Fertilization

What is fertilization?

The process where the union of two gametes produces a genetically distinct organism.

What is syngamy?

The fusion of two gametes.

What are the major steps of fertilization?

Sperm transport/capacitation → sperm-zona pellucida binding → acrosome reaction → sperm-oocyte fusion → oocyte activation → polyspermy block.

What is capacitation?

The process that makes sperm capable of fertilizing the oocyte.

Where does capacitation occur?

It occurs naturally in the female reproductive tract (in utero) and can also be performed in vitro.

What happens during capacitation?

Sperm undergo membrane and biochemical changes that allow them to bind to and fertilize the oocyte.

What is sperm hyperactivation?

A change to vigorous, high-amplitude sperm motility that helps sperm move through the reproductive tract and interact with the oocyte.

Where can sperm be stored in the female reproductive tract?

Sperm can be stored in the oviduct, where they interact with oviductal epithelial cells (OEC).

How long can sperm storage occur in some species?

Approximately 1-2 days in pigs, cattle, and sheep.

What is the zona pellucida?

A glycoprotein-rich extracellular layer surrounding the oocyte.

What happens when sperm bind to the zona pellucida?

Binding helps initiate the acrosome reaction.

What are the proposed models of sperm-zona pellucida binding?

Glycan, supramolecular, hybrid, and domain-specific models.

What should you know about sperm-zona pellucida binding?

Multiple species-specific models exist, so the exact mechanism can differ among species.

What is the acrosome reaction?

A process in which the sperm acrosome undergoes exocytosis and releases enzymes that help the sperm penetrate the zona pellucida.

What triggers the acrosome reaction?

Sperm-zona pellucida interactions and associated signaling involving calcium and other pathways.

What are three controllers of the acrosome reaction?

Increased acrosomal Ca++, increased acrosomal pH, and phosphorylation regulation of enzymes.

What happens after the acrosome reaction?

The sperm penetrates the zona pellucida and can interact with the oocyte plasma membrane.

What is sperm-oocyte fusion?

The fusion of the sperm and oocyte plasma membranes that allows the sperm nucleus to enter the oocyte.

What is oocyte activation?

The completion of meiosis and formation of a zygote.

What sperm-derived molecule is associated with oocyte activation?

PLC-ζ (phospholipase C zeta).

What does PLC-ζ do?

It promotes Ca++ release in the oocyte, initiating activation processes.

Is PLC-ζ universally present in sperm?

No. PLC-ζ is present in sperm in some species but not others.

What is the major intracellular signal following sperm-oocyte fusion?

A rise in intracellular Ca++.

What are three major actions of Ca++ influx during oocyte activation?

Block polyspermy, complete meiosis II, and control maternal mRNA translation.

What is polyspermy?

Fertilization of one oocyte by more than one sperm.

Why must polyspermy be prevented?

Multiple sperm entering the oocyte can produce an abnormal chromosome complement and prevent normal development.

What is the fast polyspermy block?

A rapid change in the oocyte membrane potential that makes it less receptive to additional sperm.

What is the slow polyspermy block?

Changes to the zona pellucida following fertilization that prevent additional sperm from binding or penetrating.

What happens to cortical granules during the polyspermy block?

They release their contents, modifying the zona pellucida and helping prevent additional sperm entry.

What is the role of cortical granules?

They contribute to the zona reaction that prevents additional sperm from fertilizing the oocyte.

How does fertilization resume meiosis?

PLC-ζ causes Ca++ influx, which activates CAMK-II and leads to Emi2 degradation, APC/C activation, MPF degradation, and completion of meiosis II.

What is CAMK-II?

Calmodulin-dependent protein kinase II, activated by the Ca++ signal during oocyte activation.

What is Emi2?

Early meiosis inhibitor 2, a protein whose degradation is necessary for progression through meiosis II.

What is APC/C?

Anaphase-promoting complex/cyclosome, which promotes protein degradation during cell-cycle progression.

What happens to MPF during oocyte activation?

MPF is degraded/inactivated, allowing the oocyte to exit M-phase and complete meiosis II.