Do adult stem cells form by lineage commitment or from normal differentiated cells?

As adult stem cells are different from differentiated cells only in transcription profile, maybe they just form form differentiated cells if there is a need for them?
There is some evidence in this thesis that differentiated cells can de differentiate into the originating stem cell state, however transformation into different cell type is unusual. This is kind of expected if DNA methylation indeed determines cell type, but stemness is only determined by gene expression which is much more plastic.