[en] Over the last 500 Myr, Petromyzontiformes (lampreys) have evolved independently from the rest of vertebrates, representing one of the most basal lineages currently known. Previous work has described the presence of a very peculiar group of endogenous retroviruses in the genomes of Petromyzon marinus and Lethenteron camtschaticum, initially called lokiretroviruses, and more recently lokiorterviruses, which have representatives in a large number of fish, amphibian and reptile species, so that their origin could, in principle, be very ancient. However, it is uncertain whether this is true or whether its origin is much more recent and its widespread distribution is due to horizontal transmission. Consequently, this work aimed to study the presence of representatives of this class of endogenous retroviruses in the currently sequenced genomes of Petromyzontiformes (Petromyzon marinus, Entosphenus tridentatus, Lethenteron reissneri and Lethenteron camtschaticum) and the phylogenetic relationships between them. In addition, the aim was to determine the abundance of proviruses and the existence of inconsistencies between the phylogenetic trees of retroviruses and host species, as well as between those obtained from different retroviral domains.To carry out this study, an in silico analysis was performed using databases published in the NCBI, which were screened to locate the insertions present in the genome of Petromyzontiformes. Once characterised, they were used to create phylogenetic trees. The results show that lokiorterviruses are "alive" within the genus Lethenteron and that they are actively transposed throughout their genome. This could indicate that the insertion of these retroviruses into the lamprey genome would have occurred earlier than expected or that they appear in the genome of this genus by horizontal transmission. On the other hand, the existence of two different episodes of endogenisation of lokiorterviruses was observed. The results also demonstrate the presence of horizontal transmission by mixing insertions belonging to different species across clades. Finally, inconsistencies were found between the phylogenies of RH and RT domains indicating a mosaic evolution.

[gl] Dende hai 500 Ma, os Petromyzontiformes (lampreas) evolucionan de forma independente con respecto ó resto dos vertebrados, representando unha das liñaxes máis basais coñecidas. En anteriores traballos, describiuse a presenza dun grupo moi peculiar de retrovirus endóxenos no xenoma de Petromyzon marinus e de Lethenteron camtschaticum, inicialmente denominados lokiretrovirus, e máis recentemente lokiortervirus, que conta con representantes nun gran número de especies de peixes, anfibios e réptiles, polo que a súa orixe podería ser, en principio, moi antiga. Con todo, non se sabe con seguridade se isto é certo ou se a súa orixe é moito máis recente e a súa extensa distribución é debida a transmisión horizontal. En consecuencia, neste traballo propúxose estudar a presenza de representantes desta clase de retrovirus endóxenos nos xenomas actualmente secuenciados dos Petromyzontiformes (Petromyzon marinus, Entosphenus tridentatus, Lethenteron reissneri e Lethenteron camtschaticum) e as relacións filoxenéticas que se establecen entre eles. Ademais, pretendíase determinar a abundancia de provirus e a existencia de incongruencias entre as árbores filoxenéticas dos retrovirus e das especies hospedadoras, así como entre as obtidas a partir de distintos dominios retrovirais. Para levar a cabo este estudo, realizouse unha análise in silico empregando bases de datos publicadas no NCBI, que foron minadas para localizar as insercións presentes no xenoma dos Petromyzontiformes. Unha vez caracterizadas, foron empregadas para construír árbores filoxenéticas. Os resultados demostran que os lokiortervirus están "vivos" dentro do xénero Lethenteron e que se traspoñen activamente ó longo do seu xenoma. Isto podería indicar que a inserción destes retrovirus no xenoma das lampreas tivo lugar antes do previsto ou que aparecen no xenoma deste xénero por transmisión horizontal. Por outro lado, observouse a existencia de dous episodios diferentes de endoxenización dos lokiortervirus. Tamén, os resultados amosan a presenza de transmisión horizontal por mestura de insercións pertencentes a distintas especies ao longo dos distintos clados. Por último, atopáronse incoherencias entre as filoxenias dos dominios RH e RT, indicativas dunha evolución en mosaico.