Xi Lan

Reverse Transcription-Loop-Mediated Isothermal Amplification Assay for Rapid Detection of Hepatitis E Virus

ABSTRACT The one-step single-tube betaine-free reverse transcription (RT)-loop-mediated isothermal amplification assay was developed for rapid diagnosis of hepatitis E virus. This assay amplified the target gene in less than 45 min (even as short as 20 min) under isothermal conditions at 63°C, and the sensitivity of this assay was 100-fold greater than that of RT-PCR. This assay demonstrated a detection limit of 0.045 fg (nine copies/reaction).

FMD subunit vaccine produced using a silkworm―baculovirus expression system: Protective efficacy against two type Asia1 isolates in cattle

Cattle vaccinated with a single dose of subunit vaccine containing the capsid and 3C proteinase coding regions of foot-and-mouth disease virus (FMDV) Asia I/HNK/CHA/05 strain were protected when challenged 28 days later with a homologous virus. Here, the 50% bovine protective dose (PD(50)) test was performed to assess the potency of the subunit vaccine. When challenged with two Chinese isolates, the subunit vaccine could achieve 6.5 PD(50) (challenged with Asia I/HNK/CHA/05 strain) and 5.2 PD(50) (challenged with Asia I/JSL/05 strain) per dose.

Rescue of Newcastle disease virus from cloned cDNA using an RNA polymerase II promoter

A new system was developed to improve the efficiency and simplify the procedure of recovery of Newcastle disease virus (NDV) from cloned cDNA. A full-length cDNA clone of mesogenic NDV vaccine strain Mukteswar was assembled from five subgenomic cDNA fragments and cloned into a plasmid allowing transcription driven by cellular RNA polymerase II. The full-length viral cDNA was flanked by hammerhead ribozyme (HamRz) and hepatitis delta virus ribozyme (HdvRz) sequences, resulted in the synthesis of antigenomic RNA with exact termini. Without supplying T7 RNA polymerase, infectious NDV could be generated efficiently in some eukaryotic cell lines by simultaneous transcription of antigenomic RNA from the full-length plasmid and expression of NP, P and L proteins from helper plasmids introduced by cotransfection. The efficiency of recovery with the conventional T7 promoter system based on BRS-T7 cells and the cytomegalovirus (CMV) promoter system was compared, and the results demonstrate that the new system facilitates the generation of recombinant NDV and more efficient than the T7 rescue system using BRS-T7.

Molecular characterization of China rabies virus vaccine strain.

BackgroundRabies virus (RV), the agent of rabies, can cause a severe encephalomyelitis in several species of mammals, including humans. As a human rabies vaccine strain employed in China, the genetic knowledge of the aG strain has not been fully studied. The main goal of the present study is to amplify the whole genome of aG strain, and genetic relationships between other vaccine strains and wild strains were analyzed.ResultsThe entire genome of human rabies virus vaccine strain aG employed in China was sequenced; this is the second rabies virus vaccine strain from China to be fully characterized. The overall organization and the length of the genome were similar to that of other lyssaviruses. The length of aG strain was 11925nt, comprising a leader sequence of 58nt, nucleoprotein (N) gene of 1353nt, phosphoprotein (P) gene of 894 nt, matrix protein (M) gene of 609nt, glycoprotein (G) gene of 1575nt, RNA-dependent RNA polymerase (RdRp,L) gene of 6384nt, and a trailer region of 70 nt. There was TGAAAAAAA (TGA7) consensus sequence in the end of each gene, except AGA7 at the end of G gene. There was AACAYYYCT consensus start signal at the beginning of each gene.ConclusionsIn this report, we analyzed the full genome of China human rabies vaccine strain aG. Our studies indicated that the genome of aG retained the basic characteristics of RV. At gene level, N was the most conserved among the five coding genes, indicating this gene is the most appropriate for quantitative genotype definition. The phylogenetic analysis of the N indicated the aG strain clustered most closely with Japanese and Russian rabies vaccine strains, suggesting that they may share the same ancestor; also, the aG strain did not share high homology with wild strains isolated from China, making it may not be the best vaccine strain, more research is needed to elucidate the genetic relationship among the RV circulating in China.

Rabies virus nucleoprotein expressed in silkworm pupae at high-levels and evaluation of immune responses in mice.

Rabies is one of the most fatal zoonotic diseases in developing countries, where a safe, cheap and effective vaccine against the disease remains unaffordable. In this paper, we describe a new silkworm-baculovirus expression system to express the nucleoprotein (N) gene of rabies virus and evaluation of the immune response in BALB/c mice. A recombinant baculovirus -rBmNPV(RV-N) carrying the N gene of rabies virus Evelyn Rokitniki Abelseth (ERA) strain was constructed and the N protein expression was evaluated in Bombyx mori (BmN) cells and silkworm pupae by immunofluorescence staining, Western blots and enzyme-linked immunosorbent assay (ELISA). The immune response to vaccines was evaluated based on serum IgG antibody titers and challenge experiments. The study revealed that N protein of rabies virus can be highly expressed in silkworm baculovirus expression system and the vaccine of N antigen presents a promising approach for the prevention of rabies virus.

Complete sequencing and phylogenetic analysis of porcine kobuvirus in domestic pigs in Northwest China

Abstract Porcine kobuvirus, a member of the genus Kobuvirus that is associated with diarrhea, has been reported in many countries. We determined the complete genome sequence and investigated the genetic evolution of the kobuvirus strain swKoV CH441, which was detected in the highland of Gansu province in Northwest China. The viral genome is 8149 nucleotides (nt) long, including a 29-nt poly(A) tail of the 3′ end, and is 90 nt shorter in the 2B coding region than those of other kobuvirus strains whose sequences are available in the GenBank database. Phylogenetic analysis showed that swKoV CH441was most closely related to porcine kobuvirus CH/HNXX-4 but more distantly related to other strains, including the strains GS-1/2012/CH and GS-2/2012/CH, which were detected in Gansu province, indicating that porcine kobuvirus may have geographic and host differences in evolution.

Prokaryotic expression and potential application of the truncated PCV-2 capsid protein.

Three pairs of specific primers were designed to amplify the F2-1, F2-2 and XF2-2 truncated sequences of ORF2 which encodes the capsid protein of porcine circovirus type 2 (PCV-2). The F2-1 sequence had most of the NLS region of ORF2, but the F2-2 and XF2-2 genes had the NLS region deleted. Truncated genes were subcloned into pET-32a(+) vectors to construct recombinant fusion expression vectors. The vectors were then transformed into Rosetta(DE3) E. coli and expressed by induction of IPTG. Expressed proteins were detected by western blotting and ELISA. The protein with best immunoreactivity was confirmed and selected, then utilized to inoculate SPF rabbits to prepare polyclonal antibodies. The protein and prepared polyclonal antibody were utilized to detect sera samples against PCV-2 from Shandong province and PCV-2 particles in PK-15 cells. In our study, three recombinant fusion proteins were successfully obtained, and the molecular weights of fusion proteins were 35.9 kDa, 33.6 kDa and 38.6 kDa respectively detected by SDS-PAGE. All of the proteins showed positive reaction with anti-PCV-2 antisera, and His-XF2-2 showed better immunoreactivity than the others. The protein of His-XF2-2 was coated as antigen in ELISA to detect the seroprevalence of PCV-2 in certain districts of Shandong province, the seropositivity rate was 27.7 % (73/264). Specific fluorescence and positive signals for PCV-2 could be detected in PK-15 cells inoculated with PCV-2 with the participation of prepared antibodies against His-XF2-2 in IFA and IPMA. Experimental results indicated that the truncated PCV-2 ORF2 gene containing most of the NLS region was successfully expressed in E. coli, and His-XF2-2 was demonstrated to have better immunoreactivity with anti-PCV-2 antisera than the other two fusion proteins. His-XF2-2 and prepared polyclonal antibodies against it had a satisfactory capability in detecting PCV-2 infection.

Cloning the Structure Genes and Expression the N Gene of Porcine Epidemic Diarrhea Virus DX

The structure genes spike (S), nucleocapsid (N), membrane (M), small membrane (sM) of a porcine epidemic diarrhea virus (PEDV) strain DX isolated in Gansu province, North-west of China, were cloned, sequenced and compared with published sequences of PEDV strains. The nucleotide sequences encoding the entire S, sM, M and N genes open reading frame (ORF) of DX were 4 152, 231, 681 and 1 326 bases long respectively. There were transcription regulatory sequences (TRSs) upstream of the initiator ATG of the S, N and M genes. The amino acids sequences of S, M and N contained 30, 3 and 7 potential asparagine (N)-linked glycosylation sites. Homologous analysis and phylogenetic trees showed that DX had the closest relationship with strains LJB/06, JS-2004-2Z and CH/HLJH/06 that were also isolated from China and indicated the prevalence of some PEDV isolates in China were widespread since the JS-2004-2Z strain originated from the south of the China, and LJB/06 and CH/HLJH/06 were isolated from northeast China. The N gene was cloned using two primers which contained Nco I and BamH I restriction enzyme sites and subcloned into expression vector pET30a. The recombinant plasmid was then transformed into E.coli Rossta. SDS-PAGE showed there was a protein of about 55kDa as expected and Western blot indicated the N protein had biological activity.

Development of a reverse genetics system for the aG strain of rabies virus in China

Abstract The aG rabies virus strain has been attenuated through multiple passages in cells and is now used as a vaccine strain in China. We attempted to develop a reverse genetics system using the aG strain. Recombinant full-length genomic cDNA was flanked by a hammerhead ribozyme and the hepatitis delta virus ribozyme. Three helper plasmids encoding the nucleoprotein, the phosphoprotein, and the large protein were produced and introduced together with a plasmid containing the full-length aG viral genome into BHK-21 cells by transfection. Recombinant virus was successfully recovered from the cloned cDNA under the control of a CMV promoter driven by RNA polymerase II. The recombinant virus was confirmed by RT-PCR, and the titer of the recombinant virus was 6.2 log LD50.

Phylogenetic analysis reveals the coexistence of interfamily and interspecies horizontal gene transfer in Streptococcus thermophilus strains isolated from the same yoghurt

Horizontal gene transfer (HGT) is an important evolutionary mechanism that has shaped prokaryotic genomes. For Streptococcus thermophilus, there is no direct evidence that the bacteria might acquire a second paralog from a different origin in the same niche. In this study, we found that four isolates of S. thermophilus (B, C, E and F) from the same yoghurt contained two putative homologs of the eno genes (eno-1 and eno-2) and two putative homologs of the guaB genes (guaB-1 and guaB-2). Both eno-1 and guaB-1 shared 100% nucleotide identity among the four isolates, and with isolate A and S. thermophilus ND03. Phylogenetic and nucleotide divergence analyses indicated that guaB-2 of these isolates may have been acquired from species in the genus Streptococcus, while eno-2 of isolates B and C may have been acquired from a donor in the genus Streptococcus. The eno-2 genes of isolates E and F may have been acquired from a donor in the Enterococcus genera. Relative synonymous codon usage analysis confirmed the eno-2 genes of isolates E and F as being acquired from a donor in genus Enterococcus. This study provides evidence that interfamily and interspecies HGT occur in S. thermophilus strains isolated from the same niche.