Japanese researchers announced that they can make adult differentiated cells behave like embryonic stem cells, just by exposing them to four different proteins. The findings, reported yesterday in the journal Cell, could be the first step toward the holy grail of stem cell biology: a way to create stem cells without the use of human eggs.

Human eggs are a very limited resource and using them for research is ethically questionable to many people (see my “Stem Cells Reborn”). However, eggs and embryos are currently the only source of new lines of embryonic stem cells. In addition, eggs are the only known way to make “patient-matched” stem cells, a feat that has been carried out successfully in mice and other animals, but not yet in humans.

The Japanese researchers picked 24 genes known to be expressed in early embryos and tested the genes’ ability to reprogram adult cells. They found that a combination of four of these genes can make adult cells behave much like stem cells. The cells could differentiate into the three main tissue types found in human embryos, which eventually give rise to all organs.

While the results are exciting, it’s not yet clear if the same process will work with types of adult cells other than the fibroblast cells, found in connective tissue, that the current experiment focused on. And further research is needed to determine if these reprogrammed cells truly behave like embryonic stem cells and would be useful for cell replacement therapies. – By Emily Singer