Retroviral Insertion Polymorphism (RIP) of Porcine Endogenous Retroviruses (PERVs) in Pig Genomes

Abstract

Endogenous retroviruses (ERVs) are one of the superfamilies of long terminal repeat retrotransposons (LTRs) in mice and humans. Approximately 8% of the pig genome is composed of sequences derived from LTRs. While the majority of ERVs in pigs have decayed, a small number of full-length copies can still mobilize within the genome. This study investigated the unexplored retroviral insertion polymorphisms (RIPs) generated by the mobilization of full-length ERVs (Fl-ERVs), and evaluated their impact on phenotypic variation to gain insights into the biological role of Fl-ERVs in pigs. Overall, 39 RIPs (insertions or deletions relative to the pig reference genome) generated by Fl-ERVs were predicted by comparative genomic analysis, and 18 of them were confirmed by PCR detection. Four RIP sites (D5, D14, D15, and D18) were further evaluated by population analysis, and all of them displayed polymorphisms in multiple breeds. The RIP site of ERV-D14, which is a Fl-ERV inserted in the STAB2-like gene, was further confirmed by sequencing. Population analysis of the polymorphic site of ERV-D14 reveals that it presents moderate polymorphism information in the Large White pig breed, and the association analysis reveals that the RIP of ERV-D14 is associated with age variations at 30 kg body weight (p < 0.05) and 100 kg body weight (p < 0.01) in the population of Large White pigs (N = 480). Furthermore, the ERV-D14 RIP is associated with changes in the expression of the target gene STAB2-like in the liver, backfat, and leaf fat in Sushan pigs. These data suggest that some Fl-ERVs are still mobilizing in the pig’s genome, and contribute to genomic and phenotypic variations.

Evolution of Endogenous Retroviruses in the Subfamily of Caprinae

“…The presence of full-length ERV insertion polymorphisms, which typically consist of large structural variations exceeding 5 kb, can result in a stronger genetic impact and can be considered as an indicator of activity [ 34 ]. In this study, we performed PCR verification and genotyping analysis on six sheep breeds, with five individuals from each breed, using the primers of four RIPs from each group of full-length ERVs.…”

“…If both shorter and longer bands were observed, it signified that this RIP genotype must be heterozygous (labeled as ERV+/−). The methodology employed in this part of the study was based on the framework proposed by Du et al [ 34 ].…”