Fig. 7.

Schematic depiction of aspects of adult olfactory GBC regulation. Expansion-competent stem cells (SC) are defined by expression of SOX2, HES1, Id genes and BMI1/PRC proteins. c-KIT signaling promotes self-renewal rather than progression to progenitor cells that will commit to differentiation. PRC proteins regulate proliferation. Neural progenitor cell GBCs (NPC) express the bHLH factors ASCL1 (early) or NEUROG1 (late), while immature olfactory neurons (ONi) express neurotubulin (Tubb3) and mature neurons (ONm) express OMP. TGFβ ligands signal via Alk5 receptor-mediated Smad2/3 phosphorylation to inhibit GBC activity, and blockage of this pathway using SB431542 facilitates GBC culture expansion.