It is known that nutrient availability affects cell proliferation, but how nutrients affect the proliferation-differentiation programme of cells is unclear. On , Nicola Love and colleagues address this issue, using the ciliary marginal zone (CMZ) of the Xenopus retina as a model. They find that nutrient deprivation (ND) reduces the proliferation, and hence the number, of committed retinal progenitors in the CMZ. By contrast, retinal stem cells at the CMZ peripheral edge are relatively insensitive to ND. Furthermore, ND prevents cells from acquiring a committed progenitor fate, suggesting the presence of a nutrient-sensitive restriction point in the retinal progenitor proliferation-differentiation programme. Finally, the authors show that this restriction point involves mTOR signalling; blocking mTOR mimics many of the effects of ND, whereas activation of mTOR stimulates differentiation. Together, these findings suggest that an mTOR-dependent restriction point in the proliferation-differentiation programme of retinal progenitors exists to couple nutrient availability to tissue growth and development, thus allowing regrowth in ND tissue when conditions of plenty return.
