• Kyodo

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A team of researchers has achieved a world’s first by using induced pluripotent stem cells from a mouse tail to produce a large number of eggs in vitro, according to a study published in the British science journal Nature.

Until now, mouse iPS cells had to be transplanted to a different mouse ovary for eggs to become capable of fertilization, but the team, consisting of researchers from Kyushu University, Kyoto University and other institutions, achieved the process using only cultures.

Further improving the technology could within several years open up the possibility of producing human eggs from iPS cells, said Kyushu University professor Katsuhiko Hayashi, one of the researchers.

The technology may also help “shed light on the cause of infertility” if the team can replicate the egg creation process using iPS cells derived from infertile women, and “be useful for the conservation of endangered species” if a large number of eggs can be created in vitro, Hayashi said.

The creation of human eggs, however, may raise ethical problems. In theory, the technology could enable humans, regardless of gender, to create eggs from iPS cells generated from their skin.

In Japan, government guidelines allow iPS cells, which can grow into any type of human body tissue, to be converted to eggs and sperm, but prohibit their use to create fertilized eggs.

According to the latest study, the team first created what is known as “premordial germ cells” from iPS cells derived from a 10-week-old mouse’s tail. Eggs and sperm originate from premordial germ cells.

The team then cultured the premordial germ cells by using various reagents for about five weeks, the time a mouse usually needs to create an egg.

Around 4,000 eggs were created under certain conditions and the eggs were fertilized in vitro by using ordinary sperm. As a result, about 1,300 fertilized eggs were produced and eight mice were born from them.

But challenges remain in the process because the mouse birthrate using the process stood at less than 1 percent. If normal eggs are used, the success rate of in vitro fertilization stands at 60 to 70 percent, according to Kyushu University.

The team acknowledged that improving the quality of the eggs, such as by creating better culture conditions, is an issue that needs to be tackled.