Dogma on mammals' eggs scrambled
18:00 10 March 04

Contrary to popular belief, female mammals produce new eggs after birth, a
new study in mice suggests.

Male mammals continually produce sperm from a store of stem cells. But since
the 1950s, biologists insisted that no egg stem cell source existed in adult
female mammals, so that a woman only has the eggs she was born with. The
numbers simply decline until the menopause, when the supply is exhausted.

Years of research supported this belief. For example, when biologists opened
mouse ovaries and counted the number of healthy follicles - the tiny sacs in
which eggs grow - they found the number declined slowly with age.

Jonathan Tilly says his team at the Massachusetts General Hospital in Boston
took a different approach because they studied atresia, the process by which
the follicles die.

They discovered that follicles were dying so rapidly in mouse ovaries that
the egg supply should have been depleted in a few weeks, even though female
mice are fertile for more than a year.

Text book

Since the number of living follicles dropped much more slowly, that
suggested - contrary to every text book on reproductive biology - that new
egg follicles were being created well into adult life from stem cells. "We
didn't expect to challenge the dogma," says Tilly. "We are just as shocked
as everyone else."

To prove directly that new egg cells were being created, his team implanted
parts of the ovaries of normal mice into mice that were genetically
engineered to produce a glowing protein in all their cells.

After a few weeks, the implanted ovary grew new follicles, containing the
glowing protein. Stem cells from the modified mice had infiltrated the
transplant and formed new eggs.

If such stem cells exist in women, they could provide a way to treat
infertility problems, such as the destruction of eggs during cancer
chemotherapy. "Women could essentially grow back their ovaries after
therapy," says Tilly. "The possibilities are almost too numerous to
mention."

Journal reference: Nature (vol 428, p 145)

Philip Cohen

>From NewScientist
http://www.newscientist.com/news/news.jsp?id=ns99994765

Posted by
Robert Karl Stonjek.
---
þ RIMEGate(tm)/RGXPost V1.14 at BBSWORLD * Info{at}bbsworld.com

---
 * RIMEGate(tm)V10.2áÿ* RelayNet(tm) NNTP Gateway * MoonDog BBS
 * RgateImp.MoonDog.BBS at 3/11/04 8:35:05 PM