Mosquito genomes are frequently invaded by transposable elements through horizontal transfer

A large fraction of most eukaryotic genomes is derived from DNA fragments that can multiply by inserting themselves in other regions of the genome, generating genomic instability and variability. These fragments are called Transposable Elements (TEs). Since they are a constituent part of the eukaryote genomes, these DNA pieces are normally inherited vertically along with other genes to the host offspring. Host genomes have an arsenal of molecular mechanisms that were naturally selected to control TEs replication avoiding most deleterious damage to the genome and hence leading to long-term TEs inactivation and degeneration. However, TEs sometimes get out of control and invade other species through horizontal transfer, the transfer of genetic information through other means than sexual intercourse. This phenomenon is poorly studied in mosquitoes, a highly important Insect taxa that transmit many human pathogens. We characterized the whole TE content of 24 mosquito genomes and investigated the TE inheritance mode uncovering hundreds of horizontal transfer events among these species and distantly related ones. We also identify a mosquito parasitic filarial worm, that is involved as a transfer vector between many species of mosquitoes and that horizontally transferred TEs contributed significantly to mosquito’s genome expansion and variation.

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