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MHC class II beta sequence diversity in the deer mouse (Peromyscus maniculatus): implications for models of balancing
A D Richman1, L G Herrera, D Nash
1Plant Sciences Department, MSU Bozeman, Bozeman, MT 59719, USA, Department of Zoology, Universidad Nacional Autónoma de México, Instituto de Biología, México, México. arichman@montana.edu
Abstract:
We studied population polymorphism at a major histocompatibility complex (MHC) class II beta gene in the deer mouse (Peromyscus maniculatus). We found that: (i) a single population of P. maniculatus has significantly higher levels of DNA and protein sequence diversity than worldwide samples from homologous genes in other taxa, including humans and mice; and (ii) the genealogy of allelic sequences in P. maniculatus deviates significantly from theoretical expectation under a model of symmetric balancing selection, in that alleles are relatively more divergent than expected. We suggest that the observation of high levels of pairwise allelic sequence divergence and deviation of the genealogy from theoretical expectation in P. maniculatus together provide support for a divergent allele advantage model for the maintenance of MHC polymorphism.
Insights
Deer mice exhibit exceptional genetic diversity in their major histocompatibility complex (MHC) class II beta gene. This high polymorphism suggests a unique evolutionary mechanism, potentially a divergent allele advantage, maintains MHC diversity in this species.
Area of Science:
- Evolutionary biology
- Immunogenetics
- Population genetics
Background:
- The Major Histocompatibility Complex (MHC) is crucial for immune response and exhibits high polymorphism in vertebrates.
- Understanding the evolutionary forces maintaining MHC diversity is key to comprehending host-pathogen interactions and speciation.
Purpose of the Study:
- To investigate the population polymorphism of the MHC class II beta gene in deer mice (Peromyscus maniculatus).
- To compare sequence diversity and allelic genealogy in deer mice to theoretical expectations and other taxa.
Main Methods:
- DNA and protein sequence analysis of the MHC class II beta gene in Peromyscus maniculatus.
- Phylogenetic and genealogical analyses of allelic sequences.
- Comparison with homologous genes from human and mouse populations.
Main Results:
- Peromyscus maniculatus populations show significantly higher DNA and protein sequence diversity in the MHC class II beta gene than humans and mice.
- The genealogy of MHC alleles in deer mice deviates from the expected pattern under symmetric balancing selection, with more divergent alleles than predicted.
- High pairwise allelic sequence divergence and genealogical deviations were observed.
Conclusions:
- The observed high MHC polymorphism in deer mice supports the divergent allele advantage model.
- This model provides a potential explanation for the maintenance of MHC diversity beyond simple balancing selection.
- Population-specific evolutionary pressures may drive unique MHC evolution in Peromyscus maniculatus.