Iron incorporation and haemoglobin synthesis in erythropoietic cells during the ontogenesis of the mouse.

Iron incorporation (59Fe) into erythropoietic cells from adult and foetal (11- to 15-day) peripheral blood and from foetal (12- to 15-day) livers has been investigated. Ion-exchange chromatography of haemolysates from such cells revealed two groups of 59Fe-containing proteins. The first group (X-fraction) was eluted from CMC-columns in the void volume and was highest in lysates of immature erythropoietic cells. This fraction contained a radiolabelled haemprotein of high molecular weight as well as other 59Fe-containing proteins. The haemprotein does not appear to be related to haemoglobin. The second group consisted of haemoglobins. One major (A1) and two minor (A2 and A3) haemoglobins were found in adult peripheral blood. In foetal liver lysates two major (F1 and A1) and two minor (F2 and A3) haemoglobins were present. The relative proportion of the major haemoglobins changed during development. Haemoglobin F1 was highest in the more mature livers. F1 proved to be different from A1 by chromatographic behaviour, in polypeptide chain composition and in fingerprints. A unique foetal polypeptide chain, intermediate in electrophoretic behaviour between the adult alpha- and beta-chain, was identified. In young foetal peripheral blood (11-day), in which 95% of the cells are of yolk-sac origin, one major (E1), two intermediate (E2 and E3) and one minor (F1) haemoglobin were demonstrable. Haemolysates of the peripheral blood of older embryos contain haemoglobins from erythroid cells of both yolk-sac and foetal liver origin. The haemoglobin pattern of such lysates is explicable in terms of the decreasing amount of embryonic haemoglobins (E1, E2 and E3) and the increasing amount of foetal haemoglobins (F1 and A1). Since A1 and E1 are the most prominent haemoglobins of livers from young embryos and yolk-sac erythrocytes respectively, and since they are very similar in chromatographic behaviour, foetal peripheral blood at all stages contain one dominant haemoglobin peak in the A1-E1 region. Most authors have neglected the relatively slight elevation of the foetal haemoglobin peak (F1) in front of A1-E1, the more because the F1-A1 region has been suspected sometimes to contain artificial haemoglobin components (Riggs, 1965). This probably explains why no foetal haemoglobin (F1) has been reported previously in the peripheral blood of foetal mice.