Transferrin mRNA level in the mouse mammary gland is regulated by pregnancy and extracellular matrix

We have isolated an almost full length cDNA to transferrin from a mouse mammary tumor virus-induced tumor cDNA library. On Northern blots of RNA isolated from liver and mammary glands, the cDNA hybridized to a single band of 2.4 kilobases. The authenticity of the probe is shown further by 83% sequence homology to human cDNA and identical amino acid sequence to a small cDNA probe isolated from a mouse liver library. The level of transferrin mRNA is very low in the glands from virgin mice, but is as abundant in the glands from pregnant and lactating mice as in the liver. We further show that the steady-state transferrin mRNA level in culture is relatively insensitive to lactogenic hormones compared to that of beta-casein mRNA. Culturing the cells on extracellular matrix, however, markedly affects its expression. These findings raise the possibility that the composition of the basement membrane in the mammary gland may play a role in regulation of transferrin levels in vivo.