Novel approaches and hurdles to somatic cloning in cattle

The overall efficiency of somatic cloning in cattle is still low. Many factors are necessary for successful birth of live offspring. Among them, the source of donor cells reveals the importance of the donor genotype but also the influence of the cell line itself. The cell cycle stage has been intensively investigated, and recent results indicate that, in cattle, the G0 stage of the donor nuclei is not a prerequisite for reprogramming, as highly proliferating cultured fibroblasts also result in live offspring after nuclear transfer. A technical approach using direct microinjection of fibroblast nuclei, instead of fusion of the whole cell, has proved to result in high in vitro development rates in cattle. However, full-term development of somatic cloned embryos is still limited by long-lasting effects and a high incidence of losses at periimplantation time (as well as in late gestation and around calving).