Genomic architecture of the major histocompatibility complex genes in the Neotropical Midas cichlid

Amphilophus citrinellus has 298 MHC-related loci across 18 chromosomes, including 30 MHC-I, 15 MHC-IIA, and 20 MHC-IIB genes, with non-linkage across chromosomes.

• Why it matters: MHC genomic organization is still unclear in many evolutionary model systems, limiting how well immune diversification can be studied during cichlid radiation.
• What they did: The team combined chromosome-level genome annotation, TE profiling, transcriptomics, phylogenetics, molecular selection tests, and protein structural modeling to map and evaluate MHC loci.
• The result: Positive selection is detected in MHC-I and MHC-IIB genes, while MHC-IIA shows more limited evidence; tissue expression and structural models support a diverse, evolutionarily shaped repertoire.

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