In attempting to gain greater insight in the placental abnormalities that frequently occur in cloned animals, Japanese scientists M. Oda et al. from the University of Tokyo reported in today's (September 22nd) issue of PNAS their results on successfully isolating and cultivating mouse trophoblast stem (TS) cells from blastocysts produced by somatic cell nuclear transfer (NT). The isolated cells had the typical morphology of TS cells from native blastocysts. The investigators were able to maintain undifferentiated TS cells in vitro and genetic analysis revealed that the ntTS cells were indistinguishable from control TS cells. When the ntTS cells were implanted into a normal blastocysts, the researchers found that the cells contribute exclusively to the development of the mouse placenta until term in chimeras. The authors concluded that "NT blastocysts contain cells that can produce TS cells in culture, suggesting that proper commitment to the trophoblast cell lineage in NT embryos occurs by the blastocyst stage."