SUMMARY
The intestinal epithelium is maintained by a small number of self-renewing stem cells in homeostasis. In addition committed progenitors can contribute to the functional stem cell compartment at a low level during homeostasis and substantially during regeneration following tissue damage. However the mechanism of, and requirement for, progenitor plasticity in mediating pathological response has not been demonstrated. Here we show that multisite phosphorylation of the transcription factor Atoh1 is required both for the contribution of secretory progenitors to the intestinal stem cell pool and for a robust regenerative response following damage. In lineage tracing experiments Atoh1+ cells (Atoh1(WT)CreERT2 mice) show stem cell activity by giving rise to multilineage intestinal clones both in the steady state and after tissue damage. Notably in the colonic epithelium a single generation of Atoh1+ progenitors sustains 1 in 15 stem cells. In an activating Atoh1(9S/T-A)CreERT2 line, the loss of phosphorylation sites on the Atoh1 protein promotes secretory differentiation and inhibits the contribution of these cells to self-renewal. Finally, in a chemical colitis model the Atoh1+ cells of Atoh1(9S/T-A)CreERT2 mice have reduced clonogenic capacity that impacts overall regenerative response of the epithelium. Thus progenitor plasticity plays an integral part in maintaining robust self-renewal in the intestinal epithelium and the balance between stem and progenitor fate behaviour is directly co-ordinated by Atoh1 multi-site phosphorylation.
