TRANSFERRIN GENE-EXPRESSION IN THE MAMMARY-GLAND OF THE RAT - THE ENHANCING EFFECT OF 17-BETA-ESTRADIOL ON THE LEVEL OF RNA IS TISSUE-SPECIFIC

We have investigated the physiological factors which regulate transfer rin gene expression in the mammary gland of the rat. Our studies by do t blot analysis have demonstrated that multiple doses of 17 beta-oestr adiol (OE(2); 0.5 mg/kg per day for 3 days) elicit a specific 3.5-fold increase in the transferrin mRNA levels in the mammary glands of virg in rats. The hormonal action of OE(2) in mammary tissue was specific f or the transferrin gene, as judged by hybridization with beta-actin cD NA. The accumulation of transferrin mRNA induced by OE(2) treatment wa s similar to the developmentally regulated expression of the gene obse rved during the reproductive cycle. The steady-state level of mammary transferrin mRNA increased by up to 4.5-fold at day 21 of lactation, w hen compared with virgin and pregnant rats. Our results show that the pattern of transferrin gene expression is different in mouse and rat m ammary glands. The specific response of the transferrin gene to OE(2) was not found in the liver or in the uterus. In the uterus alone, OE(2 ) produced a significant increase in the content of nucleic acids and also induced the accumulation of transferrin and beta-actin mRNAs. We have detected for the first time an induction of transferrin gene expr ession in the mammary gland in response to OE(2), and these results su pport the view that the pattern of transferrin gene multimodulated exp ression is tissue- and species-specific.