Investigation of Polymorphisms Induced by the Solo Long Terminal Repeats (Solo-LTRs) in Porcine Endogenous Retroviruses (ERVs)

Homologous recombination events take place between the 5' and 3' long terminal repeats (LTRs) of ERVs, resulting in the generation of solo-LTR, which can cause solo-LTR-associated polymorphism across different genomes. In the current study, specific criteria were established for the filtration of solo-LTRs, resulting in an average of 5630 solo-LTRs being identified in 21 genomes. Subsequently, a protocol was developed for detecting solo-LTR polymorphisms in the pig genomes, resulting in the discovery of 927 predicted solo-LTR polymorphic sites. Following verification and filtration processes, 603 highly reliable solo-LTR polymorphic sites were retained, involving 446 solo-LTR presence sites (solo-LTR⁺) and 157 solo-LTR absence sites (solo-LTR^-) relative to the reference genome. Intersection analysis with gene/functional regions revealed that 248 solo-LTR^- sites and 23 solo-LTR⁺ sites overlapped with genes or were in the vicinity of genes or functional regions, impacting a diverse range of gene structures. Moreover, through the utilization of 156 solo-LTR polymorphic sites for population genetic analysis, it was observed that these solo-LTR loci effectively clustered various breeds together, aligning with expectations and underscoring their practical utility. This study successfully established a methodology for detecting solo-LTR polymorphic sites. By applying these methods, a total of 603 high-reliability solo-LTR polymorphic sites were pinpointed, with nearly half of them being linked to genes or functional regions.