MAMMARY-GLAND TYPE-I IODOTHYRONINE DEIODINASE IS ENCODED BY A SHORT MESSENGER-RIBONUCLEIC-ACID

Lactating rat mammary gland expresses a deiodinating activity that, on the basis of kinetic characteristics, corresponds to the so-called 5' -deiodinase type I(D1). In the present study we amplified and sequence d several D1 complementary DNA (cDNA) fragments from rat lactating mam mary gland. The mammary cDNA was found to be identical to the previous ly reported rat liver cDNA in the coding region, but 465 nucleotides s horter on its 3'-untranslated region, suggesting that the D1 is the sa me in both tissues. D1 messenger RNA (mRNA) was also detected by rever se transcriptase-PCR in mammary glands from puberal and late pregnant rats, but not in virgin animals. Densitometric analysis showed a close and direct correlation between mRNA content and enzyme specific activ ity in mammary gland. Our results also show that rat liver contains bo th D1 mRNA forms and that the large form may respond to the thyroid st atus. These data suggest a differential and organ-specific expression of these mRNA forms, which could play a role in the functional regulat ion of D1 activity.