Flashcards in Fertilization Deck (27):
What is fertilization?
the event that sees a single sperm nucleus unite with the egg nucleus within the activated oocyte cytoplasm
What surrounds the oocyte?
-cumulus oophorus (granulosa cells)
Explain the transport of the oocyte
-upon ovulation, oocyte picked up by fimbria of oviduct and transported through the infundibulum to the ampulla
-on entry to the ampulla, it immediately attaches to the oviductal epithelium
(vital that oocyte is still contained within its expanded cumulus matrix during transport)
What is capacitation?
maturational changes sperm undergo in the female tract (acquire capacity to bind to and fertilize the egg)
What is involved with capacitation?
1. removal or modification of proteins that were acquired by the sperm during epididymis passage
2. lowering of cholesterol/phospholipid ratio of sperm plasma membrane
3. hyperpolarization of membrane resting potential in region overlaying acrosome
4. aggregation of lipid microdomains of plasma membrane that contain zona pellucida-binding protein complexes
5. phosphorylation of surface tyrosine residues
Capacitation is speculated to be mediated by changes in what?
1. hormone milieu
2. contents of the oviductal lumen from the ovulated follicular fluid
3. increasing oviductal fluid bicarbonate concentration
What is hyperactivated motility?
increased amplitude of tail movement which also causes side-side movement of the head
What is the function of hyperactivated motility?
detaching sperm from oviductal reservoir
locating the egg
penetration of outer egg coats
What are the 2 thoughts on why capacitation occurs?
1. events surrounding ovulation signal oviductal epithelium to secrete something that triggers capacitation
2. capacitation occurs because of changing conditions as they move up the oviduct
Do sperm have a shorter lifespan once they go through capacitation?
How does the sperm find the oocyte in non-mammalians?
oocyte secretes substances that effect intracellular calcium levels in the sperm (low calcium causes linear swimming and sperm continue up attractant concentration gradient towards egg)
How does the sperm find the oocyte in mammals?
thermotaxis at long distances
some chemotaxis at short distances
How do sperm penetrate the cumulus oophorus?
only capacitated sperm can penetrate the cumulus oophorus because of hyperactivated motility
also have hyaluronidase, which helps break down the hyaluronic acid matrix of the cumulus oophorus
How do sperm penetrate the zona pellucida?
capacitated sperm bind to ZP and undergo acrosome reaction
What is the acrosome reaction?
fusion of outer acrosomal membrane with the plasma membrane of the sperm resulting in exposure of acrosomal content to extracellular environment
What 2 substances are thought to induce the acrosome reaction?
the ZP itself
Binding to the ZP causes a rapid increase in cytosolic calcium in the sperm resulting in what?
1. sperm plasma membrane fuses at multiple points with outer acrosomal membrane causing membrane vesiculation
2. acrosomal contents released, exposing inner acrosomal membrane
3. inner acrosomal membrane binds to ZP2 (glycoprotein on ZP)
What happens to the sperm after the acrosome reaction and binding to the ZP?
-sperm plasma membrane fuses with vitelline membrane, which wells up to surround the sperm
-sperm is now incorporated into the ooplasm
-membrane then breaks down and the sperm nucleus is released into the egg cytoplasm
What are the contributions of the sperm to the next generation?
1. paternal haploid genome
2. signal to initiate egg metabolism/activation
What happens when the egg is activated?
1. escapes 2nd meiotic arrest
2. undergoes the cortical reaction
How does the sperm increase calcium in the oocyte?
introduces a soluble sperm-derived factor (oscillin/oscillogen) that enhances the calcium-induced calcium release from intracellular stores
(calcium triggers entry into meiosis)
What is the male pronucleus?
upon entering the ooplasm, the sperm head separates from the tail and the nuclear membrane degenerates and a new nuclear envelope is formed around it
What is the female pronucleus?
following completion of 2nd meiosis, the female chromatin is decondensed and acquires a nuclear envelope
What is pronuclear migration?
male and female pronuclei are directed towards the center of the cell
What occurs in syngamy?
chromatin in each pronucleus duplicates and condenses and the nuclear membranes break down
Name 3 methods of avoiding polyspermy
1. limiting the number of sperm at the site of fertilization
2. cortical granules of the ooplasm fuse with the vitelline membrane, discharging their enzymatic contents into the perivitelline space (cause zona hardening)
3. vitelline or membrane block (sperm cannot bind or fuse to vitelline membrane)