In response to physiological demand, the pituitary gland generates new hormonesecreting cells from committed progenitor cells throughout life. It remains unclear to what extent
pituitary stem cells (PSCs), which uniquely express SOX2, contribute to pituitary growth and
renewal. Moreover, neither the signals that drive proliferation nor their sources have been
elucidated. We have used genetic approaches in the mouse, showing that the WNT pathway is
essential for proliferation of all lineages in the gland. We reveal that SOX2+
stem cells are a key
source of WNT ligands. By blocking secretion of WNTs from SOX2+
PSCs in vivo, we demonstrate
that proliferation of neighbouring committed progenitor cells declines, demonstrating that
progenitor multiplication depends on the paracrine WNT secretion from SOX2+
PSCs. Our results
indicate that stem cells can hold additional roles in tissue expansion and homeostasis, acting as
paracrine signalling centres to coordinate the proliferation of neighbouring cells
