events of fertilization

immediate transport of sperm

retrograde loss of sperm to mucus phagocytosis; some sperm enter into cervix/uterus

cervix

privileged pathway (sperm must have forward motility); some sperm continue to uterus, some stop in cervical crypts

uterus

more phagocytosis; capacitation

capacitation

biochemical change to sperm that allows the true acrosome reaction to occur; 5-6 hrs in cow, 2-3 hrs in sow, 4-6 hrs in ewe, 2-3 hrs in doe, 6-22 hrs in mare

hyperactive motility

step 1 after capacitation - modification of flagellar beat to maximize chance of contact with oocyte

binding to zona pellucida

step 2 after capacitation - ZP1, ZP2, ZP3 proteins

ZP1

structural protein

ZP2

structural protein receptor (2nd binding after acrosome reaction to direct forward movement of sperm)

ZP3

receptor, binds to proteins on sperm

ZBR

zona binding region

ARPR

acrosome reaction promoting region

acrosome reaction

step 3 - true rxn results in fertilization, false = degeneration, post-acrosomal region breaks down; binds to receptor for enzyme release

vesiculation

formation of membrane vesicles, part of acrosome rxn where plasma membrane of sperm binds with its outer acrosomal membrane to expose equatorial region for binding with egg

penetration of zona pellucida

step 4 - acrosomal enzymes allow sperm to digest a hole in zona pellucida big enough to fit through

sperm-oocyte membrane fusion

step 5 - oocyte plasma membrane fuses with equatorial segment of sperm; sperm is engulfed

decondensation of sperm nucleus

step 6 - disulfide bonds on nucleus are reduced to allow male and female chromosomes to interact

cortical reaction

signaled to occur by sperm/oocyte membrane fusion; zona and vitelline blocks (polyspermy blocks)

formation of male pronucleus

step 7 - sperm nucleus becomes pronucleus after entering egg, allows male and female DNA to interact

sygnamy

final fusion of male and female pronuclei into one nucleus (last step of fertilization)