Exalign: a new method for comparative analysis of exon-intron gene structures

The evolution of genes is usually studied and reconstructed at the sequence level, that is, by comparing and aligning their genomic, transcript or protein sequences. However, including the exonintron structure of genes in the analysis can provide further and useful information, for example to draw reliable phylogenetic relationships left unsolved by traditional sequence-based evolutionary studies, or to shed further light on patterns of intron gain and loss. In spite of this, no tool especially devised for this task is currently available. In this work we present Exalign, an algorithm designed to retrieve, compare and search for the exon-intron structure of existing gene annotations, that has been implemented in a software tool freely accessible through a web interface as well as available for download. We present different applications of our method, from the reconstruction of the evolutionary history of homologous gene families to the detection of as of today unknown cases of intron loss in human and rodents, and, remarkably, two never reported intron gain events in human and mouse. The web interface for accessing Exalign is available at http:// www.pesolelab.it/exalign/ or http:// www.beacon.unimi.it/exalign/.