Stem cells: How to make an egg

A set of eight transcription factors can convert mouse stem cells into egg-like cells in the laboratory, reports a study in Nature. The findings further our understanding of egg development and may have implications for reproductive medicine.

The development of oocytes (immature egg cells) occurs in multiple stages, but the regulatory network of genes involved in this process is unknown.

Using embryonic stem cells from mice, Katsuhiko Hayashi and colleagues identified eight transcription factors (proteins that regulate gene expression) that were required to trigger oocyte growth. The authors then tested whether the eight transcription factors were sufficient to drive oocyte growth, by inducing their expression in mouse pluripotent stem cells. They found that this resulted in the production of egg-like cells, which they named directly induced oocyte-like cells. While these cells did not undergo meiosis, they were capable of being fertilized and could divide up to the 8-cell stage of embryonic development. However, further development beyond this point was compromised.

The authors suggest that their egg-like cells could provide a possible source of oocyte cytoplasm, a unique material that is highly valuable in assisted reproductive technologies.