Haemoglobin and globin synthesis in the isolated primitive and definitive erythroid cells of chicken embryos. Evidence for a non-clonal mechanism at the haemoglobin switch.

Primitive and definitive erythroid cells of chicken embryos aged 4-8 days, were separated by unit gravity sedimentation and pulse labelled with [3H]- and [14C]leucine. The haemoglobin and globin synthesis in the cell populations was analysed by chromatofocussing, isoelectric focussing, urea starch gel electrophoresis, and immunofluorescence or radioimmunoassay, using globin specific antibodies. We found that both embryonic and adult alpha globins are present in primitive erythroid cells, but relatively more of the adult alpha-type globins are synthesized in the late primitive erythroid cells. In young definitive erythroid cells exclusively adult alpha-type globins are synthesized. From these findings we conclude that a command to synthesize adult alpha globin is perceived in both cell types at the time of the switch. This supports an environmental model rather than a clonal model of haemoglobin switching.