Identification of novel porcine endogenous betaretrovirus sequences in miniature swine

PCR amplification of genomic DNA from miniature swine peripheral blood lymp hocytes, using primers corresponding to highly conserved regions of the pol ymerase (pol) gene, allowed the identification of two novel porcine endogen ous retrovirus (PERV) sequences, PMSN-1 and PMSN-4. Phylogenetic analyses o f the nucleotide sequences of PMSN-1 and PMSN-4 revealed them to be most cl osely related to betaretroviruses. The identification of PERVs belonging to the Betaretrovirus genus shows that endogenous retroviruses of this family are more broadly represented in mammalian species than previously apprecia ted. Both sequences contained inactivating mutations, implying that these p articular loci are defective. However, Southern blot analysis showed additi onal copies of closely related proviruses in the miniature swine genome. An alyses of fetal and adult miniature swine tissues revealed a broad mRNA exp ression pattern of both PMSN-1 and PMSN-4, The most abundant expression was detected in whole bone marrow c-kit(+) (CD117(+)) progenitor bone marrow c ells, fetal liver, salivary gland, and thymus. It appears unlikely that fun ctional loci encoding these novel PERV sequences exist, but this remains to be established. The betaretrovirus sequences described in this report will allow such investigations to be actively pursued.