MCDB 240: Fertilization II Flashcards
what’s the difference b/t the acrosomal reactions between urchins and mammals?
urchin: sperm interfaces w/ jelly coat to digest it
mammal: sperm interfaces w/ zona pellucida to digest it
define capacitation: does it occur in mammls and/or urchins?
sperm must spend time in female reproductive tract to enter egg (priming the pump); physiology and contents of sperm are altered and become hyperactivated
compare and contrast first contact of sperm b/t mammals and urchins
urchins: tip of sperm fuses w/ egg
mammals: side of sperm contacts ZP; lytic enzymes are releases FROM the egg, enter to ZP
define chemotaxis and thernitaxis
chemotaxis is the use of a chemical gradient; thermotaxis is the use of a thermal gradient
define the roles of chemotaxis and thermotaxis in urchins and mammals
urchins: utilize chemotaxis (resact gradient’)
mammals: there is little hard evidence of chemotaxis in vivo (purported near fertilization and near cumulus cells). Sperm reacts positively to molecules found in female repro tract and those released by egg; in immediate vicinity of egg there might be a FINAL chemotatctic step in which sperm responds to egg secretions. However, thermotaxis b/t site of egg and storage site of sperm is primary (cold –> hot)
compare acrosomal reactions between the two organisms
urchins: filaments formed, use of bindin
mammals: side-on approach, no formation of acrosomal filament
how is polyspermy blocked in mammals?
there is no clear evidence of a fast block; the slow block consists of changes in ZP, as well as plasma membrane
describe the experiment used to elucidate the role of ZP1/2/3, utilizing mice (NON transgenic)
components of ZP were purified and added back to eggs to see which blocks acrosomal reaction.
Results: 1 crosslinks w/ 2 and 3; 3 is the only protein that blocks acrosomal reaction. 3 initially binds sperm; 2 CAN bind sperm (secondary binding agent); 1 never binds sperm.
it was found that the release of granules, the change in ZP components don’t allow ZP components to bind to sperm anymore.
describe the results from said experiment w/ transgenic mice
mice w/ human ZP2/3 were still producing eggs; said eggs were perceived by mice sperm as mouse eggs still, as they were recognized by the glycoprotein sacc chains on the eggs.
Caveat: human sperm can’t bind mouse eggs even w/ human ZP 2/3, b/c oligosaccaharide side chains of ZP are important for sperm recognition. Mice enzymes responsible for glycosylation are different from glycosylases in humans. ZP still glycosylated like MOUSE ZP; human sperm doesn’t recognize it.
which ZP components are essential for fertility?
experiment: mutated ZP1 still allows for formation of ZP and fertilization; mutated ZP 2/3 –> ZP NOT formed, NO fertilization
describe the Ducibella experiment and why is it significant
experiment proved that there are waves of calcium release, not a single spike.
experiment consisted of egg placed near calcium source, potential was changed so calcium flooded the inside and washed the surface of the egg. goal was to mimic # and duration of waves in fertilized egg; results showed that post-fertilization events are dependent on MULTIPLE spikes of calcium
explain the IP3 and calcium release pathway
sperm triggers PLC (phospholipase C-y) activation, PLC glides to cleave PIP2, embedded to plasma membrane
IP3 and DAG are produced; former mobilizes release of calcium ions, opens channels in ER to flood cytoplasms
later activates protein kinase C; gates the IP3 receptor, which is a calcium-ion channel
do another comparison of urchin and mammal fertilization
urchin: is external, uses chemotaxis, there’s a large # of gametes releases and most are fertilized; large fraction initiates development; meiosis is completed by fertilization, and there is a fast AND slow block.
mammals: internal, unknown chemotaxis (proven thermotaxis), there’s a small # of gametes released; probability of fertilization low, large fraction of fertilizations never develop; meiosis needs fertilization to be COMPLETE, and there is a SLOW block
BOTH: there are immediate post-fertilization events triggered by release of calcium from internal stores
do another comparison of urchin and mammal fertilization
both processes mostly the same, EXCEPT that in mammals, sperm needs to be activated first (capacitation), and the acrosome reaction for urchins has an “acrosome process/filament(?)”; in mammals sperm lyses hole in ZP. in urchins, it’s the fusion of acrosome process membrane and egg membrane (not sperm membrane)
go over the fertilization process in an urchin again
1) sperm reacts to resact gradient
2) sperm makes contact w/ jelly coat -> fast block
3) acrosomal cap has bindin, assists w/ production of acrosomal filament
4) sperm binds w/ plasma membrane
5) corticol reaction (granules releases in perivitelline space)
6) slow block - singular calcium waves (?)
7) hydration of different soluble materials - increases space b/t the two membranes
