ABSTRACT
The synthesis of globins in the chick embryo before the onset of circulation has been studied in situ by specific immunofluorescence labelling of embryonic sections and by labelling newly synthesized proteins in ovo and in vitro in embryonic explants with [3Hjleucine.
The presence of major primitive haemoglobins is observed by 28 h of incubation. The minor primitive haemoglobins become detectable by immunofluorescence after 40 h of development, shortly before the onset of circulation. 3H-labelling shows that one definitive a chain is synthesized, though in low concentration, from the initial globin detection. The other definitive a chain is observed in embryos of at least 40 h of development. The relative concentration of the two definitive α chains changes rapidly with development indicating a specific mechanism of regulation.
An erythropoietic site is observed in the wall of the dorsal aorta in embryos of about 45–50 h of development. From the initial detection, those cells contain all four primitive embryonic haemoglobins, in contrast to what is observed for the cells of the blood islands.
Abbrevations. HbP and HbP’: major primitive embryonic haemoglobins; respective chain composition: π2Qi π’ 2 ϱ 2 .
HbM and HbE: minor primitive embryonic haemoglobins; respective chain composition: αD ε2, αA ε 2.
PBS: 40mM-NaCl in 30mM-sodium phosphate, pH7· 2.
