Fertilisation and Subfertility treatment

Question 1

What is fertilisation

Answer 1

• sperm and egg gametes fuse to give rise to new individuals (zygote)

the sperm has to travel from vagina via uterus to oviduct, the sperm is transported to the oviduct by muscular activity of female genital tract

Question 2

How does the sperm travel to the oviduct

Answer 2

• in the oviduct, the sperm is attracted to the egg by CHEMOTAXIS and THERMOTAXIS
• in the female reproductive tract, the sperm undergoes physiological changes (capacitation) which allows fertilisation of the egg, changes include surface membrane proteins changing and increased motility

Question 3

What happens once the sperm reaches the oocyte

Answer 3

• the sperm passes through the corona radiata and zona pellucida before fusing with the plasma membrane of the oocyte
• enzymes of sperm surface allow passage through cumulus cells (corona radiata) and release of acrosomal contents allowing passage through zona pellucida
• sperm and zona pellucida and membrane proteins of oocyte undergo species-specific interactions

Question 4

How does penetration of the cumulus layer occur

Answer 4

cumulus matrix made of hyaluronia acid
- hyalutonidase enzymes (HYAL3) are associated with the sperm membrane allowing the sperm to penetrate through the cumulus layer

Question 5

What is the sperm acrosome reaction

Answer 5

• binding of sperm to the zona pellucida includes acrosome reaction
• binding of sperm triggers release of acrosomal enzymes which digest a path through zona pellucida
• during acrosome reaction the sperm membrane that mediates binding to ZP3/ZP4 is shed
• after the reaction, sperm maintains adhesion to zona pellucida by binding to ZP2

Question 6

What occurs in gamete fusion

Answer 6

proteins involved
egg: CDR and sperm Izumo

• fusion of sperm and egg occurs at equatorial domain of the sperm
• fusion of the sperm and egg plasma membranes is mediated by membrane proteins in sperm and egg plasma membranes
• protein interaction causes fusion of membranes leading to genetic release of sperm content)

Question 7

How does the cortical reaction to prevent polyspermy occur

Answer 7

• fusion of sperm and egg membrane triggers release of cortical granule content
• modification of zona pellucida prevents further sperm binding and penetration
• after passing through layers surrounding oocyte, plasma membrane of sperm and oocyte fuse, oocyte then completes meiosis II and change prevents polyspermy
• fusion of vesicles in the oocyte with the plasma membrane, releasing content of the vesicle - enzymes released modify zona pellucida and prevent further binding and penetration of zona pellucida by spermW

Question 8

What is subfertility and the causes of it

Answer 8

subfertility: the failure to conceive within one year of frequent intercourse
- occurs in 10-15% of couples
- cause is unexplained, from sperm defects, ovulatory problems, tubual damage and endometriosis
- mutations in the gonadal functions and FSH/LH secretion

Question 9

What are the treatments of subfertility

Answer 9

• IVF (in vitro fertilisation)
• IOSI (intracytoplasmic sperm injection - sperm injected directly into cytoplasm)
• zona drilling (small hole into zona pellucida by laser or chemicals but could lead to polyspermy)
• subzonal insemination

Question 10

What is the process of IVF

Answer 10

• simultaneous maturation of several follicles is achieved by treatment with gonadotrophins, in combination with an inhibitor of gonadotrophin release from anterior pituitary
• this ensures maturation of several follicles but prevents surge of FHS/LH
• final follicle maturation achieved with hCG
• eggs are removed in surgery from ovaries and mixed with capacitated sperm fertilisation
  -after early cleavage stage embryo is transferred into the uterus, progesterone and estrogen given to prevent shedding of uterine lining