E.J.N.G. is supported by the Wellcome Trust (grant 106098/Z/14/Z). Other funding has been provided by the SMA Trust (SMA UK Consortium; T.H.G. &#38; Y-T.H.), SMA Europe (T.H.G, D.v.D.H. &#38; E.J.N.G.), the University of Edinburgh DTP in Precision Medicine (T.H.G., L.L. &#38; A.M.M.), and the Euan MacDonald Centre for Motor Neurone Disease Research (T.H.G).

Tissues for this procedure were obtained from animal studies that were approved by the internal ethics committee at the University of Edinburgh and were performed in concordance with institutional and UK Home Office regulations under the authority of relevant personal and project licenses.
NOTE: This protocol has been optimized using standardized, commercially available kits and reagents in order to increase reproducibility (see Table of Materials).
1...

<ol>
	<li>Bertoni, T. A., Perenha-Viana, M. C., Patussi, E. V., Cardoso, R. F., Svidzinski, T. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Western+blotting+is+an+efficient+tool+for+differential+diagnosis+of+paracoccidioidomycosis+and+pulmonary+tuberculosis.">Western blotting is an efficient tool for differential diagnosis of paracoccidioidomycosis and pulmonary tuberculosis.</a> Clinical and Vaccine Immunology. 19 (11), 1887-1888 (2012).</li><li>Hutchinson, A. B., 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=Costs+and+outcomes+of+laboratory+diagnostic+algorithms+for+the+detection+of+HIV.">Costs and outcomes of laboratory diagnostic algorithms for the detection of HIV.</a> Journal of Clinical Virology. 58 Suppl 1, (2013).</li><li>Towbin, H., Staehelin, T., Gordon, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrophoretic+transfer+of+proteins+from+polyacrylamide+gels+to+nitrocellulose+sheets:+procedure+and+some+applications.">Electrophoretic transfer of proteins from polyacrylamide gels to nitrocellulose sheets: procedure and some applications.</a> Proceedings of the National Academy of Sciences of the United States of America. 76 (9), 4350-4354 (1979).</li><li>Eaton, S. L., 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=Total+protein+analysis+as+a+reliable+loading+control+for+quantitative+fluorescent+Western+blotting.">Total protein analysis as a reliable loading control for quantitative fluorescent Western blotting.</a> PloS One. 8 (8), e72457 (2013).</li><li>Ghosh, R., Gilda, J. E., Gomes, A. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+necessity+of+and+strategies+for+improving+confidence+in+the+accuracy+of+western+blots.">The necessity of and strategies for improving confidence in the accuracy of western blots.</a> Expert Rev Proteomics. 11 (5), 549-560 (2014).</li><li>Jensen, B. C., Swigart, P. M., Simpson, P. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ten+commercial+antibodies+for+alpha-1-adrenergic+receptor+subtypes+are+nonspecific.">Ten commercial antibodies for alpha-1-adrenergic receptor subtypes are nonspecific.</a> Naunyn-Schmiedebergs Archives of Pharmacology. 379 (4), 409-412 (2009).</li><li>Jositsch, G., 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=Suitability+of+muscarinic+acetylcholine+receptor+antibodies+for+immunohistochemistry+evaluated+on+tissue+sections+of+receptor+gene-deficient+mice.">Suitability of muscarinic acetylcholine receptor antibodies for immunohistochemistry evaluated on tissue sections of receptor gene-deficient mice.</a> Naunyn-Schmiedebergs Archives of Pharmacology. 379 (4), 389-395 (2009).</li><li>Smejkal, G., Gallagher, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determination+of+semidry+protein+transfer+efficiency+with+transverse+gradient+gel+electrophoresis.">Determination of semidry protein transfer efficiency with transverse gradient gel electrophoresis.</a> Biotechniques. 16 (2), (1994).</li><li>Eaton, S. L., 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=A+guide+to+modern+quantitative+fluorescent+western+blotting+with+troubleshooting+strategies.">A guide to modern quantitative fluorescent western blotting with troubleshooting strategies.</a> Journal of Visualized Experiments. (93), e52099 (2014).</li><li>Hunter, G., Roche, S. L., Somers, E., Fuller, H. R., Gillingwater, T. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+influence+of+storage+parameters+on+measurement+of+survival+motor+neuron+(SMN)+protein+levels:+implications+for+pre-clinical+studies+and+clinical+trials+for+spinal+muscular+atrophy.">The influence of storage parameters on measurement of survival motor neuron (SMN) protein levels: implications for pre-clinical studies and clinical trials for spinal muscular atrophy.</a> Neuromuscular Disorders. 24 (11), 973-977 (2014).</li><li>Fosang, A. J., Colbran, R. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transparency+Is+the+Key+to+Quality.">Transparency Is the Key to Quality.</a> Journal of Biological Chemistry. 290 (50), 29692-29694 (2015).</li><li>Taylor, S. C., Berkelman, T., Yadav, G., Hammond, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+defined+methodology+for+reliable+quantification+of+Western+blot+data.">A defined methodology for reliable quantification of Western blot data.</a> Molecular Biotechnology. 55 (3), 217-226 (2013).</li><li>Goasdoue, K., Awabdy, D., Bjorkman, S. T., Miller, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Standard+loading+controls+are+not+reliable+for+Western+blot+quantification+across+brain+development+or+in+pathological+conditions.">Standard loading controls are not reliable for Western blot quantification across brain development or in pathological conditions.</a> Electrophoresis. 37 (4), 630-634 (2016).</li><li>Rocha-Martins, M., Njaine, B., Silveira, M. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Avoiding+pitfalls+of+internal+controls:+validation+of+reference+genes+for+analysis+by+qRT-PCR+and+Western+blot+throughout+rat+retinal+development.">Avoiding pitfalls of internal controls: validation of reference genes for analysis by qRT-PCR and Western blot throughout rat retinal development.</a> PloS One. 7 (8), e43028 (2012).</li><li>Aghamaleky Sarvestany, A., 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=Label-free+quantitative+proteomic+profiling+identifies+disruption+of+ubiquitin+homeostasis+as+a+key+driver+of+Schwann+cell+defects+in+spinal+muscular+atrophy.">Label-free quantitative proteomic profiling identifies disruption of ubiquitin homeostasis as a key driver of Schwann cell defects in spinal muscular atrophy.</a> Journal of Proteome Research. 13 (11), 4546-4557 (2014).</li><li>Fuller, H. 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=Spinal+Muscular+Atrophy+Patient+iPSC-Derived+Motor+Neurons+Have+Reduced+Expression+of+Proteins+Important+in+Neuronal+Development.">Spinal Muscular Atrophy Patient iPSC-Derived Motor Neurons Have Reduced Expression of Proteins Important in Neuronal Development.</a> Frontiers in Cellular Neuroscience. 9, 506 (2015).</li><li>Liu, N. K., Xu, X. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=beta-tubulin+is+a+more+suitable+internal+control+than+beta-actin+in+western+blot+analysis+of+spinal+cord+tissues+after+traumatic+injury.">beta-tubulin is a more suitable internal control than beta-actin in western blot analysis of spinal cord tissues after traumatic injury.</a> Journal of Neurotrauma. 23 (12), 1794-1801 (2006).</li><li>Moritz, C. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tubulin+or+Not+Tubulin:+Heading+Toward+Total+Protein+Staining+as+Loading+Control+in+Western+Blots.">Tubulin or Not Tubulin: Heading Toward Total Protein Staining as Loading Control in Western Blots.</a> Proteomics. 17 (20), (2017).</li><li>Groen, E. J. N., 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=Temporal+and+tissue-specific+variability+of+SMN+protein+levels+in+mouse+models+of+spinal+muscular+atrophy.">Temporal and tissue-specific variability of SMN protein levels in mouse models of spinal muscular atrophy.</a> Human Molecular Genetics. 27 (16), 2851-2862 (2018).</li><li>Chaytow, H., Huang, Y. T., Gillingwater, T. H., Faller, K. M. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+role+of+survival+motor+neuron+protein+(SMN)+in+protein+homeostasis.">The role of survival motor neuron protein (SMN) in protein homeostasis.</a> Cellular and Molecular Life Sciences. , (2018).</li><li>Groen, E. J. N., Talbot, K., Gillingwater, T. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Advances+in+therapy+for+spinal+muscular+atrophy:+promises+and+challenges.">Advances in therapy for spinal muscular atrophy: promises and challenges.</a> Nature Reviews: Neurology. 14 (4), 214-224 (2018).</li><li>Fitzmaurice, G. M., Laird, N. M., Ware, J. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Applied longitudinal analysis. , (2004).</li><li>Jordan, C. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Population+sampling+affects+pseudoreplication.">Population sampling affects pseudoreplication.</a> PLoS Biology. 16 (10), e2007054 (2018).</li><li>LaFauci, G., Adayev, T., Kascsak, R., Brown, W. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Detection+and+Quantification+of+the+Fragile+X+Mental+Retardation+Protein+1+(FMRP).">Detection and Quantification of the Fragile X Mental Retardation Protein 1 (FMRP).</a> Genes (Basel). 7 (12), (2016).</li></ol>

The authors have no competing interests to disclose.

With the appropriate experimental design, control measures and statistical analysis, western blotting can be used to make reliable quantitative estimates of protein expression within and between a varied range of biological samples. The protocol we describe in the current manuscript aims to serve as a guideline for researchers looking to use Western blotting to undertake quantitative analysis across larger and more complex groups of samples, by using a combination of fluorescence-based detection methods, total protein lo...

Western blotting is a technique that is commonly used to detect and quantify protein expression, including in tissue homogenates or extracts. Over the years, this technique has led to many advances in both basic and clinical research, where it can be used as a diagnostic tool to identify the presence of disease1,2. Western blotting was first described in 1979 as a method to transfer proteins from polyacrylamide gels to nitrocellulose sheets and subsequently visualize proteins using secondary antibodies that were either radioactively labelled or conjugated to fluorescein or peroxidase3. Through the development of commercially available kits and equipment, Western blotting methods have been increasingly standardized and simplified over the years. Indeed, the technique is now readily performed by scientists with varying backgrounds and levels of experience. However, as with many similar experimental techniques, the outcome of Western blot analyses is easily influenced by choices made in the design and execution of the experiment. It is important, therefore, that the accessibility of standardized Western blotting methods does not obscure the need for careful experimental planning and design. Experimental considerations include, but are not limited to, sample preparation and handling, selection and validation of antibodies for protein detection, and gel-to-membrane transfer efficiency of particularly small or large (&#60;10 or &#62;140 kDa) proteins4,5,6,7,8,9. Protein quality of the original sample plays a significant role in determining the outcome of the subsequent Western blot analysis. As protein can be extracted from a wide variety of samples and sources, including cell lines, tissues from animal models, and post-mortem human tissues, consistency in handling and processing is required to obtain reproducible results. For example, when long-term storage of samples for protein extraction is required, it is important to realize that, although protein is generally stable at -80 &#176;C, differences in protein stability between extracted proteins and intact tissues at -80 &#176;C have been reported10. Moreover, to obtain reproducible estimates of protein quantities, consistent homogenization of samples is crucial. Optimizing different lysis buffers and homogenization methods (e.g., manual homogenization compared to automated methods) may be required before starting a large-scale quantitative experiment.
Normalization strategies to correct for protein loading and quantification variability are essential to obtain robust, quantitative results of protein expression. Housekeeping proteins such as &#946;-actin, &#945;-tubulin, &#946;-tubulin, and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) have traditionally been used to normalize protein levels for quantification. However, normalization to specific housekeeping proteins for quantification purposes has been increasingly criticized over the past few years11,12. For example, the expression of housekeeping proteins can change across different developmental stages13,14, across tissues from the same animal4, and under various disease conditions4,15,16,17. Therefore, the use of specific housekeeping proteins limits the possibilities of making more complex comparisons between protein expression from different tissues, at different timepoints and under varying experimental conditions. An alternative to housekeeping proteins to control for protein loading variation is the use of a total protein stain (TPS) that labels and visualizes all proteins present in a sample. TPS allows signal normalization based on total protein load rather than levels of one specific protein and therefore quantification of TPS signal should be comparable and reproducible regardless of experimental condition, sample type or developmental timepoint. Examples of total protein stains include Ponceau S, stain-free gels, Coomassie R-350, Sypro-Ruby, Epicocconone, Amydo Black, and Cy5 (reviewed in ref. 18). Each of these methods has specific advantages and limitations and method selection depends on the time and tools available as well as the experimental setup4,18.
In addition to using a TPS to correct for within-membrane loading and quantification variability, it may be necessary to compare samples between different membranes, particularly when performing large-scale protein expression analysis. However, variability in factors such as antibody binding efficiency and total protein stain intensity may introduce further variability between protein samples that are analyzed on separate gels and membranes. For robust quantification in this situation, it is therefore necessary to introduce a further normalization step to account for between-membrane variability. This can be achieved by including an internal loading standard on each of the separately analyzed membranes that is kept constant across experiments. This standard can take the form of any protein lysate that can be obtained in sufficient quantities to be used across all membranes included in the experiment. Here, we use a lysate of mouse brain (obtained from 5 day old control mice), as brain is readily homogenized and the obtained protein lysate contains a significant amount of protein at a high concentration. Loading an internal standard in triplicate allows samples on separate membranes to be normalized and compared directly.
Here, we describe a detailed protocol that we have developed to allow us to undertake complex comparisons of protein expression variation across different tissues, mouse models (including disease models), and developmental timepoints19. By combining a fluorescent TPS with the use of an internal loading standard, we were able to overcome existing limitations in the number of samples and experimental conditions that can be compared within a single experiment. This approach expands the use of traditional Western blot techniques, thereby allowing researchers to better explore protein expression across different tissues and samples.

<table>
	<tbody>
		<tr>
			<td>Fine Tipped Gel Loading Tips</td>
			<td>Alpha Laboratories</td>
			<td>GL20057SNTL</td>
			<td></td>
		</tr>
		<tr>
			<td>Halt Protease Inhibitor Cocktail, EDTA-free 100x 5mL</td>
			<td>ThermoFisher Scientific</td>
			<td>78437</td>
			<td></td>
		</tr>
		<tr>
			<td>Handheld homogeniser&#160;</td>
			<td>VWR Collection</td>
			<td>431-0100</td>
			<td></td>
		</tr>
		<tr>
			<td>iBlot 2 Gel Transfer Device</td>
			<td>ThermoFisher Scientific</td>
			<td>IB21001</td>
			<td></td>
		</tr>
		<tr>
			<td>iBlot Transfer Stack, PVDF, regular size</td>
			<td>ThermoFisher Scientific</td>
			<td>IB401031</td>
			<td></td>
		</tr>
		<tr>
			<td>Image Studio Lite</td>
			<td>Licor</td>
			<td>N/A</td>
			<td>Free download from https://www.licor.com/bio/products/software/image_studio_lite/</td>
		</tr>
		<tr>
			<td>IRDye 800CW secondary antibodies</td>
			<td>Licor</td>
			<td>--</td>
			<td>Select appropriate secondary antibody that is specific against host of primary antibody.</td>
		</tr>
		<tr>
			<td>Micro BCA Protein Assay Kit</td>
			<td>ThermoFisher Scientific</td>
			<td>23235</td>
			<td></td>
		</tr>
		<tr>
			<td>Novex Sharp Pre-stained Protein Standard</td>
			<td>ThermoFisher Scientific</td>
			<td>LC5800</td>
			<td></td>
		</tr>
		<tr>
			<td>NuPAGE 4-12% Bis-Tris Protein Gels, 1.0 mm, 15-well</td>
			<td>ThermoFisher Scientific</td>
			<td>NP0323BOX</td>
			<td></td>
		</tr>
		<tr>
			<td>NuPAGE LDS Sample Buffer (4X)</td>
			<td>ThermoFisher Scientific</td>
			<td>NP0007</td>
			<td></td>
		</tr>
		<tr>
			<td>NuPAGE MOPS SDS Running Buffer (20X)</td>
			<td>ThermoFisher Scientific</td>
			<td>NP0001</td>
			<td></td>
		</tr>
		<tr>
			<td>Odyssey Blocking Buffer</td>
			<td>Licor</td>
			<td>927-40000</td>
			<td></td>
		</tr>
		<tr>
			<td>Purified Mouse anti-SMN (survival motor neuron) monoclonal antibody</td>
			<td>BD Transduction Laboratories</td>
			<td>610646</td>
			<td>Is used extensively in the SMN/SMA literature and gives consistent results regardsless of lot number</td>
		</tr>
		<tr>
			<td>REVERT Total Protein Stain, 250 mL&#160;</td>
			<td>Licor</td>
			<td>926-11021&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>REVERT Wash Solution&#160;</td>
			<td>Licor</td>
			<td>926-11012&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>RIPA Lysis and Extraction Buffer</td>
			<td>ThermoFisher Scientific</td>
			<td>89900</td>
			<td></td>
		</tr>
		<tr>
			<td>XCell&#160;SureLock Mini-Cell</td>
			<td>ThermoFisher Scientific</td>
			<td>EI0001</td>
			<td></td>
		</tr>
	</tbody>
</table>

robust comparison of protein levels across tissues and throughout development using standardized quantitative western blotting

Western blotting is a technique that is commonly used to detect and quantify protein expression. Over the years, this technique has led to many advances in both basic and clinical research. However, as with many similar experimental techniques, the outcome of Western blot analyses is easily influenced by choices made in the design and execution of the experiment. Specific housekeeping proteins have traditionally been used to normalize protein levels for quantification, however, these have a number of limitations and have therefore been increasingly criticized over the past few years. Here, we describe a detailed protocol that we have developed to allow us to undertake complex comparisons of protein expression variation across different tissues, mouse models (including disease models), and developmental timepoints. By using a fluorescent total protein stain and introducing the use of an internal loading standard, it is possible to overcome existing limitations in the number of samples that can be compared within experiments and systematically compare protein levels across a range of experimental conditions. This approach expands the use of traditional western blot techniques, thereby allowing researchers to better explore protein expression across different tissues and samples.

We include examples of the use of TPS and an internal standard to facilitate comparisons of protein levels across tissues and time points. Figure 1 shows results from Western blotting on protein extracted from tissues obtained from neonatal (postnatal day 5) in comparison to adult mice (10-week old). TPS and Smn immunoblot are shown in Figure 1A, C. Quantification of fluorescence intensity of the TPS was achieved...

Watch this Scientific Journal Video about Robust Comparison of Protein Levels Across Tissues and Throughout Development Using Standardized Quantitative Western Blotting at JoVE.com

Robust Comparison of Protein Levels Across Tissues and Throughout Development Using Standardized Quantitative Western Blotting

This method describes a robust and reproducible approach for the comparison of protein levels in different tissues and at different developmental timepoints using a standardized quantitative western blotting approach.

Western blotting is a technique that is commonly used to detect and quantify protein expression. Over the years, this technique has led to many advances ...

This protocol can be used to address important questions in fundamental and clinical research by looking at protein expression across different tissues and time points. To perform reliable quantitative Western blotting, we combine a fluorescent total protein stain with an internal loading control. This overcomes limitations that arise when comparing various tissues across experimental conditions.To extract proteins from snap-frozen cell or tissue samples, thaw the minus-80-degree samples on ice before washing the samples as appropriate, according to the table. Using a handheld electric homogenizer with a polypropylene pestle, homogenize the washed samples, rinsing the pestle in double-distilled water and drying with a clean tissue between samples. Leave the samples on ice for 10 minutes, followed by centrifugation.Then, transfer the protein-sample-containing supernatant to a new tube on ice without disturbing the pellet. For quantification of the protein concentration, set up bovine serum albumin standards at increasing concentrations in triplicate, and add one microliter of each protein sample in duplicate to the appropriate wells of a 96-well optical plate. Incubate the protein on a 60-degree-Celsius heat block for 10 minutes or longer if the protein concentration is expected to be low and measure the absorption at 560 nanometers on a plate reader.Export the plate reader measurements and calculate the protein concentration by comparing the average absorbance values of each sample to a standard curve obtained using the protein standard. To normalize the amount of protein, prepare dilutions of the protein samples in sample buffer and ultra-pure water and incubate the samples in a 70-degree-Celsius heat block for 10 minutes. Then, place the samples on ice before vortexing and briefly centrifuging.For electrophoresis, set up a precast four to 12%Bis-Tris gradient gel in the gel electrophoresis chamber system and load 3.5 microliters of a protein standard into the well. When using an internal standard for between-membrane normalization, load an amount that is equal to the other samples into the first three wells next to the protein ladder and load 30 micrograms of each sample into the remaining wells. Then, run the samples through the stacking gel at 80 volts for 10 minutes followed by 150 volts for an additional 45 to 60 minutes.At the end of the electrophoresis, to assemble the transfer stack, place the protein gel onto the bottom stack containing the polyvinylidene difluoride membrane followed by the filter paper. Use the blotting roller to remove any air bubbles and place the top stack on the top of the filter paper before rolling the stack again to remove air bubbles. Transfer the whole stack into the transfer device with the electrode on the left side of the device and place the gel sponge on top of the stack so that the sponge is aligned with the corresponding electrical contacts on the device.After closing the lid, select and start the appropriate program. At the end of the program, cut the membrane to the gel size and wash the cut membrane quickly with double-distilled water before continuing with the total protein stain. For total protein staining, roll the membrane into a 50-milliliter tube with the protein side facing inwards and label the membrane with five milliliters of protein stain solution on a roller for five minutes at room temperature in a fume hood.At the end of the incubation, wash the membrane quickly with five milliliters of wash solution, returning the tube briefly to the roller between washes, followed by a brief rinse with ultra-pure water. Add three milliliters of blocking buffer to the membrane and return the membrane to the roller for 30 minutes at room temperature. Replace the blocking buffer with the primary antibody of interest at the appropriate optimized concentration and incubate the membrane on the roller overnight at four degrees Celsius.The next day, wash the membrane six times for five minutes with five milliliters of fresh PBS per wash on the roller at room temperature. After the last wash, incubate the membrane with the appropriate secondary antibody solution on the roller for one hour at room temperature followed by three washes for 30 minutes per wash. After the last wash, dry the membrane and use aluminum foil to keep the membrane protected from light.For image acquisition, place the membrane on the scanner with the protein side facing down and select the scanning area in the software. Then, acquire images in both channels and export the images to an appropriate image analysis program. Display the 700-nanometer channel to show the total protein staining result and Select Analysis and Draw Rectangle to define the area of interest for normalization.Then, copy and paste the first rectangle area onto each individual sample to ensure the defined region is the same size for all of the analyzed lanes. To quantify the protein concentration in each lane, copy the results from both the total protein stain and the protein of interest to a spreadsheet program and determine the highest total protein stain signal. Then, divide each total protein stain signal value by this value to obtain the normalized protein loading value and divide the 800-nanometer signal value from each individual sample by its corresponding normalized protein value to calculate the relative protein expression ratio in different samples.In these representative Western blots, proteins extracted from tissues obtained from post-natal day five mice are compared to proteins extracted from 10-week-old adult mice. Quantification of the fluorescence intensity of the total protein stain was achieved by measuring the fluorescence intensity inside the rectangle box on each lane. When whole lanes are analyzed, the fluorescence intensity remains relatively similar across samples, indicating that using the total protein stain for normalization is suitable for this purpose.The fluorescent total protein stain can also be used to compare protein levels at different developmental time points. For example, although survival motor neuron protein levels clearly decrease with age in mice, the total protein stained quantification remains constant. The use of internal standards, fluorescence-based normalization, and adequate statistics increases the robustness of complex protein expression analysis across different conditions.This protocol adds to traditional Western blot techniques, overcoming the issues of appropriate loading controls and comparisons across experimental batches, and providing flexibilities for protein expression analysis. This approach can be extended to comparing protein expression under other experimental conditions.

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Biochemistry

13.9K vistas.  University of Edinburgh. Este protocolo se puede utilizar para abordar cuestiones importantes en la investigación fundamental y clínica mirando la expresión de proteínas a través de diferentes tejidos y puntos de tiempo. Para realizar una hinchazón occidental cuantitativa fiable, combinamos una mancha de proteína total fluorescente con un control de carga interno. Esto supera las limitaciones que surgen al comparar varios tejidos a través de condiciones experimentales.Para extraer proteínas de muestra...