BovB: Jumping The Fine LINE Between Species

Genomes are made up of an abundance of different elements, including a vast number of repetitive elements. The proportion of the genome of each species that is composed of repetitive elements is vastly different. Drosophila have a significant quantity of DNA transposons (elements that replicate via a DNA intermediate), while humans have an abundance of Long Interspersed Nuclear Elements (LINEs), and cows have a remarkable 20% of their genome composed of retrotransposons (elements that replicate via an RNA intermediate). The study of repetitive elements helps us determine their effect on speciation, mutation and genome rearrangements. The discovery of a retrotransposon in cows, named BovB, is interesting due to its remarkable abundance and sporadic appearance across taxa. BovB has previously been found in snakes and marsupials with a remarkable level of conservation between distantly related species. The questions this poses are, “How is BovB found in such distantly related taxa without being present in the many other species that share a common ancestor?” and “How has BovB maintained its remarkable level of nucleotide identity?”. The likely explanation for this is horizontal transfer. Previously, a single horizontal transfer event, or possibly two, have been proposed in order for the element to move between squamates (snakes and lizards), ruminants (such as cows and sheep) and marsupials, but no vector has been determined. Our work shows that BovB is found across an even wider range of species than previously thought, and the distribution of the taxa on a phylogenetic tree built from the BovB elements indicates that up to nine transfers have occurred between the species in the tree, which includes African mammals, ticks, monotremes and horses, as well as the groups previously shown. For the first time we can show that reptile ticks, such as those studied here, are potential vectors for this horizontal transfer based on their BovB genomic content.