As far as reproduction is concerned, it is generally believed that women are not as efficient as men. Men can continuously produce sperm throughout most of their adult life because they have a regular supply of sperm precursor germline stem cells, whereas women come with fixed ovarian germline stem cells that can never be replenished. Worse, these stem cells are made even before birth, so women have no chance of producing new germline stem cells that can maintain a continuous supply of eggs after birth. This situation is cited as a reason for decline in women’s fertility as they get older.
A research paper published in Nature Medicine challenges this notion and proves with scientific evidence that women also come with replenishable germ line stem cells capable of producing oocytes or eggs, and they go on to produce self-renewable germline stem cells even after birth.
In 2004, Dr Jonathan Tilly and colleagues of Harvard Medical School published a paper in the journal Nature on postnatal (after birth) self-renewal of germline stem cells in female mice. This paper caused a storm among scientists working on reproductive biology, and some argued that the mice and human are two completely different species and what is observed in mice is not applicable to humans. Well, Dr Tilly now seems to prove them all wrong.
Dr Tilly’s group developed a technique to isolate germline stem cells from frozen human ovary tissues and replanted those stem cells into mice to see whether they are capable of generating oocytes or eggs. To his excitement, Dr Tilly found mature human eggs developing from the germline stem cells isolated from human ovarian tissue. Dr Tilly confides in an interview given to Nature video, “We knew on that day, and the hairs are standing up on my arm, that indeed these cells exist in the humans.” They have also showed that these stem cells could create human eggs in tissue culture plates in the lab and captured the first video footage of human eggs being formed on lab plates.
These results have the potential to catapult assisted human reproduction into a new trajectory of efficiency and innovation. Until now clinicians in fertility clinics across the world work on the assumption that the female eggs are of limited availability and everything has to be planned and worked within that narrow window of possibility. The results of this research open the possibility of making a million human eggs available to clinicians to assist human reproduction. Dr. Tilly says, “Women could come in and have a small biopsy taken from her ovary for us to retrieve the cells and once we get the cells out we can take hundreds of them and make millions of them, if we can get to the stage of generating functional human eggs outside the body it would rewrite human assisted reproduction.”
References:
Joshua Johnson, Jacqueline Canning, Tomoko Kaneko, James K. Pru & Jonathan L. Tilly, Germline stem cells and follicularrenewal in the postnatal mammalian ovary, Nature, 428, 145-150, 2004
Yvonne A R White, Dori C Woods, Yasushi Takai, Osamu Ishihara, Hiroyuki Seki & Jonathan L Tilly, Oocyte formation by mitotically active germ cells purified from ovaries of reproductive-age women, Nature Medicine, online publication, 2012.
Watch Nature video: http://www.youtube.com/user/NatureVideoChannel?ob=0&feature=results_main