Genetic tagging of the adenosine A2A receptor reveals its heterogeneous expression in brain regions

The adenosine A(2A) receptor (A(2A)R), a G protein-coupled receptor, is involved in numerous and varied physiological and pathological processes, including inflammation, immune responses, blood flow, and neurotransmission. Accordingly, it has become an important drug target for the treatment of neuropsychiatric disorders. However, the exact brain distribution of A(2A)R in regions outside the striatum that display relatively low levels of endogenous A(2A)R expression has hampered the exploration of A(2A)R functions under both physiological and pathological conditions. To further study the detailed distribution of the A(2A)R in low-expression regions, we have generated A(2A)R knock-in mice in which the 3xHA-2xMyc epitope tag sequence was fused to the C-terminus of A(2A)R (A(2A)R-tag mice) via CRISPR/Cas9 technology. Here, using CRISPR/Cas9 technology, we have generated A(2A)R knock-in mice in which the 3xHA-2xMyc epitope tag sequence was fused to the C-terminus of A(2A)R (A(2A)R-tag mice). The A(2A)R-tag mice exhibited normal locomotor activity and emotional state. Consistent with previous studies, A(2A)R fluorescence was widely detected in the striatum, nucleus accumbens, and olfactory tubercles, with numerous labeled cells being evident in these regions in the A(2A)R-tag mouse. Importantly, we also identified the presence of a few but clearly labeled cells in heterogeneous brain regions where A(2A)R expression has not previously been unambiguously detected, including the lateral septum, hippocampus, amygdala, cerebral cortex, and gigantocellular reticular nucleus. The A(2A)R-tag mouse represents a novel useful genetic tool for monitoring the expression of A(2A)R and dissecting its functions in brain regions other than the striatum.