GENESIS OF OLFACTORY RECEPTOR NEURONS IN-VITRO - REGULATION OF PROGENITOR-CELL DIVISIONS BY FIBROBLAST GROWTH-FACTORS

Olfactory receptor neurons are produced continuously in mammalian olfactory epithelium in vivo, but in explant cultures neurogenesis ceases abruptly. We show that in vitro neurogenesis is prolonged by fibroblast growth factors (FGFs), which act in two ways. FCFs increase the likelihood that immediate neuronal precursors (INPs) divide twice, rather than once, before generating neurons; this action requires exposure of INPs to FCFs by early G1. FCFs also cause a distinct subpopulation of explants to generate large numbers of neurons continually for at least several days. The data suggest that FCFs delay differentiation of a committed neuronal transit amplifying cell (the INP) and support proliferation or survival of a rare cell, possibly a stem cell, that acts as a progenitor to INPs.