Scientists have found the gene responsible for controlling a first key step in the creation of new life; the gene helps sperm combine DNA with the egg's DNA.

The HIRA gene is involved in the events necessary for the fertilisation that take place once a sperm enters an egg.

Faults in this gene might explain why some couples struggle to get pregnant despite having healthy sperm, say the researchers from the UK and France.

It may be worth screening infertile couples to see if they have a faulty version of HIRA, experts suggested.

Although their work in Nature is based on fruit flies, the same genetic processes are present in humans.  A slight mutation in the HIRA gene means that life does not even get started Lead researcher Dr Tim Karr [University of Bath] said: "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." When the sperm enters the egg, its DNA has to undergo a complete transformation so that it can properly join with the female DNA to form a genetically complete new life.

Sperm makes this change by swapping the type of  'packing material', known as histone proteins, it contains. The result is called the male pronucleus, which can then combine with the female pronucleus. The process is controlled by the HIRA gene.  There may be a rationale for screening infertile couples for mutations in HIRA.

Dr Karr, who worked alongside French scientists from Centre de Génétiqiue Moléculaire et Cellulaire, said: "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. This is one of the most crucial processes that takes place in sexually reproducing animals. A slight mutation in the HIRA gene means that life does not even get started."

To understand the process better, the researchers studied a type of mutant female fruit fly, known to biologists as a sesame mutant, which they know produces eggs that do not allow a proper male pronucleus to form.

They found that HIRA is the gene responsible for chaperoning the assembly of the sperm pronucleus and if it is damaged in any way in the egg then fertilisation fails.

The research was funded by a Wolfson Royal Society Merit Award, the Centre National de la Recherche Scientifique and the French Ministry of Research.

Wolf Reik of the Babaraham Institute said: "This is a really exciting discovery. This could indeed be an explanation for some types of infertility in humans; if there were females that carried this mutation, they would not be able to conceive normally. There may be a rationale for screening infertile couples for mutations in HIRA in order to provide best counselling on infertility." [BBC, Dr Tim Karr, http://news.bbc.co.uk/1/hi/health/4377898.stm; N Valko RN, 28Oct05]