Nuclear reprogramming: what has been done and potential avenues for improvements

Abstract A major challenge for reproductive biologists is the development of novel strategies to improve cloning efficiency. Even in species for which cloning is relatively successful, like cattle, the efficiency is still unacceptably low. In this review article we critically analyse all approaches that have been suggested by different laboratories in the field so far. As will be discussed below, so far none of these gives rise to a dramatic increase in cloning efficiency. Possibly, a multi-step approach including a pre-treatment of donor cells to modify their chromatin, along with improved culture system for cloned embryos would be the most promising