Abstract
GX0101 is the first field Marek’s disease virus (MDV) recombinant with an REV LTR insert isolated in China. We speculated that there was a selective advantage of GX0101 becoming the more prevalent field strain from a very low percentage of recombinant virus. In the study, dual fluorescence quantitative real-time PCR (DF-qPCR) that detects GX0101 and GX0101ΔLTR simultaneously was established based on the genomic difference of GX0101 and its LTR deletion strain GX0101ΔLTR. MDV natural transmission was simulated in specific-pathogen-free (SPF) chicks, and continuous tracking of GX0101 and GX0101ΔLTR in chicks was carried out. The results showed that GX0101 possessed high horizontal transmission capacity, which could infect SPF chicks by contact in a short time and became the predominant strain following contact infections in chicken flocks. GX0101 still had a more significant advantage of horizontal transmission than GX0101ΔLTR after continuous passage even if the initially infectious dose was significantly lower. There were 72 differentially expressed MDV genes between GX0101 and GX0101ΔLTR, with the genes and gene products mainly involved in virus replication, tegument protein, glycoprotein, nucleocapsid protein, immune evasion, tumor development and/or pathogenesis, and hypothetical protein. Sixteen genes related to virus replication and transmission were significantly up-regulated. This is the first study to illuminate that increased horizontal transmission of recombinant MDV due to REV LTR was the competitive advantage of the virus being a prevalent strain and define the differential transcription profile of viral genes between GX0101 and GX0101ΔLTR. This will be helpful for in-depth study on the molecular mechanism of increased horizontal transmission of MDV by REV LTR.
Highlights
Marek’s disease (MD), induced by the Marek’s disease virus (MDV), is a contagious lymphoproliferative disease of poultry (Churchill and Biggs, 1967)
Infectious bacterial artificial chromosome (BAC)-derived GX0101 long terminal repeat (LTR) virus was previously rescued by transfection of BAC DNA into chicken embryo fibroblast (CEF) cultures (Sun et al, 2010)
The single fluorescence quantitative real-time PCR (SF-qPCR) for detecting GX0101 or GX0101 LTR with good specificity was established after the optimization of primers and probes
Summary
Marek’s disease (MD), induced by the Marek’s disease virus (MDV), is a contagious lymphoproliferative disease of poultry (Churchill and Biggs, 1967). GX0101 is the first natural recombinant MDV field strain isolated from birds showing tumors in China (Cui et al, 2010). The complete genome of GX0101 was sequenced and analyzed using the GX0101 BAC clone (Su et al, 2012, 2013). It contains a 538-bp reticuloendotheliosis virus (REV) long terminal repeat (LTR) inserted between nucleotide bases “C” and “A” numbered 153,175–153,176 (Md5 strain) or 154,507–154,508 (RB1B strain). GX0101 is a very virulent MDV, with greater horizontal transmission ability than Md5 (Xu et al, 2009), while other reported recombinant MDV strains with an REV LTR, such as RM1 obtained from cell cultures, are attenuated and do not cause tumors (Witter et al, 1997; Sun et al, 2010). An flp recognition target (FRT) site of 84 bp in length remained in the genome of GX0101 LTR (Sun et al, 2010)
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