The study was supported by the National Key Research and Development Plan (Grant no. 2016YFD0500401) and the National Natural Science Foundation of China (Grant no. 31302043).

The use of mice in this protocol was approved by the Administrative Committee on Animal Welfare of the Institute of Military Veterinary Medicine, the Academy of Military Medical Sciences, China (Laboratory Animal Care and Use Committee Authorization, permit number JSY-DW-2010-02). All institutional and national guidelines for the care and use of laboratory animals were followed.
1. RNA Extraction
<ol>
	<li>Extract RNA from rabies-suspected brain tissue, skin biopsies, saliva, or CSF or from RABV-infected cell culture, using guanidinium isothiocyanate-phenol-chloroform-based extraction methods or commercially available viral RNA extraction kits. Use the prepared RNA immediately or store it at -80 &#176;C until required.</li>
</ol>
2. Reverse Transcription of the Viral RNA
<ol>
	<li>Remove the RT reagents listed in Table 1 from the freezer, keep them on ice, and thaw and vortex them before use.</li>
	<li>Prepare 12 &#181;L of RT reaction mix in a 0.2 mL PCR tube with the reagents listed in Table 1. Allow for pipetting variations by preparing a volume of master mix at least one reaction size greater than required.</li>
	<li>Add 8 &#181;L sample, positive control RNA or negative control to the RT reaction mix within a PCR workstation in a template room. The RT positive control is RNA extracted from the cell culture infected with fixed RABV strain CVS-11 (challenge virus standard-11) and stored at -80 &#176;C. The negative control contains RNase-free ddH2O.</li>
	<li>Mix the contents of the RT tubes by vortexing; then, centrifuge briefly.</li>
	<li>Load the reaction tubes into a thermal cycler. Set up the cDNA synthesis program with the following conditions: 42 &#176;C for 90 min, 95 &#176;C for 5 min, and 4 &#176;C on hold. Set the reaction volume to 20 &#181;L. Start the RT run.</li>
</ol>
3. First-round PCR
<ol>
	<li>Keep the PCR reagents listed in Table 2 on ice in a clean room until use; then, thaw and vortex them.</li>
	<li>Prepare the first-round PCR mix in a 0.2 mL PCR tube with the reagents listed in Table 2.</li>
	<li>Add a 2 &#181;L sample of cDNA or plasmid into the first-round PCR mix within a PCR workstation in a template room. The PCR positive control is CVS-11 cDNA prepared as mentioned in step 2.3 for the above RT method. The PCR negative control is ddH2O.</li>
	<li>Transfer the sealed tubes to a PCR thermal cycler and cycle using the parameters listed in Table 3.</li>
</ol>
4. Second-round PCR
<ol>
	<li>Prepare the second-round PCR mix in a 0.2 mL PCR tube using the reagents listed in Table 4.</li>
	<li>Add 2 &#181;L of first-round PCR product into the second-round PCR mix. In addition, include ddH2O as a negative control of the second-round PCR.</li>
	<li>Perform PCR thermal cycling using the same parameters as given in step 3.4.</li>
</ol>
5. Analysis of the PCR Products by Electrophoresis on Agarose Gels
<ol>
	<li>Prepare a 1.5% agarose gel by adding 1.5 g of agarose to 100 mL of Tris-acetate-EDTA (TAE) and dissolving it thoroughly by heating it in a microwave oven.</li>
	<li>Add ethidium bromide (EB) (at a final concentration of 0.01%) or another commercial EB substitution. Pour the gel into the mold and leave it to solidify at ambient temperature for at least 30 min.</li>
	<li>Prepare the loading samples by mixing 5 &#181;L of each PCR product with 1 &#181;L of 6x loading buffer.</li>
	<li>Load the samples and suitable DNA marker separately into the wells and run the gel for approximately 30-45 min at 120 V until the dye line is approximately 75%-80% down the gel.</li>
	<li>Turn off the power, disconnect the electrodes from the power source, and then, carefully remove the gel from the gel box.</li>
	<li>Use a UV gel documenting device to visualize and photograph the DNA fragments.</li>
</ol>
6. Characterization of Nested RT-PCR
<ol>
	<li>6.1. Specificity and sensitivity for the detection of 18 lyssaviruses plasmids 
	<ol>
		<li>Order 18 commercial plasmids containing the full N gene of each lyssavirus (16 ICTV species and two novel species) for the PCR.</li>
		<li>Calculate the copy number of the plasmid using Avogadro&#8217;s number (NA) and the following formula. 
		[(g/&#181;L plasmid DNA)/(plasmid length in bp x 660)] x 6.022 x 1023 = number of molecules/&#181;L</li>
		<li>Prepare stock solutions (2.24 x 109 molecules/&#181;L) of all 18 plasmids in ddH2O.</li>
		<li>Perform nine 10-fold serial dilutions of all 18 plasmids in ddH2O. Dilute 10 &#181;L of each plasmid stock with 90 &#181;L of ddH2O. Vortex and centrifuge briefly.</li>
		<li>Perform PCR amplification as described in sections 3-5.</li>
		<li>Analyze the specificity and sensitivity of the nested PCR by detecting a series of lyssavirus plasmids.</li>
	</ol>
	</li>
	<li>Determination of the detection limit
	<ol>
		<li>Adjust the titer of the rabies virus strain CVS-11 cell culture to 105.5 TCID50/mL (virus titer determined according to the OIE Manual)5.</li>
		<li>Perform five 10-fold serial dilutions of CVS-11 (stock solution is 105.5 TCID50/mL) as described in step 6.1.4.</li>
		<li>Perform the RNA extraction and nested RT-PCR amplification procedures of all viral dilutions as described in sections 1-5.</li>
	</ol>
	</li>
	<li>Comparison of the nested RT-PCR with the &#34;gold standard&#34;&#160;FAT
	<ol>
		<li>Test all clinical samples by nested RT-PCR, and then, confirm the results with the FAT5 and N gene sequencing9.</li>
		<li>Use normalized data for a statistical analysis with SAS 9.1. Use the kappa test and McNemar&#8217;s chi-squared test for a statistical comparison of the diagnostic tests (SAS command: proc freq; table/agree). Calculate confidence intervals assuming abinomial distribution.</li>
	</ol>
	</li>
	<li>Evaluation of the efficacy in testing degraded samples
	<ol>
		<li>Expose two confirmed clinical brain tissue samples of rabid dogs at 37 &#176;C.</li>
		<li>Assay the two samples on each day of exposure at 37 &#176;C by nested RT-PCR, the FAT, and the MIT5.</li>
	</ol>
	</li>
</ol>

<ol>
	<li>Hemachudha, T., Laothamatas, J., Rupprecht, C. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Human+rabies:+a+disease+of+complex+neuropathogenetic+mechanisms+and+diagnostic+challenges.">Human rabies: a disease of complex neuropathogenetic mechanisms and diagnostic challenges.</a> Lancet Neurology. 1 (2), 101-109 (2002).</li><li>Amarasinghe, G. K., Arechiga Ceballos, N. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Taxonomy+of+the+order+Mononegavirales:+update+2018.">Taxonomy of the order Mononegavirales: update 2018.</a> Archives of Virology. 163 (8), 2283-2294 (2018).</li><li>Nokireki, T., Tammiranta, N., Kokkonen, U. M., Kantala, T., Gadd, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tentative+novel+lyssavirus+in+a+bat+in+Finland.">Tentative novel lyssavirus in a bat in Finland.</a> Transboundary and Emerging Diseases. 65 (3), 593-596 (2018).</li><li>Hu, S. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lyssavirus+in+Japanese+Pipistrelle,+Taiwan.">Lyssavirus in Japanese Pipistrelle, Taiwan.</a> Emerging Infectious Diseases. 24 (4), 782-785 (2018).</li><li>Rupprecht, C. E., Fooks, A. R., Abela-Ridder, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Laboratory+techniques+in+rabies.">Laboratory techniques in rabies.</a> World Health Organization. , 74-195 (2018).</li><li>Mani, R. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Utility+of+real-time+Taqman+PCR+for+antemortem+and+postmortem+diagnosis+of+human+rabies.">Utility of real-time Taqman PCR for antemortem and postmortem diagnosis of human rabies.</a> Journal of Medical Virology. 86 (10), 1804-1812 (2014).</li><li>Fooks, A. R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Emerging+technologies+for+the+detection+of+rabies+virus:+challenges+and+hopes+in+the+21st+century.">Emerging technologies for the detection of rabies virus: challenges and hopes in the 21st century.</a> PLOS Neglected Tropical Diseases. 3 (9), 530 (2009).</li><li>Jiang, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+outbreak+of+pig+rabies+in+Hunan+province,+China.">An outbreak of pig rabies in Hunan province, China.</a> Epidemiology and Infection. 136 (4), 504-508 (2008).</li><li>Liu, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+the+complete+genome+of+the+first+Irkut+virus+isolate+from+China:+comparison+across+the+Lyssavirus+genus.">Analysis of the complete genome of the first Irkut virus isolate from China: comparison across the Lyssavirus genus.</a> Molecular Phylogenetics and Evolution. 69 (3), 687-693 (2013).</li><li>Chen, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Possible+Transmission+of+Irkut+Virus+from+Dogs+to+Humans.">Possible Transmission of Irkut Virus from Dogs to Humans.</a> Biomedical and Environmental Sciences. 31 (2), 146-148 (2018).</li><li>Feng, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Disease+outbreaks+caused+by+steppe-type+rabies+viruses+in+China.">Disease outbreaks caused by steppe-type rabies viruses in China.</a> Epidemiology and Infection. 143 (6), 1287-1291 (2015).</li><li>Feng, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Livestock+rabies+outbreaks+in+Shanxi+province,+China.">Livestock rabies outbreaks in Shanxi province, China.</a> Archives of Virology. 161 (10), 2851-2854 (2016).</li></ol>

The authors have nothing to disclose.

Currently, RABV is a major lyssavirus responsible for nearly all human and animal rabies in China, as well as in other countries. In addition, an IRKV variant was first identified from a Murina leucogaster bat in the Jilin province in Northeast China in 201210, and it has been reported to cause a dog&#8217;s death in the Liaoning Province in 201711. Most recently, a novel lyssavirus, TWBLV, was also identified from a Japanese pipistrelle bat in Taiwan, Chi...

Rabies is a worldwide zoonotic disease caused by viruses within the genus Lyssavirus1. Lyssaviruses (family&#160;Rhabdoviridae) are single-negative-stranded RNA viruses with an approximately 12 kb genome that encodes five proteins: N, phosphoprotein (P), matrix protein (M), glycoprotein (G), and the large protein or polymerase (L).&#160;Based on nucleotide sequences of the N gene, genetic distance, and antigenic patterns, the lyssaviruses have been divided into 16 species, comprising classical rabies virus (RABV) and the rabies-related viruses (RRV): Lagos bat virus (LBV), Duvenhage virus (DUVV), Mokola virus (MOKV), European bat lyssavirus 1 (EBLV-1), European bat lyssavirus 2 (EBLV-2), Australian bat lyssavirus (ABLV), Aravan virus (ARAV), Ikoma virus (IKOV), Bokeloh bat lyssavirus (BBLV), Gannoruwa bat lyssavirus (GBLV), Irkut virus (IRKV), Khujand virus (KHUV), West Caucasian bat virus (WCBV), Shimoni bat virus (SHIBV), and Lleida bat lyssavirus (LLEBV)2. Recently, two additional lyssaviruses have been identified: Kotalahti bat lyssavirus (KBLV) isolated from a Brandt&#8217;s bat (Myotis brandtii) in Finland in 20173 and Taiwan bat lyssavirus (TWBLV) isolated from a Japanese pipistrelle (Pipistrellus abramus) in Taiwan, China in 2016&#8211;20174.
All mammals are susceptible to rabies; however, no gross pathognomonic lesions or specific clinical signs permit its identification, and diagnosis can only be made in the laboratory5. The most widely used method for rabies diagnosis is the FAT, which is considered as the gold standard by both the WHO and the OIE5,6. Nevertheless, the FAT can produce unreliable results on degraded/autolyzed brain tissue samples. Additionally, it cannot be used to assay biological fluid specimens such as cerebrospinal fluid (CSF), saliva, and urine, thereby largely precluding its employment in antemortem diagnosis7. Alternative conventional diagnostic tests, such as the rabies tissue culture infection test (RTCIT) and the mouse inoculation test (MIT), require several days6, a major drawback when a rapid diagnosis is essential.
Various molecular diagnostic tests (e.g., the detection of viral RNA by RT-PCR, the PCR&#8211;enzyme-linked immunosorbent assay [PCR-ELISA], in situ hybridization, and real-time PCR) are used as rapid and sensitive techniques for rabies diagnosis8. RT-PCR is now recommended by OIE for routine rabies diagnosis, and a heminested (hn) PCR is described in the OIE Manual of Diagnostic Tests and Vaccines for Terrestrial Animals to detect all lyssaviruses5. Here we describe a pan-lyssavirus nested RT-PCR, which allows the specific and sensitive detection of all 18 lyssavirus species comparable to or exceeding that obtained by the FAT. The principle of the method is an RT of the target RNA (conserved region of the lyssavirus N gene) into cDNA, followed by the amplification of the cDNA by two rounds of PCR. The cDNA undergoes the first-round PCR with outer primers to amplify an 845 bp fragment; then, the second-round PCR uses the first-round PCR product as a template to amplify a 371 bp fragment with inner primers. The two rounds of PCR significantly increase the sensitivity of the assay.

<table border="0" cellpadding="0" cellspacing="0" style="width:636px;" width="636">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">50 &#215; TAE</td>
			<td style="width:177px;">Various</td>
			<td style="width:108px;">Various</td>
			<td style="width:91px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">6 &#215; loading buffer</td>
			<td style="width:177px;">TakaRa</td>
			<td style="width:108px;">9156</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">Agarose</td>
			<td style="width:177px;">US Everbright&#174; Inc</td>
			<td style="width:108px;">A-2015-100g</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:260px;">ddH2O</td>
			<td style="width:177px;">Various</td>
			<td style="width:108px;">Various</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">DL 2,000 Marker</td>
			<td style="width:177px;">Takara</td>
			<td style="width:108px;">3427A</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">dNTPs (10 mM)</td>
			<td style="width:177px;">TakaRa</td>
			<td style="width:108px;">4019</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">dNTPs (2.5 mM)</td>
			<td style="width:177px;">TakaRa</td>
			<td style="width:108px;">4030</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">Electrophoresis System</td>
			<td style="width:177px;">Tanon</td>
			<td style="width:108px;">EPS300</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">Ex-Taq (5 U/&#956;L)</td>
			<td style="width:177px;">TakaRa</td>
			<td style="width:108px;">RR001</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">Gel Imaging System</td>
			<td style="width:177px;">UVITEC</td>
			<td style="width:108px;">Fire Reader</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">Microcentifuge tubes</td>
			<td style="width:177px;">Various</td>
			<td style="width:108px;">Various</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">M-MLV reverse transcriptase (200 IU/&#181;L)</td>
			<td style="width:177px;">TakaRa</td>
			<td style="width:108px;">2641A&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">NanoDrop 1000 Spectrophotometer</td>
			<td style="width:177px;">Thermoscientific</td>
			<td style="width:108px;">ND1000</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:260px;">Oligo (dT)15</td>
			<td style="width:177px;">TakaRa</td>
			<td style="width:108px;">3805</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">PCR Machine</td>
			<td style="width:177px;">BIO-RAD</td>
			<td style="width:108px;">T100</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">PCR Tubes</td>
			<td style="width:177px;">Various</td>
			<td style="width:108px;">Various</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:260px;">Phusion High-Fidelity DNA Polymearase</td>
			<td style="width:177px;">NEW ENGLAND BioLabs</td>
			<td style="width:108px;">M0530S</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">Pipettors</td>
			<td style="width:177px;">Various</td>
			<td style="width:108px;">Various</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">Random Primer</td>
			<td style="width:177px;">TakaRa</td>
			<td style="width:108px;">3801</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">RNase Inhibitor (40 IU/&#181;L)</td>
			<td style="width:177px;">TakaRa</td>
			<td style="width:108px;">2313A</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:260px;">RNase-free ddH2O</td>
			<td style="width:177px;">TakaRa</td>
			<td style="width:108px;">9102</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">Taq Buffer (10&#215;)</td>
			<td style="width:177px;">TakaRa</td>
			<td style="width:108px;">9152A</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">Tips</td>
			<td style="width:177px;">Various</td>
			<td style="width:108px;">Various</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:260px;">Vortex mixer</td>
			<td style="width:177px;">Various</td>
			<td style="width:108px;">Various</td>
			<td></td>
		</tr>
	</tbody>
</table>

evaluation of a universal nested reverse transcription polymerase chain reaction for the detection of lyssaviruses

To detect rabies virus and other member species of the genus Lyssavirus within the family Rhabdoviridae, the pan-lyssavirus nested reverse transcription polymerase chain reaction (nested RT-PCR) was developed to detect the conserved region of the nucleoprotein (N) gene of lyssaviruses. The method applies reverse transcription (RT) using viral RNA as template and oligo (dT)15 and random hexamers as primers to synthesize the viral complementary DNA (cDNA). Then, the viral cDNA is used as a template to amplify an 845 bp N gene fragment in first-round PCR using outer primers, followed by second-round nested PCR to amplify the final 371 bp fragment using inner primers. This method can detect different genetic clades of rabies viruses (RABV). The validation, using 9,624 brain specimens from eight domestic animal species in 10 years of clinical rabies diagnoses and surveillance in China, showed that the method has 100% sensitivity and 99.97% specificity in comparison with the direct fluorescent antibody test (FAT), the gold standard method recommended by the World Health Organization (WHO) and the World Organization for Animal Health (OIE). In addition, the method could also specifically amplify the targeted N gene fragment of 15 other approved and two novel lyssavirus species in the 10th Report of the International Committee on Taxonomy of Viruses (ICTV) as evaluated by a mimic detection of synthesized N gene plasmids of all lyssaviruses. The method provides a convenient alternative to FAT for rabies diagnosis and has been approved as a National Standard (GB/T36789-2018) of China.

Results of nested RT-PCR to detect 18 lyssavirus species are shown in Figure 1. All PCR positive controls showed the expected 845 bp in the first- and 371 bp in the second-round amplifications with no band in the negative control. All 18 lyssaviruses produced the expected 845 and/or 371 bp bands, indicating that the nested RT-PCR detected all 18 lyssaviruses. Sixteen lyssaviruses plasmids had efficient amplification in two rounds of PCR, but two, namely ARAV and IKOV, had amplification in ei...

Watch this Scientific Journal Video about Evaluation of a Universal Nested Reverse Transcription Polymerase Chain Reaction for the Detection of Lyssaviruses at JoVE.com

Evaluation of a Universal Nested Reverse Transcription Polymerase Chain Reaction for the Detection of Lyssaviruses

A pan-lyssavirus nested reverse transcription polymerase chain reaction has been developed to detect specifically all known lyssaviruses. Validation using rabies brain samples of different animal species showed that this method has a sensitivity and specificity equivalent to the gold standard fluorescent antibody test and could be used for routine rabies diagnosis.

To detect rabies virus and other member species of the genus Lyssavirus within the family Rhabdoviridae, the pan-lyssavirus nested reverse transcription ...

evaluation-universal-nested-reverse-transcription-polymerase-chain

Research

JoVE Journal

Genetics

8.3K Views.  Academy of Military Medical Sciences. A pan-lyssavirus nested reverse transcription polymerase chain reaction has been developed to detect specifically all known lyssaviruses. Validation using rabies brain samples of different animal species showed that this method has a sensitivity and specificity equivalent to the gold standard fluorescent antibody test and could be used for routine rabies diagnosis.

Video: Evaluation of a Universal Nested Reverse Transcription Polymerase Chain Reaction for the Detection of Lyssaviruses

Improved Polymerase Chain Reaction-restriction Fragment Length Polymorphism Genotyping of Toxic Pufferfish by Liquid Chromatography/Mass Spectrometry

An improved version of a polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) method for genotyping toxic pufferfish species by liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS) is described. DNA extraction is carried out using a silica membrane-based DNA extraction kit. After the PCR amplification using a detergent-free PCR buffer, restriction enzymes are added to the solution without purifying the reaction solution. A reverse-phase silica monolith column and a Fourier transform high resolution mass spectrometer having a modified Kingdon trap analyzer are employed for separation and detection, respectively. The mobile phase, consisting of 400 mM 1,1,1,3,3,3-hexafluoro-2-propanol, 15 mM triethylamine (pH 7.9) and methanol, is delivered at a flow rate of 0.4 ml/min. The cycle time for LC/ESI-MS analysis is 8 min including equilibration of the column. Deconvolution software having an isotope distribution model of the oligonucleotide is used to calculate the corresponding monoisotopic mass from the mass spectrum. For analysis of oligonucleotides (range 26-79 nucleotides), mass accuracy was 0.62 &#177; 0.74 ppm (n = 280) and excellent accuracy and precision were sustained for 180 hr without use of a lock mass standard.

An improved polymerase chain reaction-restriction fragment length polymorphism method for genotyping pufferfish species by liquid chromatography/mass spectrometry is described. A reverse-phase silica monolith column is employed for separating digested amplicons. This method can elucidate the monoisotopic masses of oligonucleotides, which is useful for identifying base composition.

An improved version of a polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) method for genotyping toxic pufferfish species by ...

Detection of Copy Number Alterations Using Single Cell Sequencing

Detection of genomic changes at single cell resolution is important for characterizing genetic heterogeneity and evolution in normal tissues, cancers, and microbial populations. Traditional methods for assessing genetic heterogeneity have been limited by low resolution, low sensitivity, and/or low specificity. Single cell sequencing has emerged as a powerful tool for detecting genetic heterogeneity with high resolution, high sensitivity and, when appropriately analyzed, high specificity. Here we provide a protocol for the isolation, whole genome amplification, sequencing, and analysis of single cells. Our approach allows for the reliable identification of megabase-scale copy number variants in single cells. However, aspects of this protocol can also be applied to investigate other types of genetic alterations in single cells.

Single cell sequencing is an increasingly popular and accessible tool for addressing genomic changes at high resolution. We provide a protocol that uses single cell sequencing to identify copy number alterations in single cells.

Detection of genomic changes at single cell resolution is important for characterizing genetic heterogeneity and evolution in normal tissues, cancers, and ...

A Universal Protocol for Large-scale gRNA Library Production from any DNA Source

The popularity of the CRISPR/Cas9 system for both genome and epigenome engineering stems from its simplicity and adaptability. An effector (the Cas9 nuclease or a nuclease-dead dCas9 fusion protein) is targeted to a specific site in the genome by a small synthetic RNA known as the guide RNA, or gRNA. The bipartite nature of the CRISPR system enables its use in screening approaches since plasmid libraries containing expression cassettes of thousands of individual gRNAs can be used to interrogate many different sites in a single experiment. 
To date, gRNA sequences for the construction of libraries have been almost exclusively generated by oligonucleotide synthesis, which limits the achievable complexity of sequences in the library and is relatively cost-intensive. Here, a detailed protocol for CORALINA (comprehensive gRNA library generation through controlled nuclease activity), a simple and cost-effective method for the generation of highly complex gRNA libraries based on enzymatic digestion of input DNA, is described. Since CORALINA libraries can be generated from any source of DNA, plenty of options for customization exist, enabling a large variety of CRISPR-based screens.

Methods for generating large-scale gRNA libraries should be simple, efficient and cost-effective. We describe a protocol for the production of gRNA libraries based on enzymatic digestion of target DNA. This method, CORALINA (comprehensive gRNA library generation through controlled nuclease activity) presents an alternative to costly custom oligonucleotide synthesis.

The popularity of the CRISPR/Cas9 system for both genome and epigenome engineering stems from its simplicity and adaptability. An effector (the Cas9 ...

Semi-quantitative Detection of RNA-dependent RNA Polymerase Activity of Human Telomerase Reverse Transcriptase Protein

Human telomerase reverse transcriptase (TERT) is the catalytic subunit of telomerase, and it elongates telomere through RNA-dependent DNA polymerase activity. Although TERT is named as a reverse transcriptase, structural and phylogenetic analyses of TERT demonstrate that TERT is a member of right-handed polymerases, and relates to viral RNA-dependent RNA polymerases (RdRPs) as well as viral reverse transcriptase. We firstly identified RdRP activity of human TERT that generates complementary RNA stand to a template non-coding RNA and contributes to RNA silencing in cancer cells. To analyze this non-canonical enzymatic activity, we developed RdRP assay with recombinant TERT in 2009, thereafter established in vitro RdRP assay for endogenous TERT. In this manuscript, we describe the latter method. Briefly, TERT immune complexes are isolated from cells, and incubated with template RNA and rNTPs including radioactive rNTP for RdRP reaction. To eliminate single-stranded RNA, reaction products are treated with RNase I, and the final products are analyzed with polyacrylamide gel electrophoresis. Radiolabeled RdRP products can be detected by autoradiography after overnight exposure.

Human telomerase reverse transcriptase (TERT) synthesizes not only telomeric DNA but also double-stranded RNA through RNA-dependent RNA polymerase activity. Here, we describe a newly established assay to detect RNA-dependent RNA polymerase activity of endogenous TERT.

Human telomerase reverse transcriptase (TERT) is the catalytic subunit of telomerase, and it elongates telomere through RNA-dependent DNA polymerase ...

CRISPR-Mediated Reorganization of Chromatin Loop Structure

Recent studies have clearly shown that long-range, three-dimensional chromatin looping interactions play a significant role in the regulation of gene expression, but whether looping is responsible for or a result of alterations in gene expression is still unknown. Until recently, how chromatin looping affects the regulation of gene activity and cellular function has been relatively ambiguous, and limitations in existing methods to manipulate these structures prevented in-depth exploration of these interactions. To resolve this uncertainty, we engineered a method for selective and reversible chromatin loop re-organization using CRISPR-dCas9 (CLOuD9). The dynamism of the CLOuD9 system has been demonstrated by successful localization of CLOuD9 constructs to target genomic loci to modulate local chromatin conformation. Importantly, the ability to reverse the induced contact and restore the endogenous chromatin conformation has also been confirmed. Modulation of gene expression with this method establishes the capacity to regulate cellular gene expression and underscores the great potential for applications of this technology in creating stable de novo chromatin loops that markedly affect gene expression in the contexts of cancer and development.

Chromatin looping plays a significant role in gene regulation; however, there have been no technological advances that allow for selective and reversible modification of chromatin loops. Here we describe a powerful system for chromatin loop re-organization using CRISPR-dCas9 (CLOuD9), demonstrated to selectively and reversibly modulate gene expression at targeted loci.

Recent studies have clearly shown that long-range, three-dimensional chromatin looping interactions play a significant role in the regulation of gene ...

Methodology for Accurate Detection of Mitochondrial DNA Methylation

Quantification of DNA methylation can be achieved using bisulfite sequencing, which takes advantage of the property of sodium bisulfite to convert unmethylated cytosine into uracil, in a single-stranded DNA context. Bisulfite sequencing can be targeted (using PCR) or performed on the whole genome and provides absolute quantification of cytosine methylation at the single base-resolution. Given the distinct nature of nuclear- and mitochondrial DNA, notably in the secondary structure, adaptions of bisulfite sequencing methods for investigating cytosine methylation in mtDNA should be made. Secondary and tertiary structure of mtDNA can indeed lead to bisulfite sequencing artifacts leading to false-positives due to incomplete denaturation poor access of bisulfite to single-stranded DNA. Here, we describe a protocol using an enzymatic digestion of DNA with BamHI coupled with bioinformatic analysis pipeline to allow accurate quantification of cytosine methylation levels in mtDNA. In addition, we provide guidelines for designing the bisulfite sequencing primers specific to mtDNA, in order to avoid targeting undesirable NUclear MiTochondrial segments (NUMTs) inserted into the nuclear genome.

Here, we present a protocol to allow accurate quantification of mitochondrial DNA (mtDNA) methylation. In this protocol, we describe an enzymatic digestion of DNA with BamHI coupled with a bioinformatic analysis pipeline which can be used to avoid overestimation of mtDNA methylation levels caused by the secondary structure of mtDNA.

Quantification of DNA methylation can be achieved using bisulfite sequencing, which takes advantage of the property of sodium bisulfite to convert ...

Single Droplet Digital Polymerase Chain Reaction for Comprehensive and Simultaneous Detection of Mutations in Hotspot Regions

Droplet digital polymerase chain reaction (ddPCR) is a highly sensitive quantitative polymerase chain reaction (PCR) method based on sample fractionation into thousands of nano-sized water-in-oil individual reactions. Recently, ddPCR has become one of the most accurate and sensitive tools for circulating tumor DNA (ctDNA) detection. One of the major limitations of the standard ddPCR technique is the restricted number of mutations that can be screened per reaction, as specific hydrolysis probes recognizing each possible allelic version are required. An alternative methodology, the drop-off ddPCR, increases throughput, since it requires only a single pair of probes to detect and quantify potentially all genetic alterations in the targeted region. Drop-off ddPCR displays comparable sensitivity to conventional ddPCR assays with the advantage of detecting a greater number of mutations in a single reaction. It is cost-effective, conserves precious sample material, and can also be used as a discovery tool when mutations are not known a priori.

Here, we present a protocol to accurately quantify multiple genetic alterations of a target region in a single reaction using drop-off ddPCR and a unique pair of hydrolysis probes.

Droplet digital polymerase chain reaction (ddPCR) is a highly sensitive quantitative polymerase chain reaction (PCR) method based on sample fractionation ...

Reverse Transcription-Loop-mediated Isothermal Amplification (RT-LAMP) Assay for Zika Virus and Housekeeping Genes in Urine, Serum, and Mosquito Samples

Infection with Zika virus (ZIKV) can be asymptomatic in adults, however, infection during pregnancy can lead to miscarriage and severe neurological birth defects. The goal of this protocol is to quickly detect ZIKV in both human and mosquito samples. The current gold standard for ZIKV detection is quantitative reverse transcription PCR (qRT-PCR); reverse transcription loop-mediated isothermal amplification (RT-LAMP) may allow for a more efficient and low-cost testing without the need for expensive equipment. In this study, RT-LAMP is used for ZIKV detection in various biological samples within 30 min, without first isolating the RNA from the sample. This technique is demonstrated using ZIKV infected patient urine and serum, and infected mosquito samples. 18S ribosomal ribonucleic acid and actin are used as controls in human and mosquito samples, respectively.

Reverse Transcription-Loop-mediated Isothermal Amplification RT-LAMP Assay for Zika Virus and Housekeeping Genes in Urine, Serum, and Mosquito Samples

This protocol provides an efficient and low-cost method to detect Zika virus or control targets in human urine and serum samples or in mosquitoes by reverse transcription loop-mediated isothermal amplification (RT-LAMP). This method does not require RNA isolation and can be done within 30 min.

Infection with Zika virus (ZIKV) can be asymptomatic in adults, however, infection during pregnancy can lead to miscarriage and severe neurological birth ...

Identification of Homologous Recombination Events in Mouse Embryonic Stem Cells Using Southern Blotting and Polymerase Chain Reaction

Relative to the issues of off-target effects and the difficulty of inserting a long DNA fragment in the application of designer nucleases for genome editing, embryonic stem (ES) cell-based gene-targeting technology does not have these shortcomings and is widely used to modify animal/mouse genome ranging from large deletions/insertions to single nucleotide substitutions. Notably, identifying the relatively few homologous recombination (HR) events necessary to obtain desired ES clones is a key step, which demands accurate and reliable methods. Southern blotting and/or conventional PCR are often utilized for this purpose. Here, we describe the detailed procedures of using those two methods to identify HR events that occurred in mouse ES cells in which the endogenous Myh9 gene is intended to be disrupted and replaced by cDNAs encoding other nonmuscle myosin heavy chain IIs (NMHC IIs). The whole procedure of Southern blotting includes the construction of targeting vector(s), electroporation, drug selection, the expansion and storage of ES cells/clones, the preparation, digestion, and blotting of genomic DNA (gDNA), the hybridization and washing of probe(s), and a final step of autoradiography on the X-ray films. PCR can be performed directly with prepared and diluted gDNA. To obtain ideal results, the probes and restriction enzyme (RE) cutting sites for Southern blotting and the primers for PCR should be carefully planned. Though the execution of Southern blotting is time-consuming and labor-intensive and PCR results have false positives, the correct identification by Southern blotting and the rapid screening by PCR allow the sole or combined application of these methods described in this paper to be widely used and consulted by most labs in the identification of genotypes of ES cells and genetically modified animals.

Here, we present a detailed protocol for identifying homologous recombination events that occurred in mouse embryonic stem cells using Southern blotting and/or PCR. This method is exemplified by the generation of nonmuscle myosin II genetic replacement mouse models using traditional embryonic stem cell-based homologous recombination-mediated targeting technology.

Relative to the issues of off-target effects and the difficulty of inserting a long DNA fragment in the application of designer nucleases for genome ...

Determining 3'-Termini and Sequences of Nascent Single-Stranded Viral DNA Molecules during HIV-1 Reverse Transcription in Infected Cells

Monitoring of nucleic acid intermediates during virus replication provides insights into the effects and mechanisms of action of antiviral compounds and host cell proteins on viral DNA synthesis. Here we address the lack of a cell-based, high-coverage, and high-resolution assay that is capable of defining retroviral reverse transcription intermediates within the physiological context of virus infection. The described method captures the 3'-termini of nascent complementary DNA (cDNA) molecules within HIV-1 infected cells at single nucleotide resolution. The protocol involves harvesting of whole cell DNA, targeted enrichment of viral DNA via hybrid capture, adaptor ligation, size fractionation by gel purification, PCR amplification, deep sequencing, and data analysis. A key step is the efficient and unbiased ligation of adaptor molecules to open 3'-DNA termini. Application of the described method determines the abundance of reverse transcripts of each particular length in a given sample. It also provides information about the (internal) sequence variation in reverse transcripts and thereby any potential mutations. In general, the assay is suitable for any questions relating to DNA 3'-extension, provided that the template sequence is known.

Here we present a deep sequencing approach that provides an unbiased determination of nascent 3&#39;-termini as well as mutational profiles of single-stranded DNA molecules. The main application is the characterization of nascent retroviral complementary DNAs (cDNAs), the intermediates generated during the process of retroviral reverse transcription.

Monitoring of nucleic acid intermediates during virus replication provides insights into the effects and mechanisms of action of antiviral compounds and ...