Studies On Telomerase Activities Of Chickens Inoculated With Different MDV Strains And Localization In Host Cells Of A MDV-Specific Sequence

Marek's disease (MD) is a contagious, lymphoproliferative disease of domesticchickens caused by highly infectious cell-asscioated oncogenic alpha-herpesvirus MDvirus serotype 1(MDV1), in which lymphoproliferactive infiltration in visceral organs,muscles, and peripheral nerves are common features. MDV strains are classified into threesetotypes based on their pathogenecity. Only serotypes 1 strains of MDV are oncogenic.It is the important position of MDV on the fields of tumorigencity and vaccineprevention from malignant neoplasm. Because MDV is the first herpesvirus proved to beoncogenic with experiment. In addition, MD is the first and only disease that can besuccessfully prevented by vaccination with antigenically related nonpathogenic orattenuated virus strains and good management practices. Though new types of vaccinewere applied , the isolation of very virulent and very virulent plus strains,and breakout ofMD has been reported within a few years. It is important to investigate the pathogenesis ofMD and wipe out it .Telomeres/Telomerase has been the focus in mordern biology, it associates with tumor,gene expression and regulation, aging and cell unmortality. Telomerase has been identifiedin 90% human tumor and 98% cultured cell lines while it is undetectable in most of normalthe somatic cells. So the hypothesis of Telomeres/Telomerase on cancer and aging wasestablished. Usually the telomerase activities were high in many tumors caused byvirus,including B-Lymphocytes transformed from EBV(Epstein-Barr virus).These resultsimplied that significant correlation between the telomerase activities and malignant tumoris probable one of the important steps during tumorigencity and development. Telomeraseactivation is the common step for tumor formation. So with MD as virus neoplastic diseasemodel, the study was performed on the role of the telomerase for tumorigencity anddevelopment so as to find tumorigencity. Many studies on MD were performed, for example, the virus structure,the sequenceand function of gene ORF . MDV genome structure, especially the repeat regions in thegenome, is implied that homologous recombination and crossing recombination couldoccur and integration of virus DNA into the host cells induce tumorigencity when hostcells are infected naturally by MDV gene. Integrated-MDV is the main pattern at thelymphocytic cell lines transformed from MDV, and chromosome telomere ornear-telomere is the main integration sites. FISH assay about six cell lines derived fromMD lymphomas of chickens and turkeys showed that the integration sites were located atthe telomeres of large-and mid-sized chromosomes or on mini chromosomes. We have thepossible experiment datas on the possibility of MDV integration into host cell genome byour investigation on telomere associated sequences in chicken chromosomes. These resultssuggest that the study on integration of virus DNA into the host cells is the important sideamong tumorigencity derived from the Herpesvirus. So, we artificially induce the MD, andstudy the localization of MDV in MD host cells genome with the part sequences ofMDV-meq gene as probe by in situ hybridization and successfully got the hybridizationresults. The results showed that integration sites were mainly located at telomeric ends oflarge-and mid-size chromosomes of chickens rarely at mini-chromosomes. And theintegratiom sites were different in each individual cell. We predict that there might be acorrelation between the integration of MDV in host chromosomes, MD tumorigencity andtelomeric ends of host cells. According to above references, we try to investigate the virus and host cells, with MDas a model. We studied the pathogenic difference of different of MDV strains, dynamics inviremia, and telomerase activities in different virulent strain-infected chickens, in order tofind virus tumor pathogenesis. The results showed that no telomerase activities inserotype 1 vaccine CVI988-inoculated chickens were measured throughout theexperimental period due to a good immunity effect. In the other hand, both virulent MDVstrains induced MD tumor, and telomerase is activated before the appearance of clinicalsymptoms and visible pathological changes. Telomerase activities were inceasing as thedays postinfection ,and after got their peak respectively, they kept the higher level duringthe all latent period while had a tendency of little descent, however telomerase remainedpositive. There was a significant positive correlation between telomerase activities anddynamics in viremia. Assay of dynamics in viremia coule used to determination the effectof vaccine inoculated and detect wild virus infection. The longevity of avian species is very long, they live for up to 30 years. This suggeststhat bird cells may require control of cell lifespan comparable with that needed by humancells to avoid immortalization and carcinogenesis. So avian species may provide a goodsystem to study the degree of conservation of the telomere clock and telomerase regulationin vertebrates. The telomerase activities of Marek's disease lymphoblastoid cell lineMDCC-MSB1, DF1 avain cell lines, chicken embryo fibroblast cell and peripheral bloodmononuclear cells of chickens were detected and comparated by using modified Trap andsoftware of Bandscane. The results showed that avain lymphoblastoid cell line expressedhigh levels of telomerase, suggesting a potential role of telomerase duting carcinogenesisinduced by avian virus. According to above references, we try to investigate the relationbeween the telomerase activities and chTERT express. The expression of hTERT gene ofthe samples were detected by RT-PCR. There was a concordance between telomeraseactivities and expression intensity of telomerase catalylic subunit ,but no parallel betweentelomerase activity and hTERT expression level. This suggests that except to catalylicsubunit there were other factors do great effects on telomerase activities Meq gene is a main oncogenic gene, and Meq protein plays an important role in thetransformation by MDV. Meq gene were detected by PCR method from chickens...