Transactivation of the Rous sarcoma virus long terminal repeat promoter by Marek's disease virus

A comprehensive analysis of avian lymphoid leukosis-like lymphoma transcriptomes including identification of LncRNAs and the expression profiles

Avian lymphoid leukosis-like (LL-like) lymphoma has been observed in some experimental and commercial lines of chickens that are free of exogenous avian leukosis virus. Reported cases of avian lymphoid leukosis-like lymphoma incidences in the susceptible chickens are relatively low, but the apathogenic subgroup E avian leukosis virus (ALV-E) and the Marek’s disease vaccine, SB-1, significantly escalate the disease incidence in the susceptible chickens. However, the underlying mechanism of tumorigenesis is poorly understood. In this study, we bioinformatically analyzed the deep RNA sequences of 6 lymphoid leukosis-like lymphoma samples, collected from susceptible chickens post both ALV-E and SB-1 inoculation, and identified a total of 1,692 novel long non-coding RNAs (lncRNAs). Thirty-nine of those novel lncRNAs were detected with altered expression in the LL-like tumors. In addition, 13 lncRNAs whose neighboring genes also showed differentially expression and 2 conserved novel lncRNAs, XLOC_001407 and XLOC_022595, may have previously un-appreciated roles in tumor development in human. Furthermore, 14 lncRNAs, especially XLOC_004542, exhibited strong potential as competing endogenous RNAs via sponging miRNAs. The analysis also showed that ALV subgroup E viral gene Gag/Gag-pol and the MD vaccine SB-1 viral gene R-LORF1 and ORF413 were particularly detectable in the LL-like tumor samples. In addition, we discovered 982 novel lncRNAs that were absent in the current annotation of chicken genome and 39 of them were aberrantly expressed in the tumors. This is the first time that lncRNA signature is identified in avian lymphoid leukosis-like lymphoma and suggests the epigenetic factor, lncRNA, is involved with the avian lymphoid leukosis-like lymphoma formation and development in susceptible chickens. Further studies to elucidate the genetic and epigenetic mechanisms underlying the avian lymphoid leukosis-like lymphoma is indeed warranted.

Endogenous Avian Leukosis Virus in Combination with Serotype 2 Marek's Disease Virus Significantly Boosted the Incidence of Lymphoid Leukosis-Like Bursal Lymphomas in Susceptible Chickens

Lymphoid leukosis (LL)-like lymphoma is a low-incidence yet costly and poorly understood disease of domestic chickens. The observed unique characteristics of LL-like lymphomas are that the incidence of the disease is chicken line dependent; pathologically, it appeared to mimic avian leukosis but is free of exogenous ALV infection; inoculation of the nonpathogenic ALV-E or MDV-2 (SB-1) boosts the incidence of the disease; and inoculation of both the nonpathogenic ALV-E and SB-1 escalates it to much higher levels. This study was designed to test the impact of two new ALV-E isolates, recently derived from commercial broiler breeder flocks, in combination with the nonpathogenic SB-1 on LL-like lymphoma incidences in both an experimental egg layer line of chickens and a commercial broiler breeder line of chickens under a controlled condition. Data from this study provided an additional piece of experimental evidence on the potency of nonpathogenic ALV-E, MDV-2, and ALV-E plus MDV-2 in boosting the incidence of LL-like lymphomas in susceptible chickens. This study also generated the first piece of genomic evidence that suggests host transcriptomic variation plays an important role in modulating LL-like lymphoma formation.

In 2010, sporadic cases of avian leukosis virus (ALV)-like bursal lymphoma, also known as spontaneous lymphoid leukosis (LL)-like tumors, were identified in two commercial broiler breeder flocks in the absence of exogenous ALV infection. Two individual ALV subgroup E (ALV-E) field strains, designated AF227 and AF229, were isolated from two different breeder farms. The role of these ALV-E field isolates in development of and the potential joint impact in conjunction with a Marek’s disease virus (MDV) vaccine (SB-1) were further characterized in chickens of an experimental line and commercial broiler breeders. The experimental line 0.TVB*S1, commonly known as the rapid feathering-susceptible (RFS) line, of chickens lacks all endogenous ALV and is fully susceptible to all subgroups of ALV, including ALV-E. Spontaneous LL-like tumors occurred following infection with AF227, AF229, and a reference ALV-E strain, RAV60, in RFS chickens. Vaccination with serotype 2 MDV, SB-1, in addition to AF227 or AF229 inoculation, significantly enhanced the spontaneous LL-like tumor incidence in the RFS chickens. The spontaneous LL-like tumor incidence jumped from 14% by AF227 alone to 42 to 43% by AF227 in combination with SB-1 in the RFS chickens under controlled conditions. RNA-sequencing analysis of the LL-like lymphomas and nonmalignant bursa tissues of the RFS line of birds identified hundreds of differentially expressed genes that are reportedly involved in key biological processes and pathways, including signaling and signal transduction pathways. The data from this study suggested that both ALV-E and MDV-2 play an important role in enhancement of the spontaneous LL-like tumors in susceptible chickens. The underlying mechanism may be complex and involved in many chicken genes and pathways, including signal transduction pathways and immune system processes, in addition to reported viral genes.

IMPORTANCE Lymphoid leukosis (LL)-like lymphoma is a low-incidence yet costly and poorly understood disease of domestic chickens. The observed unique characteristics of LL-like lymphomas are that the incidence of the disease is chicken line dependent; pathologically, it appeared to mimic avian leukosis but is free of exogenous ALV infection; inoculation of the nonpathogenic ALV-E or MDV-2 (SB-1) boosts the incidence of the disease; and inoculation of both the nonpathogenic ALV-E and SB-1 escalates it to much higher levels. This study was designed to test the impact of two new ALV-E isolates, recently derived from commercial broiler breeder flocks, in combination with the nonpathogenic SB-1 on LL-like lymphoma incidences in both an experimental egg layer line of chickens and a commercial broiler breeder line of chickens under a controlled condition. Data from this study provided an additional piece of experimental evidence on the potency of nonpathogenic ALV-E, MDV-2, and ALV-E plus MDV-2 in boosting the incidence of LL-like lymphomas in susceptible chickens. This study also generated the first piece of genomic evidence that suggests host transcriptomic variation plays an important role in modulating LL-like lymphoma formation.

Horizontal gene transfers with or without cell fusions in all categories of the living matter

This article reviews the history of widespread exchanges of genetic segments initiated over 3 billion years ago, to be part of their life style, by sphero-protoplastic cells, the ancestors of archaea, prokaryota, and eukaryota. These primordial cells shared a hostile anaerobic and overheated environment and competed for survival. "Coexist with, or subdue and conquer, expropriate its most useful possessions, or symbiose with it, your competitor" remain cellular life's basic rules. This author emphasizes the role of viruses, both in mediating cell fusions, such as the formation of the first eukaryotic cell(s) from a united crenarchaeon and prokaryota, and the transfer of host cell genes integrated into viral (phages) genomes. After rising above the Darwinian threshold, rigid rules of speciation and vertical inheritance in the three domains of life were established, but horizontal gene transfers with or without cell fusions were never abolished. The author proves with extensive, yet highly selective documentation, that not only unicellular microorganisms, but the most complex multicellular entities of the highest ranks resort to, and practice, cell fusions, and donate and accept horizontally (laterally) transferred genes. Cell fusions and horizontally exchanged genetic materials remain the fundamental attributes and inherent characteristics of the living matter, whether occurring accidentally or sought after intentionally. These events occur to cells stagnating for some 3 milliard years at a lower yet amazingly sophisticated level of evolution, and to cells achieving the highest degree of differentiation, and thus functioning in dependence on the support of a most advanced multicellular host, like those of the human brain. No living cell is completely exempt from gene drains or gene insertions.

Enhancement of reticuloendotheliosis virus-induced bursal lymphomas by serotype 2 Marek's disease virus

The effect of serotype 2 and 3 Marek's disease virus (MDV) vaccines on the pathogenesis of reticuloendotheliosis virus (REV)-induced bursal and non-bursal lymphomas was examined in chickens of RPRL lines 15I(5) X 7(1) and 6(3) X 0, respectively. At hatch, chickens were vaccinated with strain 301B/1 of serotype 2 MDV or strain FC126 of turkey herpesvirus (HVT), a serotype 3 MDV and inoculated with spleen necrosis virus (SNV), a non-defective strain of REV. In another experiment, bursas from 14-week-old 15I(1) X 7(1) chickens coinfected with strain 301B of serotype 2 MDV and SNV strain of REV at hatch were examined microscopically for REV-induced transformed follicles by methyl green pyronin stain and for the presence of MDV by in situ hybridization. The incidence of REV-induced bursal lymphomas was significantly higher in 15I(5) X 7(1) chickens vaccinated with serotype 2 MDV than in unvaccinated chickens or chickens vaccinated with HVT. On the other hand, the incidence of REV induced nonbursal lymphoma in chickens of line 63 X 0 vaccinated with serotype 2 MDV was comparable to that in unvaccinated chickens or chickens vaccinated with HVT. The average number of hyperplastic follicles in bursas from REV-infected 15I(5) X 7(1) chickens was significantly higher in chickens vaccinated with serotype 2 MDV than that in unvaccinated chickens or chickens vaccinated with HVT, and the MDV was more frequently detected in REV-transformed than in untransformed bursal follicles. Data from this study suggest that serotype 2, but not serotype 3, of MDV may enhance the development of REV-induced bursal lymphomas, and that neither serotype 2 nor serotype 3 MDV influence the development of REV-induced nonbursal lymphomas. The data also suggest that the enhancement effects of serotype 2 MDV on REV bursal lymphomas may be at the stage of formation of hyperplastic or transformed bursal follicles.

Analysis of the bovine neutrophil transcriptome during glucocorticoid treatment

The objective of this study was to characterize a large portion of the bovine neutrophil transcriptome following treatment with the anti-inflammatory glucocorticoid dexamethasone (Dex). Total RNA was isolated from blood neutrophils of healthy cattle (5 castrated male Holsteins) immediately following cell purification (0 h) or after ex vivo aging for 4 h with or without added Dex. Additional neutrophils were cotreated with a glucocorticoid receptor (GR) antagonist (RU486) and Dex for 4 h. RNA was amplified, dye labeled (Cy3 or Cy5), and hybridized to a series of National Bovine Functional Genomics Consortium (NBFGC) microarrays. LOWESS data normalization followed by mixture model analyses showed that 11.15% of the spotted NBFGC cDNAs (2,036/18,263) were expressed in 4-h (untreated) neutrophils. Subsequent two-step mixed-model analysis detected ( P ≤ 0.05) 1,109 differentially expressed genes, of which contrast analysis indicated those that were independently responsive to aging (1,064), Dex (502), RU486 + Dex (141), or RU486 (357). In silico analysis revealed that 416 of the differentially expressed genes are unknown, 59 did not cluster well based on known function, and 634 clustered into 20 ontological categories. Independent validation of differential expression was done for 14 of the putatively Dex-responsive genes across these categories. Results showed that Dex induced rapid translocation of GR into the neutrophil nucleus and signaled dramatic alterations in expression of genes that delay apoptosis, enhance bactericidal activity, and promote tissue remodeling without inflammation or fibrosis. Thus these findings revealed hitherto unappreciated plasticity of blood neutrophils and potentially novel anti-inflammatory/wound-healing actions of glucocorticoids.

Persistence of chicken herpesvirus and retroviral chimeric molecules upon in vivo passage

Mareks disease virus (MDV), a herpesvirus, and avian leucosis virus subgroup J (ALV-J), a retrovirus, were used for experimental coinfection of chickens. Chimeric molecules having sequences of both viruses were detected by the hotspot-combined polymerase chain reaction (HS-cPCR) system. The detection of chimeric molecules provided evidence for avian retroviral inserts in the herpesvirus genome. The persistence of chimeric molecules on in vivo passage served to indicate the infectivity of the recombinant virus. The evaluation of formation and persistence of the chimeric molecules was performed in two trials involving three in vivo passages. The chimeric molecules were identified according to the primer sets, their product length, and pattern. The persistence of chimeric molecules on in vivo passages served as an indication of their ability to replicate in and infect chickens. In the first experimental passage, MDV and ALV-J prototype strains, MD11 and HC-1, were intraperitoneally (i.p.) injected into 1-day-old chicks. The second trial included two passages. Passage II chicks were injected i.p. and passage III chickens were in contact with the chickens of passage II. For passage II, enriched white blood cells from blood samples of chickens from the first trial that had chimeric molecules were injected i.p. into 1-day-old chicks. For passage III, uninfected chicks were included together with the infected chicks. Synthesis evidence for the various species of chimeric molecules was assessed in the tissues of birds of the second trial. DNA was extracted from blood and feathers and analyzed by the hotspot-combined PCR and by pulsed field gel electrophoresis. To overcome the limits of detection, three amplification assays followed by hybridization of the products to specific viral probes were conducted. A variety of chimeric molecules were detected in low concentrations. Five species of chimeric molecules were characterized in blood, tumors, and feathers. Chimeric molecules were detected in 18 of 36 dually infected birds from the first trial and in 14 of 21 dually infected birds from the second trial. The findings show that, in four out of seven groups of the second trial, the chimeric molecule species persisted on passage.

Transactivation of latent Marek's disease herpesvirus genes in QT35, a quail fibroblast cell line, by herpesvirus of turkeys

The QT35 cell line was established from a methylcholanthrene-induced tumor in Japanese quail (Coturnix coturnix japonica) (C. Moscovici, M. G. Moscovici, H. Jimenez, M. M. Lai, M. J. Hayman, and P. K. Vogt, Cell 11:95-103, 1977). Two independently maintained sublines of QT35 were found to be positive for Marek's disease virus (MDV)-like genes by Southern blotting and PCR assays. Sequence analysis of fragments of the ICP4, ICP22, ICP27, VP16, meq, pp14, pp38, open reading frame (ORF) L1, and glycoprotein B (gB) genes showed a strong homology with the corresponding fragments of MDV genes. Subsequently, a serotype 1 MDV-like herpesvirus, tentatively name QMDV, was rescued from QT35 cells in chicken kidney cell (CKC) cultures established from 6- to 9-day-old chicks inoculated at 8 days of embryonation with QT35 cells. Transmission electron microscopy failed to show herpesvirus particles in QT35 cells, but typical intranuclear herpesvirus particles were detected in CKCs. Reverse transcription-PCR analysis showed that the following QMDV transcripts were present in QT35 cells: sense and antisense meq, ORF L1, ICP4, and latency-associated transcripts, which are antisense to ICP4. A transcript of approximately 4.5 kb was detected by Northern blotting using total RNA from QT35 cells. Inoculation of QT35 cells with herpesvirus of turkeys (HVT)-infected chicken embryo fibroblasts (CEF) but not with uninfected CEF resulted in the activation of ICP22, ICP27, VP16, pp38, and gB. In addition, the level of ICP4 mRNA was increased compared to that in QT35 cells. The activation by HVT resulted in the production of pp38 protein. It was not possible to detect if the other activated genes were translated due to the lack of serotype 1-specific monoclonal antibodies.

Retrovirus-induced disease in poultry

Three species of avian retrovirus cause disease in poultry: the avian leukosis/sarcoma virus (ALSV), reticuloendotheliosis virus (REV), and lymphoproliferative disease virus (LPDV) of turkeys. The ALSV can be classified as slowly transforming viruses, which lack a viral oncogene, and acutely transforming viruses, which possess a viral oncogene. Slowly transforming viruses induce late onset leukoses of the B cell lymphoid, erythroid, and myeloid cell lineages, and other tumors, by viral promoter insertion into the genome of a host cell and activation of a cellular protooncogene. The various acutely transforming leukemia and sarcoma viruses induce leukotic or other tumors rapidly and carry one or anther (sometimes two) viral oncogenes, of which some 15 have been identified. The ALSV fall into six envelope subgroups, A through E, and the recently recognized J subgroup, which induces myeloid leukosis. With the exception of Subgroup E viruses, these viruses spread vertically and horizontally as infectious virions, and are termed exogenous viruses. Subgroup E viruses are usually spread genetically as DNA proviruses (often defective) in host germ cell genome, and are termed endogenous viruses. Several other families of endogenous viruses also exist, one of which, endogenous avian retrovirus (EAV), is related to Subgroup J ALV. Exogenous viruses, and sometimes endogenous viruses, can have detrimental effects on commercially important production traits. Exogenous viruses are currently controlled by virus eradication schemes. Reticuloendotheliosis virus, which lacks a viral oncogene, causes chronic B cell and T-cell lymphomas in chickens, and also chronic lymphomas in turkeys and other species of birds. An acutely transforming variant of REV, Strain T, carries a viral oncogene, and induces reticuloendotheliosis within a few days. In chickens and turkeys, REV spreads vertically and horizontally. No commercial control schemes are operated. In turkeys, LPDV infection has occurred in several countries, where it caused a lymphoproliferative disease of uncertain nature.

The U3 region of the long terminal repeat of a subgroup A transformation-defective rous sarcoma virus (tdPH2010) converts a noncytopathic virus to a cytopathic virus

The molecular basis of the cytopathic effects (CPE) of the transformation-defective avian retrovirus mutant, tdPH2010, was studied. tdPH2010 is a subgroup A virus isolated from the Schmidt-Ruppin (NY) subgroup A strain (SRA(NY)). Subgroup A avian retroviruses are generally considered noncytopathic. Integrated tdPH2010 was molecularly cloned from infected quail cells. A noncytopathic, transformation-defective control strain, BSU, was created by deleting the src gene from the molecularly cloned wild type SRA(NY) virus. Chimeras between tdPH2010 and BSU were constructed and viruses were recovered from transfected chick embryo fibroblasts. Growth curves of cells infected with chimeric viruses indicated that the long terminal repeat (LTR) of tdPH2010 converts BSU to a cytopathic virus. Nucleotide sequencing revealed two point mutations unique to tdPH2010 in the U3 region of LTR at positions -126 and -23 from the transcription start site. Both mutations were located inside or near the promoter/enhancer elements of U3. The mutation at -126 (G to T) converted one of the very well-conserved pentanucleotide repeat (PRE) motifs from GGTGG to GGTGT. The other at -23 (G to A) is located next to the TATA box. The G at this position is conserved in all other known avian retrovirus promoters.

Avian retroviruses

Avian leukosis virus (ALV) and reticuloendotheliosis virus (REV) are the most common naturally occurring avian retroviruses associated with neoplastic disease conditions in domesticated poultry. Avian leukosis virus infects primarily chickens, whereas REV infects chickens, turkeys, and other avian species. In addition to causing tumors, both ALV and REV can reduce productivity and induce immunosuppression and other production problems in affected flocks.

Retroviral insertional activation of the c-myb proto-oncogene in a Marek's disease T-lymphoma cell line

Marek's disease virus (MDV) is an avian herpesvirus that causes, in chickens, a lymphoproliferative disease characterized by malignant transformation of T lymphocytes. The rapid onset of polyclonal tumors indicates the existence of MDV-encoded oncogenic products. However, the molecular basis of MDV-induced lymphoproliferative disease and latency remains largely unclear. Several lines of evidence suggest that MDV and Rous-associated virus (RAV) might cooperate in the development of B-cell lymphomas induced by RAV. Our present results indicate for the first time that MDV and RAV might also act synergistically in the development of T-cell lymphomas. We report an example of an MDV-transformed T-lymphoblastoid cell line (T9) expressing high levels of a truncated C-MYB protein as a result of RAV integration within one c-myb allele. The chimeric RAV-c-myb mRNA species initiated in the 5' long terminal repeat of RAV are deprived of sequences corresponding to c-myb exons 1 to 3. The attenuation of MDV oncogenicity has been strongly related to structural changes in the MDV BamHI-D and BamHI-H DNA fragments. We have established that both DNA restriction fragments are rearranged in the T9 MDV-transformed cells. Our results suggest that retroviral insertional activation of the c-myb proto-oncogene is a critical factor involved in the maintenance of the transformed phenotype and the tumorigenic potential of this T-lymphoma cell line.

Avian herpesvirus as a live viral vector for the expression of heterologous antigens

Control of Marek's disease in the poultry industry has been successfully achieved for several decades by large-scale vaccination of day-old chickens with live herpesvirus of turkeys (HVT) strains. Several features of this virus including lack of pathogenicity and long-term immune protection due to a persistent viraemic infection made us decide to use HVT as a live viral vector for the expression of foreign antigens. Potential sites for the integration of foreign DNA in the unique short region of the HVT genome were identified by the insertion of a beta-galactosidase expression cassette. Vaccination trials with recombinant virus strains indicated that the marker gene was expressed and stably maintained during animal passage. Based on an insertion site mapping in one of the open reading frames of the unique short region, a general recombination vector was designed for the integration of foreign genes into HVT. Recombinant virus-directed expression of individual antigens from Newcastle disease virus was driven by a strong promoter element derived from the lung terminal repeat sequence of Rous sarcoma virus.

Cell-mediated cytolysis of lymphoblastoid cells expressing Marek's disease virus-specific phosphorylated polypeptides

Cell-mediated immune responses against Marek's disease virus (MDV)-antigens were examined using reticuloendotheliosis virus (REV)-transformed lymphoblastoid cell line CU91 and three cell lines derived from CU91. CU210 was established by establishing a latent MDV infection in CU91. Transfection of CU210 with pNL1, a selectable plasmid or with pNL1 and the cloned BamHI A fragment of MDV DNA resulted in the establishment of CU212 and CU211, respectively. CU211 expressed a MDV-specific phosphorylated polypeptide, while CU210 and CU212 were negative for MDV antigens. Only CU211 was lysed by MDV-specific effector cells. All cell lines were lysed by syngeneic REV-specific effector cells, although high levels of expression of the phosphorylated protein reduced the level of REV-specific lysis.

Persistence of Marek's disease virus in a subpopulation of B cells that is transformed by avian leukosis virus, but not in normal bursal B cells

Previous studies have described an augmentation of avian leukosis virus (ALV)-induced lymphoid leukosis in chickens that were coinfected with a serotype 2 Marek's disease virus (MDV) strain, SB-1. As a first step toward understanding the mechanism of this augmentation, we have analyzed the tropism of the MDV for the ALV-transformed B cell. After hatching, chickens were coinfected with ALV and a nonpathogenic strain of MDV, SB-1. Seventy primary and metastatic ALV-induced lymphomas that developed in chickens between 14 and 20 weeks of age were found, with only one exception, to carry SB-1 DNA. The MDV genome was maintained in cell lines derived from the tumors. However, MDV DNA could not be detected in nontransformed bursal B cells from chickens carrying ALV lymphomas. Moreover, during and after the lytic phase of MDV infection, SB-1 DNA was near or below the level of detection in bursal cells, suggesting that MDV most likely infects only a small subpopulation of bursal cells. By contrast, ALV-transformed B cells from MDV-free chickens could be persistently infected with MDV in vitro. These findings indicate that ALV lymphoma cells, unlike nontransformed bursal B cells, are susceptible to persistent MDV infection and can serve as a reservoir of MDV that can potentially influence the physiology of the transformed cell.

Antigen B of the vaccine strains of Marek's disease virus and herpesvirus of turkeys presents heat-labile group and serotype specific epitopes

Antigen B of Marek's disease virus (MDV) vaccine strains CVI988 and SB1 (serotypes 1 and 2) and herpesvirus of turkeys (HVT) (serotype 3) is formed of oligomeric molecules that are detergent-stable and heat-labile. Immunoblots of native membranal extracts of HVT- and MDV-infected chick embryo fibroblasts (CEF) probed with avian monoserotypic antisera, murine monoclonal antibodies (mAb) to the three serotypes and mAb to antigen B showed two distinct patterns of high molecular weight oligomeric antigens. Serotypes 1 and 3 vaccine viruses formed one set and serotype 2, the other. Avian monotypic sera to serotypes 1 and 3 viruses detected two high molecular weight bands of 230 and > or = 300 kDa in MDV-1 and HVT-infected CEF but only a weak diffuse zone ranging from 130 to 230 kDa in extracts of SB1-infected CEF. No 300 kDa band was discernible in the SB1 extract when blotted with avian monotypic 1 and 3 antisera. MAbs to MDV serotypes 1 and 3 and to antigen B also detected the 230 and > or = 300 kDa antigens, while the mAb to SB1 detected a 50 kDa antigen in the SB1-infected extract only. Furthermore, the antigen B mAb did not reveal high mol. wt. oligomers in SB1-infected CEF extracts. Antigen B oligomers were rapidly destroyed by heating at 95 degrees C and the rate of denaturation of the 230 and > or = 300 kDa oligomers differed for each of the three vaccine viruses. We propose that antigen B of MDV1 and HVT has a complex conformation created by juxtaposition of dimers (230-250 kDa) and trimers (> or = 300 kDa), and is inserted in the infected cell membrane so that conformational, discontinuous epitopes are formed in addition to continuous epitopes. It appears that HVT protects chickens against oncogenic strains of MDV1 by virtue of the cross reactivity of the conformational determinants located on these oligomers. Serotype 2 vaccine shares some of its antigenic determinants with serotypes 1 and 3, while its unique immunogenic features form the basis of the protective synergism achieved when serotypes 2 and 3 vaccines are combined together.

Retrovirus insertion into herpesvirus in vitro and in vivo

Retroviruses and herpesviruses are naturally occurring pathogens of humans and animals. Coinfection of the same host with both these viruses is common. We report here that a retrovirus can integrate directly into a herpesvirus genome. Specifically, we demonstrate insertion of a nonacute retrovirus, reticuloendotheliosis virus (REV), into a herpesvirus, Marek disease virus (MDV). Both viruses are capable of inducing T lymphomas in chickens and often coexist in the same animal. REV DNA integration into MDV occurred in a recently attenuated strain of MDV and in a short-term coinfection experiment in vitro. We also provide suggestive evidence that REV has inserted into pathogenic strains of MDV in the past. Sequences homologous to the REV long terminal repeat are found in oncogenic MDV but not in nononcogenic strains. These results raise the possibility that retroviral information may be transmitted by herpesvirus and that herpesvirus expression can be modulated by retroviral elements. In addition, retrovirus may provide a useful tool to characterize herpesviral function by insertional mutagenesis.

Marek's disease virus-mediated enhancement of avian leukosis virus gene expression and virus production

Direct interaction between two viruses in coinfected cells may promote replication and pathogenesis of one or both virus types. Synergism between herpesviruses and retroviruses is an important factor in diagnosis, treatment, and prevention of animal and human diseases. In birds, Marek's disease virus (MDV) may be an important cofactor in avian leukosis virus induced disease. Infection of susceptible cells with non-oncogenic serotype 2 MDV, an avian herpesvirus, and Rous-associated virus type 2 (RAV-2 ALV), a leukemogenic avian retrovirus, results in enhanced (greater than 3-fold) transcription of retroviral genes, relative to infection with ALV alone. A direct relationship between concentrations of retroviral gene expression and amount of input MDV suggests that MDV-encoded or -induced factors are responsible for enhanced ALV gene expression, ultimately leading to increased accumulation of ALV-specific RNA (greater than 5-fold) and protein (greater than 10-fold). At lower doses of input MDV, ALV virus production increased over 3-fold, relative to cells infected with ALV alone. Interactive laser cytometry was used to detect accumulation of both MDV and ALV antigens within single cells from coinfected cultures. These results suggest a direct role for MDV-encoded or -induced factors in enhancement of ALV gene expression and demonstrate the importance of herpesviruses as cofactors in retrovirus replication and pathogenesis in coinfected cells.

Purification and characterization of infectious Marek's disease virus genomes using pulsed field electrophoresis

Marek's disease virus (MDV) is an acutely oncogenic avian herpesvirus. The tightly cell-associated in vitro growth characteristics of MDV present unique problems when attempting to purify, analyze, and manipulate MDV genomes. To facilitate molecular characterization of MDV, contour-clamped homogeneous electric fields electrophoresis (CHEF) was used to purify infectious MDV genomes. CHEF techniques were optimized for evaluation of total genome size and alterations in structure which occur during in vitro attenuation of oncogenic MDV. Our results indicated that genomes of attenuated serotype 1 MDV strain JM may contain deletions totaling 15 kbp while high-passage serotype 2 nononcogenic MDV strains SB-1 and 281MI/1 were 5 and 3 kbp larger, respectively, than their low-passage counterparts. Using cell-free CHEF-purified MDV genomes as hybridization probes, we identified a 200-bp deletion in attenuated genomes of the very virulent MDV strain MD11. At present, it is unclear if this 200-bp is related to mutations which lead to loss of oncogenicity or pathogenicity in MD11. This study is the first report which describes procedures for purification of infectious herpesvirus genomes from pulsed-field gels. Our results demonstrate that pulsed-field-purified viral DNA will facilitate molecular characterization of MDV and other cell-associated herpesviruses.

Identification of a novel transcription factor, ACF, in cultured avian fibroblast cells that interacts with a Marek's disease virus late gene promoter

Interactions between factors in duck and chick embryo fibroblast (DEF and CEF, respectively) nuclear extracts and the Marek's disease virus (MDV) gp57-65 gene promoter were investigated. Results of in vitro transcription and gel mobility-shift assays indicated that multiple cellular factors interact with 5'-flanking sequences of the MDV gp57-65 gene. One sequence-specific DNA binding activity (termed ACF for avian cell factor(s)) was identified by interaction of DEF and CEF nuclear extract proteins with a particular site (nucleotides -193 to -177) in the MDV gp57-65 gene promoter. Binding of ACF to its apparent recognition sequence, contained within the 17-bp oligonucleotide 5'-CTAGTTTACTTGTTTGT-3' (ACF-12), was highly sequence-specific. Radiolabeled ACF-12 oligonucleotide bound significant ACF protein in the presence of a 400-fold molar excess of unlabeled nonspecific competitor DNA. A similar amount of specific competitor completely abolished ACF binding to probe DNA. Deletion of the ACF binding site from MDV gp57-65 gene promoters linked to a chloramphenicol acetyltransferase (CAT) reporter gene reduced expression of CAT activity by twofold relative to that seen with a gp57-65 promoter-CAT construct containing an intact ACF binding site. Transfection inhibition assays using double-stranded ACF binding site competitors reduced steady-state levels of gp57-65 mRNA in MDV infected cells by over twofold relative to those in control infected cells. Introduction of a similar amount of nonspecific double-stranded oligonucleotide had no adverse effect on gp57-65 mRNA levels. These data suggest that ACF is important for efficient expression of gp57-65.