Foxj1 controls olfactory ciliogenesis and differentiation program of the olfactory sensory neurons

Olfaction plays important roles in food and mate choice, and also in the avoidance of predators, making it a vital sensory modality for preservation and reproduction. In the vertebrates, olfactory receptors are thought to localise on multiple cilia elaborated on the dendritic knobs of olfactory sensory neurons (OSNs). Although olfactory cilia dysfunction can cause loss of the sense of smell, how their differentiation is programmed at the transcriptional level has remained largely unexplored. We discovered in zebrafish and mice that Foxj1, a fork head-domain containing transcription factor traditionally linked with motile cilia biogenesis, is expressed in OSNs and required for olfactory epithelium formation. In keeping with the immotile nature of the olfactory cilia, we observed that ciliary motility genes that are the targets of Foxj1 in motile ciliated cells, are repressed in the OSNs. Strikingly, we also found that besides ciliogenesis, Foxj1 controls the differentiation of the OSNs by regulating their cell type-specific gene expression, such as that of olfactory marker protein (omp) involved in odour-evoked signal transduction. In line with these requirements, response to bile acid, an odour detected by OMP-positive OSNs, was significantly diminished in the foxj1 mutant zebrafish. Taken together, our findings establish how the canonical Foxj1-mediated motile ciliogenic transcriptional program has been repurposed for the biogenesis of the immotile olfactory cilia and for the development of the OSNs themselves. Overall design: to investigate the role of Foxj1 genes in zebrafish, foxj1a and foxj1b knock-out fish used for RNA isolation at 4 dpf.