Endogenization of a prosimian retrovirus during lemur evolution

Studies of viruses that coevolved with lemurs provide an opportunity to understand the basal traits of primate viruses and provide an evolutionary context for host-virus interactions. Germline integration of endogenous retroviruses (ERVs) are fossil evidence of past infections. Hence, characterization of novel ERVs provides insight into the ancient precursors of extant viruses and the evolutionary history of their hosts. Here, we report the discovery of a novel endogenous retrovirus present in the genome of a lemur, Coquerel’s sifaka (Propithecus coquereli). Using nextgeneration sequencing, we identified and characterized the complete genome sequence of a retrovirus, named prosimian retrovirus 1 (PSRV1). Phylogenetic analyses indicate that PSRV1 is a gammatype betaretrovirus basal to the other primate betaretroviruses and most closely related to simian retroviruses. Molecular clock analysis of PSRV1 long terminal repeat (LTR) sequences estimated the time of endogenization within 4.56 MYA (±2.4 MYA), placing it after the divergence of Propithecus species. These results indicate that PSRV1 is an important milestone of lemur evolution during the radiation of the Propithecus genus. These findings may have implications for both human and animal health in that the acquisition of a gamma-type env gene within an endogenized betaretrovirus could facilitate a cross-species jump between vertebrate class hosts.