Flashcards in Devo Lect 5 - Fertilization Deck (25)
Why is chemotaxis important for marine organisms?
Sperm released into water - low chance of coming together without it. Molecule Resact responsible for this
Chemotaxis in mammals?
Sperm swim faster towards follicular fluid; Rantes (chemokine) responsible for this; Rantes receptor on sperm’s head; also an odorant receptor on sperm
Fertilization evens in sea urchin*
Sperm contacts jelly layer (resact); acrosome reaction initiated by proteins in jelly, digestive enzymes, actin molecules stick out; digestion of jelly layer; binding to vitelline envelope (species specific proteins like bindin); fusion of acrosomal process membrane and egg membrane
Fertilization events in mouse*
Sperm activated by female reproductive tract (rantes, progesterone; breaks through cumulus layer); sperm binds zone pellucida (ZP3 protein - species specific); acrosome reaction (digestive enzymes; no actin process); sperm lyses hole in zona; sperm and egg membranes fuse
Compare events in mouse and sea urchin fertility
Mouse digests into the zona not jelly layer; no acrosomal process; acrosome reaction happens at zona not outside jelly layer; zona is thick
Where are the main recognition proteins found in the gametes for sea urchins and mammals?
Bindin is on acrosomal process of sea urchin sperm.
ZP3 is found on the zona of the egg in mammals
Changes in sperm motility as they progress
Don’t really move in epididymis; move in the uterus; slow down in isthmus (narrowing), capacitation occurs near the ampulla and they speed up
Sperm move faster than they swim due to contractions of the uterus caused by prostaglandins in seminal fluid
Sperm signaled by ovulation; sperm gain hyperactivity (move really fast), and they get primed for acrosome reaction so they can bind; essential for fertilization
Ion channel (Ca) found only in tail of sperm; knockouts lacked hyperactivity and speed; only affects males (durr); activated by progesterone; could be good target for contraceptive since it has no other effects
Entry of sperm into egg
Sperm get through zona, certain proteins needed (Izumo on sperm, CD9 on egg). Egg extends some micro villi to make fertilization cone, then plasma membranes merge.
Fast block to polyspermy
(sea urchins and amphibians). Membrane potential depolarized after fusion with sperm. Changes membrane proteins (like sperm binding), last a few minutes
Slow block to polyspermy in urchins and amphibians
Cortical granule vesicles fuse to membrane; contain enzymes and proteins like hyalin which increases osmotic pressure, which separates plasma membrane and vitelline envelope more; hardens to form a fertilization envelope
Slow block to polyspermy in mammals
Cortical granules modifies ZP3
Fertilization signal transduction pathways
Increase [Ca]:activates gene expression, mitosis, stimulates membrane production, slow block to polyspermy; Na influx; fast block; increase in pH: promotes gene expression
Calcium pathway at fertilization
Sperm bind, activate tyrosine kinase, PLC, makes IP3 from PIP2, release Ca from ER, triggers cyclins (cell cycle); you can see Ca wave across egg
Early protein synthesis after fertilization in urchins
Initial burst and second burst. Initial one is unaffected by transcription inhibitors because mRNA already present in egg.
Early protein synthesis after fertilization in mammals
Almost all proteins are newly transcribed, no initial burst
Fusion of genetic Material*
Sperm pronucleus separates from mito. and flagella; egg completes meiosis; sperm chromatin decondenses; sperm centriole contacts female pronucleus and they are pulled together and their pronuclear envelopes degrade
Haploid, smaller nucleus with pronuclear envelope
What happens to sperm mitochondria?
Some enter the egg, but so small in number that it doesn’t affect maternal mitochondrial DNA
Rearrangement of egg cytoplasm
Fertilization starts movement of cytoplasm, sets up morphogenetic determinants; movement due to parallel microtubules
Colchincine and UV effects on development
Prevents cytoplasm rearrangement; colchicine prevents microtubule formation; UV causes just a clump to form. However spinning UV treated cells causes normal development;
Factors that will lead to the asymmetry of the mature organism (ie head, tail, organs)