A comprehensive analysis of teleost MHC class I sequences

Area of Science:

• Immunogenetics
• Evolutionary Biology
• Comparative Genomics

Background:

• Major Histocompatibility Complex class I (MHCI) molecules present intracellular peptides to CD8+ T-cells.
• While MHCI genes were identified in fish in the 1990s, their functional relevance remains largely unknown.
• This study investigates teleost fish MHCI molecules, leveraging expanded cod MHCI data and available genome sequences.

Purpose of the Study:

• To comprehensively study deduced teleost fish MHCI molecules.
• To identify and characterize novel MHCI lineages in teleosts.
• To compare teleost MHCI evolution with that of tetrapods.

Main Methods:

• Bioinformatic analysis of deduced teleost fish MHCI molecules.
• Identification of novel MHCI lineages.
• Comparative analysis of MHCI domain evolution across species.

Main Results:

• Five MHCI lineages identified in teleosts, including a new lineage 'P'.
• Lineages U and Z, containing peptide-binding molecules, are present in all analyzed teleosts.
• Teleosts exhibit unique evolutionary patterns in MHCI, including conserved peptide-binding grooves in Z lineage molecules and expanded ancient lineages in U.

Conclusions:

• Teleosts share polymorphic classical and non-classical MHCI molecules with tetrapods.
• Teleost classical MHCI polymorphism involves multiple ancient domain lineages, unlike tetrapods.
• Teleosts possess highly conserved 'Z' lineage MHCI molecules, with conserved peptide-binding grooves over 400 million years, presenting an evolutionary enigma.