Researchers have identified a mechanism by which cells undergo reprogramming in live mice, a phenomenon that had previously been poorly understood. The finding could potentially lead to new therapies to boost tissue repair and regeneration. Scientists have shown that when "adult" cells with an established identity are manipulated to express four transcription factors, collectively called OSKM, they revert to an immature state and can then differentiate into new cell types. This work had been done with cells growing in a laboratory dish, however. Whether and how such "reprogramming" occurs in living animals was unclear. To gain further insights, Lluc Mosteiro and colleagues studied cell reprogramming in a mouse model. They found that OSKM triggers reprogramming in vivo - but by a complex mechanism. OSKM appears to trigger cell damage and cell senescence (a state in which cells stop dividing but do not die). The senescent cells secrete certain proteins, including an inflammatory cytokine called interleukin-6, that promote reprogramming of neighboring cells. The authors note that senescent cells accumulate in injured tissue and they speculate that the reprogramming mechanism they identified may contribute to the normal process of tissue repair as well. If so, this newly uncovered mechanism could potentially be exploited as a therapy to promote tissue repair.