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Transcriptional properties of chick embryonic erythroid nuclei in vitro
Insights
Chick embryo red blood cells show developmental changes in gene expression, with embryonic globin and rRNA genes active early and adult globin genes later. RNA polymerase I activity decreases significantly with development.
Area of Science:
- Developmental biology
- Molecular genetics
- Cell biology
Background:
- Chick embryo red blood cells undergo significant gene expression changes during development.
- Specific globin genes (embryonic vs. adult) and rRNA genes are differentially expressed.
- Understanding transcriptional regulation is key to deciphering developmental processes.
Purpose of the Study:
- To investigate the transcriptional activity of chick embryo red blood cell nuclei at different developmental stages (5 vs. 12 days).
- To analyze the roles of RNA polymerases I and II in gene expression changes.
- To examine the regulation of beta-globin gene domains during erythroid development.
Main Methods:
- Isolation of nuclei from 5-day and 12-day chick embryo red blood cells.
- In vitro transcription assays to assess overall and specific RNA polymerase activities.
- Analysis of transcriptional properties using cloned genomic hybridization probes.
Main Results:
- Nuclei from 5-day embryos exhibited higher transcriptional activity than those from 12-day embryos.
- RNA polymerase I was highly active at 5 days but inactive by 12 days.
- Transcriptional modulation between 5 and 12 days delineated embryonic and adult beta-globin domains, extending beyond gene boundaries.
- RNA polymerase II transcribed all globin gene region transcripts, including repeat sequences.
Conclusions:
- Developmental stage significantly impacts red blood cell transcriptional activity and gene regulation.
- RNA polymerase I activity is developmentally regulated and specific to early erythroid development.
- Beta-globin gene domain regulation involves extensive genomic regions and is mediated by RNA polymerase II.
Abstract:
Chick embryo red blood cells express the embryonic globin and the rRNA genes before 5 days of development but only the adult globin genes and no rRNA after 12 days of development. We have isolated nuclei from the red blood cells of these developmental stages and allowed them to transcribe in vitro. We have analyzed the overall transcriptional properties of these nuclei, the overall activities of RNA polymerases I and II and the sequence-specific activity of RNA polymerase II in the beta-globin domain using cloned genomic hybridization probes. Among our findings are the following. 1) Erythroid nuclei of 5-day embryos are more transcriptionally active than those at 12 days. 2) RNA polymerase I is a very active at 5 days but is off by 12 days. 3) A template-independent activity which yields labeled RNA is present in the red cell nuclei of 12-day but not 5-day embryos. 4) Between 5 and 12 days of development transcriptional modulation delineates embryonic and adult beta-globin domains. 5) These domains exceed the boundaries of the genes themselves by several kilobases. 6) All transcripts which hybridize to sequences in the beta-globin gene region, including repeat sequence transcripts, are transcribed by RNA polymerase II.