Resumo
Background: Short interspersed nuclear elements (SINEs) are transposable elements which are transcribed by RNA polymerase III and widespread in mammalian genomes. Can-SINE is a family of SINE sequences specific to carnivores, predominant in their genomes and present in high copy numbers. The aim of this study was to characterize sequences of Can-SINEs integrated into sequences of endogenous retroviruses (ERVs) from Brazilian wild cats Puma concolor and Leopardus geoffroyi. Additionally, these sequences are considered from some perspectives of their evolution. Material, Methods and Results: By using PCR and sequencing to screen for ERVs within the genomes of L. geoffroyi and P. concolor, two new ERV sequences were amplified with an insertion around 220 nucleotides long, similar to published carnivore SINEs. The sequences were further identified and characterized using a combination of BLAST, BLAT searches and phylogenetic analyses. The results showed that SINE sequences integrated into the ERV from P. concolor (SINE_Pco) and L. geoffroyi (SINE_Lg) are lysine-tRNA derived. These sequences presented a typical RNA polymerase III-specific internal promoter sequence followed by a microsatellite region (TC)n and by an A/T-rich tail with the polyadenylation signal AATAAA. BLAST searches using the whole sequence of L. geoffroyi clone as query (ERV plus SINE) detected two sequences which were highly similar to the cougar (P. concolor) and the domestic cat. However, the SINE from Leopardus geoffroyi is not present in these related sequences. On the other hand, during searches using the whole sequence of the P. concolor clone as query, we found the same SINE insertion in a very similar ERV from domestic cat. All insertions occurred in the RT domain, but SINE_Lg was integrated in a distinct site when compared to SINE_Pco. Another interesting difference between these SINE sequences was that the statistics reported in BLAST searches recovered a much higher number of hits from the domestic cat genome using SINE_Lg as seed than in searches for sequences related to SINE_Pco. The phylogenetic tree based on the SINE fragment grouped these new SINE sequences with Can-SINEs from felids. Within this major clade SINE_Lg and SINE_Pco are related to different lineages of felids Can-SINEs. Discussion: In this study we showed that two different sequences from felid endogenous retrovirus harbor Can-SINE sequences. These insertions are not surprising taking account that ~11% of domestic cat genome is composed of SINE sequences and they are ubiquitous in felid genomes. Furthermore, the insertions of SINEs into the ERV sequences reported here are not unique events. However, they are curious insertions representing genomic fossils and a little piece of felid history. Based on the results of the phylogenetic analyses and position of the integration sites, we suggest that SINE_Lg and SINE_Pco represent independent integration events originated by derived copies from different progenitors. We hypothesized that SINE_Lg is a "young" integration due to the absence of highly similar ERVs from Puma concolor and Felis catus. This lineage may be recently active in felid genomes given that we found very similar MegaBLAST hits at EST database from domestic cat. Instead, SINE_Pco seems to be "old", sharing an identical insertion site to ERVs from domestic cat and its lineage could be inactive in felids considering that any MegaBLAST hits resulted from EST database searches. The latter suggests an integration event in an ancestor species at least 6.7 million years ago, which represents the split between puma and domestic cat lineages.