The abundance of ferritin in yolk-sac derived red blood cells of the embryonic mouse.

Abstract

Circulating red blood cells formed early in development have several distinctive properties which include retention of the nucleus (mammals), large size and characteristic haemoglobin type (mammals, birds, amphibia). The primitive or embryonic red cells of early development are replaced by the definitive red cells which contain fetal or adult haemoglobin; a second developmental change occurs in the haemoglobin of some mammals (man, cattle, sheep) but does not involve a cell replacement. Circulating yolk-sac derived red cells from embryonic mice are siderocytes; elevated ferritin levels are associated with the circulating red cells of bullfrog tadpoles, but not with those of the adult frog, again indicating that red cell iron metabolism can change during development. In order to extend the observations made on an amphibian to a mammal, the ferritin content of circulating red cells from embryonic mice was determined and found to be 0.65 mg/100 mg of soluble protein; no ferritin (less than or equal to 0.007 mg/100 mg of soluble protein) was detected in adult mouse red cells. Elevated ferritin levels appeared to be specifically associated with the yolk-sac derived population of red cells since a decline in red-cell ferritin content coincided with the replacement of yolk-sac derived red cells by definitive red cells derived from the liver. Fractionation of mixtures of yolk-sac derived and liver derived red cells showed that fractions rich in the definitive red cells contained less ferritin than the mixture. The results suggest that elevated ferritin levels may be a general characteristic of the circulating, haemoglobinized red cells formed early in development.