Multiple gains of spliceosomal introns in a superfamily of vertebrate protease inhibitor genes

Abstract

Abstract Background Intron gains reportedly are very rare during evolution of vertebrates, and the mechanisms underlying their creation are largely unknown. Previous investigations have shown that, during metazoan radiation, the exon-intron patterns of serpin superfamily genes were subject to massive changes, in contrast to many other genes. Results Here we investigated intron dynamics in the serpin superfamily in lineages pre- and postdating the split of vertebrates. Multiple intron gains were detected in a group of ray-finned fishes, once the canonical groups of vertebrate serpins had been established. In two genes, co-occurrence of non-standard introns was observed, implying that intron gains in vertebrates may even happen concomitantly or in a rapidly consecutive manner. DNA breakage/repair processes associated with genome compaction are introduced as a novel factor potentially favoring intron gain, since all non-canonical introns were found in a lineage of ray-finned fishes that experienced genomic downsizing. Conclusion Multiple intron acquisitions were identified in serpin genes of a lineage of ray-finned fishes, but not in any other vertebrates, suggesting that insertion rates for introns may be episodically increased. The co-occurrence of non-standard introns within the same gene discloses the possibility that introns may be gained simultaneously. The sequences flanking the intron insertion points correspond to the proto-splice site consensus sequence MAG↑N, previously proposed to serve as intron insertion site. The association of intron gains in the serpin superfamily with a group of fishes that underwent genome compaction may indicate that DNA breakage/repair processes might foster intron birth.