Name: a quantitative dot blot assay for aav titration and its use for functional assessment of the adeno-associated virus assembly-activating proteins
Uploaded: 2018-06-12T13:00:00
Description: Watch this Scientific Journal Video about A Quantitative Dot Blot Assay for AAV Titration and Its Use for Functional Assessment of the Adeno-associated Virus Assembly-activating Proteins at JoVE.com

We thank Xiao Xiao at the University of North Carolina at Chapel Hill for providing us with the pEMBL-CMV-GFP plasmid. We thank Christopher Cheng and Samuel J. Huang for critical reading of the manuscript. This work was supported by Public Health Service grants (NIH R01 NS088399 and T32 EY232113).

NOTE: Recipes for the solutions and buffers needed for this protocol are provided in Table 1. The protocol described below is for the VP-AAP cross-complementation dot blot assay to study the roles of the AAP proteins in capsid assembly. The method for the more generic quantitative dot blot assay for purified AAV vector titration is explained in the Representative Results section.
1. Construction of VP3, AAP, and AAV2 Rep Expressing Plasmids
<ol>
	<li><strong...

<ol>
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In this report, the utility of quantitative dot blot assays to study AAV AAPs and their role in capsid assembly is described. Knowledge gained from these studies can provide detailed insights into the innate differences in the process of AAV capsid assembly and the functional role of AAPs between different serotypes. In this respect, the AAV VP3-AAP cross-complementation dot blot assay revealed that Snake AAV VP3 displayed a strict dependency on the co-expression of its cognate AAP for capsid assembly and that Snake AAP ...

Adeno-associated virus (AAV) is a small, non-enveloped, single-stranded DNA virus with a genome of approximately 4.7 kilobases (kb). The AAV genome contains open-reading frames (ORFs) for the rep and cap genes. In 2010, a previously unidentified nonstructural protein encoded by a +1 frame-shifted ORF within the AAV2 cap gene was discovered by Sonntag et al. and found to play a critical role in the assembly of AAV2 capsid VP monomer proteins into a viral capsid1. This novel protein has been named assembly-activating protein (AAP) after the role it plays in promoting capsid assembly1.
The ORFs for AAP have been identified bioinformatically in the genomes of all parvoviruses within the genus Dependoparvovirus, but not within the genomes of viruses of different genera of the parvovirus family1,2. Functional studies of this novel protein were initially focused on the AAP from the prototype AAV2 (AAP2), which has established the essential role of AAP2 in targeting unassembled VP proteins to the nucleolus for their accumulation and formation into fully assembled capsids1,3,4. The inability of the AAV2 capsids to assemble in the absence of AAP expression has been independently confirmed by multiple groups, including ours1,2,3,4,5. Subsequent studies on AAV serotypes 1, 8, and 9 corroborated the critical role of AAPs in capsid assembly, as VP3 monomer proteins of AAV1, 8, and 9 were unable to form a fully assembled capsid in the absence of co-expression of AAP2.
Recently, through approaches that include the use of quantitative dot blot assays, we investigated the ability of AAV1 to 12 VP3 monomers to assemble into capsids in the absence of AAP expression and the ability of AAP1 to 12 to promote assembly of VP3 monomers from heterologous serotypes. This study has revealed that AAV4, 5, and 11 VP3 monomers can assemble without AAP. Additionally, it was found that eight out of the twelve AAP serotypes we examined (i.e., all but AAP4, 5, 11, and 12) displayed a broad ability to support capsid assembly of heterologous AAV serotype capsids, while AAP4, 5, 11 and 12 displayed a substantially limited ability in this regard6. These four serotypes are phylogenetically distant from the other AAP serotypes2,3. Moreover, the study has uncovered significant heterogeneity in subcellular localizations of different AAPs6. Furthermore, the study has suggested that the tight association of AAP with assembled capsids and the nucleolus, the hallmark of AAV2 capsid assembly, cannot necessarily be extended to other serotypes including AAV5, 8, and 9, which display nucleolar exclusion of assembled capsids6. Thus, the information gained from the study of any particular serotype AAP is not broadly applicable to all AAP biology. Such puzzling nature of AAP biology underscores the need to investigate the role and function of each AAP from both canonical and non-canonical AAV serotypes.
The biological role of AAP in capsid assembly can be assessed by determining the fully-packaged AAV viral particle titers produced in human embryonic kidney (HEK) 293 cells, the most commonly used cell line for AAV vector production, with or without AAP protein expression. The standard methods for AAV quantitation are quantitative PCR (qPCR)-based assays7,8 and quantitative dot blot-based assays9. Other methods for AAV viral particle quantitation such as enzyme-linked immunosorbent assay10,11 or optical density measurement12 are not ideal for samples derived from many different AAV serotypes or samples contaminated with impurities (crude lysates or culture media), which are often the samples used for AAV research. Currently, qPCR is most widely used for AAV quantitation; however, it is necessary to acknowledge potential caveats of the qPCR-based assay, as the assay can result in systemic errors and significant titer variations13,14. PCR-based assays are affected by a number of potentially confounding factors, such as the presence of covalently closed terminal hairpins in PCR templates that inhibit amplification13. Even an experienced individual can introduce potential confounding factors into a qPCR-based assay unknowingly13. In contrast, quantitative dot blot assays are a classical molecular biology technique that does not involve genome amplification and uses a much simpler principle with a minimal risk of errors as compared to qPCR-based assays. The method is less technically challenging; therefore, the assay results are reasonably reproducible even by inexperienced individuals.
In this report, we describe the methodological details of a quantitative dot blot assay we routinely use for AAV vector quantitation and provide an example of how to apply the assay to study the assembly-promoting role of AAPs in common serotypes (AAV5 and AAV9) and a previously uncharacterized AAP from Snake AAV14. In nature, AAV VP proteins and AAP proteins are expressed in cis from a single gene (i.e., VP-AAP cis-complementation), while in the assay described here, VP and AAP proteins are supplied in trans from two separate plasmids (i.e., VP-AAP trans-complementation). Since each VP or AAP protein from different serotypes can be expressed from each independent plasmid, it becomes possible to test heterologous VP-AAP combinations for capsid assembly (i.e., VP-AAP cross-complementation). Briefly, AAV VP3 from various serotypes is expressed in HEK 293 cells by plasmid DNA transfection to package an AAV vector genome in the presence or absence of the cognate serotype AAP, or in the presence of a heterologous serotype AAP. Following production, culture media and cell lysates are subjected to a dot blot assay to quantify the viral genome within the capsid shell. The first step of the dot blot assay is to treat samples with a nuclease to remove contaminating plasmid DNAs and unpackaged AAV genomes in samples. Failure to do so would increase the background signals in particular when unpurified samples are assayed. This is then followed by a protease treatment to break viral capsids and release nuclease-resistant viral genomes into sample solutions. Next, viral genomes are denatured, blotted on a membrane, and hybridized with a viral genome-specific DNA probe for quantitation. In the example assay reported here, we demonstrate that Snake AAV VP3 requires Snake AAP for capsid assembly and that Snake AAP does not promote the assembly of AAV9 capsids unlike many of the AAPs derived from AAP-dependent serotypes that can also promote assembly of heterologous serotype capsids. Lastly, we report an important caveat to qPCR or dot blot-based AAV quantitation assays that the choice of nuclease significantly affects the assay results.

<table>
	<tbody>
		<tr>
			<td>Benzonase</td>
			<td>MilliporeSigma</td>
			<td>1016970001</td>
			<td>Referred to as Serratia marcescen endonuclease in the main text.</td>
		</tr>
		<tr>
			<td>DNase I</td>
			<td>Roche</td>
			<td>4716728001</td>
			<td>Referred to as DNase I Enzyme A in the main text.</td>
		</tr>
		<tr>
			<td>DNase I</td>
			<td>Invitrogen</td>
			<td>18047019</td>
			<td>Referred to as DNase I Enzyme B in the main text.</td>
		</tr>
		<tr>
			<td>DNase I</td>
			<td>New England Biolabs</td>
			<td>M0303L</td>
			<td>Referred to as DNase I Enzyme C in the main text.</td>
		</tr>
		<tr>
			<td>1.5 mL Attached O-Ring Screw Cap Microcentrifuge Tubes</td>
			<td>Corning</td>
			<td>430909</td>
			<td></td>
		</tr>
		<tr>
			<td>1.5 mL Microcentrifuge Tubes</td>
			<td>Thermo Fisher Scientific</td>
			<td>05-408-129</td>
			<td></td>
		</tr>
		<tr>
			<td>15 mL Polypropylene Conical Tube</td>
			<td>Corning</td>
			<td>352097</td>
			<td></td>
		</tr>
		<tr>
			<td>3 M Sodium Acetate</td>
			<td>Teknova</td>
			<td>S0298</td>
			<td></td>
		</tr>
		<tr>
			<td>50 mL Polypropylene Conical Tube</td>
			<td>Corning</td>
			<td>430291</td>
			<td></td>
		</tr>
		<tr>
			<td>AAV-293 Cells</td>
			<td>Agilent</td>
			<td>240073</td>
			<td>HEK-293 cell line optimized for the packaging of AAV virions.</td>
		</tr>
		<tr>
			<td>AccuGENE 0.5 M EDTA Solution</td>
			<td>Lonza</td>
			<td>51234</td>
			<td></td>
		</tr>
		<tr>
			<td>AccuGENE 1 M Tris-HCl pH 8.0</td>
			<td>Lonza</td>
			<td>51238</td>
			<td></td>
		</tr>
		<tr>
			<td>AccuGENE 10% SDS</td>
			<td>Lonza</td>
			<td>51213</td>
			<td></td>
		</tr>
		<tr>
			<td>AccuGENE 1X TE Buffer</td>
			<td>Lonza</td>
			<td>51235</td>
			<td></td>
		</tr>
		<tr>
			<td>Bio-Dot Apparatus</td>
			<td>Bio-Rad</td>
			<td>1706545</td>
			<td></td>
		</tr>
		<tr>
			<td>Bovine Serum Albumin</td>
			<td>MilliporeSigma</td>
			<td>A3294</td>
			<td></td>
		</tr>
		<tr>
			<td>Cell Lifter</td>
			<td>Corning</td>
			<td>3008</td>
			<td></td>
		</tr>
		<tr>
			<td>Chloroform</td>
			<td>MilliporeSigma</td>
			<td>372978</td>
			<td></td>
		</tr>
		<tr>
			<td>DNA Extractor Kit</td>
			<td>Wako Pure Chemical Industries</td>
			<td>295-50201</td>
			<td>This is used for quantitative dot blots on purified virus. We use only a half volume of all the reagents in each step recommended for the Protocol Scheme 2 in the manual provided by the manufacturer.</td>
		</tr>
		<tr>
			<td>Dulbecco&#8217;s Modified Eagle Medium (DMEM)-high glucose (4.5 g/L)</td>
			<td>Lonza</td>
			<td>12-614F</td>
			<td></td>
		</tr>
		<tr>
			<td>ElectroMAX DH10B Cells</td>
			<td>Thermo Fisher Scientific</td>
			<td>18290015</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethanol 200 Proof</td>
			<td>Decon Labs</td>
			<td>2716</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal Bovine Serum</td>
			<td>VWR</td>
			<td>1500-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Ficoll 400</td>
			<td>Alfa Aesar</td>
			<td>B22095</td>
			<td>Referred to as Polysucrose 400.</td>
		</tr>
		<tr>
			<td>Fluorescence&#160;Microscope</td>
			<td>Zeiss</td>
			<td>Axiovert 40 CFL</td>
			<td></td>
		</tr>
		<tr>
			<td>Glycogen</td>
			<td>Roche</td>
			<td>10901393001</td>
			<td></td>
		</tr>
		<tr>
			<td>Herring Sperm DNA</td>
			<td>Invitrogen</td>
			<td>15634-017</td>
			<td></td>
		</tr>
		<tr>
			<td>Hybridization Tubes</td>
			<td>Thermo Fisher Scientific</td>
			<td>13-247-150</td>
			<td></td>
		</tr>
		<tr>
			<td>ImageQuant TL</td>
			<td>GE Healthcare Life Sciences</td>
			<td>ImageQuant TL</td>
			<td></td>
		</tr>
		<tr>
			<td>L-glutamine 200 mM</td>
			<td>Lonza</td>
			<td>17-605E</td>
			<td></td>
		</tr>
		<tr>
			<td>Magnesium Choloride Hexahydrate</td>
			<td>MilliporeSigma</td>
			<td>M0250</td>
			<td></td>
		</tr>
		<tr>
			<td>MicroPulser Electroporator</td>
			<td>Bio-Rad</td>
			<td>1652100</td>
			<td></td>
		</tr>
		<tr>
			<td>Mini Quick Spin DNA Columns</td>
			<td>MilliporeSigma</td>
			<td>11814419001</td>
			<td></td>
		</tr>
		<tr>
			<td>pAAV-RC2 Vector</td>
			<td>Cell Biolabs Inc</td>
			<td>VPK-422</td>
			<td></td>
		</tr>
		<tr>
			<td>Penicillin/Streptomycin 10K/10K</td>
			<td>Lonza</td>
			<td>17-602E</td>
			<td></td>
		</tr>
		<tr>
			<td>Phosphate Buffered Saline</td>
			<td>Lonza</td>
			<td>17-516F</td>
			<td></td>
		</tr>
		<tr>
			<td>Phosphorimaging Exposure Cassette</td>
			<td>GE Healthcare Life Sciences</td>
			<td>Various</td>
			<td></td>
		</tr>
		<tr>
			<td>Phosphorimaging Screen</td>
			<td>GE Healthcare Life Sciences</td>
			<td>Various</td>
			<td></td>
		</tr>
		<tr>
			<td>Plasmid Maxi Kit</td>
			<td>QIAGEN</td>
			<td>12162</td>
			<td></td>
		</tr>
		<tr>
			<td>Platinum Pfx DNA Polymerase</td>
			<td>Invitrogen</td>
			<td>11708013</td>
			<td></td>
		</tr>
		<tr>
			<td>Polyethylenimine</td>
			<td>Polysciences Inc</td>
			<td>23966-2</td>
			<td></td>
		</tr>
		<tr>
			<td>Polyvinylpyrrolidone</td>
			<td>MilliporeSigma</td>
			<td>P5288</td>
			<td></td>
		</tr>
		<tr>
			<td>Prime-It II Random Primer Labeling Kit</td>
			<td>Agilent Technologies</td>
			<td>300385</td>
			<td></td>
		</tr>
		<tr>
			<td>Primer AAP Forward (N25 nucleotides from the 4th nucleotide in the AAP ORF, RE1 is a restriction enzyme site for cloning): CTAA-RE1-CACCATGGACTACAAGGACGACGATGACAAA-N25</td>
			<td>MilliporeSigma</td>
			<td>Custom Primer</td>
			<td></td>
		</tr>
		<tr>
			<td>Primer AAP Reverse (N25 is the last 25 nucleotides of the AAP ORF, RE2 is a restriction enzyme site for cloning): TCTT-RE2-N25</td>
			<td>MilliporeSigma</td>
			<td>Custom Primer</td>
			<td></td>
		</tr>
		<tr>
			<td>Primer VP3 Forward (N25 the first 25 nucleotides of the VP3 ORF, RE1 is a restriction enzyme site for cloning): CTAA-RE1-CACC-N25</td>
			<td>MilliporeSigma</td>
			<td>Custom Primer</td>
			<td></td>
		</tr>
		<tr>
			<td>Primer VP3 Reverse (N25 is the last 25 nucleotides of the AAP ORF, RE2 is a restriction enzyme site for cloning): TCTT-RE2-N25</td>
			<td>MilliporeSigma</td>
			<td>Custom Primer</td>
			<td></td>
		</tr>
		<tr>
			<td>Proteinase K Solution</td>
			<td>Invitrogen</td>
			<td>25530-049</td>
			<td></td>
		</tr>
		<tr>
			<td>Restriction Enzymes</td>
			<td>New England Biolabs</td>
			<td>Various</td>
			<td></td>
		</tr>
		<tr>
			<td>Salmon Sperm DNA</td>
			<td>Invitrogen</td>
			<td>15632011</td>
			<td></td>
		</tr>
		<tr>
			<td>Serological Pipettes</td>
			<td>Thermo Fisher Scientific</td>
			<td>13-678-11D / 13-678-11E / 13-678-11</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Chloride</td>
			<td>Thermo Fisher Scientific</td>
			<td>S271-10</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Citrate Tribasic Dihydrate</td>
			<td>MilliporeSigma</td>
			<td>C8532</td>
			<td></td>
		</tr>
		<tr>
			<td>T4 DNA Polymerase</td>
			<td>New England Biolabs</td>
			<td>M0203L</td>
			<td></td>
		</tr>
		<tr>
			<td>Thermal Cycler</td>
			<td>Eppendorf</td>
			<td>6321000515</td>
			<td></td>
		</tr>
		<tr>
			<td>Tissue-culture Treated 6-well Plate</td>
			<td>Corning</td>
			<td>353046</td>
			<td></td>
		</tr>
		<tr>
			<td>Tris Base</td>
			<td>Thermo Fisher Scientific</td>
			<td>BP152-5</td>
			<td></td>
		</tr>
		<tr>
			<td>Typhoon FLA 7000</td>
			<td>GE Healthcare Life Sciences</td>
			<td>28955809</td>
			<td></td>
		</tr>
		<tr>
			<td>UltraPure Buffer-Saturated Phenol</td>
			<td>Invitrogen</td>
			<td>15513-047</td>
			<td></td>
		</tr>
		<tr>
			<td>UV Crosslinker</td>
			<td>Spectroline</td>
			<td>XLE-1000</td>
			<td>Optimal Crosslink mode is used, providing a UV energy dosage of 120 mJ/cm2.</td>
		</tr>
		<tr>
			<td>Zeta-Probe Membrane</td>
			<td>Bio-Rad</td>
			<td>162-0165</td>
			<td></td>
		</tr>
	</tbody>
</table>

a quantitative dot blot assay for aav titration and its use for functional assessment of the adeno-associated virus assembly-activating proteins

While adeno-associated virus (AAV) is widely accepted as an attractive vector for gene therapy, it also serves as a model virus for understanding virus biology. In the latter respect, the recent discovery of a non-structural AAV protein, termed assembly-activating protein (AAP), has shed new light on the processes involved in assembly of the viral capsid VP proteins into a capsid. Although many AAV serotypes require AAP for assembly, we have recently reported that AAV4, 5, and 11 are exceptions to this rule. Furthermore, we demonstrated that AAPs and assembled capsids of different serotypes localize to different subcellular compartments. This unexpected heterogeneity in the biological properties and functional roles of AAPs among different AAV serotypes underscores the importance of studies on AAPs derived from diverse serotypes. This manuscript details a straightforward dot blot assay for AAV quantitation and its application to assess AAP dependency and serotype specificity in capsid assembly. To demonstrate the utility of this dot blot assay, we set out to characterize capsid assembly and AAP dependency of Snake AAV, a previously uncharacterized reptile AAV, as well as AAV5 and AAV9, which have previously been shown to be AAP-independent and AAP-dependent serotypes, respectively. The assay revealed that Snake AAV capsid assembly requires Snake AAP and cannot be promoted by AAPs from AAV5 and AAV9. The assay also showed that, unlike many of the common serotype AAPs that promote heterologous capsid assembly by cross-complementation, Snake AAP does not promote assembly of AAV9 capsids. In addition, we show that the choice of nuclease significantly affects the readout of the dot blot assay, and thus, choosing an optimal enzyme is critical for successful assessment of AAV titers.

A representative result of quantitative dot blots for quantitation of purified AAV vector stocks produced on a large scale is shown in Figure 1. With this dot blot assay, the titer of a double-stranded AAV2G9-CMV-GFP vector stock was determined. The vector was purified by two rounds of cesium chloride (CsCl) density-gradient ultracentrifugation followed by dialysis as previously described20. In general, for purified AAV vector stocks, ...

Watch this Scientific Journal Video about A Quantitative Dot Blot Assay for AAV Titration and Its Use for Functional Assessment of the Adeno-associated Virus Assembly-activating Proteins at JoVE.com

A Quantitative Dot Blot Assay for AAV Titration and Its Use for Functional Assessment of the Adeno-associated Virus Assembly-activating Proteins

This manuscript details a straightforward dot blot assay for quantitation of adeno-associated virus (AAV) titers and its application to study the role of assembly-activating proteins (AAPs), a novel class of non-structural viral proteins found in all AAV serotypes, in promoting the assembly of capsids derived from cognate and heterologous AAV serotypes.

While adeno-associated virus (AAV) is widely accepted as an attractive vector for gene therapy, it also serves as a model virus for understanding virus ...

This method can determine both purified and the non-purified AV vac titers and assess the ability for the AAV AAP to promote assembly of cognate and heterologous AV serotype-capsis. The main advantage of this technique is that it is a straightforward inexpensive method that avoids the drawbacks of other AAV titration methods. Though this method has commonly been used for AAV vector quantitation, it can also be applied to address various fundamental questions about AAV biology as shown in this protocol.On day zero, after culturing HEK 293 cells to 90%confluency, prepare the transfection reagent by mixing the plasmids in 96 microliters of PBS without calcium or magnesium in sterile 1.5 milliliter micro-centrifuge tubes. As indicated in this table, the total amount of DNA is two micrograms per well. Add four microliters of PEI solution to the PBS plasmid DNA mix.The final volume is approximately 100 microliters or 5%volume of the culture medium. Vortex the tubes briefly and incubate the DNA PEI mixture at room temperature for 15 minutes. Following the incubation, briefly spin the tubes in a micro centrifuge to collect the liquid to the bottom.And add the DNA PEI mixture drop-wise to the culture medium in each well of the HEK 293 culture plate. Then gently agitate the plates and return them to a 37 degree Celsius incubator with 5%CO2. Transfection of HEK 293 cell is a critical component of this protocol for high-titer virus production.Healthy, low-passage number cells should be used and care should be taken not to disrupt the cells'monolayer. On days one and two, under an inverted fluorescence microscope, observe cells transfected with the PCMVGFP plasmid to assess the transfection efficiency. On day five, pipette the cells and virus-containing medium up and down or use a cell scraper to scrape all the cells.Then, transfer the suspension into 15 milliliter polypropylene conical tubes. Store the samples at minus 80 degree Celsius until use. To recover the viral particles, quickly thaw the frozen tubes in a 37 degree Celsius water bath.Then, vortex the tubes vigorously for one minute to maximize the recovery of AAV from the cells. Pellet the cell debris by centrifugation at 3, 700 times G and four degrees Celsius for 10 minutes. Then transfer 200 microliters of the supernatant from each tube into labeled micro-centrifuge tubes with screw caps for the dot blot assay.To treat the samples with Serratia marcescens endonuclease, prepare mix A and mix B reagents. Add 10 microliters of each reagent to each sample tube. Vortex the samples for five seconds and briefly spin them to collect the liquid to the bottom of the tubes.Then incubate the tubes at 37 degrees Celsius for at least one hour. After briefly spinning the samples, carry out proteinase K treatment by preparing mix C reagent and adding 180 microliters to each tube. Then after vortexing and briefly spinning the tubes again, incubate them at 55 degrees Celsius for one hour.Once the samples have returned to room temperature, add 200 microliters of phenol-chloroform and vortex the tubes for one minute. Then spin the samples in a micro-centrifuge at 16, 100 times G and room temperature for at least five minutes. Transfer 320 microliters of the aqueous layer or 80%of the aqueous fluid volume to a new standard micro-centrifuge tube.This transfer step is critically important as the same volume must be taken from the sample to maintain accuracy for AAV quantitation. Care should be taken to avoid the organic phase while removing the aqueous layer. Prepare the mix D reagent and add 833 microliters to each sample tube.After vortexing the tubes, incubate them at minus 80 degrees Celsius for at least 20 minutes. Following centrifugation, pour off supernatant and blot the tubes once on a clean paper towel. Pipette approximately 500 microliters of 70%ethanol into each tube and vortex the tubes for five seconds.After spinning the samples again, pour off the supernatant and blot the tubes once on a clean paper towel. Then dry the pellets at 65 degrees Celsius before resuspending them in TE buffer. To carry out the dot blot assay, prepare plasmid DNA standards by diluting AAV vectored genome plasmid DNA to 10 nanograms per microliter in water or Tris-HCL buffer.Transfer a 25 microliter aliquot of the diluted plasmid DNA to a fresh tube and linearize it with an appropriate restriction enzyme in a 50 microliter reaction volume for one hour. Add 450 microliters of water or TE to the tube containing the digested plasmid DNA standard and mix thoroughly. Then transfer 70 microliters of this mixture to a new 1.5 milliliter micro-centrifuge tube with 1, 330 microliters of water or TE to make a diluted plasmid standard.To set up the dot blot apparatus, using scissors, cut the blotting membrane to an appropriate size for the number of samples and standards. Soak the membrane with water for 10 minutes before placing it on the dot blot apparatus. Then, cover the unused wells.Add water to the wells to which the samples will be loaded. Apply a vacuum, pull the water through the wells, check for errors, and then retighten the screws. Retest if necessary.Apply 400 microliters of each diluted plasmid DNA standard to each well and run four lanes of standard dilutions. Use two separate aliquots of the standard digest and load each in duplicate. Then apply 200 microliters per well of each viral DNA sample.Apply a gentle vacuum to pull the DNA solutions through the wells. Then once all the wells have emptied, release the vacuum by adjusting the three-way valve. Add 400 microliters of one X alkaline solution to each well.Then wait for five minutes before reapplying the vacuum to empty the wells. Reapply the vacuum and disassemble the dot blot apparatus. Then remove the membrane and rinse it with two X SSC.Place the membrane on a clean paper towel with the DNA-bound side facing up to remove the excess buffer. Use an appropriate UV crosslinker to UV crosslink the blotted DNA to the membrane. The membrane is now ready for hybridization.Place the membrane in a hybridization bottle with the DNA-bound side up. Rinse the membrane with five to 10 milliliters of pre-warmed hybridization buffer and discard the buffer. Then add 10 milliliters of pre-warmed hybridization buffer and place the bottle in a rotating hybridization oven set to 65 degrees Celsius.Rotate the bottle for at least five minutes. Quickly add the denatured sperm DNA and radioactive probe to the hybridization buffer in the bottle and shake it for 10 seconds to mix. Return the bottle to the 65 degree Celsius oven and incubate it with rotation at 65 degrees Celsius for at least four hours.Once hybridization is complete, stop the rotation. Remove the hybridization bottle and then pour the radioactive probe solution into a 50 milliliter conical tube with a leakproof plug seal cap. To wash the membrane, add 20 to 30 microliters of pre-warmed wash buffer to the hybridization bottle and rotate it for five minutes.Repeat this wash two more times. After the third wash, remove the membrane from the hybridization bottle, and with paper towels, remove the excess buffer from the membrane. Then place the membrane in a clear plastic paper holder.With a Geiger counter, check the radioactive signals on the membrane. After exposing the erased phosphor-imaging screen to the membrane, scan the screen using a phosphor-image scanning system and obtain the data on signal intensity of each dot. Carry out data analysis according to the text protocol.This quantitative dot blot for AAV 2G9 vector titration has two sets of standards and three different amounts of an AAV vector preparation, including 0.3, 0.1, and 0.03 microliters in duplicate. The amounts to be assayed on the blot are determined empirically or based on a preliminary assay. It was determined by interpolation that 0.3, 0.1, and 0.03 microliter aliquots of the AAV 2G9 vector had on average a titer of 5.16, 0.27 nanograms equivalent microliters.All possible cognate and heterologous serotype combinations of VP3 cas-pid and AAP proteins from AAV5, AAV9, and snake AAV were assessed for capsid assembly by a quantitative dot blot assay. The results of this graph show that AAV5 VP3 assembles regardless of whether AAP was provided in trans. In addition, AAP5 and AAP9 can promote AAV9 VP3 capsid assembly, although AAP5 functions less effectively than AAP9.Neither AAP5 nor AAP9 exhibits an assembly promoting activity on snake AAV VP3, and snake AAP only promotes assembly of snake AAV VP3. A dot blot analysis was applied to asses nuclease activity of three commercially available nucleases under non-optimized conditions containing cell and culture medium-derived impurities. Enzyme A was found not as active as the other two enzymes, showing that the choice of nuclease could significantly affect the readout of the dot blot assay.This technique is straightforward for AAV vector quantitation and instrumental in assessing the role of AAP in promoting assembly of AAV capsids derived from cognate and heterologous serotypes. Once mastered, this technique can be done in a day if it performed properly once assay samples are obtained in cell culture experiments. While attempting this procedure, it is important to remember to carefully pipette the correct liquid volume to ensure quantitative accuracy.After its development, the application of the quantitative dot blot assay to study AAP have paved the way for researchers in the field of AAV biology to further understand the mechanism of AAV capsid assembly. Please do not forget that working with human cells, viral agents, phenol-chloroform, and radioactive materials can be extremely hazardous. And the use of lab coats, gloves, and goggles are needed to limit exposure.These materials should only be handled in approved areas. After watching this video, you should have a good understanding on how to prepare dot blot samples for AAV quantitation, set up dot blot apparatus, determine AAV titer, and apply the procedure to the study of AAV biology. Following this procedure, other assays like AAV vector transduction assays in culture cells can be performed to answer additional questions, such as the functional titer of vectorized compared to the physical particle titer determined by dot blot assay.

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