A hierarchy in reprogramming capacity in different tissue microenvironments: what we know and what we need to know.

Ectopic expression of certain transcription factors induces reprogramming of somatic cells to a pluripotent state. A number of studies have shed light on the reprogramming capacity of various cell populations. As a result, it has been shown that stem/progenitor cells derived from organs of all germ layers exhibit a superior reprogramming efficiency compared to their differentiated progeny. Although proliferative capacity and endogenous expression levels of pluripotency factors are likely to be involved in this superiority, the detailed molecular understanding remains elusive so far. Recently, we have shown that the BAF-complex (BAF155 and Brg1), mediating epigenetic changes during reprogramming, is critical for the increased reprogramming efficiency of liver progenitor cells. In this review, we summarize recently acquired findings of the increased reprogramming capacity of adult stem/progenitor cell populations compared to their differentiated counterparts and discuss the potential mechanisms involved.