Stem cells: Differentiated cells in a back-up role

Abstract

Two independent studies show that, if push comes to shove, differentiated cells of the stomach and lung can act as adult stem cells generating various cell types of the tissue, including a pool of stem cells.

Figure 1. Two tissues, similar dedifferentiation process

a, In the crypts of the stomach body, undifferentiated adult stem cells (asterisk) occupy the stem-cell zone, whereas functional, enzyme-secreting chief cells (blue) reside at the base. During cellular turnover, stem cells generate all cell types of the crypt (Normal, stem cell descendants in orange). But Stange et al. find that if stem cells are destroyed, mature chief cells assume a stem cell role, renewing even the depleted stem cells (Stem cell ablation, chief cell descendants in blue). Note, chief cells infrequently renew crypts in the absence of obvious injury (dotted line). b, The adult tracheal stem cells called basal cells (asterisk) replenish secretory Clara cells and multiciliated cells under physiological and injury conditions (Normal, basal cell descendants in orange). Rao Tata et al. report that if these stem cells are ablated, differentiated Clara cells become activated to regenerate basal cells, which resume the task of maintaining tracheal cell types (Stem cell ablation, Clara cell descendants in blue).