EXPRESSION OF THE GENE ENCODING METALLOTHIONEIN-3 IN ORGANS OF THE REPRODUCTIVE-SYSTEM

Metallothionein-3 (MT-3) is a new MT gene-family member that inhibits survival of rat neurons cultured in presence of brain extracts. Contra ry to other MT genes, which are expressed in most tissues and which ar e highly inducible by metals, MT-3 expression was reported to be mainl y in the brain, and it failed to respond to metals in vivo. We show he re that MT-3 mRNA is present in several organs other than the brain, a s assayed by Northern analyses. In the rat, MT-3 mRNA was detected in the testis, prostate, epididymis, tongue, ovary, uterus, stomach, hear t, and seminal vesicles. The MT-3 mRNA levels in the testis, epididymi s, prostate, and tongue were 22% of those in brain, while in ovary, ut erus, and stomach, they were 4% of the brain level, and they were lowe r still in the other organs. The MT-3 gene was not inducible by CdCl2 or lipopolysaccharide in rat testis and prostate. In the mouse and the human, relative MT-3 mRNA levels were lower than those found in the r at when compared with those present in brain. Testicular MT-3 transcri pt levels remained quite constant during rat postnatal development in animals aged from 6 to 43 days. In situ hybridization analyses on huma n testis sections showed that MT-3 mRNA was present at different level s in both the Leydig cells and the seminiferous tubules. In orchiectom ized rats, prostatic MT-3 mRNA was decreased by 75%, and injections of dihydrotestosterone restored MT-3 mRNA levels to control values. Over all, these results show that MT-3 tissue-specific gene expression is b roader than previously reported and provide new experimental systems t o study the function and mechanism of action of the MT-3 protein.