What is the nuclear maturation state of human gametes at fertilization?
The spermatozoon has completed meiosis, while the oocyte is arrested at metaphase II.
What percentage of spermatozoa are lost from the vagina after coitus?
99% of spermatozoa are lost from the vagina; only a few enter the tract and may survive in cervical crypts.
What is the typical sperm:oocyte ratio at the site of fertilization in vivo?
The sperm:oocyte ratio approaches 1:1 at the ampulla. Only about 5 spermatozoa were found in a human female ampulla, and in mice it was observed as 1:1 with no supernumerary spermatozoa.
What is the principal chemoattractant that guides sperm to the oocyte?
Progesterone acts as the principal chemoattractant, with calcium entry as an important second messenger.
What are the three major components of semen and their sources?
Prostatic liquid (rich in acid phosphatase)
Vas deferens fraction (containing spermatozoa)
Seminal vesicle fraction (containing fructose)
What is capacitation and how long does it take in humans?
Capacitation is the process by which spermatozoa develop the capacity to fertilize an oocyte. It takes 1-4 hours (5-6 hours) in humans and involves membrane changes, cholesterol efflux, and development of hyperactive motility.
What percentage of spermatozoa are capacitated at any one time?
Only 10% of the available sperm population are capacitated at any one time. Capacitated spermatozoa are continuously replaced from the stored pool.
What is hyperactivation and what is its purpose?
Hyperactivation is a change in flagellar beating with increased amplitude. It helps release spermatozoa from oviductal epithelium, enhances navigation toward the oocyte, and helps penetrate the zona pellucida
What are the three stages of the acrosome reaction?
Outer acrosomal membrane fuses with sperm head plasma membrane
Acrosomal granule breaks down, releasing lysins
Sperm head plasma membrane contacts and fuses with oocyte plasma membrane
What ion is required for the acrosome reaction to occur?
Ca²⁺ (calcium) is required. The acrosome reaction only occurs in the presence of calcium.
How long does the acrosome reaction take in vitro?
The acrosome reaction is relatively rapid, taking 2-15 minutes in vitro once triggered.
What is the composition of the zona pellucida?
The zona pellucida consists of 70% protein, 20% hexose, 3% sialic acid, and 2% sulfate.
What is the role of ZP3 in fertilization?
ZP3 binds to primary receptors on capacitated spermatozoa and induces the acrosome reaction. It serves as the primary adhesion molecule.
Where are sperm receptors for ZP2 located?
Sperm receptors for ZP2 are located on the inner acrosomal membrane, so they are only unmasked after the acrosome reaction has taken place.
What are the two protein kinases that maintain metaphase II arrest in oocytes?
Maturation Promoting Factor (MPF)
Cytostatic Factor (CSF)
What are the core components of MPF?
The core components are CSF and cyclin-dependent kinase 1 (Cdk1/Cdk2), though more accurately MPF consists of cyclin B and Cdk1/p34cdc2.
What is the ZP domain (ZPD) and how many amino acids does it contain?
The ZPD is a structural element found in all ZP proteins, composed of 260 amino acids. This domain is also found in many other proteins with different functions.
What are Izumo1 and Juno?
Izumo1: A sperm transmembrane protein (named after a Japanese marriage shrine)
Juno: An oocyte surface receptor (named after the Roman goddess of fertility)
These proteins interact as a necessary adhesion step for gamete fusion.
What happens to Juno after fertilization?
Juno is rapidly lost from the oocyte surface after fertilization.
What are lipid rafts and what is their role in fertilization?
Lipid rafts are membrane domains of 10-200 nm enriched in cholesterol, sphingomyelin, and gangliosides. They may concentrate signaling proteins at the site of gamete interaction to promote adhesion and fusion.
What type of channels does the spermatozoon activate in the human oocyte?
The spermatozoon induces an outward current by activating calcium-gated potassium channels in the oocyte plasma membrane.
What are cortical granules and where are they located?
Cortical granules are spherical membrane-bound organelles containing enzymes and mucopolysaccharides that lie peripherally in the oocyte cortex. They are synthesized during early oocyte growth
What is ovastacin?
Ovastacin is a protein of the metalloproteinase family found in cortical granules, similar to hatching enzyme.
What are the two hypotheses for how spermatozoa trigger intracellular calcium release?
- The G-protein hypothesis: Sperm acts as an “honorary hormone” triggering IP3 formation through a G-protein receptor
- The soluble sperm factor hypothesis: A diffusible messenger in sperm cytoplasm enters the oocyte after fusion
