Placental insufficiencies in cloned animals - a workshop report.

This workshop focused on describing clinical problems identified in the placentae of cloned animals and some of the potential biological mechanisms by which these anomalies arise. It was shown that placental anomalies related to somatic cell nuclear transfer (SCNT) in cattle often can be detected by ultrasonography early in gestation, enabling preventive clinical intervention. On the mechanistic front, the vascular defects in the placenta appear to be associated with anomalies in the expression of VEGF system, which could lead to the aberrant placentomes and generalized oedema seen in some gestations. Moreover, an upstream transcription factor (Mash2) controlling the differentiation of trophoblast into binucleate cells may be involved in the poor implantation rates of SCNT embryos. Finally, epigenetic patterns in placenta can be disrupted by fairly simple in vitro manipulations, which could explain the extreme anomalies observed in the placenta of SCNT pregnancies.