Development of a mouse reporter strain for the purinergic P2X2 receptor.

The ATP-sensitive P2X2 ionotropic receptor plays a critical role in a number of signal processes including taste and hearing, carotid body detection of hypoxia, the exercise pressor reflex and sensory transduction of mechanical stimuli in the airways and bladder. Elucidation of the role of P2X2 has been hindered by the lack of selective tools. In particular, detection of P2X2 using established pharmacological and biochemical techniques yields dramatically different expression patterns, particularly in the peripheral and central nervous systems. Here, we have developed a knockin P2X2-cre mouse, which we crossed with a cre-sensitive tdTomato reporter mouse to determine P2X2 expression. P2X2 was found in more than 80% of nodose vagal afferent neurons, but not in jugular vagal afferent neurons. Reporter expression correlated in vagal neurons with sensitivity to αβmATP. P2X2 was expressed in 75% of petrosal afferents, but only 12% and 4% of dorsal root ganglia and trigeminal afferents, respectively. P2X2 expression was limited to very few cell types systemically. Together with the central terminals of P2X2-expressing afferents, reporter expression in the CNS was mainly found in brainstem neurons projecting mossy fibers to the cerebellum, with little expression in the hippocampus or cortex. The structure of peripheral terminals of P2X2-expressing afferents was demonstrated in the tongue (taste buds), carotid body, trachea and esophagus. P2X2 was observed in hair cells and support cells in the cochlear, but not in spiral afferent neurons. This mouse strain provides a novel approach to the identification and manipulation of P2X2-expressing cell types. Significance statement Inhibitor and knockout studies have demonstrated the critical role of P2X2 in multiple sensory signaling pathways. Nevertheless, P2X2 expression patterns are controversial, as biochemical studies suggest widespread expression whereas functional studies suggest restricted expression. Functional characterization is further complicated by heteromeric P2X2/3 channels that have hybrid pharmacology and biophysical properties. We have developed a P2X2-cre mouse to determine the expression pattern of P2X2. In the periphery, P2X2 expression is found in almost all nodose sensory afferents but is limited to only minor subsets of trigeminal and DRG afferents. Centrally, P2X2 is mostly expressed in neurons projecting mossy fibers to the cerebellum. Thus we provide novel evidence for the specific expression of P2X2, which is more limited than previously thought.