Porcine Endogenous Retroviruses (PERV) : Integration and Inhibition

  • Rashmi Wali

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)


Porcine endogenous retroviruses (PERV) inherited as proviruses in the pig genome can infect human cells, posing a potential risk of zoonosis in pig-to-human xenotransplantation. PERVs are found integrated in the genome of all pigs and more than 100 proviral integration sites are present at multiple locations in the pig genome. Three different replication competent types of PERVs have been identified and are classified based on a combination of sequence variation, receptor interference, and in vitro cell line specificity. Introduction of PERV into the pig genome is relatively recent and integration sites are highly polymorphic. It is predicted that only a limited number of PERV loci are active and can direct production of infectious viruses. Identification of such active PERV loci and determination of their distribution in the pig population would help identify, breed or genetically engineer pigs free from problematic PERV. For xenotransplantation to be successful, identification of full length loci that are capable of replication, and methods by which these PERV can be inhibited are paramount.

The aims of this study were two-fold: 1) to identify integration sites using the swine whole genome sequence (SWGS derived from a Duroc sow) and 2) to assess the role of several restriction factors and their inhibitory effects on PERV replication.

PERV integration sites were identified by the RetroTector program (Sperber et al.,2007) as well as manual BLAT/BLAST analyses. Around 40 potential sequences were identified and 500 bps of genomic flank sequences and ~800 bps PERV terminal sequences were extracted from SWGS for each locus. These sequences have been further identified 20 PERV-yl and 4 (33 full length loci by blast analysis. Primers were designed specifically to amplify these sequences and used to screen a panel of pigs (n= 170) belonging to different
geographical locations and herds. As expected, distribution of these integrations was clearly different in both individual pigs and between breeds. In addition, PERV sequence information in SWGS has its limitations in revealing the PERV integration pattern in pigs as a population, but supports previous estimations that majority of PERV proviruses are defective. The results obtained are breed and region specific providing a launch pad to identify site-specific active PERVs in the pig genome and a selection criterion for pigs for Xenotransplantation.

In the second part of the project, an attempt to explore the restriction properties of Zinc finger protein 809 (ZFP809), and a number of TRIM factors was made. TRIM28 has been shown previously to recruit ZFP809 in mouse embryonic stem cells to silence the expression of retroviral cDNAs. Also, TRIM28 controls the expression of ERVs during early embryonic stages. Here, ZFP809, hTRIM28 and ssTRIM28 were over expressed in either porcine or human cell lines expressing PERV subtypes A/B (PK15) and A/C (14/420 and 15/150) or expressed in non-infected cells and challenged with PERV. Any subsequent reduction in PERV activity was determined by reduction in pol activity as seen by real time PCR (Q-PCR) and GAG levels as measured by Western blot analysis. Data obtained suggested that both ZFP809 and TRIM28 when expressed in human cell lines were effective against recombinant PERV subtype PERV-A/C and could potentially be considered for developing transgenic pigs xenotransplantation. However, neither were effective at reducing the expression of PERV A/B. TRIM 11 was also investigated for restriction against PERV subtypes, however no restriction was seen for either PERV subtypes. In conclusion, a suitable restriction factor that will abrogate expression of all PERV subtypes is yet to be identified.
Date of Award2015
Original languageEnglish
Awarding Institution
  • Glasgow Caledonian University
SupervisorLinda Scobie (Supervisor)

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