1. Gametogenesis
2009

2. Gametes – reproductive cells
Ovum
Spermatozoon
Gametogenesis – differentiation of highly specialized sex cells capable of uniting at fertilization
1. Origin of the germ cell
2. Multiplication in the gonads by mitosis
3. Reduction of chromosomes – meiosis
4. Final stages of maturation and differentiation

3. Origin of primordial cells
Germ cell can be recognized very early – vegetal pole cytoplasm in the zygote
Epiblast – temporary residence in extraembryonic tissues – recognizable at 24 ED in the endoderm of yolk sac
Migration within mesenchyme of posterior wall of yolk sac (near the allantois), gut, and dorsal mesentery (4 -6 week) to the gonads
Extracellular matrix and chemotactic influence from gonad – resident germ cells induce formation of gonads
Number of cells increases during migration

4. Proliferation Oogonia and spermatogonia
Proliferative phase of development – from thousands to about 7 million (in female) – mitosis
Oogonia – division during months
By the seventh month oogonia entere the prophase of first meiotic division and end proliferative phase
Spermatogonia enter meiosis after puberty, mitotic capability continues as long as the male is capable of reproduction

5. Meiosis Reduction of normal number of chromosomes
From diploid to haploid
Two maturation divisions without new DNA synthesis
Reductional division
Equational meiotic division
Recombination of genetic information
Random distribution of maternal and paternal chromosomes
Exchanging of portions of homologous chromosomes by crossing over

6. First Meiotic Division
Prophase I
Leptotene
Zygotene
Pachytene
Diplotene
Diakinesis
Metaphase I
Anaphase I
Telophase I and Interphase
Second Meiotic Division

7. In Mammals - initiation of germ line development- maintain pluripotency within germ cells
Activation of differentiation – inductive signal from trophoblast
Proliferation and survival – trophic factors
Extracellular matrix – direct the migration
Final differentiation

8. Spermatogenesis - 64 days
Mitotic multiplication – spermatogonia (Type A – stem cell population, Type B – leave mitotic cycle - preleptotene spermatocytes)
Meiosis - Primary spermatocytes
Secondary spermatocytes
Spermiogenesis – Spermatides – transformation into extremely specialized cells – spermatozoa (concentration of chromatin, decrease of size, formation of acrosome, flagellum)

9. Male germ cells
Sertoli cells – isolation of germ cells, support and nutrition
Degradation of residual bodies
Synthesis of signal molecules (Anti-Müllerian factor)
Synchronization of development- waves

10. Spermiogenesis Nucleus – concentration of chromatin – head
Golgi complex- proacrosomal granules - acrosome
Centrioles – achorage of flagellum
Axoneme – microtubules (9+2) and dynein
Mitochondria – spiral investment around proximal part of flagellum – mitochondrial helix
Residual body

11. Spermatozoon Head (nucleus and acrosome) Neck (proximal centriole)
Middle piece (flagellum, centriole, mitochondrial helix)
Tail - flagellum

12. Sperm maturation
Newly formed spermatozoa are not capable of fertilization. Maturation in genital tract – activation – increase of motility
Capacitation – final step of sperm maturation- changes in acrosome, preparing the enzyme release (in female genital tract), changes in sperm membrane
Sperm attraction and hyperactivation
Acrosome reaction – fusion of the acrosome with plasma membrane, extension of the acrosomal process

13. Oogenesis
Oogonium gives arise to only one ovum – first and second polar body (DNA and only little cytoplasma)
First meiotic division is not completed untill puberty
Meoitic arrest occurs during prophase I (diplotene) – egg builds up its stores of yolk
Second arrest during metaphase II – mitosis is finished after fertilization

14. Lampbrush chromosomes
Active transcription during meiosis
Synthesis of RNA – genes loop out

15. Oogenesis At birth – 1 milion oocytes
Surrounded by a layer of follicular cells (granulosa cells) – follicle
Only 400 (one per menstrual cycle) reach maturity
Atresia (degeneration)
Folliculogenesis
Primordial
Primary
Secondary
Graafian follicle - Ovulation

16. Egg Egg accumulates yolk as reservoir of food (energy) for embryo
Proteins (Amino acids, Energy)
Ribosomes and tRNA- proteosynthesis after fertilization
mRNA – early development - morphogenic factors

18. Coverings of eggs
Zona pellucida – Glycoproteins, GAG, Hyaluronic acid, Sialic adid. It is produced by oocyte
ZP-3 Sperm receptor and induction of acrosome reaction
Corona radiata – follicular cells

19. Fertilization It is an interaction between sperm and oocyte
Spermatozoon binds to specific sperm receptor in the zona pellucida (ZP3). It induces release of enzymes from acrosome
Penetration the zona pellucida
Sperm and oocyte fuse
Cortical reaction – cortical granules release to perivitelline space (between oocyte and zona pellucida) – alteration of receptors for sperms – prevent polyspermy

20. Prevention of polyspermy
Fast block of polyspermy – change the electrical potential
Slow block of polyspermy - cortical granules -enzymes – proteases – clip off binding receptor
Fertilization envelope – space between zona pellucida and egg - GAG, peroxidase, and hyalin – zona reaction

21. Fertilization
Fusion with sperm induces oocyte to resume meiosis – second polar body and definitive oocyte
Fertilized oocyte = zygote
Female and male pronuclei
Membrane disapears
Replication
First mitotic division
24 hours

23. Imprinting
Egg-derived genome is functionally different from sperm-derived
Imprinting is inactivation of gene depending on gender - prevent parthenogenesis
Maternal genes are important for embryo development (receptor for IGFII)
Paternal genes are important for placenta development (IGFII – Beckwith-Wiederman sy)

24. Cleavage Mitotic division without cell growth
Daughter cells (Blastomeres) get smaller - embryo does not change in size
Mitotic division is equal and total
4 cells – 40 hours
3ED – 6-12 cells
4ED – cells – morula (mulberry)

25. Segregation of blastomeres into embryoblast and trophoblast
Starting at 8 cell stage – changes in intercellular juctions – compaction – polarization of cells
Tight junction and gap junctions – outer cell mass
Cells in centre – inner cell mass (embryoblast) and outer cell mass – (trophoblast).
Fluid is collected – blastocyst cavity
Blastocyst – Embryonic pole
Abembryonic (vegetative) pole

27. Genetic regulation of germ cell formation, proliferattion, migration, and development
Regulatory gene cascade – sequential activation of genes that direct the initial induction and development, proliferation, survival, migration and differentiation of the germ cells
Maternal effect genes – germ plasm in zygote

28. Twins and embryonic stem cells
Monozygotic twins - before hatching – at 5.ED – dichorionic
Later monochorionic,diamniotic
Monochorionic monoamniotic
Conjoined twins (after ED9)
Inner cell mass – embryonic stem cells