Investigation of the genes associated with tumorigenicity of Marek's disease virus.

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Marek's disease virus (MDV) is an avian herpesvirus which induces lymphoproliferative disease in chickens. It has been suggested that maintenance of tumorigenicity might be associated with the expression of the 1.8 kb gene from 6amHI-H region of MDV DNA. However, direct proof of the function of the 1.8 kb gene has been lacking. We examined the role of the 1.8 kb gene in tumorigenicity, using oligonucleotides complementary to the 1.8 kb gene. Although maintenance of latent infection of MDV seems to involve mechanisms regulating viral transcription, it is not clear which factors are responsible for transcriptional control. We investigated whether primary and higher order structures of MDV DNA are correlated with the repression of transcription from MDV genome in lymphoblastoid cell lines.1. An oligonucleotide complementary to the splice donor sequence of the 1.8 kb gene produced from 6amHI-H region of MDV DNA inhibited the proliferation of lymphoblastoid cell line. MDCC-MSBI(MSBI). but not that of the avian lymphoid leukosis-derived lymphoblastoid cell line, LSCC-BK3. Colony formation in soft agar was also inhibited by treatment of MSBI cells with antisense oligonucleotide. Thus. expression of the 1.8 kb gene family is directly associated with maintenance of tumorigenic state of transformed MDV-derived lymphoblastoid cells.2. The unique fragment flanking the region which contains the putative replication origin of MDV DNA was found in only MDV DNA from virus-nonproducing cell iine MDCC-RPI (RPI). The change in DNA structure near the region of replication origin might be associated with the loss of MDV productivity in RPI. The latent MDV genome are folded into nucleosomal structures in MSBI and RPI. There was no difference between transcriptionally active and inactive regions of MDV genome with regard to nucleosomal patterns.