A recent study has overturned one of the fundamental dogmas of reproductive biology, with the discovery that egg cells can be grown from cells extracted from human ovaries.
It had long been held that women are born with a finite number of reproductive cells, and that these cells are not replenished at all during their lifetimes.
A team at Massachusetts General Hospital first challenged this assumption in 2004, when they demonstrated the existence of ovarian stem cells in mice.
The new article, published in the journal Nature Medicine, has now shown that human ovaries also contain stem cells and suggests that contrary to the scientific consensus of the last half century or so, eggs are created throughout a woman’s lifetime.
Lead by Dr. Jonathan Tilly, the researchers scoured unwanted ovaries left over from gender reassignment surgeries for evidence of stem cells. They first used a fluorescent marker to tag cells that contained the protein DDX4, a protein known to occur on the surface of stem cells.
Having extracted the stem cells from the tissue, the cells were then grown in a laboratory, where each cell produced multiple ‘daughter’ cells.
When subjected to tests, these cells were found to have the same chromosomal structure and gene-expression profiles as immature egg cells, or oocytes. They were then injected into human ovarian tissue that had been grafted into mice, where they grew into mature egg cells, ready for fertilisation.
Tight ethical and legal restrictions prevent further research into whether these human cells can in fact be fertilised, but previous studies of mice successfully proved fertilisation was possible.
The research suggests that there is no reason not to think the same is possible with the human egg cells.
Dr. Tilly claims that it may now be possible to dispense with “the idea that there’s a fixed bank account of eggs at birth with only withdrawals and no deposits”, and suggests that it may soon be possible to have an “unlimited” supply of eggs.
The research could pave the way for new fertility treatments, including drastically reducing the cost and hassle of repeated rounds of IVF treatment. Rather than painstakingly extracting eggs in multiple procedures, all that would be needed to grow all the eggs necessary for treatment would be a small piece of ovarian tissue easily acquired by keyhole surgery.
It could also improve the way in which eggs are extracted and preserved from female cancer patients about to undergo chemotherapy.