Functional Evolution of Avian RIG-I-Like Receptors

Area of Science:

• Evolutionary Biology
• Immunology
• Genomics

Background:

• RIG-I-like receptors (RLRs) are pattern-recognition receptors vital for innate immunity against RNA viruses.
• The RLR family includes RIG-I, MDA5, and LGP2, playing key roles in detecting viral RNA.
• Understanding RLR evolution in birds provides insights into avian immune system adaptation.

Purpose of the Study:

• To investigate the molecular evolution of avian RIG-I-like receptors (RLRs).
• To analyze evolutionary conservation and selection pressures on RIG-I, MDA5, and LGP2 across bird species.
• To explore potential interactions between RLR evolution and endogenous retroviral elements in bird genomes.

Main Methods:

• Molecular evolutionary analyses were performed on coding genes of avian RLRs from 62 bird species.
• Conservation scores and dN/dS ratios were calculated to assess evolutionary constraints and positive selection.
• Spearman's correlation test was used to examine the relationship between RIG-I evolution and retroviral abundance.

Main Results:

• Avian MDA5 exhibits high conservation in the helicase domain but lower conservation in CARDs, differing from mammals.
• RIG-I and MDA5 show evidence of positive selection across bird lineages, while LGP2 shows it only in Galliformes.
• LGP2 may have undergone selection relaxation during bird evolution; RIG-I evolution negatively correlates with retroviral abundance.

Conclusions:

• Avian RLRs have undergone distinct evolutionary trajectories, with MDA5 and RIG-I experiencing positive selection.
• The evolution of LGP2, including potential selection relaxation and positive selection in Galliformes, is linked to RIG-I loss in this group.
• Evidence suggests a potential interplay between avian immune responses mediated by RLRs and endogenous retroviruses.