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Israeli and British researchers said Wednesday they have successfully used human cells to create primordial germ cells that develop into egg and sperm for the first time.
The study, published in the U.S. journal Cell, could help yield insight into fertility problems and early stages of embryonic development and potentially, in the future, enable the development of new kinds of reproductive technology.
"Researchers have been attempting to create human primordial germ cells (PGCs) in the petri dish for years," said Jacob Hanna of Weizmann Institute of Science in Israel, who led the study.
"PGCs arise within the early weeks of embryonic growth, as the embryonic stem cells in the fertilized egg begin to differentiate into the very basic cell types. Once these primordial cells become 'specified,' they continue developing toward precursor sperm cells or ova "pretty much on autopilot," said Hanna.
The idea of creating these cells took off with the 2006 invention of induced pluripotent stem (iPS) cells -- adult cells that are "reprogrammed" to look and act like embryonic stem cells, which can then differentiate into any cell type.
Several years ago, researchers in Japan successfully got mouse iPS cells to differentiate into PGCs, but efforts to replicate the achievement in human cells have failed.
The researchers found that the mouse embryonic cells are easily kept in their stem cell state in the lab, while human iPS cells have a strong drive to differentiate.
In the new study, Hanna's team created a method to tune down the genetic pathway for this differentiation, thus creating a new type of iPS cell that they dubbed "naive cells."
These naive cells appeared to rejuvenate iPS cells one step further, closer to the original embryonic state from which they can truly differentiate into any cell type, Hanna said.
Together with the lab group of Professor Azim Surani of Cambridge University, the researchers found using this method they were able to convert up to 40 percent of the iPS cells into PGC cells.
Hanna noted that PGCs are only the first step in creating human sperm and ova, but he is confident that it will one day be possible to use the findings to help enable women who have undergone chemotherapy or premature menopause to conceive.
In the meantime, the study has already yielded some interesting results, including a gene known as Sox17 that is critical for directing the iPS cells to become primordial germ cells in humans, but not in mice.
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