Expression of the transferrin gene during development of non-hepatic tissues: high level of transferrin mRNA in fetal muscle and adult brain.

Using a cloned rat transferrin cDNA probe, we looked for transferrin mRNA in the various rat tissues during development. In all the cases the mRNA detected seemed to be the same and to be product of a single gene. The transferrin gene is early expressed at a high level during liver differentiation. In the muscle and other non-hepatic and non-nervous tissues, the gene expression is maximal just before birth (19-20th day of gestational age), then markedly decreases during the postnatal development, the mRNA level being very low in the adult tissues. In brain, by contrast, transferrin mRNA level is very low before birth, then gradually increases during the postnatal development and reaches a plateau in the adult. Maximal mRNA concentration in fetal muscle (2 days before birth) and adult brain is about 1:7 to 1:10 of that obtained in adult liver. These results are analyzed in the light of the evidence that transferrin is not only an iron-binding protein, but also a factor involved in cell proliferation and differentiation, and particularly in nerve control of muscle differentiation.