Ovarian Stem Cells Make Human Eggs in Possible Aid to Fertility

February 28, 2012, 11:02 AM EST
By Ryan Flinn
Feb. 27 (Bloomberg) -- Stem cells taken from human ovaries were used to produce early-stage eggs by scientists in Boston who may have created a new method to help infertile women.
Females have a fixed number of eggs from birth that are depleted by the time of menopause. The finding, published today in the journal Nature Medicine, challenges the belief that their ovaries can�t make more. The research was led by Jonathan Tilly, the director of Massachusetts General Hospital�s Vincent Center for Reproductive Biology.
Tilly reported in 2004 that ovarian stem cells in mice create new eggs, or oocytes, in a way similar to how stem cells in male testes produce sperm throughout a man�s life. His latest work, if reproduced, would suggest the same is true for human ovaries, potentially pointing at new ways to aid fertility by delaying when the ovaries stop functioning.
�The 50-year-old belief in our field wasn�t actually based on data proving it was impossible, or not ongoing,� Tilly said in a telephone interview. �It was simply an assumption made because there was no evidence indicating otherwise. We have human cells that can produce new oocytes.�
In the study, healthy ovaries were obtained from consenting patients undergoing sex reassignment surgery. The researchers were able to identify ovarian stem cells because they express a rare protein that�s only seen in reproductive cells.
The stem cells from the ovaries were injected into human ovarian tissue that was then grafted under the skin of mice, which provided the blood supply that enabled growth. Within two weeks, early stage human follicles with oocytes had formed.
7-Million Eggs
A female is most endowed with oocytes, or eggs, as a fetus, when she has about 7 million. That number that drops to 1 million by birth, and around 300,000 by puberty. By menopause, the number is zero. Since the 1950�s, scientists thought that ovarian stem cells capable of producing new eggs are only active during fetal development.

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Ovarian Stem Cells Make Human Eggs in Possible Aid to Fertility