PHR1 is a vesicle-bound protein abundantly expressed in mature olfactory neurons

Objectives/Hypothesis. To characterize the role of Phr1, a gene highly expressed in primary sensory neurons where it encodes an integral membrane protein with an N-terminal pleckstrin homology domain and a C-terminal transmembrane domain, in the olfactory system. Methods. We studied the immunelocalization of the PHR1 protein in mouse olfactory epithelium both at steady state and during regeneration following methyl bromide (MeBr) exposure using scanning confocal microscopy. Additionally, we examined the electrophysiologic role of Phr1 in olfaction and short-term olfactory adaptation. Results. We found that PHR1 is abundantly and specifically expressed in olfactory neurons. It is widely distributed in punctate, vesiculated organelles throughout the cell bodies, axons, and glomeruli of primary olfactory neurons but is specifically excluded from the olfactory cilia. In the regenerating olfactory epithelium, PHR1 expression appears at 14 days following MeBr ablation coinciding with the onset of olfactory neuron maturity. Despite the abundant and specific expression throughout the olfactory neurons, mice lacking Phr1 did not exhibit differences in the distribution of the components of olfactory signal transduction system, the rate of olfactory regeneration following MeBr exposure, olfactory function, or short-term adaptation to odors. Conclusions. Phr1 is widely and abundantly expressed throughout mature olfactory neurons and other primary sensory neurons, but its absence does not appear to affect olfactory morphology, regeneration, sensory function, or adaptation. The exact function of Phr1 remains to be discovered.