The Telomeric Repeats of Human Herpesvirus 6A (HHV-6A) Are Required for Efficient Virus Integration

Human herpesvirus 6A (HHV-6A) and 6B (HHV-6B) are ubiquitous betaherpesviruses that infects humans within the first years of life and establishes latency in various cell types. Both viruses can integrate their genomes into telomeres of host chromosomes in latently infected cells. The molecular mechanism of viral integration remains elusive. Intriguingly, HHV-6A, HHV-6B and several other herpesviruses harbor arrays of telomeric repeats (TMR) identical to human telomere sequences at the ends of their genomes. The HHV-6A and HHV-6B genomes harbor two TMR arrays, the perfect TMR (pTMR) and the imperfect TMR (impTMR). To determine if the TMR are involved in virus integration, we deleted both pTMR and impTMR in the HHV-6A genome. Upon reconstitution, the TMR mutant virus replicated comparable to wild type (wt) virus, indicating that the TMR are not essential for HHV- 6A replication. To assess the integration properties of the recombinant viruses, we established an in vitro integration system that allows assessment of integration efficiency and genome maintenance in latently infected cells. Integration of HHV-6A was severely impaired in the absence of the TMR and the virus genome was lost rapidly, suggesting that integration is crucial for the maintenance of the virus genome. Individual deletion of the pTMR and impTMR revealed that the pTMR play the major role in HHV-6A integration, whereas the impTMR only make a minor contribution, allowing us to establish a model for HHV-6A integration. Taken together, our data shows that the HHV-6A TMR are dispensable for virus replication, but are crucial for integration and maintenance of the virus genome in latently infected cells

ライフサイクルとヒューマンケア: 高齢者への健康支援(平成23年度教養コア科目) 授業資料ナビゲータ(PathFinder)

担当教員:黒田久美子,野地有子,今村恵美子,永野みどり平成23年度(2011)教養コア科目授業B(こころと発達),授業コード:G14B1410

Mammalian deltavirus without hepadnavirus coinfection in the neotropical rodent Proechimys semispinosus.

Hepatitis delta virus (HDV) is a human hepatitis-causing RNA virus, unrelated to any other taxonomic group of RNA viruses. Its occurrence as a satellite virus of hepatitis B virus (HBV) is a singular case in animal virology for which no consensus evolutionary explanation exists. Here we present a mammalian deltavirus that does not occur in humans, identified in the neotropical rodent species Proechimys semispinosus The rodent deltavirus is highly distinct, showing a common ancestor with a recently described deltavirus in snakes. Reverse genetics based on a tandem minus-strand complementary DNA genome copy under the control of a cytomegalovirus (CMV) promoter confirms autonomous genome replication in transfected cells, with initiation of replication from the upstream genome copy. In contrast to HDV, a large delta antigen is not expressed and the farnesylation motif critical for HBV interaction is absent from a genome region that might correspond to a hypothetical rodent large delta antigen. Correspondingly, there is no evidence for coinfection with an HBV-related hepadnavirus based on virus detection and serology in any deltavirus-positive animal. No other coinfecting viruses were detected by RNA sequencing studies of 120 wild-caught animals that could serve as a potential helper virus. The presence of virus in blood and pronounced detection in reproductively active males suggest horizontal transmission linked to competitive behavior. Our study establishes a nonhuman, mammalian deltavirus that occurs as a horizontally transmitted infection, is potentially cleared by immune response, is not focused in the liver, and possibly does not require helper virus coinfection

Primers and probes for qPCR and generation of recombinant viruses.

<p>Primers and probes for qPCR and generation of recombinant viruses.</p

Integration efficiency and genome maintenance of the ΔTMR mutant in the U2OS integration system.

<p><b>(A)</b> Integration frequency was quantified by determining the integration status of at least 90 metaphases. Significant differences between wt and ΔTMR (Mann-Whitney U-test, p < 0.05) are indicated with an asterisk (*). Results are shown as means of three independent experiments with standard errors. Representative metaphase images are shown on the right. Scale bar corresponds to 10μm. <b>(B)</b> 300 interphase nuclei were examined for the presence of HHV-6A. Significant differences between wt and ΔTMR (Mann-Whitney U-test, p < 0.05) are indicated with an asterisk (*). Results are shown as means of three independent experiments with standard errors. Representative interphase images are shown on the right. Scale bar corresponds to 10μm. <b>(C)</b> Maintenance of the HHV-6A genome was determined by qPCR analysis at d0 and d14 post sorting. Copy numbers per 1x 10⁶ cells are shown as means of three independent experiments with corresponding standard errors. Significant differences between wt and ΔTMR (Mann-Whitney U-test, p < 0.01) are indicated with asterisks (**).</p

Generation and characterization of the ΔTMR mutant.

<p><b>(A)</b> Schematic representation of the HHV-6A genome with deletion of the TMR (ΔTMR). <b>(B)</b> RFLP pattern of the wt, the ΔpTMR intermediate and the double deletion mutant ΔTMR upon digestion with <i>Sac</i>I analyzed on a 0.8% agarose gel o/n at 65 V. M = marker. Sizes of the marker fragments are indicated on the left. Red boxes highlight the fragments containing the target regions, where the expected band shifts can be observed. <b>(C)</b> Corresponding southern blot analysis detecting TMR sequences of the impTMR (upper panel) and pTMR (lower panel) after <i>Sac</i>I digestion of the indicated BAC clones using a DIG-labeled TMR probe. <b>(D)</b> Growth kinetics comparing replication properties of wt and ΔTMR mutant virus in JJHan cells. HHV-6A genome copy numbers were detected by qPCR. Copy numbers per 1x 10⁶ cells are shown as means of three independent experiments with standard errors.</p