The Preliminary Establishment Of Reverse Genetics System For Class â…  Newcastle Disease Virus Strain9A5B

Newcastle disease (ND) is an acute and contacted infectious diseases that can cause substantial economic losses and remains a major threat to the poultry industry of all countries. The aetiological agent of the disease, Newcastle disease virus (NDV), is a member of the genus Avulavirus in the family Paramyxoviridae. The genome of NDV is a non-segmented, single-stranded, negative-sense RNA. Most of the reported the highly virulent isolates belong to Class Ⅱ, most of Class I strain is the low-pathogenic lentogenic strain (loNDV) or non-virulent strain, these loNDV found in various of poultry and wild birds. But the host of Class I strain have characteristics of movement of high degree, it transferred easily NDV from the wild birds or waterfowl to poultry, that make it become gradually virulent strain with clinical pathogenicity by further evolution. A non-pathogenic strains of NDV have been isolated from wild waterfowl by Shengqing Yu researcher in my laboratory. It became gradually virulent NDV strain by nine gasbag passage in SPF chickens and five passage in the brain, furthermore, designated9a5b. These results can confirm that virulence of low virulent NDV strain may generate mutation by passage in the chickens. our laboratory has sequenced the whole genome and study initially its some biological characteristics. For the further research of heredity evolutionism of Class I NDV strain in the molecular level, three expression plasmids containing NP, P or L gene from NDV9a5b strain respectively were constructed. In addition, the function of the expression plasmids was identified and evaluated by the constructed NDV mini-genome. According to the whole genome sequence, we designed primers to clone segmentally and constructed full-length cDNA cloning of9a5b strain. The full-length cDNA cloning and three expression plasmids were cotransfected into BSR T7/5cell respectively according to different proportion. The conditions of rescue of Class I NDV strain need to be explored, because so far there was not the report of rescuing successfully Class I NDV strain. The construction of reverse genetics platform can contribute to the study of functional genome of Class I NDV strain and preparation of new generation vaccine. 1. Construction of helper plasmids with NP, P and L genes of9a5b anc identification of their functionFive pairs of primers were designed on the basis of the published full-length genome sequenc(of Class I NDV strain9a5b. NP, P, L1, L2and L3gene segments were amplified from ND(?) allantoic fluid by reverse-transcription polymerase chain reaction (RT-PCR). The PCR product(?) were cloned into pGEM-T easy vector respectively. The segments of interest were from the recombinants and subcloned into eukaryotic expression vector pCI-neo to form the recombinant(?) pCI-NP, pCI-P and pCI-L with the use of restriction enzymes, respectively.The mini-genome of NDV9a5b strain containing GFP reporter gene was constructed anc refered to as TVT-LGT.With the utilization of mini-genome, we cotransfected TVT-LGT anc three helper plasmids into BSR-T7/5cell. We can apparentely see the specific green fluorescence below the inverted microscope, indicating that all constructed helper plasmids could work.2. Construction of the full-length cDNA clone of NDV strain9a5bAccording to the published full-length genome sequence of9a5b, we divided full-lengtr plasmid into six fragments(A1、A2、A3、B1、B2、B3) and designed six pairs primers. Six gene fragments were amplified from NDV allantoic fluid by reverse-transcription polymerase chair reaction (RT-PCR). The PCR products were cloned into pGEM-T easy vector respectively. With the digestion of restriction enzyme Sal Ⅰ and BssH Ⅱ, T-B2and T-B3were ligated into T-B2B3ir vitro. T-B2B3and T-B1were digested with restriction enzyme Sac Ⅱ and dephosphorylated with CIAP, that were ligated into plasmid T-B1B2B3. Plasmids T-B1B2B3and TVT-3’5’were digested with restriction enzyme Spe I, the digested products with dephosphorylation of CIAF can be ligated into TVT-B. With the digestion of restriction enzyme Sal Ⅰ and Hind Ⅲ, T-A1anc T-A2were ligated into T-A1A2. T-A1A2and TVT-3’5’were digested with restriction enzyme Eag1and dephosphorylated with CIAP, that were ligated into TVT-A1A2. PCR2.1T-A3anc TVT-3’5’were digested with Stu Ⅰ and Sac Ⅰ, the digested products were ligated into A3-TVT. A3-TVT and TVT-A1A2were ligated into TVT-A with restriction enzyme Sac Ⅰ and Mlu Ⅰ. Finally, TVT-A and TVT-B were ligated into full-length plasmid TVT-BA with the aid of restriction enzyme Sal Ⅰ and Age Ⅰ. The full-length plasmid was identified by restriction enzyme and sequenced. The sequencing results showed that the plasmid didn’t exist mutation, depletion and insertion of non-template sequence.3. The exploration of rescue conditions of NDV strain9a5bNDV strain9a5b full-length plasmid and three helper plasmids pCI-NP, pCI-P and pCI-L were cotransfected into BSR-T7/5cell. Supernatant and cell monolayers harvested48,72,96hours post-transfection were inoculated into the allantoic cavity of9to11-day-old embryonated specific-pathogen-free (SPF) chicken eggs to amplify the rescued virus. The inoculated embryonated eggs in the first passage were dead and HA titers were detected as high as81og2. HA titer was detected as high as81og2in the allantoic in the three passage.In summary:(1) The NP, P and L gene fragments of Class I NDV strain9a5b were obtained by amplification of RT-PCR, and the eukarytic expression plasmids related to replication of virus were constructed respectively.(2) The function of the constructed expression plasmids was validated with the constructed mini-genome of NDV strain9a5b. The GFP reporter gene was expressed indicating that all the expression plasmids could initiate normally replication and transcription of virus.(3) According to the published full-length genome sequence of9a5b, we divided full-length plasmid into six fragments(A1、A2、A3、B1、B2、B3) and designed six pairs primers. The six fragments were ligated into TVT-3’5’respectively, that obtained9a5b full-length genome cDNA transcriptional plasmid.(4) Rescue system of9a5b virus was explored preliminarily. Transfected products were inoculated into the allantoic cavity of9to11-day-old embryonated specific-pathogen-free (SPF) chicken eggs, HA titer was detected as high as81og2in the allantoic in the first and second and three passage.