PROLACTIN GENE-EXPRESSION IN OVINE AND CAPRINE MAMMARY-GLAND

The presence of prolactin (PRL) mRNA in the mammary gland of lactating goats and sheep was demonstrated by Northern analysis and RT-PCR. Thi s provides evidence that the PRL gene is transcribed in this tissue. T his ectopic expression is not restricted to the lactational period, as PRL transcripts were also found during the last third of pregnancy. C omparison of mammary and pituitary PRL mRNAs showed that they are simi lar in size but less abundant in mammary gland. In addition, an 847-bp cDNA fragment amplified from mammary retrotranscripts, containing the entire coding region and the major part of the 5' and 3' untranslated regions (UTRs), was found to be identical in sequence to its pituitar y counterpart. Primer extension analysis, performed to obtain further information on the structure of the mammary PRL mRNA, has shown that t he 5' UTR is 56 nucleotides (nt) long for both species. This is compar able with the size (53 nt) found using the caprine pituitary RNA as te mplate. These results strongly suggest that the PRL gene is not transc ribed from a different promoter in mammary gland, as has been demonstr ated for placental and lymphocyte cells, but is more likely transcribe d from the pituitary-specific promoter. Finally, the presence of PRL m RNA in polysomal fractions suggests that PRL, is synthesized in mammar y cells.