperm penetration of zona pellucida

Question 8

Cation channel of sperm (CatSper)

Answer 8

Ca2+ ion channel specific to sperm
activated by alkaline pH
essential for hypermotility + fertility

Question 9

What processes aid the finding of the egg?

Answer 9

oocyte and cumulus cells release chemoattractants
surface sperm hyaluronidase digests cumulus cells to let sperm reach zona pellucida

Question 10

What is the zona pellucida composed of primarily?

Answer 10

glycoproteins ZP1-4

Question 11

ZP1

Answer 11

structural protein that corss links with others

Question 12

ZP2

Answer 12

contains sperm binding domain for oocyte-sperm recognition + penetration of ZP
responsible for primary block to polyspermy

Question 13

ZP3

Answer 13

complexed with ZP4
involved in primary sperm-egg binding

Question 14

When does the acrosome reaction occur?

Answer 14

after sperm head binds to ZP
ZP proteins responsible for inducing reaction

Question 15

What happens during the acrosome reaction?

Answer 15

acrosome swells and membrane fuses with sperm PM
acrosomal vesicle undergoes exocytosis leading to release of hyaluronidase + exposure of acrosin

Question 16

Primary binding

Answer 16

sperm membrane binds ZP via ZP3/4 + species specific complementary binding partner

Question 17

Acrosin

Answer 17

protease on inner membrane of sperm exposed by acrosome reaction
further digests ZP + oocyte PM

Question 18

Secondary binding

Answer 18

sperm inner acrosomal membrane binds to ZP via ZP2 via acrosin on sperm

Question 19

PLCζ

Answer 19

released into cytoplasm of oocyte following fusion
facilitates hydrolysis of membrane bound PIP2 to DAG + IP3
triggers calcium release + oocyte activation

Question 20

What is the consequnce of PLCζ increasing intracellular calcium?

Answer 20

Ca induced Ca release
calcium oscillations which stimulate cortical granule release- ovastacin

Question 21

PKC in gamete fusion

Answer 21

stimulates phosphorylation of other proteins essential for development of conceptus

Question 22

How does ovastacin block polyspermy?

Answer 22

act on ZP to harden
inactivation of sperm receptors by cleaving ZP2
block to polyspermy

Question 23

Formation of female pronucleus

Answer 23

Ca pulses stimulate resumption of meiosis
second polar body is extruded and female pronucleus forms

Question 24

Formation of male pronucleus

Answer 24

sperm nucleus decondenses
protamines are replaced by histones

Question 25

Syngamy

Answer 25

combination of two genomes
pronuclei come together, pronuclear membranes break down and replicated chromosomes align on mitotic spindle for first cleavage

Question 26

What happens as a result of sperm-egg fusion?

Answer 26

increased oestrogen + progesterone
overrides monthly cycle and suppresses HGP axis
HCG produced by placenta