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Fertilization

Fertilization. Structure of Gametes External vs Internal Fertilization Sperm Attraction Sperm Binding to Egg and subsequent fusion Activation of Egg Fusion of Nuclear material. What is the purpose of Fertilization?. Transmit genes from Parent to offspring

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Fertilization

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  1. Fertilization • Structure of Gametes • External vs Internal Fertilization • Sperm Attraction • Sperm Binding to Egg and subsequent fusion • Activation of Egg • Fusion of Nuclear material

  2. What is the purpose of Fertilization? • Transmit genes from Parent to offspring • Initiate functions in egg cytoplasm that permits development to occur

  3. Common Elements of Fertilization • Contact and Recognition between Sperm and Egg • Regulation of sperm entry • Fusion of Genetic Material • Activation of egg metabolism to start development

  4. Sperm Cell • First observed by Leeuwenhoek (Sperma, Semen= seed) • Homunculus • Believed to contain all information for embryo • Work demonstrated that Semen required sperm cells for fertilization of egg • 1876, Hertwig and Fol demonstrate sperm entering egg and fusion of their genetic material. Studies in Sea Urchin

  5. Spermatogenesis

  6. Sperm Structure • Haploid Nucleus and Acrosome. • Flagellum- axoneme • “9+2” arrangement • Dynein-Force generator! • Mitochondria

  7. Egg Cell- Oocyte • All material needed for beginning of growth and development. • Large cytoplasm • Synthesis and absorption of proteins (yolk) • Other cytoplasmic factors: • Nutritive proteins • Ribosomes and tRNAs • Accumulated mRNA • Morphogenic factors (transcription and paracrine factors) • Protective elements against UV, give egg bad taste, and yolk contains antibodies.

  8. Oocyte Structure

  9. Fertilization patterns • External • Internal

  10. Overview of External: Sea Urchin • Many Marine animals use this method • Chemotaxis main targeting mechanism. • Species specific sperm attraction and species specific sperm activation.

  11. Overview of Internal: Mammals • Difficult to study • Sperm Heterogeneous at first. • Both gametes use biochemical and mechanical means to reach site of Fertilization(Ampula). • Translocation • Capacitation

  12. External Sperm Attraction to Egg • Species specific • Resact (14 a.a.) • Regulates Calcium influx • Increases ATP formation from Mitochondria: increase flagellar motive force.

  13. Internal: Sperm attraction to Egg • Regionally specific molecules-motility and capacitation • During capacitation, flagellum hyperactive • Directional cues: Heat and Chemotaxis (progesterone).

  14. Capacitation of Mammalian Sperm

  15. External: Recognition/fusion • Initial binding to Egg Jelly, Bindin • Species specific • EBR-1 interacts with Bindin. • Acrosome reaction • Once membranes fuse (Bindin), polymerization of actin in Egg: Fertilization cone. • Actin from gametes form a connection, sperm nucleus and tail pass into egg cell. • All regions of Egg can interact with sperm.

  16. Internal: Recognition/fusion • Sperm binds to glycoprotein matrix of ZonaPellucida (ZP). • Second interaction occurs with ZP via SED1 protein of sperm • Final interaction between proteins (ADAM3, ADAM2) interact with ZP3. Crosslinking of galactosyltransferasesCa influx and acrosome reaction

  17. Internal Recognition/Fusion • Interaction slightly different • Acrosomal fusion: • proteolytic enzymes • Secondary contacts: Zonadhesion • Other inner acrosomal proteins bind to ZP2. • Fusion not clear. Possible interaction with CD9 of oocyte.

  18. External: Block of Polyspermy • Effects of Polyspermy • Fast block • Membrane potential switches from negative to positive • Transient (1 min) • Slow block • Shortly after fast block • Cortical Granules • Increase in Calcium, from internal stores. • Fertilization envelope

  19. Slow-block for Polyspermy

  20. Internal: Block of Polyspermy • No observed fast block • Slow block- similar to Sea Urchin • N-acetylglucosaminidase cleave NAG from ZP3. • Other proteins cleave proteins from cell surface.

  21. External and Internal: Activation of Egg • Calcium-major signal. • Releases inhibitors from stored mRNAs-Maskin protein • IP3 created by phospholipase C, DAG also created • G proteins and Src induce PLC activity • IP3 causes Ca release from ER • Ca required for Na/H pump that regulates Egg internal pH. • Mammals similar…multiple waves of Ca release.

  22. External: Fusion of Genetic material. • Nucleus/centriole separate from mitochondria and tail. • Nuclear envelope vesiculates into small packets. Expose chromatin • Phosphorylation of nuclear lamin and histones-starts early • Pronucleus rotates 180o, placing centriole between sperm and egg pronuclei • Zygote nucleus formed.

  23. Internal: Fusion of Genetic material. • Takes longer in mammals • Sperm DNA bound by Protamines (disulfide bonds hold complex together) • Glutathione reduces protamine-relax chromatin • Ca release in waves. • As pronuclei meet, DNA condenses into chromosomes and orient on common mitotic spindle. • True zygote nucleus: 2 cell stage.

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