Foxg1 regulates the development of microvillous cells in the olfactory epithelium

Foxg1 is a transcription factor that plays important roles in the development of the nervous and sensory systems. In the olfactory epithelium, it is known that Foxg1 is necessary for the development of subsets of olfactory sensory neurons, though its precise role remains undefined. In this study, we show that in zebrafish Foxg1a is required for the formation of microvillous olfactory sensory neurons, as well as regulation of subsets of sensory neurons and progenitor cells in the embryonic olfactory epithelium. Using the foxg1a^a266 zebrafish line, we found that sox10 and trpc2b expression are both absent from the olfactory epithelium in these mutants, suggesting that there are defects in the development of microvillous olfactory sensory neurons. Another major class of olfactory sensory neurons in the olfactory epithelium, ciliated cells, appear to develop normally in foxg1a^a266 mutants. Additional groups of neurons, such as Islet1-positive sensory neurons and mechanosensory rod cells are decreased but not absent in foxg1a^a266 mutant embryos. Progenitor cell populations in the olfactory epithelia are differentially affected, with an increase in the number of Sox2-positive cells and a decrease in Sox3-positive and Pax6-positive cells in foxg1a^a266 mutant embryos as compared to heterozygous sibling controls. Finally, we show that foxg1^a266 embryos do not form olfactory epithelium neuron projections to the brain. These results show a nuanced role for Foxg1 in the developing olfactory epithelium.