Rapid visual detection of Mycobacterium avium subsp. paratuberculosis by recombinase polymerase amplification combined with a lateral flow dipstick

Paratuberculosis (Johne's disease) is a chronic debilitating disease of domestic and wild ruminants. However, widespread point-of-care testing is infrequent due to the lack of a robust method. The isothermal recombinase polymerase amplification (RPA) technique has applied for rapid diagnosis. Herein, RPA combined with a lateral flow dipstick (LFD) assay was developed to estimate DNA from Mycobacterium avium subsp. paratuberculosis. First, analytical specificity and sensitivity of the RPA-nfo primer and probe sets were assessed. The assay successfully detected M. paratuberculosis DNA in 30 min at 39℃ with a detection limit of up to eight copies per reaction, which was equivalent to that of the real-time quantitative polymerase chain reaction (qPCR) assay. The assay was specific, as it did not amplify genomes from five other Mycobacterium spp. or five pathogenic enteric bacteria. Six hundred-twelve clinical samples (320 fecal and 292 serum) were assessed by RPA-LFD, qPCR, and enzyme-linked immunosorbent assay, respectively. The RPA-LFD assay yielded 100% sensitivity, 97.63% specificity, and 98.44% concordance rate with the qPCR results. This is the first report utilizing an RPA-LFD assay to visualize and rapidly detect M. paratuberculosis. Our results show this assay should be a useful method for the diagnosis of paratuberculosis in resource-constrained settings.

A Study of Homologous Recombination in Foot-and-mouth Disease Virus in China / 生物化学与生物物理进展

Foot-and-mouth disease virus (FMDV) is a positive-sense RNA virus which has caused severe damage to world-wide livestock industry. The extensive genetic and antigenic diversity observed in the evolution of FMDV is generally the obstacle for controlling the disease. The homologous recombination, as a significant force driving the evolution of virus, has also effect on the epidemiological trait of FMDV. However,the role of homologous recombination in the diversification of FMDV in China has not investigated. So it is necessary to study the homologous recombination underlying the evolution of FMDV to control FMD. Based on a sound evolutionary framework, molecular evolutionary analysis was used to identify the putative recombinants. All complete FMDV genomes from China were respectively retrieved from GenBank. Homologous recombination was identified using Simplot program. Phylogenetic relations were analyzed to determine the recombination events among these FMDV isolates by using MEGA 4. The isolates O/NY00, O/China/1/99Tibet, O/Tibet/CHA/99, O/OMIII and O/ES/2001 among 16 FMDVs were identified as putative recombinants by analyzing the FMDV genomic sequences extracted from GenBank. The recombination events frequently happen between serological type Asia1 and O which are endemic FMDV circulating in China, suggesting frequent cross infection of FMDV in China. This situation further makes controlling FMDV in China more difficult. Moreover, serotypic conversion of FMDV between Asia1 and O was detected to be due to homologous recombination. These results provided clues for understanding the antigenic and genetic diversification in FMDV, and shed lights on the potential vaccination and treatment of FMD.

Cloning and Analyzing The Promoter of PPAR? / 生物化学与生物物理进展

Peroxisome proliferator-activated receptors (PPARs) are a family of nuclear hormone receptors belonging to the steroid receptor superfamily. Three PPAR isoforms, PPAR?, PPAR? (also known as PPAR?) and PPAR? have been found in the mouse. They can activate expression of many genes, including those involved in lipidmetabolism. PPAR? is ubiquitously expressed, but the level of expression differs markedly between different cell types. PPAR? is expressed in skeletal muscle at 10- and 50-fold higher levels compared with PPAR? and PPAR?, respectively. A role for PPAR? in skeletal muscle is to increase the genes expression with relation to oxidative metabolism. In order to determine the molecular mechanisms governing PPAR? gene expression in muscle, a 2 kb 5′ flanking region was cloned and analyzed. The DNA fragment is able to transcribe GFP in COS7 cells. Dual luciferase assay is used to quantify promoter activity. Deletion analysis of the 2 kb PPAR? promoter fragment in COS7 and NIH 3T3 cells shows that the proximal promoter sequence, nt -197 to +120, confers basal transcriptional activity of the mouse PPAR? gene. Computational analysis of putative cis-acting elements located within the ～2.0 kb mouse PPAR? 5′-flanking sequence was performed using the TRANSFAC database and MatInspector software and 4 potential MEF2A binding sites were found. And there is a potential binding site sharing 100% identity with positive element of MEF2A in the proximal promoter (nt -261). Co-transfection experiments of the PPAR? promoter reporter and pMEF2A expression plasmid (pMEF2A) showed that MEF2A significantly enhanced transcription activity of PPAR? promoter in NIH 3T3. Moreover, the enhancive effect depended on the concentration of plasmid pMEF2A transfected into cells. The results suggested that MEF2A may enhance transcription activity of the PPAR promoter in muscle cells.