Abstract
We have investigated the transcriptional specificity of chick embryo erythroid nuclei as a function of developmental age during progression of the hemoglobin switch. Nuclei were allowed to transcribe in vitro in the presence of high specific activity [alpha-32P]CTP and the radioactive transcripts were hybridized to a collection of plasmid clones spanning the beta-like globin gene region of the chicken genome. The results reveal locus-specific waves of transcription appearing during the interval between 5 and 12 days of incubation. The last wave, which comes in at 12 days, is highly specialized in transcription of the adult beta-globin gene locus. The most interesting wave of transcription occurs at 6-7 days. The most actively transcribed gene in the early part of this wave is the embryonic rho gene. As the wave progresses, the rho gene activity gradually gives way to beta gene transcription. Definitive red blood cells, which would be synthesizing little rho globin protein at this stage, appear to be responsible for the rho gene transcription. These results and additional data which we present indicate that during the initial stages of the hemoglobin switch the embryonic globin genes are silenced post-transcriptionally.
Highlights
We have investigated the transcriptional specificity of chick embryo erythroid nuclei as a function of developmental age during progression of the hemoglobin switch
The first red blood cells of the embryo are those of the primitive lineage which, in the chick, express only the embryonic globin genes (Chapman and Tobin, 1979)
Tight transcriptional control is thought to be operative in fully differentiated vertebrate tissues (Derman et al, 1981; Lasky and Tobin, 1979) including the fully committed primitive and definitive red blood cells of the early and late chick embryo (Groudine et al, 1981; Landes and Martinson, 1982)
Summary
Definitive red blood cells, which would be synthesizing little p globin protein at this stage, appear to be responsible for the p gene transcription These results and additional data which we present indicate that during the initial stages of the hemoglobin switch the embryonic globin genes are silenced post-transcriptionally. The first red blood cells of the embryo are those of the primitive lineage which, in the chick, express only the embryonic globin genes (Chapman and Tobin, 1979). The chick embryo possesses almost exclusively red blood cells of a different lineage These are definitive cells and they express only the adult globin genes (Chapman and Tobin, 1979). These results suggest that switching at the molecular level is initiated post-transcriptionally and completed transcriptionally
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