Tissue distribution of human monoamine oxidase A and B mRNA.

Monoamine oxidase (MAO) A and B play important roles in the metabolism of biogenic amines. Northern analysis using 32P-labeled subfragments of human liver MAO A and B cDNA clones detected a 5- and a 3-kb transcript, respectively, in most human tissues examined. However, fetal heart and thymus express minute amounts of MAO A transcript, whereas fetal brain, muscle, thymus, spleen, meninges, and placenta express minute amounts of MAO B transcript. Small intestine and placenta express, in addition to the MAO A 5-kb transcript, a 2-kb transcript, which may arise from an alternative polyadenylation site. MAO A and B transcripts are expressed in similar regions of adult human brain. The highest concentrations of these transcripts were located in frontal cortex and locus coeruleus. This study demonstrates the tissue-specific distribution of the MAO genes and will provide insight into the physiological functions of MAO A and B.