Devo Lect 5 - Fertilization

Question 1

Why is chemotaxis important for marine organisms?

Answer 1

Sperm released into water - low chance of coming together without it. Molecule Resact responsible for this

Question 2

Chemotaxis in mammals?

Answer 2

Sperm swim faster towards follicular fluid; Rantes (chemokine) responsible for this; Rantes receptor on sperm’s head; also an odorant receptor on sperm

Question 3

Fertilization evens in sea urchin*

Answer 3

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

Question 4

Fertilization events in mouse*

Answer 4

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

Question 5

Compare events in mouse and sea urchin fertility

Answer 5

Mouse digests into the zona not jelly layer; no acrosomal process; acrosome reaction happens at zona not outside jelly layer; zona is thick

Question 6

Where are the main recognition proteins found in the gametes for sea urchins and mammals?

Answer 6

Bindin is on acrosomal process of sea urchin sperm.

ZP3 is found on the zona of the egg in mammals

Question 7

Changes in sperm motility as they progress

Answer 7

Don’t really move in epididymis; move in the uterus; slow down in isthmus (narrowing), capacitation occurs near the ampulla and they speed up

Question 8

Translocation

Answer 8

Sperm move faster than they swim due to contractions of the uterus caused by prostaglandins in seminal fluid

Question 9

Capacitation

Answer 9

Sperm signaled by ovulation; sperm gain hyperactivity (move really fast), and they get primed for acrosome reaction so they can bind; essential for fertilization

Question 10

CatSper

Answer 10

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

Question 11

Entry of sperm into egg

Answer 11

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.

Question 12

Fast block to polyspermy

Answer 12

(sea urchins and amphibians). Membrane potential depolarized after fusion with sperm. Changes membrane proteins (like sperm binding), last a few minutes

Question 13

Slow block to polyspermy in urchins and amphibians

Answer 13

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

Question 14

Slow block to polyspermy in mammals

Answer 14

Cortical granules modifies ZP3

Question 15

Fertilization signal transduction pathways

Answer 15

Increase [Ca]:activates gene expression, mitosis, stimulates membrane production, slow block to polyspermy; Na influx; fast block; increase in pH: promotes gene expression

Question 16

Calcium pathway at fertilization

Answer 16

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

Question 17

Early protein synthesis after fertilization in urchins

Answer 17

Initial burst and second burst. Initial one is unaffected by transcription inhibitors because mRNA already present in egg.

Question 18

Early protein synthesis after fertilization in mammals

Answer 18

Almost all proteins are newly transcribed, no initial burst

Question 19

Fusion of genetic Material*

Answer 19

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

Question 20

Pronucleus

Answer 20

Haploid, smaller nucleus with pronuclear envelope

Question 21

What happens to sperm mitochondria?

Answer 21

Some enter the egg, but so small in number that it doesn’t affect maternal mitochondrial DNA

Question 22

Rearrangement of egg cytoplasm

Answer 22

Fertilization starts movement of cytoplasm, sets up morphogenetic determinants; movement due to parallel microtubules

Question 23

Colchincine and UV effects on development

Answer 23

Prevents cytoplasm rearrangement; colchicine prevents microtubule formation; UV causes just a clump to form. However spinning UV treated cells causes normal development;

Question 24

Morphogenetic determinants

Answer 24

Factors that will lead to the asymmetry of the mature organism (ie head, tail, organs)

Question 25

Gray crescent in amphibians

Answer 25

Eggs usually half pigmented, half clear; at fertilization the pigment moves and forms a larger clear/gray area; occurs on opposite side of sperm entry;