Faithful reprogramming to pluripotency in mammals - what does nuclear transfer teach us?

Nuclear reprogramming toward pluripotency has been now achieved either in vivo by somatic cell nuclear transfer into the ooplasm of an enucleated egg, or in vitro by three different approaches, namely cell fusion, treatment with cell extracts and more recently, forced expression of a reduced set of defined transcription factors. This last technique has expanded our view of genome plasticity with important applied perspectives in regenerative biomedicine. Because of their ease of generation, induced pluripotent stem cells represent a major hope in the field of regenerative medicine. However, the extent to which such an in vitro induced pluripotency can be considered to be equivalent to embryonic-derived pluripotency remains undetermined and also largely dependent on how pluripotency is assessed. Here, we provide an overwiew of the data published in the recent literature on the ability of each of the above techniques to reprogram somatic nuclei into pluripotent embryonic-like nuclei. These data support the view that even though nuclear transfer is technically demanding, it remains a fast and efficient means for a systematic derivation of bona fide embryonic stem cells from somatic donor cells. We conclude that nuclear transfer has still much to teach us about faithful nuclear reprogramming to pluripotency.