SPATIAL AND TEMPORAL EXPRESSION OF TRANSFERRIN GENE IN THE RAT MAMMARY-GLAND

The distribution and concentration of transferrin mRNA in the rat mamm ary gland was analyzed using in situ hybridization, and the results we re compared with those obtained for other milk protein mRNA. The [S-35 ]RNA probes prepared from rat cDNA for transferrin and for alpha-, bet a-, and gamma-caseins, alpha-lactalbumin, and whey acidic protein were used to probe mammary tissue from rats in late pregnancy and at diffe rent stages of lactation. The overall level of transferrin gene expres sion varied in a biphasic manner, decreasing after parturition to bare ly detectable levels at d 2 to 10 of lactation before increasing again markedly in late lactation. This temporal pattern contrasts sharply w ith that observed for the other genes, for which levels tended to rise or to remain relatively stable until late lactation. The spatial patt erns of transferrin expression were also quite distinct, and, even dur ing the period of low expression, some alveoli showed high concentrati ons of transferrin mRNA. In contrast, intramammary distribution of mRN A for the other genes was relatively uniform. Our results show that th e patterns of transferrin gene expression differ both spatially and te mporally from those of five other milk protein genes and suggest that transferrin gene expression is controlled by a regulatory system that turns individual alveoli either fully on or fully off.