Fertilization - Video Notes

Flashcards covering the key concepts and details from the fertilization lecture notes.

What are the four major events generally involved in fertilization?

1) Contact and recognition between sperm and egg; 2) Regulation of sperm entry into the egg to prevent polyspermy; 3) Fusion of the genetic material (amphimixis); 4) Activation of egg metabolism to start development.

Which event ensures that the sperm and egg are of the same species?

Contact and recognition between sperm and egg.

How is sperm entry into the egg regulated to prevent polyspermy?

Only one sperm fertilizes the egg; mechanisms prevent additional sperm from entering (polyspermy block).

What is amphimixis?

Fusion of the genetic material of sperm and egg.

What triggers activation of egg metabolism to start development?

Activation of egg metabolism following sperm entry (egg activation).

What is chemotaxis in fertilization and give an example from the notes?

Sperm are attracted/activated by diffusible molecules secreted by the egg; example: Resact from the egg jelly of the sea urchin Arbacia punctulata, leading sperm to aggregate near eggs.

What is capacitation in mammals?

A conditioning period in the female reproductive tract (about 7 hours in humans) that enables sperm to fertilize the egg.

Where does fertilization occur in mammals?

In the ampullary region of the uterus/fallopian tube.

How many sperm are deposited and how many reach the fertilization site in mammals?

300–500 million deposited; about 200–300 reach the site of fertilization.

What are the key zona pellucida glycoproteins and their roles?

ZP3 mediates sperm-specific egg binding; ZP2 mediates subsequent sperm binding; ZP1 cross-links ZP2 and ZP3 and provides structural integrity.

What happens if O-linked oligosaccharides are removed from ZP3?

Destroys ZP3’s ability to serve as a sperm receptor.

What is the role of ZP1 in the zona pellucida?

Cross-links ZP2 and ZP3; not essential for fertilization but important for structural integrity; lack of ZP1 can cause hatch problems.

What sperm enzyme is involved in binding to ZP3 and what happens if it is absent?

Galactosyl transferase (GalTase); its absence (GalTase-null) impairs acrosome reaction and penetration into the ZP.

What happens when GalTase interacts with GlcNAc on the zona?

Causes clustering of receptors on the sperm head, increases Ca2+ in the sperm, and initiates signal transduction.

What occurs during the acrosome reaction?

Release of acrosomal contents; Na+ and Ca2+ influx; H+ efflux with a rise in intracellular pH; enables penetration of the zona pellucida.

Name the acrosomal enzymes released during the acrosome reaction.

Acid proteinase, collagenase, acrosin, β-glucuronidase, hyaluronidase, neuraminidase, phospholipase C.

How is mammalian sperm penetration of the zona pellucida achieved?

Sperm tail hyperactivated motility driven by Ca2+ influx through CatSpers (CatSper channels) is required for penetration.

Where does sperm-egg fusion occur on the egg?

At the equator of the sperm head; the sperm interacts tangentially with the egg plasma membrane.

What happens to the oocyte’s second meiotic division after fertilization?

Ca2+ rise inactivates cytostatic factor and allows completion of meiosis II; the second polar body is extruded.

What is cortical reaction and its consequence?

Release of cortical granule contents into the perivitelline space; hydrolyzes ZP3 and hardens the zona pellucida (zona reaction), helping prevent polyspermy.

What is ZP3f?

Modified ZP3 after cortical reaction due to removal of O-linked oligosaccharides; contributes to zona hardening.

What blocks polyspermy after fertilization?

Proteolysis of ZP2 by ovastacin and shedding of JUNO from the oolemma prevent further sperm binding and fusion.

What is JUNO in fertilization biology?

A receptor on the oolemma that blocks sperm adhesion/fusion after fertilization; it is shed into the perivitelline space.

What triggers egg activation after sperm entry?

Alkalinization of the cytoplasm and increased oxidative metabolism; a sperm-derived factor triggers completion of meiosis and egg activation.

What is amphimixis in fertilization?

Fusion of male and female pronuclei; the sperm contributes the centriole and the nucleus merges with the egg nucleus.

What provides the spindle apparatus for the zygote’s first divisions?

The centrosome provided by the sperm.

What happens to the pronuclei after fusion?

Each pronucleus replicates its DNA; nuclear membranes break at contact and nucleoplasm becomes part of the zygote nucleus.

What is a Complete Hydatidiform Mole (CHM) and how is it different from a Partial Hydatidiform Mole (PHM)?

CHM: oocyte nucleus lost and fertilized by 1–2 sperm; embryo does not develop, but placenta grows. PHM: oocyte nucleus retained and fertilized by 1–2 sperm; triploid; fetus is abnormal.

What is parthenogenesis?

Virgin birth; development of an unfertilized oocyte; common in plants, insects, reptiles; experimentally induced in mammals (e.g., parthenogenic mouse) with various methods.