Prolactin Gene Expression in Ovine and Caprine Mammary Gland

Abstract

The presence of prolactin (PRL) mRNA in the mammary gland of lactating goats and sheep was demonstrated by Northern analysis and RT-PCR. This provides evidence that the PRL gene is transcribed in this tissue. This ectopic expression is not restricted to the lactational period, as PRL transcripts were also found during the last third of pregnancy. Comparison of mammary and pituitary PRL mRNAs showed that they are similar 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 pituitary counterpart. Primer extension analysis, performed to obtain further information on the structure of the mammary PRL mRNA, has shown that the 5’ UTR is 56 nucleotides (nt) long for both species. This is comparable with the size (53 nt) found using the caprine pituitary RNA as template. These results strongly suggest that the PRL gene is not transcribed from a different promoter in mammary gland, as has been demonstrated for placental and lymphocyte cells, but is more likely transcribed from the pituitary-specific promoter. Finally, the presence of PRL mRNA in polysomal fractions suggests that PRL is synthesized in mammary cells.

Rat prolactin synthesis by lactating mammary epithelial cells

“…Subsequently, no relationship between the level of circulating PRL and the amount of PRL mRNA could be established. This variability was also reported in other species [12,13].…”

“…The PRL mRNA has been observed in several cell types [6][7][8][9], including mammary epithelial cells (MEC) of lactating rat, goat, sheep and rabbit [10][11][12][13] and of normal and neoplastic tissue [14]. Newly synthesized PRL has been detected in a breast cancer cell line [15].…”

EGF stimulates Pit-1 independent transcription of the human prolactin pituitary promoter in human breast cancer SK-BR-3 cells through its proximal AP-1 response element

“…Decidual/lymphoid type PRL transcripts were detected in some, but not all mammary tissues and cells (Shaw-Bruha et al, 1997), while a study performed in goat and sheep showed that the size of the mammary gland mRNA is similar to the pituitary hPRL mRNA (Le Provost et al, 1994).…”

Genetic and Breeding Aspects of Lactation

“…Prolactin gene disruption experiments proved its important roles in mammary gland development (mammogenesis), lactogenesis, maintenance of milk secretion (galactopoiesis), and expression of milk protein genes [10]. It is also chiely accountable for synthesis of lactose, lipids, and all other major components of milk [11]. Consequently, the bovine prolactin gene seems to be an outstanding candidate for linkage analysis with quantitative trait loci (QTL) afecting milk production traits.…”