These do-over cells are progeny of renin-secreting cells. The renin–angiotensin system controls body fluid and electrolyte levels. Although many cells make renin during development, those that hold this job in the adult are restricted to a small region of the kidney. During stresses such as dehydration, this population may be unable to make enough renin. To remedy the situation, more cells in and near the kidney begin to produce renin. Gomez's group shows that these helpers come from differentiated cells that had been embryogenic renin producers.
The authors permanently marked any cell in a mouse that ever expressed renin. In the adult, marked cells included nonrenin-producing vascular smooth muscle, epithelial, and mesangial kidney cells. When fluid homeostasis was threatened, it was these marked cells that dedifferentiated and reverted to their renin-secreting ways.
Cells that had never made renin did not contribute. “At least for this system,” says Ariel, “the change in cell identity is determined by the lineage of the cell. Not all cells can do anything.” ▪