Variation of transferrin mRNA concentration in the rabbit mammary gland during the pregnancy–lactation–weaning cycle and in cultured mammary cells. A comparison with the other major milk protein mRNAs
Authors: Puissant C , Bayat-Sarmadi M , Devinoy E , Houdebine L-M 
Published: December 2008

Puissant C, Bayat-Sarmadi M, Devinoy E, Houdebine L-M. Variation of transferrin mRNA concentration in the rabbit mammary gland during the pregnancy–lactation–weaning cycle and in cultured mammary cells. A comparison with the other major milk protein mRNAs. Eur J Endocrinol 1994;130:522–9. ISSN 0804–4643

The concentration of transferrin mRNA was evaluated during pregnancy and lactation in rabbit mammary gland and liver using northern blot and dot blot assays. Transferrin mRNA was present in the virgin rabbit mammary gland and its concentration increased as pregnancy proceeded, with a major enhancement after day 15. A high concentration was reached 3 days after parturition, with no additional increase during lactation and with a marked decline after weaning. During the same period, the concentration of transferrin mRNA showed only a very weak variation in liver. This mRNA was six times more abundant in mammary gland than in liver of lactating rabbit. The accumulation of transferrin mRNA in the mammary gland was concomitant with the accumulation of αs1-, β-, kcasein and WAP (whey acidic protein) mRNAs. The concentration of glyceraldehyde 3-phosphate dehydrogenase mRNA, taken as a non-inducible control mRNA, declined progressively during pregnancy to reach its lower level in lactation. These observations suggest that casein, WAP and transferrin mRNAs are subjected to a similar control mechanism in vivo, at least in the second half of pregnancy and during lactation. Experiments carried out in vitro using isolated rabbit epithelial mammary cells cultured on collagen I gel indicated that transferrin mRNA was abundant and only weakly inducible by the lactogenic hormones insulin, cortisol and prolactin, as opposed to caseins and WAP mRNAs. R5020, an analogue of progesterone, inhibited at most very slightly the accumulation of αs1-casein mRNA in the presence of prolactin and it did not reduce the expression of transferrin gene. The mammary cells cultured on a plastic support contained much less transferrin mRNA than those maintained on collagen gel or on EHS (Engelbreth–Holm–Swarm) extracellular matrix independently of any hormonal stimulation. These data suggest that although caseins, WAP and transferrin mRNAs have parallel variations during the pregnancy–lactation–weaning cycle, they are subjected to different mechanisms of regulation at the molecular level. The accumulation of the mRNAs for caseins and WAP is positively regulated by lactogenic hormones and by the presence of the extracellular matrix, whereas the accumulation of transferrin mRNA is positively regulated essentially by the presence of the matrix. The fact that the levels of all the mRNAs studied here are increased simultaneously as progesterone starts declining suggests that the steroid controls the action of a factor, possibly the presence of the extracellular matrix, that regulates the expression of all the milk protein genes.

L-M Houdebine, Unité de Differenciation Cellulaire, Institut National de la Recherche Agronomique, 78352 Jouy-en-Josas Cédex, France