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Evolutionary aspects, structure, and expression of the rat interleukin 4 gene
G Richter1, T Blankenstein, T Diamantstein
1Institut für Immunologie, Klinikum Steglitz, Freie Universität, Berlin, FRG.
Cytokine
|May 1, 1990
Summary
Researchers isolated the rat interleukin 4 (IL 4) gene, finding its structure highly conserved across species. Despite conserved elements, the rat IL 4 protein sequence shows significant divergence from mouse IL 4, indicating complex evolutionary pressures.
Area of Science:
- Immunology
- Molecular Biology
- Genetics
Background:
- Interleukin 4 (IL 4) is a critical cytokine involved in immune responses.
- Understanding the genetic basis of IL 4 across species aids in comparative immunology and drug development.
Purpose of the Study:
- To isolate and characterize the rat interleukin 4 (IL 4) gene.
- To compare the structural and sequence homology of the rat IL 4 gene with its mouse and human counterparts.
- To investigate the evolutionary conservation and selective pressures on the IL 4 gene.
Main Methods:
- Isolation of the rat IL 4 gene from a genomic lambda phage library using cross-hybridization with mouse IL 4 cDNA.
- Analysis of gene structure, including exon-intron organization and restriction fragment length polymorphism.
- Sequence homology analysis and comparison of predicted amino acid sequences.
- Functional confirmation through gene expression and induction of MHC class II antigen expression.
Main Results:
- The rat IL 4 gene was successfully isolated and found to be a single-copy gene with four exons, similar to mouse and human IL 4.
- The overall structure of the IL 4 locus, including the promoter region and conserved sequence motifs, is highly conserved across species.
- Despite structural conservation, the predicted amino acid sequence of rat IL 4 shows low homology (57%) with mouse IL 4, particularly in the carboxy-terminal region (47%).
- Selective pressures on the IL 4 gene appear complex, with evidence for both positive and negative selection on amino acid substitutions.
- Expressed rat IL 4 protein demonstrated functional identity by inducing MHC class II antigen expression on spleen cells.
Conclusions:
- The rat IL 4 gene shares significant structural conservation with homologous genes in other species, suggesting functional importance.
- The observed divergence in amino acid sequences points to distinct evolutionary trajectories and potentially species-specific roles for IL 4.
- The functional confirmation validates the isolated rat IL 4 gene and its biological activity in immune modulation.