Photo/Illutration Mitinori Saitou, right, at a news conference in Kyoto on May 17 with Yusuke Murase, center, and Ryuta Yokogawa, two of his fellow researchers at the Institute for the Advanced Study of Human Biology at Kyoto University (Rintaro Sakurai)

In a potential breakthrough for infertility and genetic disease treatments, scientists at Kyoto University have succeeded in mass-generating precursors to sperm and eggs from human iPS cells.

Two weeks after a human egg is fertilized, primordial germ cells (PGCs), which develop into sperm and eggs, are formed.

In six to 10 weeks after fertilization, PGCs differentiate into pro-spermatogonia and oogonia, which are precursors to sperm and eggs, respectively.

Mitinori Saitou, a professor of cell biology, and his fellow researchers announced they successfully created pro-spermatogonia and oogonia by culturing PGCs derived from human induced pluripotent stem cells after adding a protein called BMP2.

They said the number of cells amplified by more than 10 billion times when PGCs were cultured for about four months.

The team’s findings were published in the online edition of the British scientific journal Nature on May 20. 

The technology will make it easy to conduct experiments using pro-spermatogonia and oogonia, which could substantially advance research on germ cells.

Future research could allow scientists to create sperm and eggs from skin, blood and other human body parts and fertilize eggs with sperm, both derived from those body parts.

“We have made a gigantic first step in research to replicate the developmental process of human germ cells in vitro,” Saitou said. “We expect that this achievement will lead to various applications in reproductive medicine and open up a whole range of possibilities.”

Hidenori Akutsu, who heads the Center for Regenerative Medicine at the National Center for Child Health and Development, said the latest research marked a significant step forward in the elucidation of life phenomena, although sperm and eggs cannot be immediately produced.

“Cells that will become the basis of sperm and eggs are formed in a fetus even before various organs are formed,” said Akutsu, who is not part of the research team. “The scientists have reproduced an important process that links generations.”

Saitou and other researchers successfully created human oogonia from iPS cells in 2018.

But they had to employ a special, complicated method of culturing human cells utilizing ovary cells of mouse fetus. The number of oogonia generated was also limited.

Saitou and others earlier created sperm from mouse iPS cells in 2011 and eggs in 2012. A baby mouse was born from the sperm derived from iPS cells.

Even if sperm and eggs are created from human iPS cells, the science ministry’s guidelines on basic research prohibits them from being used for fertilization.

An expert panel on bioethics under the Cabinet Office is discussing how broadly research should be allowed on fertilization using sperm and eggs created from human iPS cells.

(This article was written by Rintaro Sakurai and Shigeko Segawa.)

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