The nature of stem cells: state rather than entity.

Stem cells are endowed with self-renewal and multipotential differentiation capacities. Contrary to the expectation that stem cells would selectively express specific genes, these cells have a highly promiscuous gene-expression pattern. Here, I suggest that the transient stem cell state, termed the 'stem state', may be assumed by any cell and that the search for specific genes expressed by all stem cells, which would characterize the stem cell as a cell type, might be futile.