Histones help clones forget their pasts

Amid the hype surrounding cloning by somatic cell nuclear transfer, the astonishingly low success rate of the process has received relatively little attention. Now, on page 37, Kim et al. show that histone deacetylation is an important feature of the nuclear reprogramming that occurs in oocytes, both during normal meiosis and in nuclear transfer experiments. The work suggests strategies that could improve the efficiency of cloning, and also helps to explain how somatic cells retain their identities during mitosis.

Using immunocytochemistry, the authors examined changes in histone acetylation in oocytes during meiosis, and compared these with mitotic acetylation patterns. In meiotic oocytes, histone acetylation levels drop markedly. A similar decrease occurs in somatic cell nuclei that are transferred into enucleated oocytes. During mitosis, however, the same sites on histones remain acetylated. The histone...