Brave new eggs

For anyone proposing to generate a clone army, or even to do therapeutic cloning for tissue repair, the culturing of oocytes is a major stumbling block. The poor success rate of cloning means that hundreds of oocytes are needed to receive transferred nuclei. Luckily, every woman has millions of oocytes. But almost all of those oocytes are trapped in an immature state that is not competent for either fertilization or productive receipt of a transferred nucleus.

Yayoi Obata, Izuho Hatada (Gunma University, Gunma, Japan), and colleagues have made some progress along these lines by successfully culturing female germ cells derived from mouse fetuses. Unfortunately, progression through meiosis and then efficient blastocyte development required successive nuclear transfers into the cytoplasm of mature oocytes. These nuclear transfer steps make this approach useless from the...