Stem cell terminology and 'synthetic' embryos: a new debate on totipotency, omnipotency, and pluripotency and how it relates to recent experimental data.

The rapid progress in the stem cell field, in particular in cell reprogramming, combined with certain recent observations from experimental embryology, has ignited a new discussion on stem cell terminology. The current use of terms describing stem cell potentiality is inconsistent and can be confusing, in particular the widely used term pluripotency and its distiction from totipotency. For cells possessing a complete differentiation potential (but lacking an autonomous embryo-structuring capacity) the term omnipotency (or, as recently proposed, plenipotency) has been coined. The present commentary takes up this discussion and confronts it with recent reports on 'engineering' viable fish embryos or gastrulating human germ disc models using 'pluripotent'/omnipotent cells, as well as on symmetry breaking in aggregates of mouse embryonic stem cells. It is concluded that we should start contemplating not only the terminology but also, even more urgently, the ethical implications of the perspective of constructing embryonic anlagen in humans.