CLINICAL AND EXPERIMENTAL EMBRYOLOGY
Human reproduction ...............................................................................................................2
Gametogenesis ...................................................................................................................2
Fertilization .........................................................................................................................8
Embryonic development ......................................................................................................9
Assisted reproductive technology .......................................................................................... 10
Subfertility ......................................................................................................................... 10
Fertility treatments............................................................................................................. 13
Complications and success rates ....................................................................................... 15
Pre-implantation genetic testing ............................................................................................ 16
Legal aspects (Belgium) ..................................................................................................... 16
different types ................................................................................................................... 17
Nuclear transfer: mitochondrial diseases and infertility .......................................................... 20
Mitochondrial diseases ...................................................................................................... 20
Reproductive options ......................................................................................................... 21
Major concerns .................................................................................................................. 25
Oocyte activation deficiency .................................................................................................. 26
Oocyte activation mechanism ............................................................................................ 26
Failed fertilization after ICSI ............................................................................................... 27
Genome editing in the human germline .................................................................................. 30
Genetics recap .................................................................................................................. 30
Genome editing ................................................................................................................. 30
CRISPR/Cas9 technology ................................................................................................... 31
CRISPR/Cas9 germline genome editing............................................................................... 35
Scientific and ethical considerations .................................................................................. 38
1
,HUMAN REPRODUCTION
! look at the studies performed by professor Heindryckx laboratory
GAMETOGENESIS
= formation of gametes
− Gametes = cells specialised to pass on maternal/paternal chromosomes to the next generation
• Germs cells = gametes + precursor-stadia
o Can undergo meiosis or cleavages
- Entails 2 divisions: one 2n – 4C ➔ four 1N – 1C
▪ Halving analogue chromosomes (haploid): 2n – 4C ➔ 1n – 2C
! homologous recombination + crossing-over: genetic diversity
▪ Chromatide-separation to daughtercells ≈ mitosis: 1n - 2C ➔ 1n 1C
- Keeps chromosome number constant in each generation
soma(tic cells)
o undergo mitosis keeps diploid chromosome number: 2n ➔ two 2n
• Originate from oergonocyten or primordial germ cells
Differentiate early in development to oogonia or spermatogonia
Gametogenesis: development to ripe haploid gametes (mature oocytes or spermatozoid)
= oogensis or spermatogenesis
− Germ cells: primordials reside temporarily in the wall of the yolk sac
• Week 3 foetal period: yolk sac formation
• Week 4 FP: production of gonads
• Week 5 FP: migration of germ cells to developing gonads (migration + proliferation)
• Week 7 FP: PCGs not bipotential = sex determination
2
,• Start gametogenesis
o Month 3 FP: oogenesis
o Month 7: simultaneous stop in prophase I = primary oocyte
- Surrounded by one layer of flattened follicular cells = primordial follicle
! girls contain at birth a definitive stock of primary oocytes in the ovarium
recent studies: stem cells in adult ovarium
o Puberty: folliculogenesis
- FSH (follicle stimulating hormone) and LH (luteinisation hormone)
= produced by the hypophysis
- Finish meiosis I of the primary follicle
+ follicle cells become cubical and multilayered = granulosa
- Secondary follicle
▪ Formation of holes in granulosa
- Antral follicle
▪ Holes fuse into a big central follicle cavity = antrum
▪ The oocyte is surrounded by corona radiata of granulosa in antrum
= cumulus oophorus
! in meiosis I and II of the primary/secondary oocyte: ‘rejection’ of polar bodies
! follicle attrition
▪ Follicle selection: 5-15 activated per ovaria cycle
▪ Only 1 = ripe follicle
Degeneration of remaining follicles
Month 5: 6.000.000-7.000.000 ➔ birth: 2.000.000
Puberty: 300.000 ➔ 400 ripen
! meiosis II only finishes when fertilized
3
, o Puberty: ovulation
- Ripe follicle bursts open at the surface of the ovarium
- ‘secretion’ of secondary oocyte
- Capture by infundibulum and transport by fimbriae
➔ secondary oocyte needs to be fertilized within 12 hours
- Corpus luteum: mass of granulosa and theca-cells remaining in ovarium
▪ Secretion of oestrogen and progesterone: prepares the
endometrium for implantation
▪ If not fertilized: degeneration into corpus albicans
- Reproductive cycle: GnRH = neurohormones
▪ The axons of the nucleus arcuatus of hypothalamus induce pulses
Autonomous rhythm from puberty
Pulses change in the cycle (28 days)
➔ hypothalamus release GnRH into the portal vascular system
Axons to capillary vascular bed
Neuro-vascular communication
Flow to venous blood vessels
Capillary vascular bed that irrigates gonadotropic cells
GnRH not measurable in blood
➔ transport to anterior pituitary gland: release of LH and FSH
= adenohypophysis
Induces gonads – adrenal – thyroid – GH – prolactin
Regulation via portal vasculature
4
Human reproduction ...............................................................................................................2
Gametogenesis ...................................................................................................................2
Fertilization .........................................................................................................................8
Embryonic development ......................................................................................................9
Assisted reproductive technology .......................................................................................... 10
Subfertility ......................................................................................................................... 10
Fertility treatments............................................................................................................. 13
Complications and success rates ....................................................................................... 15
Pre-implantation genetic testing ............................................................................................ 16
Legal aspects (Belgium) ..................................................................................................... 16
different types ................................................................................................................... 17
Nuclear transfer: mitochondrial diseases and infertility .......................................................... 20
Mitochondrial diseases ...................................................................................................... 20
Reproductive options ......................................................................................................... 21
Major concerns .................................................................................................................. 25
Oocyte activation deficiency .................................................................................................. 26
Oocyte activation mechanism ............................................................................................ 26
Failed fertilization after ICSI ............................................................................................... 27
Genome editing in the human germline .................................................................................. 30
Genetics recap .................................................................................................................. 30
Genome editing ................................................................................................................. 30
CRISPR/Cas9 technology ................................................................................................... 31
CRISPR/Cas9 germline genome editing............................................................................... 35
Scientific and ethical considerations .................................................................................. 38
1
,HUMAN REPRODUCTION
! look at the studies performed by professor Heindryckx laboratory
GAMETOGENESIS
= formation of gametes
− Gametes = cells specialised to pass on maternal/paternal chromosomes to the next generation
• Germs cells = gametes + precursor-stadia
o Can undergo meiosis or cleavages
- Entails 2 divisions: one 2n – 4C ➔ four 1N – 1C
▪ Halving analogue chromosomes (haploid): 2n – 4C ➔ 1n – 2C
! homologous recombination + crossing-over: genetic diversity
▪ Chromatide-separation to daughtercells ≈ mitosis: 1n - 2C ➔ 1n 1C
- Keeps chromosome number constant in each generation
soma(tic cells)
o undergo mitosis keeps diploid chromosome number: 2n ➔ two 2n
• Originate from oergonocyten or primordial germ cells
Differentiate early in development to oogonia or spermatogonia
Gametogenesis: development to ripe haploid gametes (mature oocytes or spermatozoid)
= oogensis or spermatogenesis
− Germ cells: primordials reside temporarily in the wall of the yolk sac
• Week 3 foetal period: yolk sac formation
• Week 4 FP: production of gonads
• Week 5 FP: migration of germ cells to developing gonads (migration + proliferation)
• Week 7 FP: PCGs not bipotential = sex determination
2
,• Start gametogenesis
o Month 3 FP: oogenesis
o Month 7: simultaneous stop in prophase I = primary oocyte
- Surrounded by one layer of flattened follicular cells = primordial follicle
! girls contain at birth a definitive stock of primary oocytes in the ovarium
recent studies: stem cells in adult ovarium
o Puberty: folliculogenesis
- FSH (follicle stimulating hormone) and LH (luteinisation hormone)
= produced by the hypophysis
- Finish meiosis I of the primary follicle
+ follicle cells become cubical and multilayered = granulosa
- Secondary follicle
▪ Formation of holes in granulosa
- Antral follicle
▪ Holes fuse into a big central follicle cavity = antrum
▪ The oocyte is surrounded by corona radiata of granulosa in antrum
= cumulus oophorus
! in meiosis I and II of the primary/secondary oocyte: ‘rejection’ of polar bodies
! follicle attrition
▪ Follicle selection: 5-15 activated per ovaria cycle
▪ Only 1 = ripe follicle
Degeneration of remaining follicles
Month 5: 6.000.000-7.000.000 ➔ birth: 2.000.000
Puberty: 300.000 ➔ 400 ripen
! meiosis II only finishes when fertilized
3
, o Puberty: ovulation
- Ripe follicle bursts open at the surface of the ovarium
- ‘secretion’ of secondary oocyte
- Capture by infundibulum and transport by fimbriae
➔ secondary oocyte needs to be fertilized within 12 hours
- Corpus luteum: mass of granulosa and theca-cells remaining in ovarium
▪ Secretion of oestrogen and progesterone: prepares the
endometrium for implantation
▪ If not fertilized: degeneration into corpus albicans
- Reproductive cycle: GnRH = neurohormones
▪ The axons of the nucleus arcuatus of hypothalamus induce pulses
Autonomous rhythm from puberty
Pulses change in the cycle (28 days)
➔ hypothalamus release GnRH into the portal vascular system
Axons to capillary vascular bed
Neuro-vascular communication
Flow to venous blood vessels
Capillary vascular bed that irrigates gonadotropic cells
GnRH not measurable in blood
➔ transport to anterior pituitary gland: release of LH and FSH
= adenohypophysis
Induces gonads – adrenal – thyroid – GH – prolactin
Regulation via portal vasculature
4
