Model in which molecular gradients along the apical-basal axis of the olfactory epithelium (OE) generate the neuronal stem cell niche. In the OE, differentiation proceeds in a basal-apical direction, with stem cells (yellow) and intermediate progenitors (shown in red and green) lying in a basal compartment, underneath the post-mitotic olfactory receptor neurons (shown in blue) to which they give rise. Note that localized expression, along with the interaction of growth differentiation factor (GDF)11 and activin with Fst (a high affinity antagonist of both proteins), create a niche within the OE in which the activity of factors that promote neurogenesis (for example, GDF7) is high, and that of factors that inhibit neurogenesis (for example, GDF11, activin) is low.
Lander et al. BMC Biology 2012 10:19 doi:10.1186/1741-7007-10-19