Transposable elements (TEs) are able to jump to new locations (transposition) in the genome, usually after replication. They constitute the so-called selfish or junk DNA and take over large proportions of some genomes. Due to their ability to move around they can change the DNA landscape of genomes and are therefore a rich source of innovation in genes and gene regulation. Surge of sequence data in the past years has significantly facilitated large scale comparative studies. Cephalochordates have been regarded as a useful proxy to ancestral chordate condition partially due to the comparatively slow evolutionary rate at morphological and genomic level. In this study, we used opsin gene family from three Branchiostoma species as a window into cephalochordate genome evolution. We compared opsin complements in terms of family size, gene structure and sequence allowing us to identify gene duplication and gene loss events. Furthermore, analysis of the opsin containing genomic loci showed that they are populated by TEs. In summary, we provide evidence of the way transposable elements may have contributed to the evolution of opsin gene family and to the shaping of cephalochordate genomes in general.

Department of Transcriptional Regulation Institute of Molecular Genetics of the ASCR v v i Videnska 1083 14220 Prague 4 Czech Republic

Laboratory of Eye Biology Institute of Molecular Genetics of the ASCR v v i Division BIOCEV Prumyslová 595 252 50 Vestec Czech Republic

Laboratory of Eye Biology Institute of Molecular Genetics of the ASCR v v i Division BIOCEV Prumyslová 595 252 50 Vestec Czech Republic Department of Transcriptional Regulation Institute of Molecular Genetics of the ASCR v v i Videnska 1083 14220 Prague 4 Czech Republic

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