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Enhancer complexes located downstream of both human immunoglobulin Calpha genes
F C Mills1, N Harindranath, M Mitchell
1Laboratory of Cell and Viral Regulation, Division of Hematologic Products, Center for Biologics Evaluation and Research, Food and Drug Administration, Bethesda, Maryland 20892, USA. millsf@fdacb.cber.fda.gov
The Journal of Experimental Medicine
|September 18, 1997
Summary
Researchers identified DNA segments downstream of human Calpha genes that regulate immunoglobulin heavy chain expression. These segments show enhancer activity and are homologous to mouse locus control regions, suggesting conserved mechanisms for B cell development.
Area of Science:
- Immunology
- Molecular Biology
- Genetics
Background:
- Regulation of human immunoglobulin heavy chain expression is crucial for immune response.
- Locus control regions (LCRs) in mice contain enhancers that regulate immunoglobulin isotype switching.
- Understanding conserved regulatory elements between mouse and human is key to deciphering immune gene expression.
Purpose of the Study:
- To identify and characterize DNA sequences downstream of human Calpha genes that may function as LCRs.
- To investigate the potential enhancer activity and B lymphoid-specific regulatory roles of these sequences.
- To compare these human sequences with known regulatory elements in the murine immunoglobulin heavy chain locus.
Main Methods:
- Cloning of DNA downstream from human Calpha1 and Calpha2 genes.
- Assessing DNA segments for B lymphoid-specific DNase I hypersensitivity.
- Performing transient transfections to evaluate enhancer activity.
- Sequence homology analysis between human and murine DNA segments.
Main Results:
- Identified DNA segments downstream of human Calpha genes exhibiting B lymphoid-specific DNase I hypersensitivity and enhancer activity.
- These human sequences show significant homology to the murine LCR, particularly the HS12 region.
- Human HS12 enhancers share approximately 90% identity within a core region with their murine counterparts, including conserved functional motifs.
- Some functional elements present in the murine enhancer, like the B cell-specific activator protein site, are not conserved in human HS12.
- Human HS3 and HS4 homologs show lower conservation but retain critical motifs like kappaB and octamer sites.
- An additional hypersensitivity site in humans, between HS3 and HS12, shows high sequence conservation with mouse and may represent a novel functional element.
Conclusions:
- Human Calpha genes possess downstream regulatory elements analogous to the murine LCR, suggesting conserved mechanisms for immunoglobulin heavy chain gene regulation.
- These identified human enhancers, particularly HS12, play a role in regulating immunoglobulin expression and isotype switching.
- Sequence comparisons reveal both conserved and divergent functional elements between human and mouse enhancers, highlighting species-specific regulatory nuances.
- The novel hypersensitivity site suggests potential undiscovered regulatory functions within the human immunoglobulin heavy chain locus.