Scientists have identified the gene responsible for controlling a first key step in the creation of new life, according to new research published in the journal Nature.
The gene, known as HIRA, 'chaperones' the early processes that take place once a sperm enters an egg, giving it a crucial role in the most fundamental process in sexually reproducing animals.
The absence or mutation of this gene in the maternal (mother's) genome explains why eggs fail to produce a zygote – or early embryo - despite the presence of 'healthy' sperm.
Although the researchers use the fruit fly Drosophila melanogaster to discover the basic genetic processes of sex, the same genetic processes are present in all sexually reproducing animals, including humans.
"All sexually reproducing animals do the same kind of DNA 'dance' when the DNA from the mother's egg cell and the father's sperm cell meet for the first time," said Dr Tim Karr from the University of Bath (UK) who worked closely with Drs Benjamin Loppin and Pierre Couble from Centre de Génétique Moléculaire et Cellulaire (France) on the project.
"When the sperm enters the egg, the DNA it carries needs to be re-packaged so that it can engage in normal cellular activities, including combining with the maternal DNA in the first act of genetic fertilisation.
"A single gene, HIRA, looks after this re-packaging process, making it fundamental for those first 15 minutes in the regeneration of a new life."
When sperm cells are created, the molecule that the sperm DNA is wrapped around (called chromatin) is remodelled by swapping the type of 'packing material', known as histone proteins, it contains.
When it arrives at the egg cell, however, the sperm DNA needs to be re-packaged with a new set of histone proteins so that the sperm DNA can engage in normal cellular activities. The result is called the male pro-nucleus.
To understand how this process occurs, the researchers used a type of mutant fruit fly, known to biologists as a sésame mutant, which they know does not form a proper male pro-nucleus.
By highlighting the chromatin and watching the changes it goes through at different stages of the fertilisation process, the scientists found that the pro-nucleus in sésame mutant is wound into a tight ball that could not interact with its female counterpart, the egg pro-nucleus.