Metallothionein-3 is expressed in the brain and various peripheral organs of the rat

Metallothionein-3 (MT-3), also known as growth inhibitory factor (GIF), was originally identified in the brain. An essential step in elucidating the potential roles of MT-3 is to evaluate its expression levels in organs other than the brain. In this present study, we carried out RT-PCR, Western blot and immunohistochemical analyses to quantify MT-3 mRNA and its protein in the cerebrum, eye, heart, kidney, liver, prostate, testis, tongue, and muscle in male Wistar rats. MT-3 mRNA was detected in the cerebrum, the dorsolateral lobe of the prostate, testis, and tongue. Using a monoclonal anti-MT-3 antibody, we detected MT-3 in the cerebrum, the dorsolateral lobe of the prostate, testis, and tongue as a single band on an immunoblot. Immunohistochemical staining showed MT-3 in some astrocytes in the deep cortex, ependymal cells, and choroidal cells in the cerebrum. MT-3 was also detected in some cells of the glomerulus and the collective tubules in the kidney, some cells in the glandular epithelium of the dorsolateral lobe of the prostate, some Sertoli cells and Lydig cells in the testis, and taste bud cells in the tongue. Although MT-3 immunopositivity was obviously demonstrated in the kidney by the immnunohistochemical method, the expression of MT-3 was not fully detectable by RT-PCR and Western blot analyses. Interestingly, only a subset of cells showed positivity for MT-3, not all cells in all tissues. The localization of MT-3 in peripheral organs outside the brain suggests that MT-3 has roles in these tissues besides its role in growth inhibition of neurites.