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Adaptive evolution of the IgA hinge region in primates.
Kenta Sumiyama1, Naruya Saitou, Shintaroh Ueda
1Department of Biological Sciences, Graduate School of Science, University of Tokyo. Laboratory of Evolutionary Genetics, National Institute of Genetics, Mishima 411-8540, Japan. kenta.sumiyama@yale.edu
Molecular Biology and Evolution
|June 26, 2002
Summary
Immunoglobulin A (IgA) antibodies prevent bacterial invasion. Genomic analysis reveals positive selection in the IgA hinge region across primates, suggesting adaptive evolution driven by host-parasite interactions.
Area of Science:
- Evolutionary biology
- Immunology
- Genomics
Background:
- Immunoglobulin A (IgA) is crucial for mucosal immunity, protecting against pathogenic bacteria.
- Pathogenic bacteria produce IgA-specific proteases that cleave IgA at its hinge region, compromising its function.
Purpose of the Study:
- To investigate evidence of positive selection in the IgA hinge region across primate species.
- To analyze the evolutionary dynamics of the IgA hinge region in response to bacterial pressures.
Main Methods:
- Genomic sequence analysis of IgA genes (first intron and second exon) from diverse primates.
- Calculation of nonsynonymous to synonymous substitution ratios (d(N)/d(S)) on a phylogenetic tree.
- Statistical significance testing using Fisher's exact probability test.
Main Results:
- High d(N)/d(S) ratios observed in hominoids (5.4), Old World monkeys (6.3), and New World monkeys (4.2).
- Statistically significant evidence of positive selection in Old World monkeys.
- Accelerated nonsynonymous substitution rates in the IgA hinge region compared to flanking sequences.
Conclusions:
- The IgA hinge region exhibits high sequence variability and accelerated evolution in primates.
- This suggests adaptive evolution of IgA, likely driven by host-parasite co-evolutionary dynamics.
- Findings provide molecular evidence for host-pathogen interactions shaping immune system evolution.