The scientists, from Kyoto University, first produced healthy mouse pups in 2011 using stem cell-derived sperm. They have now achieved the same by using eggs which were created in the same way.
Scientists are describing the Kyoto team's feat as a "significant achievement" which will have a profound impact on reproductive cell biology and genetics research.
In both cases, the scientists used ES (embryonic stem) cells and iPS (induced pluripotent stem) cells. ES are taken from embryos while iPS come from reprogrammed adult tissue cells that mimic stem cell behavior.
Theory suggests that both ES and iPS cells can produce all the cell types in the body. However, the majority of scientists have not been able to make them turn into germ cells, which eventually become eggs or sperm.
Mitinori Saitou and team hit upon a process that managed to turn stem cells into germ cells. They started off with ES and iPS cells and cultured them into a mix of proteins to produce primordial germ cell-like cells.
Their aim was to get precursor egg cells, known as oocytes. They mixed the primordial cells with fetal ovarian cells, and formed reconstituted ovaries which were grafted onto natural ovaries within live mice. Exactly four weeks and four days later, the primordial germ cell-like cells had turned into oocytes. The ovaries were removed from the mice and the oocytes harvested, fertilized in petri dishes, and the resulting embryos were implanted into surrogate mothers.
Baby mice born without the need for any fathersWithin around three weeks, the surrogate mothers gave birth to healthy mouse pups.
The journal Science quoted Davor Solter, from Singapore's Institute of Medical Biology, as saying:
"It is remarkable that one can produce oocytes capable of sustaining complete development starting with embryonic stem cells."
The team now plan to get a better understanding of the molecular mechanisms that were at work when the germ cells were being formed.
They believe that they may eventually be able to coax the cells through the entire oocyte development process in a lab dish, effectively bypassing the grafting.
This breakthrough could eventually pave the way for treating infertility in humans, the authors believe.
In an interview with Science, Amander Clark, a stem cell biologist at University of California, Los Angeles, USA, said:
"This study has provided the critical proof of principle that oocytes can be generated from induced pluripotent stem cells."
We could eventually create oocytes from iPS cells taken from infertile women, Clark added. However, Saitou said that we are still far from using this technology on humans, and there are some "thorny ethical issues and technical difficulties".
At the extreme, with this breakthrough scientists will eventually be able to produce human embryos from tissue samples and cell lines. However, Solter warns that "defining the status of such 'parentless' human embryos and the biological, ethical, and legal issues they will raise defies the imagination."
In February, 2012, US researchers managed to isolate stem cells from the ovaries of reproductive age women and use them to make egg cells that appear to behave normally.
Written by Christian Nordqvist