Recently, researchers at Kyoto University in Japan were able to induce stem cells of rats to become viable eggs, which were then implanted in surrogate mothers. The resultant offspring were fertile, anatomically intact rats that were bred for additional generations, their ancestor being only a cell in a petri dish. This discovery has excited scientists the world over because it marks the first step towards making eggs for infertile humans or gays and lesbians.
The scientists at Kyoto began by taking female embryonic cells and “induced pluripotent stem cells”, and then inducing them to become an early form of eggs. Induced pluripotent stem cells (iPSCs) are adult cells that have been reprogrammed to express certain genes that make them effectively embryonic cells. There is some debate as to whether iPSCs differ from embryonic stem cells taken from harvested embryos, but in this instance they acted identically to the conventional stem cells.
The immature eggs, called “primordial germ-like cells” or PGCLCs, were then surrounded by “female gonadal somatic cells” (cells usually found in an ovary) to create a reconstituted ovary. These constructed ovaries were implanted into surrogate mothers, where the PGCLCs matured into “germinal vesicle-stage oocytes” or early embryos formed during the primary oocyte stage of oogenesis (egg formation), which occurs before birth. The mice that had been implanted with these constructed ovaries eventually gave birth to fertile offspring, which were followed by a few additional generations.
Though scientists have called this discovery a major step forward in reproductive biology, the lead scientist on the Kyoto team, Dr. Hayashi, cautioned: “it is impossible to immediately adapt this system to human stem cells” for a number of reasons scientific and moral. Creating egg cells from stem cells in humans could allow menopausal women to conceive, which brings its own set of moral quandaries as well. Ronald Green, a bioethicist at Dartmouth University, commented on NPR that one had to consider “the commercial possibilities of people selling to infertile people babies produced from George Clooney or Jennifer Aniston.” Evidently, the possibility that egg manufacture might one day be possible has sparked heated debate, but one must remember that it may only be speculation.