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Maintenance of DQB1 polymorphisms in primates.
L K Gaur1, A L Hughes, E R Heise
1Department of Microbiology and Immunology, Bowman Gray School of Medicine.
Molecular Biology and Evolution
|July 1, 1992
Summary
The primate major histocompatibility complex (MHC) DQB1 locus shows more diversity within species than between species, indicating allele maintenance over evolutionary history. This suggests antigen presentation drives DQB1 gene evolution through overdominant selection.
Area of Science:
- Evolutionary biology
- Immunogenetics
- Primate genetics
Background:
- The Major Histocompatibility Complex (MHC) plays a crucial role in immune responses.
- Class II MHC genes, like DQB1, are highly polymorphic and involved in antigen presentation.
- Understanding MHC evolution in primates provides insights into immune system adaptation.
Purpose of the Study:
- To investigate the evolutionary dynamics of the primate class II MHC DQB1 locus.
- To compare genetic diversity within and between non-human primate species at the DQB1 locus.
- To explore the selective pressures shaping DQB1 evolution, particularly at antigen-binding sites.
Main Methods:
- Amplification of the second exon of seven DQB1 alleles from five non-human primate species using polymerase chain reaction (PCR).
- Sequence comparison of amplified DQB1 alleles with other primate sequences.
- Analysis of nucleotide substitution patterns, focusing on antigen-binding-site codons.
Main Results:
- No greater diversity was observed between primate species than within species at the DQB1 locus.
- A high frequency of nonsynonymous nucleotide substitutions was found at antigen-binding-site codons.
- This pattern contrasts sharply with the closely related, presumably nonfunctional DQB2 gene.
Conclusions:
- DQB1 alleles have likely been maintained throughout the evolutionary history of Old-World primates.
- The observed pattern of substitutions supports the hypothesis of overdominant selection acting on DQB1.
- Antigen presentation is a significant factor driving the polymorphism observed in the DQB1 locus.