Coevolution between MHC Class I and Antigen-Processing Genes in Salamanders

Area of Science:

• Immunogenetics
• Evolutionary biology
• Comparative genomics

Background:

• Antigen-processing genes (APGs) supply peptides to major histocompatibility complex class I (MHC-I) molecules.
• In mammals, MHC-I is polymorphic and APGs are monomorphic, while in some non-mammals, both are polymorphic and coevolve.
• This coevolution was thought to limit MHC-I to a single gene, but salamanders possess multiple MHC-I genes, questioning this hypothesis.

Purpose of the Study:

• To investigate the relationship between MHC-I and APG diversity in salamanders.
• To test if MHC-I and APG diversity are positively correlated, supporting coevolution.
• To determine if coevolution restricts MHC-I gene family expansion.

Main Methods:

• Comparative analysis of MHC-I and APG (TAP1, TAP2, PSMB8, PSMB9, TAPBP) diversity across 30 salamander species.
• Statistical correlation analysis to assess the relationship between MHC-I diversity and APG diversity.
• Examining diversity at both within-individual and species-wide levels.

Main Results:

• MHC-I diversity significantly explained the diversity of TAP1 and TAP2, supporting their coevolution.
• No consistent coevolutionary effect was observed for PSMB8, PSMB9, and TAPBP.
• Salamanders exhibit coevolution between MHC-I and specific APGs without limiting MHC-I gene family size.

Conclusions:

• Coevolution between MHC-I and certain APGs (TAPs) occurs in salamanders.
• Coevolution does not preclude the expansion of the MHC-I gene family in this lineage.
• Nonmammalian vertebrates can balance coevolutionary benefits with MHC-I gene family flexibility.