Fate of MHCII in salmonids following 4WGD

Area of Science:

• Evolutionary immunology
• Comparative genomics
• Teleost fish genetics

Background:

• Major Histocompatibility Complex (MHC) genes are crucial for adaptive immunity in vertebrates.
• Teleost MHC class II (MHCII) molecules exhibit structural differences from mammalian counterparts, impacting their function.
• Previous studies indicated no shared syntenic MHCII regions among major teleost groups, suggesting genomic instability.

Purpose of the Study:

• To investigate the evolutionary trajectory of MHCII genes in salmonids.
• To compare MHCII evolution in salmonids with their diploid sister group, the Northern pike.
• To understand the impact of whole genome duplication events on salmonid MHCII gene evolution.

Main Methods:

• Bioinformatic analysis of available Northern pike and salmonid genomes.
• Identification and characterization of MHCII genes across selected species.
• Phylogenetic comparison of MHCII gene families between Northern pike and salmonids.

Main Results:

• Identified a total of 120 MHCII genes in Northern pike and salmonids, with 11-20 genes per species.
• Observed significant expansion in DB-group MHCII genes within the analyzed species.
• Documented extensive gene loss, translocations, and genome rearrangements in salmonid MHC regions compared to Northern pike.

Conclusions:

• Salmonid MHCII evolution is characterized by dynamic genomic changes, including gene loss and rearrangements, likely influenced by whole genome duplication.
• Northern pike serves as a valuable outgroup for understanding the ancestral state and divergence of salmonid MHCII genes.
• The findings provide insights into the complex evolutionary history of immune gene families in teleost fishes.