Abstract
BackgroundThe identification of sequence innovations in the genomes of mammals facilitates understanding of human gene function, as well as sheds light on the molecular mechanisms which underlie these changes. Although gene duplication plays a major role in genome evolution, studies regarding concerted evolution events among gene family members have been limited in scope and restricted to protein-coding regions, where high sequence similarity is easily detectable.ResultsWe describe a mammalian-specific expansion of more than 20 rapidly-evolving genes on human chromosome Xq22.1. Many of these are highly divergent in their protein-coding regions yet contain a conserved sequence motif in their 5' UTRs which appears to have been maintained by multiple events of concerted evolution. These events have led to the generation of chimaeric genes, each with a 5' UTR and a protein-coding region that possess independent evolutionary histories. We suggest that concerted evolution has occurred via gene conversion independently in different mammalian lineages, and these events have resulted in elevated G+C levels in the encompassing genomic regions. These concerted evolution events occurred within and between genes from three separate protein families ('brain-expressed X-linked' [BEX], WWbp5-like X-linked [WEX] and G-protein-coupled receptor-associated sorting protein [GASP]), which often are expressed in mammalian brains and associated with receptor mediated signalling and apoptosis.ConclusionDespite high protein-coding divergence among mammalian-specific genes, we identified a DNA motif common to these genes' 5' UTR exons. The motif has undergone concerted evolution events independently of its neighbouring protein-coding regions, leading to formation of evolutionary chimaeric genes. These findings have implications for the identification of non protein-coding regulatory elements and their lineage-specific evolution in mammals.
Highlights
The identification of sequence innovations in the genomes of mammals facilitates understanding of human gene function, as well as sheds light on the molecular mechanisms which underlie these changes
We suggest that the occurrence of concerted evolution events during mammalian evolution led to multiple chimaeric genes, with 5' untranslated regions (UTRs) and protein-coding sequences possessing different evolutionary pedigrees
We have described the evolutionary history of a large region of human chromosome X, which appears to be an innovation of placental mammals. This region encompasses three previously unrelated protein-coding gene families, BEX, WEX and GASP, which have been the product of multiple gene duplications and large proteincoding sequence diversification since the earliest eutherian mammal
Summary
The identification of sequence innovations in the genomes of mammals facilitates understanding of human gene function, as well as sheds light on the molecular mechanisms which underlie these changes. Non-allelic gene conversion results in phylogenetic trees which display significantly greater proximity between a species' gene paralogues than for gene orthologues of a sister species [11]. Such phylogenetic relationships, are indicative of lineage-specific gene duplication events. When the affected genes are widely-spread on the genome these relationships are usually indicative of non-allelic gene conversion. This is because gene duplication most frequently results in tandem consecutive genes along the chromosome
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