PFC has also developed a method to ease hatching of the embryo, given that vitrification can harden the outer shell surrounding it (the zona
pellucida).
Day 20 of pregnancy sees the zona
pellucida being replaced by the trophoblast (also known as the trophoderm).
The most promising contraceptive is porcine zona
pellucida (PZP), which causes a mare's immune system to attack fertilised eggs.
Hay's team also showed that the same approach could be used to make female mice generate antibodies to the zona
pellucida, a layer of proteins that surrounds egg cells.
Human sperm adhered to the mouse zona
pellucida if it contained human ZP2 but not if it carried human ZP3, confirming the importance of ZP2.
A study in The Journal of Cell Biology now identifies the protein in the zona
pellucida that sperm latch onto.
The zona
pellucida protects the egg and the early embryo before implantation.
The images depict what might be called embryology in flagrante: micrographs of sperm cells, trailing accordion - like pleats of white zags as they streak across a vast blue ocean of ooplasm; a multihued blastocyst in the process of hatching out of the egg's zona
pellucida; and egg cells with a fringe of glowing, fate - determining proteins, looking a bit like a solar eclipse inside a cell.
When a sperm cell meets an egg cell (the oocyte), it burrows through the thick outer rind surrounding the egg (the zona
pellucida), enters the internal cytoplasm of the egg (the ooplasm), and locomotes its male DNA — half of the typical number of chromosomes — to the female half within about three to four hours.
However, he notes, some sperm can attach to the egg even with distracting sialyl - Lewisx molecules nearby, suggesting that binding to the zona
pellucida involves another interaction, probably between a protein on the sperm and a protein on the egg.
Their sperm can bind to an egg, the team found, and even burrow through the zona
pellucida, but fertilization never occurs.
As the team reports online today in Science, the sugars from human zona
pellucida predominantly carry one kind of carbohydrate branch, a structure known as sialyl - Lewisx.
Sperm racing to fertilize an egg face numerous hurdles, including burrowing through the zona
pellucida, a thick wall surrounding the cell membrane.
The researchers then used mass spectrometry to identify the carbohydrates in zona
pellucida material from the eggs.
The zona
pellucida in humans contains four kinds of proteins.
«It's the first time we've had any detailed analysis of the human zona [
pellucida],» says Christopher Barratt, a reproductive biologist at the University of Dundee in the United Kingdom.
Before fertilization can occur, a sperm must fasten to the zona
pellucida, a membrane that encases the egg.
One - step collagenase method for zona
pellucida removal in unfertilized eggs: easy and gentle method for large - scale preparation.
Four different stages of oocytes, striped of their zona
pellucida (ZP), were assayed: 1) GV (germinal vesicle), 2) MI (metaphase I), 3) MII (spontaneously matured metaphase II before IVM) and 4) IVM - MII (in vitro matured metaphase II).
This technology — vectored contraception — utilizes a single intramuscular injection to bring about transgene - mediated expression of proteins that inhibit fertility through action on targets such as GnRH, a master reproductive hormone, the egg zona
pellucida, which is an essential binding site for sperm, or sperm.
Two reproductive antigens, zona
pellucida and GnRH, have been identified as possible targets for fertility control in cats.