Stem cells reported to produce human eggs
BOSTON, MA – At birth, a woman has all the oocytes (eggs) available for reproduction. Unlike a man, who continually produces sperm throughout his lifetime, no more will develop. At puberty, one or more ova mature and can be fertilized. At menopause, oocyte production ceases. Furthermore diseases such as cancer or infection can leave a woman without the ability to reproduce. Currently, women who need to need to preserve their fertility can have oocytes, a portion of an ovary, or fertilized embryos for future use.
Now, researchers have developed a new method of fertility preservation: generating human oocytes from stem cells. A research team lead by reproductive biologist Jonathan Tilly, PhD and colleagues at Massachusetts General Hospital (Boston, MA) published their findings online on February 26 in the journal Nature Medicine. Their research was conducted on a mouse model as well as women who were undergoing gender reassignment because of a gender identity disorder. (Individuals with a gender identity disorder are born with normal genitalia of one sex but identify with the opposite sex.)
Dr. Tilly discovered that the ovaries of reproductive-age women contain a small amount of gemline stem cells. The next step of the research was to develop a method of isolating them from the rest of the cells in a laboratory setting. Initially, using mice, the researchers used a cell-sorting machine to separate out a germline stem cells from ovaries that can produce oocytes, which are capable of fertilization. The researchers then applied the same process to human ovaries. The ovaries were donated by women at the Saitama Medical Center in Japan who were undergoing sex reassignment. The researchers were able to retrieve germline stem cells, which were capable of producing oocytes capable of fertilization.
To identify the germline stem cells, the researchers developed a fluorescence-activated cell sorting-based protocol. Once established in vitro (in the laboratory), these cells divide for months; thus, spontaneously generating oocytes. For the human study, the stem cells were injected into the donated ovarian tissue. One to two weeks following injection, the cells developed into mature oocytes, which contained a single set of chromosomes.
Although the research has practical applications for women interested in preserving their fertility, it currently is at an early stage and hurdles need to be overcome. One obstacle is that the human ovum is susceptible to the development of mutations over time. An example of this is the fact that genetic disorders such as Down syndrome increase in frequency with older women. Many researchers feel that growing oocytes in a laboratory setting could accelerate that process.
Reference: Nature Medicine