Examination of the expression of G-protein-coupled receptor (GPR) 37 across whole-body organs using GPR37-deficient mice by Western blotting.

G-protein-coupled receptor (GPR) 37 is a G-protein-coupled receptor implicated in diverse physiological and pathological processes, including myelination and Parkinson's disease. Although its expression has been reported in the central nervous system (CNS), testis, and immune cells, the distribution of GPR37 at the protein level in peripheral tissues has remained unclear, partly because it is technically difficult to detect GPR37 specifically, which shares highly similar domains with other G protein-coupled receptors. In this study, to survey the protein expression of GPR37 in the major organs, we generated GPR37‑deficient mice by deleting the exon 1 start‑codon region using CRISPR/Cas9, and the protein expression of GPR37 in the major organs was compared between wild-type and GPR37‑deficient mice by western blotting. We confirmed GPR37 expression in the CNS and testis and newly demonstrated its protein‑level expression in the eye and inner ear, the latter representing a previously unreported organ in mammals. Across tissues, the 40 kDa short form of GPR37 was the predominant variant, whereas the 75 kDa form was restricted to the eye, revealing tissue‑specific differences in molecular forms. These findings provide reliable evidence for the tissue distribution of GPR37 and establish a robust framework for validating GPCR expression in vivo, offering new insights into its potential roles in neural, reproductive, and sensory systems.