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The divergence of major histocompatibility complex class I genes in Sciurus aberti
P J Wettstein1, M Strausbauch, S L Johnston
1Department of Surgery, Mayo Foundation, Rochester, Minnesota 55905, USA.
Molecular Biology and Evolution
|January 1, 1996
Summary
The evolution of Major Histocompatibility Complex (MHC) class I genes in isolated squirrel subspecies reveals significant differences in peptide binding sites. These findings challenge current models for rodent MHC class I evolution.
Area of Science:
- Immunogenetics
- Evolutionary Biology
- Mammalian Genetics
Background:
- Major histocompatibility complex (MHC) class I genes are crucial for immune response, presenting peptides to T lymphocytes.
- Investigating MHC evolution in isolated populations can reveal adaptive genetic changes.
Purpose of the Study:
- To explore the evolution of MHC class I genes in isolated tassel-eared squirrel (Sciurus aberti) subspecies.
- To analyze sequence variations and their impact on peptide binding in MHC class I.
Main Methods:
- Cloning and sequencing of MHC class I cDNAs from two S. aberti subspecies.
- Phylogenetic analyses using neighbor-joining and maximum parsimony methods on exons 2, 3, and 4.
Main Results:
- Nucleotide substitutions in MHC class I sequences were concentrated in peptide binding sites, with nonsynonymous changes predominating.
- An insertion of two amino acids in a beta-strand adjacent to pocket B was observed, potentially altering peptide specificity.
- Phylogenetic analysis placed Scab class I sequences intermediate to murid and other mammalian groups, highlighting similarities in exons 2 and 3.
Conclusions:
- The study questions the use of a single rodent model for MHC class I sequences.
- Inclusion of exons 2 and 3 in phylogenetic analyses may obscure true evolutionary relationships due to convergent evolution under selective pressure.