ISOFORM-SPECIFIC EXPRESSION OF METALLOTHIONEIN MESSENGER-RNA IN THE DEVELOPING AND ADULT HUMAN KIDNEY

The organization of the metallothionein (MT) gene family has been demo nstrated to be much more complex in humans than in the mouse, and poss ibly rodents in general. For humans, the MTs are encoded by a family o f genes located at 16q13 representing 10 functional and 7 non-function al MT isoforms. In the present study, the 5' and 3' untranslated regio n sequences of the highly conserved, functional MT genes were utilized to generate primer pairs for the analysis of isoform-specific MT mRNA using reverse transcriptase-polymerase chain reaction (RT-PCR). Human kidneys from 13 weeks gestation through adulthood were examined for t he expression of MT protein and mRNA. Immunohistochemical analysis dem onstrated MT immunoreactivity to be confined exclusively to the proxim al tubules of the adult and developing kidney. For all MT-positive cel ls, MT was localized in the cytoplasm and nuclear localization was var iable. There was no correlation between nuclear staining and stage of development. Of the 10 MT genes examined (MT-1A, MT-1B, MT-1E, MT-1F, MT-1G, MT-1H, MT-1X, MT-2A, MT-3, and MT-4), mRNAs representing the MT -1E, MT-1F, MT-1X, and MT-2A genes were consistently expressed in all samples regardless of gestational age. There was no indication of a 'f etal form' of MT analogous to that noted to occur inhuman liver. Messe nger RNA for the MT-1A gene was detected in 2 of 6 renal samples witho ut correlation to gestational age. In no instance was mRNA for the MT- 1B, MT-1G, MT-1H, MT-3, or MT-4 genes detected. These studies detail t he initial determination of MT gene expression in the human renal syst em and provide the PCR primers for testing and determination of MT gen e expression in other organ systems.