The research has important implications for understanding the damaging side-effects of the menopause, which is caused when a woman's ovaries go into decline and stop producing female hormones.
Researchers have extended the working life of ovaries in a strain of laboratory mouse that had one of its genes deleted. The "bax" gene normally controls the gradual destruction of follicle egg cells in the two ovaries. Jonathan Tilly, who led the research team at the Massachusetts General Hospital in Boston, said the understanding of what controls the menopause has "major implications" for women.
"This will have enormous impact in terms of understanding the changes in women's health associated with the menopause.
"It is a little premature to talk about the applications of the research to humans but for the first time we now have an animal model that may allow us to extend the lifetime of ovaries in humans." The research is published in the journal Nature Genetics.
Menopause usually occurs between the ages of 45 and 55 and involves a gradual reduction in the levels of the hormones progesterone and oestrogen, which can lead to the dilation of blood vessels as well as having direct effects on the nervous system.
Women can experience mood swings, loss of libido, anxiety and depression as well as suffering physical symptoms such as osteoporosis (brittle-bone disease), head-aches, "hot flushes" and an increased risk of heart disease.
Dr Tilly said that if the studies on mice can lead to a method of delaying menopause by interfering with the body's genetic switch, it would provide a more natural alternative to hormone replacement therapy.
"The problem with HRT is that we can never quite replicate what the body does naturally. This new approach would in effect be a natural hormone- replacement therapy, because the ovaries keep on functioning." Another area of interest would be to understand what happens in women who experience premature menopause in their twenties or thirties, he said.
Menopause is characterised by the exhaustion of the finite number of egg cells a woman is endowed with at birth and uses during the course of her reproductive life.
Dr Tilly and his colleagues were able to show that they can prevent the process of "cell suicide" within the ovary, which normally results in the destruction of egg cells and with them the loss of hormone production. Mice with the genetic switch destroyed continued to have viable ovaries with healthy egg cells well into old age, when they usually suffer a deterioration of ovary tissue that is similar although not identical to what happens in the human menopause.
The scientists found that the old mice which still had functioning ovaries showed signs of retaining many of the faculties that deteriorate in normal females, although tests on bone, heart muscle and brain tissues have yet to prove this, Dr Tilly said.
However, when the older females with rejuvenated ovaries were put in cages with males, they did not become pregnant, showing that fertility is not retained, he added.Reuse content