Fertilization

Sperm What is involved in the maturation of a sperm cell? formation of acrosome from Golgi; formation of flagellum from centriole

Sperm

Sperm

Sperm How does flagellar structure contribute to sperm motility? dynein, attached to microtubules hydrolyzes ATP; sliding of outer doublet protofilaments consist of tublulin dimers histone H1 stabilizes flagellar microtubules ATP comes from mitocondria in midpiece in mammals sperm undergo capacitation in female reproductive tract – will not bind egg otherwise

Egg Why is egg so much larger than sperm? yolk proteins ribosomes t-RNA m-RNA morphogenic factors protective chemicals much yolk protein made in liver morphogenic factors are differentially distributed in cytoplasm protective chemicals include MAA’s, photolyases, etc

Egg What are some of the structural components of the egg? nucleus, cell membrane, vitelline envelope (zona pellucida), cortex and cortical granules, mitocondria, jelly cortical granules analogous to acrosome – contains enzymes, mucopolysaccharides, adhesive glycopoteins, etc

Egg When sperm enters at what meiotic stage is the egg?

Gametogenesis

Sperm Attraction What is chemotaxis? 1 4 2 3 Movement toward a chemical In Arbacia punctulata – the effects of adding resact to sperm suspension resact isolated from egg jelly 1 4 2 3

Sperm Attraction What is a sperm-activating peptide? causes increases in sperm respiration and motility via a signal transduction mechanism – example is resact

Sperm – Egg Interaction What is involved in the acrosomal reaction in sea urchins? components of egg jelly bind to receptors on sperm cell membrane calcium channels opened, calcium enters sperm head and induces fusion of acrosomal vesicle with membrane leading to exocytosis of enzymes acrosomal process forms from polymerization of actin also facilitated by calcium

Sperm – Egg Interaction What role does the bindin protein play in this interaction? mediates species-specific recognition bindin receptors on egg cell surface

Sperm – Egg Interaction How does gamete recognition and binding occur in mammals? ZP3 glycoprotein of egg binds sperm and initiates acrosomal reaction by binding to receptors that activates G protein and opens calcium channels leading to exocytosis enzymes digest opening in zona, as sperm crosses zona loses ZP3 binding sites but ZP2 binding sites come into play

Sperm – Egg Interaction What follows the initial penetration of egg by the sperm? fusion of sperm and egg membranes polymerization of egg actin leads to formation of fertilization cone in sea urchin in some species parts of egg membrane specialized to fuse with sperm, in sea urchins all regions are capable fusion mediated by certain proteins – bindin in sea urchins has secondary role

Sperm – Egg Interaction What makes this interaction in mammals different? contact occurs on side of sperm head; CD9 associated integrin protein in egg needed for fusion along with fertilin in sperm

Preventing Polyspermy Why is polyspermy a problem? Too many chromosomes, too many centrioles; multiple initial divisions (irregular no. of chromosomes)

Preventing Polyspermy What two mechanisms exist in sea urchins to prevent polyspermy? fast block – elevation of potential of egg cell membrane – within seconds – influx of sodium ions – not seen in mammals slow block – cortical granule reaction

Preventing Polyspermy cortical granule exocytosis releases several enzymes and mucopolysaccharides formation of fertilization membrane hyaline layer around egg – supports blastomeres during cleavage

Preventing Polyspermy How is the cortical granule reaction different in mammals? Why is calcium so important to the cortical granule reaction? no fert. envelope; enzymes modify ZP sperm receptors; in mice N-acetylglucosaminidase enzymes cleave it from ZP3 increase in intracellular Ca+2 conc.initiates fusion of cortical granules

Egg Activation How does egg metabolism respond to stimulation by sperm? increase in calcium levels trigger many reactions – can block with EGTA can activate artificially using calcium ionophore most prot. syn comes from stored mRNA by removing an inhibitor

Egg Activation What signaling pathway releases intracellular calcium ion concentration? src family of of protein kinases may link sperm to PLC activation

Fusion of Genetic Material What does the sperm contribute to the developing embryo? What must happen for fusion to occur in sea urchins? How is the fusion different in mammals? DNA & centriole to form initial spindle for division sperm nucleus must decondense to form pronucleus – involves phosphorylation of lamin protein in envelop and two sperm histones – can fuse with egg pronucleus longer process – sperm DNA bound to protamines in compacted form – glutathione breaks dissulfide bonds to de-compact DNA; when sperm enters egg hasn’t complete meiosis; DNA synthesis occurs separately in each pronucleus; true diploid nucleus doesn’t form untill 2-cell stage

Rearrangement of Egg Cytoplasm What kind of cytoplamic rearrangement occurs as a result of fertilization? Parallel microtubles between cortical and inner cytoplasm appear responsible for movement