Fas-associated factor 1 as a regulator of olfactory axon guidance

Axon guidance is a crucial part of neural circuit formation. While precise axonal targeting forms the basis of accurate information delivery, the mechanisms that regulate this process are still unclear. Apoptotic signaling molecules have been identified in the axon terminal, but their specific role in axon guidance is not well understood. Here we use the mouse olfactory system as an in vivo model to demonstrate that by modulating Fas-associated factor 1 (FAF1), an apoptosis regulatory molecule, we can rewire axonal projections. Interestingly, FAF1 is highly expressed in the developing mouse olfactory system, but its expression is downregulated postnatally. Using a tetracycline-inducible promoter Tet-Off system, we generated transgenic mice in which FAF1 is specifically expressed in immature olfactory sensory neurons (OSNs) and show that overexpression of FAF1 not only misroutes OSN axons to deep layers of the olfactory bulb but also leads to widespread disruption of the glomerular layer. In addition, we also demonstrate that the specific convergence of P2 receptor OSN axons is completely distorted in the FAF1 mice. Strikingly, all of the mutant phenotypes can be recovered by shutting down FAF1 expression through the administration of doxycycline. Together, our study provides clear in vivo evidence that an apoptotic molecule can indeed regulate axon targeting and that OSNs can restore their organization even after broad disruption.