Genomic complexity of the variable region-containing chitin-binding proteins in amphioxus

Area of Science:

• Genomics
• Immunology
• Evolutionary Biology

Background:

• Variable region-containing chitin-binding proteins (VCBPs) are found in protochordates, featuring immunoglobulin variable (V)-type and chitin-binding domains.
• These polymorphic genes, primarily expressed in the gut, exhibit characteristics of immune genes.

Purpose of the Study:

• To describe the genomic organization of VCBP genes.
• To characterize adjacent and intervening genetic features influencing VCBP polymorphism and transcriptional repertoire.

Main Methods:

• BAC and PAC screening and sequencing of the Branchiostoma floridae genome.
• Multi-animal cDNA screening and transcriptional profiling using a novel transfection system.

Main Results:

• VCBP genes are organized in distinct chromosomal regions, with extensive haplotype variation including copy number variation (CNV) and indel polymorphism.
• Elevated variation in repeat type and density, with frequent inverted repeats in some haplotypes.
• Haplotype-specific transcriptional variants suggest a contribution to VCBP genetic diversity.

Conclusions:

• The amphioxus genome reveals a limited number of VCBP genes with exceptionally high haplotype variation.
• VCBP haplotypes contribute diverse allelic variants, including CNV, pseudogenes, and other polymorphisms.
• These variations have secondary effects on gene transcription, enhancing immune gene diversity.