Transferrin in foetal and adult mouse tissues: synthesis, storage and secretion.

Transferrin is an important growth-promoting serum glycoprotein synthesized chiefly in the liver in adults. The transferrin found in the mouse foetus is thought to be wholly a product of the foetus itself and its synthesis starts at lest as early as the 7th day of gestation. The major sites of synthesis in mouse foetuses are the visceral yolk sac (VYS) and liver (Adamson, 1982). We now report that other murine foetal tissues synthesize readily detectable amounts, namely lung, spleen, spinal cord and rib cage. Very low levels are also synthesized by the brain, muscle and pancreas. We can detect no synthesis of transferrin in late foetal thymus, heart or skin although mid-gestation foetal skin may make a very small amount. No synthesis of transferrin can be detected in adult brain, lung and spleen, but approximately equal rates of synthesis are detected in adult liver and adult ear pinna. Transferrin is accumulated by foetal and adult tissues in widely varying amounts and these have been measured by enzyme-linked immunosorbent assays of extracts. In addition to VYS and liver, high levels of transferrin are found in foetal skin, lung and rib cage with lower amounts in spinal cord, spleen and muscle tissues. Tissues of the 15th day foetus accumulate the highest concentrations of transferrin. A role for the mediation of transferrin in the stimulation of growth and differentiation by interaction tissues is discussed.