Sequencing Analysis Of Genomic Repeat Regions Of Three Marek's Disease Virus Isolates

Marek's disease (MD) is a highly contagious,malignant T-lymphomatosis of chickens caused by Marek's disease virus and it caused economic losses to the poultry.Today the disease is the only cancer that can be prevented by vaccine.Divided by serological properties,MDV consists of three serotypes:MDV-1,MDV-2 and HVT, only MDV-1 have pathogenicity. Although we use a number of strategies to control and prevent MD,but it show that its virulence is still increasing in recent decades, because its pathogenicity vary widely in different strains.Studies show that epidemic strains'direction of evolution are more virulent,but the molecular basis of evolution is still unknown.Therefore,the study about virulence-related genes will help to understanding of the pathogenesis of MDV.MDV genome length is approximately 170-180Kb,consist of single area and repeat zone.Repeat region includes the internal repeat region and terminal repeat region,both of them are the inverted repeats.The length of the internal repeat region is about 24Kb,including the long internal repeat region(IRL) and the short internal repeat region(IRS).The viral replication and induced tumor-related genes concentrate in the region,such as Meq gene,the virus-encoded telomerase RNA,vIL-8,RLORF4,RLORF12, ICP4, etc, and most of them are the unique of MDV-1. Analysis of the primary structure of the region of MDV have a important significance to study of the pathogenesis and genetic variability of MDV.In this study, sequences of genomic repeat regions of three Marek's disease virus isolates were and compared with the sequence logged in the GenBank.The long repeat regions of these strains genome were about 12 kb in length with 43,40,43 predicted ORFs separately, and the short repeat regions were about 12 kb in length with 27,25,26 predicted ORFs separately.The unique and common amino acid mutations were occurred in some ORFs of these strains. It was the unique genetic characteristics of MDV-1 strains in domestic.These strains belonged to an independent phylogenetic branch.The study will provide the research materials to the prevalence, genetic variation, protection and control of MDV in domestic.