One step closer to creating human egg, sperm

Israeli and British researchers say they have used human cells successfully to create primordial germ cells that develop into egg and sperm for the first time.

The study, published in the US journal Cell on Wednesday, could provide an insight into fertility problems and early stages of embryonic development.

In the future, it could potentially enable the development of new kinds of reproductive technology.

Researchers have been attempting to create human primordial germ cells in the petri dish for years," said Jacob Hanna of the 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," Hanna said.

"Once these primordial cells become 'specified', they continue developing toward precursor sperm cells or ova pretty much on autopilot."

The idea of creating these cells took off with the invention in 2006 of induced pluripotent stem cells. These iPS cells are 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 kept easily in their stem cell state in the laboratory, 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, creating a new type of iPS cell that team members dubbed "naive cells."

These cells appeared to rejuvenate iPS cells a step further, closer to the original embryonic state from which they can truly differentiate into any cell type, Hanna said.

With a laboratory group under Azim Surani, a professor of physiology and reproduction at Cambridge University in Britain, the researchers found that by using this method they could convert up to 40 percent of the iPS cells into PGC cells.

Hanna said PGCs are only the first step in creating human sperm and ova, but he is confident that eventually it will be possible to use the findings to help enable women who have undergone chemotherapy or premature menopause to conceive.

The study has already yielded some interesting results, including a gene known as Sox17 that is critical for directing iPS cells to become primordial germ cells in humans, but not in mice.