L2 pt 2: Fertilisation and Maternal-gamete/embryo interactions

Question 1

Roles of ZP proteins:

Answer 1

• ZP3: Glycoprotein which initiates acrosome reaction upon sperm binding
• ZP2: mediates secondary sperm binding
• ZPF upregulated over ZP2 upon corticol granule exocytosis

Question 2

Role of corticol granule exocytosis:

Answer 2

• Released upon successful fertilisation
• Contains hydrolytic enzymes
• They are released, hardening the zona pellucida
• Prevents polyspermy

Question 3

List first 7 stages of embryonic development:

Answer 3

• Zygote (from male and female pronucleus)
• Two-cell
• Four-cell
• Eight-cell
• Morula
• Blastocyst
• Hatching of blastocyst

Question 4

What changes occur in early vs late stages of capacitation?

Answer 4

• First stages: Removal of glycoproteins like EPPIN, cholesterol efflux
• Later stages: inc. pH, Ca2+ influx -> cAMP and PKA activation, pTyr -> protein expression changes

Question 5

Why is secretion of hylarunonidase important in fertilisation?

Answer 5

• Cumulus cells are sticky, surrounded by an ECM rich in hyaluronan
• This is digested by hyaluronidase secreted from sperm acrosome, exposing the zona pellucida
• It has been posited that earlier sperm act sacrificially in order to achieve this effect

Question 6

List 4 candidates for spermatozoal-zona interactions:

Answer 6

• Lectins
• Galactosyl trasnferases
• Selectin
• Zonadhesin

Question 7

What are the two key SOAFs?

Answer 7

• SOAF: Spermatozoal ooctye activating factor
• PLC-S (via IP3)
• PAWP (mechanism unclear)

Question 8

Outline the sequence of events following sperm binding to oocyte:

Answer 8

• Sperm binds ZP3 (recognition receptor)
• Acrosome reaction takes place -> membrane fusion upon Izumo1-Juno binding -> sperm factors enter oocyte
• Sperm factors trigger calcium wave via IP3 (catalysed by PLC-S) -> granule exocytosis and pronuclei formation
• Maternal mRNA is recruited, and meiosis II is resumed -> Zygote formation, expression of embryonic genes

Question 9

What 2 activating effects does the sperm-initiated calcium wave have on the oocyte?

Answer 9

• Inactivation of MAPK -> increased DNA synthesis
• Increased cyclin B proteolysis -> reduced Cdk1 activity -> checkpoint progression into meiosis II
• The oscillations are dependent on CICR (via IP3R and RYR in ER); the initial spike alone can only temporarily inactivate cyclin B so meiosis will not progress

Question 10

What process is the main contributor to the paternal epigenetic profile?

Answer 10

• Protamine incorporation (during spermatogenesis) and clearing

Question 11

How do gametes affect the maternal environment? (3x examples) -> for each example, include species and situation

Answer 11

• Mice: Alteration in oviduct transcriptome profile 6hrs post-mating, in vitro
• Exposure of pig oviduct to gametes in vitro -> alterations to secretory proteome -> 4% altered by oocytes and/or sperm
• Flies: mating induces changes in oviduct transcript expression level (in vivo)