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Evolution of the multifaceted eukaryotic akirin gene family.

ABSTRACT: BACKGROUND: Akirins are nuclear proteins that form part of an innate immune response pathway conserved in Drosophila and mice. This studies aim was to characterise the evolution of akirin gene structure and protein function in the eukaryotes. RESULTS: akirin genes are present throughout the metazoa and arose before the separation of animal, plant and fungi lineages. Using comprehensive phylogenetic analysis, coupled with comparisons of conserved synteny and genomic organisation, we show that the intron-exon structure of metazoan akirin genes was established prior to the bilateria and that a single proto-orthologue duplicated in the vertebrates, before the gnathostome-agnathan separation, producing akirin1 and akirin2. Phylogenetic analyses of seven vertebrate gene families with members in chromosomal proximity to both akirin1 and akirin2 were compatible with a common duplication event affecting the genomic neighbourhood of the akirin proto-orthologue. A further duplication of akirins occurred in the teleost lineage and was followed by lineage-specific patterns of paralogue loss. Remarkably, akirins have been independently characterised by five research groups under different aliases and a comparison of the available literature revealed diverse functions, generally in regulating gene expression. For example, akirin was characterised in arthropods as subolesin, an important growth factor and in Drosophila as bhringi, which has an essential myogenic role. In vertebrates, akirin1 was named mighty in mice and was shown to regulate myogenesis, whereas akirin2 was characterised as FBI1 in rats and promoted carcinogenesis, acting as a transcriptional repressor when bound to a 14-3-3 protein. Both vertebrate Akirins have evolved under comparably strict constraints of purifying selection, although a likelihood ratio test predicted that functional divergence has occurred between paralogues. Bayesian and maximum likelihood tests identified amino-acid positions where the rate of evolution had shifted significantly between paralogues. Interestingly, the highest scoring position was within a conserved, validated binding-site for 14-3-3 proteins. CONCLUSION: This work offers an evolutionary framework to facilitate future studies of eukaryotic akirins and provides insight into their multifaceted and conserved biochemical functions.

SUBMITTER: Macqueen DJ

PROVIDER: S-EPMC2660306 | biostudies-literature | 2009

REPOSITORIES: biostudies-literature

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Evolution of the multifaceted eukaryotic akirin gene family.

Macqueen Daniel J DJ Johnston Ian A IA

BMC evolutionary biology 20090206

<h4>Background</h4>Akirins are nuclear proteins that form part of an innate immune response pathway conserved in Drosophila and mice. This studies aim was to characterise the evolution of akirin gene structure and protein function in the eukaryotes.<h4>Results</h4>akirin genes are present throughout the metazoa and arose before the separation of animal, plant and fungi lineages. Using comprehensive phylogenetic analysis, coupled with comparisons of conserved synteny and genomic organisation, we ...[more]

PMID: 19200367

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Project description:BACKGROUND: Forkhead box, class O (FoxO) belongs to the large family of forkhead transcription factors that are characterized by a conserved forkhead box DNA-binding domain. To date, the FoxO group has four mammalian members: FoxO1, FoxO3a, FoxO4 and FoxO6, which are orthologs of DAF16, an insulin-responsive transcription factor involved in regulating longevity of worms and flies. The degree of homology between these four members is high, especially in the forkhead domain, which contains the DNA-binding interface. Yet, mouse FoxO knockouts have revealed that each FoxO gene has its unique role in the physiological process. Whether the functional divergences are primarily due to adaptive selection pressure or relaxed selective constraint remains an open question. As such, this study aims to address the evolutionary mode of FoxO, which may lead to the functional divergence. RESULTS: Sequence similarity searches have performed in genome and scaffold data to identify homologues of FoxO in vertebrates. Phylogenetic analysis was used to characterize the family evolutionary history by identifying two duplications early in vertebrate evolution. To determine the mode of evolution in vertebrates, we performed a rigorous statistical analysis with FoxO gene sequences, including relative rate ratio tests, branch-specific dN/dS ratio tests, site-specific dN/dS ratio tests, branch-site dN/dS ratio tests and clade level amino acid conservation/variation patterns analysis. Our results suggest that FoxO is constrained by strong purifying selection except four sites in FoxO6, which have undergone positive Darwinian selection. The functional divergence in this family is best explained by either relaxed purifying selection or positive selection. CONCLUSION: We present a phylogeny describing the evolutionary history of the FoxO gene family and show that the genes have evolved through duplications followed by purifying selection except for four sites in FoxO6 fixed by positive selection lie mostly within the non-conserved optimal PKB motif in the C-terminal part. Relaxed selection may play important roles in the process of functional differentiation evolved through gene duplications as well.

Dataset Information

Evolution of the multifaceted eukaryotic akirin gene family.

Publications

Evolution of the multifaceted eukaryotic akirin gene family.

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