Low stringency hybridization study of the dopamine D4 receptor revealed D4-like mRNA distribution of the orphan seven-transmembrane receptor, APJ, in human brain

We recently reported that the density of mRNA for the dopamine D4 receptor was extremely low in human cerebral cortex but unexpectedly higher in the corpus callosum and spinal cord both of which contain substantial white-matter area. Under low stringency conditions, Northern blot analysis using the D4 probe detected cross-hybridized mRNAs having a similar distributional profile to the D4 mRNA in human brain regions, suggesting the mRNA distributional profile is not peculiar to the D4 receptor. Homology screening revealed one of the mRNAs to be an orphan seven-transmembrane receptor, APJ, abundantly expressed in the corpus callosum and spinal cord. In porcine spinal cord the APJ mRNA was detected at a higher level in white-matter rather than in gray-matter area. These data suggest that a group of seven-transmembrane receptors, including the D4 and APJ receptor, is preferentially expressed in the white-matter area probably in non-neuronal glial cells.