slide1 n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Gametogenesis PowerPoint Presentation
Download Presentation
Gametogenesis

Loading in 2 Seconds...

play fullscreen
1 / 28

Gametogenesis - PowerPoint PPT Presentation


  • 204 Views
  • Uploaded on

2009. Gametogenesis. 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

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Gametogenesis' - abel


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
gametes reproductive cells
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
origin of primordial cells
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
proliferation
Proliferation
  • Oogonia and spermatogonia
  • Proliferative phase of development – from thousands to about 7 million (in female) – mitosis
  • Oogonia – division during 2.-5. 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
meiosis
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
first meiotic division
First Meiotic Division
  • Prophase I
    • Leptotene
    • Zygotene
    • Pachytene
    • Diplotene
    • Diakinesis
  • Metaphase I
  • Anaphase I
  • Telophase I and Interphase
  • Second Meiotic Division
slide7
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
spermatogenesis 64 days
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)
male germ cells
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
spermiogenesis
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
spermatozoon
Spermatozoon
  • Head (nucleus and acrosome)
  • Neck (proximal centriole)
  • Middle piece (flagellum, centriole, mitochondrial helix)
  • Tail - flagellum
sperm maturation
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
oogenesis
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
lampbrush chromosomes
Lampbrush chromosomes
  • Active transcription during meiosis
  • Synthesis of RNA – genes loop out
oogenesis1
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
slide16
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
coverings of eggs
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
fertilization
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
prevention of polyspermy
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
fertilization1
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
imprinting
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)
cleavage
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 – 16 -32 cells – morula (mulberry)
segregation of blastomeres into embryoblast and trophoblast
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
genetic regulation of germ cell formation proliferattion migration and development
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
twins and embryonic stem cells
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