Immunoglobulin D (IgD) of Atlantic cod has a unique structure

Area of Science:

• Immunology
• Fish Genetics
• Molecular Evolution

Background:

• Immunoglobulin heavy-chain (IgH) genes are crucial for adaptive immunity in vertebrates.
• Teleost fish possess unique IgH gene organizations compared to mammals.
• Previous studies identified novel IgD-like genes in channel catfish and Atlantic salmon.

Purpose of the Study:

• To clone and sequence a new IgD heavy-chain gene from Atlantic cod (Gadus morhua L.).
• To compare the structure and organization of the Atlantic cod IgD gene with those found in other teleost species.
• To understand the evolutionary implications of the identified gene structure.

Main Methods:

• Gene cloning and sequencing of the immunoglobulin heavy-chain locus in Atlantic cod.
• Bioinformatic analysis to identify gene structure, homology, and potential functional domains.
• Comparative analysis with known IgD genes from channel catfish, Atlantic salmon, and mammalian species.

Main Results:

• A novel IgD heavy-chain gene was identified in Atlantic cod with similarities to catfish and salmon IgD.
• The cod IgD gene exhibits unique features: deletion of delta3-delta6 domains, tandem duplication of delta1-delta2 domains, a truncated delta7 domain, and a novel deltay exon.
• The gene product is chimeric, with the mu1 exon spliced to the delta1 exon, similar to other teleost IgD.

Conclusions:

• The Atlantic cod IgD gene possesses a unique genomic organization distinct from other teleost fish.
• These structural variations likely arose after the evolutionary divergence of cod from catfish and salmon lineages.
• The findings provide insights into the diversification of IgH genes and immune system evolution in teleost fish.