Cluster expansion of apolipoprotein D (ApoD) genes in teleost fishes

Abstract

BackgroundGene and genome duplication play important roles in the evolution of gene function. Compared to individual duplicated genes, gene clusters attract particular attentions considering their frequent associations with innovation and adaptation. Here, we report for the first time the expansion of the ligand (e.g., pheromone and hormone)-transporter genes, apolipoprotein D (ApoD) genes in a cluster, specific to teleost fishes.\n\nResultsThe single ApoD gene in the ancestor expands in two clusters with a dynamic evolutionary pattern in teleost fishes. Based on comparative genomic and transcriptomic analyses, protein 3D structure comparison, evolutionary rate detection and breakpoint detection, orthologous genes show conserved expression patterns. Lineage-specific duplicated genes that are under positive selection evolved specific and even new expression profiles. Different duplicates show high tissue-specific expression patterns (e.g., skin, eye, anal fin pigmentation patterns, gonads, gills, spleen and lower pharyngeal jaw). Cluster analyses based on protein 3D structure comparisons, especially the four loops at the opening side, show segregation patterns with different duplicates. Duplicated ApoD genes are predicted to be associated with forkhead transcription factors and MAPK genes, and they are located next to the breakpoints of genome rearrangements.\n\nConclusionsHere, we report the expansion of ApoD genes specific to teleost fishes in a cluster manner for the first time. Neofunctionalization and subfunctionalization were observed at both protein and expression levels after duplication. Evidence from different aspects, i.e. abnormal expression induced disease in human, fish-specific expansion, predicted associations with forkhead transcription factors and MAPK genes, highly specific expression patterns in tissues related to sexual selection and adaptation, duplicated genes that are under positive selection, and their locations next to breakpoints of genome rearrangement, suggests the potential advantageous roles of ApoD genes in teleost fishes. Cluster expansion of ApoD genes specific to teleost fishes thus provides an ideal evo-devo model for studying gene duplication, cluster maintenance and new gene function emergence.