Nuclear remodeling after SCNT: a contractor's nightmare

As the success rate of somatic cell nuclear transfer (SCNT) remains low, researchers are turning to the very early stages of pre-implantation development to try to improve the developmental potential of reconstructed mammalian embryos. Two recent papers highlight the role of regulated proteolysis in nuclear remodeling after SCNT. First, Gao et al. describe a rapid, programmed replacement of the somatic-type linker histone H1 inside donor-cell nuclei with an oocyte-derived homolog after SCNT, which is subsequently reversed at the time of maternal embryonic transition. Second, Zhou et aL report the first successful cloning of a rat by using selective blockers of the ubiquitin-dependent degradation of cell-cycle regulator cyclin B. Therefore, a fast, programmed proteolysis might be of central importance for nuclear remodeling after SCNT, particularly in the ubiquitin-proteasome pathway.