Name: quantitative immunoblotting of cell lines as a standard to validate immunofluorescence for quantifying biomarker proteins in routine tissue samples
Uploaded: 2019-01-07T14:00:00
Description: Watch this Scientific Journal Video about Quantitative Immunoblotting of Cell Lines as a Standard to Validate Immunofluorescence for Quantifying Biomarker Proteins in Routine Tissue Samples at JoVE.co

This work was partially funded by the Fredrick Banting and Charles Best Canada Graduate Scholarship (A.M.).

Approval to use primary human tissue samples was obtained from the Health Sciences and Affiliated Teaching Hospitals Research Ethics Board (HSREB) at Queen&#39;s University.
1. Building a Cell-line Tissue Microarray (TMA)
<ol>
	<li>Harvest and wash cells. 
	NOTE: This protocol has been tested on various established immortalized cell lines (e.g. HeLa, Jurkat, RCH-ACV).
	<ol>
		<li>For adherent cells, harvest approximately 1.3 x 107 cells once they reach approximately ...

<ol>
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We have described a method that makes use of quantitative immunoblotting (IB) to demonstrate the utility of immunofluorescence (IF) for ascertaining the relative abundance of a target protein in FFPE tissue samples. Current protein quantification methods are limited by their categorical nature, such as chromogenic IHC2,3, or by the need to homogenize samples, preventing investigation into the sample structure and cell populations, such as with IB and mass spectro...

The need to quantify proteins in formalin-fixed, paraffin-embedded (FFPE) tissue biopsy samples exists in many clinical fields. For example, quantification of biomarker proteins in routine biopsy specimens is used to elucidate prognosis and inform treatment for cancer patients1. However, current methods are typically subjective and lack validation.
Immunohistochemistry (IHC) is used routinely in pathology laboratories and generally depends on a primary antibody directed at the target protein and a secondary antibody conjugated with an enzymatic label such as horseradish peroxidase2. Conventional IHC is sensitive, can make use of minute samples and preserves the morphological integrity of tissue samples thereby permitting assessment of protein expression within its relevant histological context. However, because the chromogenic signal generated by IHC is subtractive, it suffers from a relatively narrow dynamic range and offers limited potential for multiplexing2,3,4. Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) preserves morphological integrity. However, this developing technology is associated with modest morphological resolution and requires significant calibration and normalization, impairing its feasibility for routine clinical use5,6,7. Alternative techniques to quantify protein in tissue samples include immunoblotting8, mass spectrometry9,10,11, and enzyme-linked immunosorbent assay (ELISA)12, each of which begins with a homogenized lysate of sample tissue. Primary tissue samples are heterogeneous in that they contain a multitude of cell types. Therefore, techniques that entail homogenizing the samples do not permit quantification of a protein in a particular cell population of interest such as cancer cells.
Like IHC, IF is applicable to small FFPE samples and permits the retention of histological integrity13. However, thanks to the additive nature of fluorescence signals, IF is amenable to the application of multiple primary antibodies and fluorescent labels. Thus, a protein of interest may be relatively quantified within specific cells or cellular compartments (for example, nucleus versus cytoplasm) defined using other antibodies. Fluorescence signals also have the advantage of a greater dynamic range13,14. The superiority, reproducibility, and multiplexing potential of IF applied to FFPE samples has been demonstrated13,14,15.
Herein we describe the use of quantitative immunoblotting using established cell lines as a gold standard to ascertain the quantitative nature of IF coupled with computer-assisted image analysis in determining the relative abundance of a protein of interest in histological sections from FFPE tissue samples. We have applied this method successfully in a multiplex approach to quantify biomarker proteins in clinical biopsy samples16,17,18.

<table border="0" cellpadding="0" cellspacing="0" style="width:675px;" width="673">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:223px;">697</td>
			<td style="width:116px;">DSMZ</td>
			<td style="width:123px;">ACC 42</td>
			<td style="width:213px;">Cell line</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:223px;">JeKo-1</td>
			<td style="width:116px;">ATCC</td>
			<td style="width:123px;">CRL-3006</td>
			<td>Cell line</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:223px;">Jurkat</td>
			<td style="width:116px;">ATCC</td>
			<td style="width:123px;">TIB-152</td>
			<td>Cell line</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:223px;">RCH-ACV</td>
			<td style="width:116px;">DSMZ</td>
			<td style="width:123px;">ACC 548</td>
			<td>Cell line</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:223px;">Granta-519</td>
			<td style="width:116px;">DSMZ</td>
			<td style="width:123px;">ACC 342</td>
			<td>Cell line</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:223px;">REH</td>
			<td style="width:116px;">DSMZ</td>
			<td style="width:123px;">ACC 22</td>
			<td>Cell line</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:223px;">Raji</td>
			<td style="width:116px;">ATCC</td>
			<td style="width:123px;">CCL-86</td>
			<td>Cell line</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:223px;">HeLa</td>
			<td style="width:116px;">ATCC</td>
			<td style="width:123px;">CCL-2</td>
			<td>Cell line</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:223px;">Trypsin/EDTA solution</td>
			<td style="width:116px;">Invitrogen</td>
			<td style="width:123px;">R001100</td>
			<td>For detaching adhesive cells</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:223px;">Fetal bovine serum (FBS)</td>
			<td style="width:116px;">Wisent Inc.</td>
			<td style="width:123px;">81150</td>
			<td>To neutralize trypsin</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:223px;">Neutral Buffered Formalin</td>
			<td style="width:116px;">Protocol</td>
			<td style="width:123px;">245-684</td>
			<td>For fixing cell pellets</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:223px;">UltraPure low melting point agarose</td>
			<td style="width:116px;">Invitrogen</td>
			<td style="width:123px;">15517-022</td>
			<td>For casting cell pellets</td>
		</tr>
		<tr height="62">
			<td height="62" style="height:62px;width:223px;">Mouse monoclonal anti-human Bcl-2 antibody, clone 124</td>
			<td style="width:116px;">Dako (Agilent)</td>
			<td style="width:123px;">cat#: M088729-2, RRID: 2064429</td>
			<td style="width:213px;">To detect Bcl-2 by immunoflourencence and immunoblot (lot#:&#160;00095786</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:223px;">Ventana Discovery XT</td>
			<td style="width:116px;">Roche</td>
			<td style="width:123px;">-</td>
			<td style="width:213px;">For automation of immunofluorescence staining</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:223px;">EnVision+ System- HRP labelled polymer (anti-mouse)</td>
			<td style="width:116px;">Dako (Agilent)</td>
			<td style="width:123px;">K4000</td>
			<td style="width:213px;">For immunofluorescence signal amplification</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:223px;">EnVision+ System- HRP labelled polymer (anti-rabbit)</td>
			<td style="width:116px;">Dako (Agilent)</td>
			<td style="width:123px;">K4002</td>
			<td style="width:213px;">For immunofluorescence signal amplification</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:223px;">Cyanine 5 tyramide reagent</td>
			<td style="width:116px;">Perkin Elmer</td>
			<td style="width:123px;">NEL745001KT</td>
			<td style="width:213px;">For immunofluorescence signal amplification</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:223px;">Aperio ImageScope</td>
			<td style="width:116px;">Leica Biosystems</td>
			<td style="width:123px;">-</td>
			<td style="width:213px;">To view scanned slides</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:223px;">HALO image analysis software</td>
			<td style="width:116px;">Indica Labs</td>
			<td style="width:123px;">-</td>
			<td style="width:213px;">For quantification of immunofluorescence</td>
		</tr>
		<tr height="62">
			<td height="62" style="height:62px;width:223px;">Protease inhibitors (Halt protease inhibitor cocktail, 100X)</td>
			<td style="width:116px;">Thermo Scientific</td>
			<td style="width:123px;">1862209</td>
			<td>To add to RIPA buffer</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:223px;">Ethylenediaminetetraacetic acid (EDTA)</td>
			<td style="width:116px;">BioShop</td>
			<td style="width:123px;">EDT001</td>
			<td>For RIPA buffer</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:223px;">NP-40</td>
			<td style="width:116px;">BDH Limited</td>
			<td style="width:123px;">56009</td>
			<td>For RIPA buffer</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:223px;">Sodium deoxycholate</td>
			<td style="width:116px;">Sigma-Aldrich</td>
			<td style="width:123px;">D6750</td>
			<td>For RIPA buffer</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:223px;">Glycerol</td>
			<td style="width:116px;">FisherBiotech</td>
			<td style="width:123px;">BP229</td>
			<td>For Laemlli buffer</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:223px;">Bromophenol blue</td>
			<td style="width:116px;">BioShop</td>
			<td style="width:123px;">BRO777</td>
			<td>For Laemlli buffer</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:223px;">Dithiothreitol (DTT)</td>
			<td style="width:116px;">Bio-Rad</td>
			<td style="width:123px;">161-0611</td>
			<td>For Laemlli buffer</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:223px;">Bovine serum albumin (BSA)</td>
			<td style="width:116px;">BioShop</td>
			<td style="width:123px;">ALB001</td>
			<td>For immunoblot washes</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:223px;">Protein ladder (Precision Plus Protein Dual Color Standards)</td>
			<td style="width:116px;">Bio-Rad</td>
			<td style="width:123px;">161-0374</td>
			<td>For running protein gel</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:223px;">Filter paper (Extra thick blot paper)</td>
			<td style="width:116px;">Bio-Rad</td>
			<td style="width:123px;">1703969</td>
			<td>For blotting transfer</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:223px;">Nitrocellulose membrane</td>
			<td style="width:116px;">Bio-Rad</td>
			<td style="width:123px;">162-0115</td>
			<td>For blotting transfer</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:223px;">Trans-blot SD semi-dry transfer cell</td>
			<td style="width:116px;">Bio-Rad</td>
			<td>1703940</td>
			<td>For semi-dry transfer</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:223px;">Skim milk powder (Nonfat dry milk)</td>
			<td style="width:116px;">Cell Signaling Technology</td>
			<td style="width:123px;">9999S</td>
			<td>For blocking buffer</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:223px;">Tween 20</td>
			<td style="width:116px;">BioShop</td>
			<td style="width:123px;">TWN510</td>
			<td>For wash buffer</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:223px;">GAPDH rabbit monoclonal antibody</td>
			<td style="width:116px;">Epitomics</td>
			<td style="width:123px;">2251-1</td>
			<td style="width:213px;">Primary antibody of control protein (lot#: YE101901C)</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:223px;">Goat anti-mouse IgG (HRP conjugated) antibody</td>
			<td style="width:116px;">abcam</td>
			<td style="width:123px;">cat#: ab6789, RRID: AB_955439</td>
			<td style="width:213px;">Secondary antibody for immunoblot</td>
		</tr>
		<tr height="62">
			<td height="62" style="height:62px;width:223px;">Goat anti-rabbit IgG (HRP conjugated) antibody</td>
			<td style="width:116px;">abcam</td>
			<td style="width:123px;">cat#: ab6721, RRID: AB_955447</td>
			<td style="width:213px;">Secondary antibody for immunoblot (lot#: GR3192725-5)</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:223px;">Clarity Western ECL substrates</td>
			<td style="width:116px;">Bio-Rad</td>
			<td style="width:123px;">1705060</td>
			<td style="width:213px;">For immunoblot signal detection</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:223px;">Amersham Imager 600</td>
			<td style="width:116px;">GE Healthcare Life Sciences</td>
			<td style="width:123px;">29083461</td>
			<td>For immunoblot signal detection</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:223px;">ImageJ software</td>
			<td style="width:116px;">Freeware, NIH</td>
			<td style="width:123px;">-</td>
			<td>For densitometry analysis</td>
		</tr>
	</tbody>
</table>

quantitative immunoblotting of cell lines as a standard to validate immunofluorescence for quantifying biomarker proteins in routine tissue samples

Quantification of proteins of interest in formalin-fixed, paraffin-embedded (FFPE) tissue samples is important in clinical and research applications. An optimal method of quantification is accurate, has a broad linear dynamic range and maintains the structural integrity of the sample to allow for identification of individual cell types. Current methods such as immunohistochemistry (IHC), mass spectrometry, and immunoblotting each fail to meet these stipulations due to their categorical nature or need to homogenize the sample. As an alternative method, we propose the use of immunofluorescence (IF) and image analysis to determine the relative abundance of a protein of interest in FFPE tissues. Herein we demonstrate that this method is easily optimized, yields a wide dynamic range, and is linearly quantifiable as compared to the gold standard of quantitative immunoblotting. Furthermore, this method permits the maintenance of the structural integrity of the sample and allows for the distinction of various cell types, which may be crucial in diagnostic applications. Overall, this is a robust method for the relative quantification of proteins in FFPE samples and can be easily adapted to suit clinical or research needs.

This protocol was used to confirm the ability of IF to determine the relative quantity of the anti-apoptotic protein Bcl-2 in cell lines made into FFPE tissue blocks. Quantifying Bcl-2 selectively in cancer cells can elucidate oncogenic mechanisms and can be useful in pathological diagnosis and in informing clinical management decisions24. More specifically, Bcl-2 plays a role in proper B-lymphocyte development and its expression is commonly investigated in the con...

Watch this Scientific Journal Video about Quantitative Immunoblotting of Cell Lines as a Standard to Validate Immunofluorescence for Quantifying Biomarker Proteins in Routine Tissue Samples at JoVE.co

Quantitative Immunoblotting of Cell Lines as a Standard to Validate Immunofluorescence for Quantifying Biomarker Proteins in Routine Tissue Samples

We describe the use of quantitative immunoblotting to validate immunofluorescence histology coupled with image analysis as a means of quantifying a protein of interest in formalin-fixed, paraffin-embedded (FFPE) tissue samples. Our results demonstrate the utility of immunofluorescence histology for ascertaining the relative quantity of biomarker proteins in routine biopsy samples.

Quantification of proteins of interest in formalin-fixed, paraffin-embedded (FFPE) tissue samples is important in clinical and research applications. An ...

This method can help answer key questions in the field of cancer pathology, by quantifying biomarker proteins from routinely processed biopsy material. The main advantages of this technique in relation to conventional immunohistochemistry, are that it is objective, has a wide dynamic range, and permits for the quantification of proteins in specific cell types. The presence or absence of certain so-called biomarker proteins, or more particularly, the relative abundance of those proteins in cancer biopsy specimens can be very useful in making a specific pathological diagnosis of specific kinds of cancers.But it can also be useful in predicting the response to cancer treatments, so that's why this technique is relevant both to the diagnosis and the treatment of patients with cancer. This protocol is mainly about how to use protein quantification in immortalized cell lines to validate the quantitative nature of immunofluorescence based assay. But it's important to note that immunofluorescence can easily be incorporated into a multiplexed approach, and applied to primary biopsy samples.Assisting and demonstrating this procedure will be Lee Boudreau, a technician, and Shakeel Virk, the director of operations. Both from the Queen's Laboratory for Molecular Pathology. To begin, centrifuge the previously harvested cells in a 50 milliliter conical tube at 225 Gs for five minutes.Decant the supernatant, and resuspend the cell pellet in 10 milliliters of PBS. Then, centrifuge the resuspended cells at 225 Gs for five minutes. Suspend the cell pellet with 10 milliliters of 10%NBF.Then incubate the cells at room temperature on a rocker at 24 RPMs overnight. After fixing the cells, centrifuge the cells at 225 Gs for five minutes. Then remove the supernatant and resuspend the cells in 500 microliters of PBS.Transfer the cells to a 1.5 milliliter microcentrifuge tube, and pellet the cells via centrifugation. Then, aspirate the supernatant. Add approximately 500 microliters of 1%agarose solution to each tube containing cells.Then, pipette the mixture up and down to mix. After the agarose cell solution hardens, add one milliliter of 10%NBF to the tubes. Later, remove the NBF from the samples.Use a razor blade to remove the cell plug, and place the plug into a plastic tissue cassette. Process samples overnight with an automated tissue processor. Then, embed the samples in paraffin wax, using standard histology methods.Using a tissue arrayer instrument, harvest duplicate 6 millimeter cores from the paraffin block, and insert them into an empty paraffin block. After this, use a microtome to prepare two histological sections of the newly created cell line, TMA. Then mount the sections on a histology slide, and deparaffinize them.First, load the two slides of the cell line TMA into an automated staining system. Stain one side with the optimal primary antibody dilution, leaving the other as a negative control slide. To both slides, apply a nuclear counterstain, and secondary antibody.After the staining process, add the tyramide signal amplification reagents. After this, scan the immunostained slides using the appropriate excitation and detection wavelengths for the fluorophores that were used. Use image analysis software to identify the cellular compartment of interest, whether nucleus or cytoplasm, and quantify the mean fluorescence intensity, or MFI, for each line.To determine which cell line has the greatest abundance of the target protein, aliquot preciously prepared cell lysate into microcentrifuge tubes. Then add 2.5 microliters of 6x laemly buffer, and enough RIPA lysis buffer to bring the total volume to 15 microliters. Next, load an SDS page gel, with a protein ladder, and the previously prepared samples.After this, load laemly buffer into the empty wells. Run the gel until the blue dye reaches the bottom of the plate. After performing a semi-dry protein transfer, use a razor blade to cut the membrane horizontally to separate the protein of interest from the control protein.Perform blocking and antibody incubations according to the manufacturers instructions. Then place the membrane strips in a clear plastic bag. Use a P1000 pipette to cover the membranes with ECL mixture.Then seal the bag, and incubate the membranes at room temperature in the dark for one to two minutes. Next, place the plastic bag containing the membranes in a digital imaging platform. Use chemiluminescence and colorimetric marker detection to capture various exposures of the membrane.Using image analysis software, or visual observation, determine which cell line expresses the most target protein. After immunoblotting a serial dilution of this cell line, open the exposure images using image analysis software. Use the rectangular selections tool to select the first lane of the gel.Then go to analyze, gels, and select first lane. Repeat this process by moving the rectangular selections tool over to the next lane, and go to analyze, gels, and select next lane. Next, go to analyze, gels, and plot lanes.Use the straight line tool to draw lines across the bases of each peak, to remove the background noise. Then use the wand tool to select each peak, and obtain the band intensity of each peak from the results window. Create a scatterplot of band intensity versus the amount of total protein loaded for each primary antibody using the densitometry output.Then, use a line of best fit and visual observation to determine the location of the linear dynamic range of each antibody. Select a protein concentration that yields a band intensity within the linear range, and perform an immunoblot of all cell line lysates with that protein concentration, as demonstrated previously. Next, perform densitometry on the digital scans, selecting exposures that yield signals within the previously identified linear ranges for each antibody.After this, calculate the ratio of target protein band intensity to loading control band intensity for each cell line. Finally, use statistical software to perform a Pearson correlation test between the values obtained from image analysis of the IF staining, and those obtained from immunoblotting. This protocol was used to confirm the ability of IF to determine the relative quantity of the anti-apoptotic protein Bcl-2.Varying dilutions of the primary antibody were tested on human tonsil tissue with an immunohistology stainer. For this experiment, a one to 50 dilution was determined to be the optimal dilution that yielded a strong signal with little background noise. This dilution was used to stain the cell line TMA by immunofluorescence, and image analysis was used to quantify the cytoplasmic Cy5 signal attributed to Bcl-2.Based upon the immunoblot for all the tested cell lines, Granta-519 had the greatest abundance of Bcl-2. An immunoblot of the serial dilution of Granta-519 lysate was then used to find the linear dynamic range of Bcl-2, and control protein GAPDH. The dynamic range for Bcl-2 in this assay ranged from a band intensity of nearly 0, to 7500 units.The dynamic range for GAPDH ranged from 3000 to 6500 units. The immunoblot was repeated with exposures within that linear range. And the ratio of Bcl-2 to GAPDH was calculated for each cell line.A Pearson correlation test demonstrated that the intensity ratios from immunoblotting were strongly and positively correlated with the intensity readings from quantitative IF.While attempting this procedure, it's important to remember to expose the final membrane for multiple time points, In order to find the optimal exposure where all of the bands are within their respective linear ranges. After validating the quantitative nature of the IF protocol, it can be modified for multiplex IF, in routinely processed tissue samples in order to answer clinical questions such as where a target protein is expressed.

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Research

JoVE Journal

Biology

Actin Co-Sedimentation Assay; for the Analysis of Protein Binding to F-Actin

The actin cytoskeleton within the cell is a network of actin filaments that allows the movement of cells and cellular processes, and that generates tension and helps maintains cellular shape.  Although the actin cytoskeleton is a rigid structure, it is a dynamic structure that is constantly remodeling.  A number of proteins can bind to the actin cytoskeleton.  The binding of a particular protein to F-actin is often desired to support cell biological observations or to further understand dynamic processes due to remodeling of the actin cytoskeleton. The actin co-sedimentation assay is an in vitro assay routinely used to analyze the binding of specific proteins or protein domains with F-actin.  The basic principles of the assay involve an incubation of the protein of interest (full length or domain of) with F-actin, ultracentrifugation step to pellet F-actin and analysis of the protein co-sedimenting with F-actin.  Actin co-sedimentation assays can be designed accordingly to measure actin binding affinities and in competition assays.

Proteins bind to filamentous actin (F-actin) through distinct actin binding modules. In this video we demonstrate the procedure of actin co-sedimentation, which is an in vitro assay routinely used to analyze proteins or specific domains that bind F-actin.

The actin cytoskeleton within the cell is a network of actin filaments that allows the movement of cells and cellular processes, and that generates ...

Quantitative Comparison of cis-Regulatory Element (CRE) Activities in Transgenic Drosophila melanogaster

Gene expression patterns are specified by cis-regulatory element (CRE) sequences, which are also called enhancers or cis-regulatory modules. A typical CRE possesses an arrangement of binding sites for several transcription factor proteins that confer a regulatory logic specifying when, where, and at what level the regulated gene(s) is expressed. The full set of CREs within an animal genome encodes the organism&prime;s program for development1, and empirical as well as theoretical studies indicate that mutations in CREs played a prominent role in morphological evolution2-4. Moreover, human genome wide association studies indicate that genetic variation in CREs contribute substantially to phenotypic variation5,6. Thus, understanding regulatory logic and how mutations affect such logic is a central goal of genetics. 
Reporter transgenes provide a powerful method to study the in vivo function of CREs. Here a known or suspected CRE sequence is coupled to heterologous promoter and coding sequences for a reporter gene encoding an easily observable protein product. When a reporter transgene is inserted into a host organism, the CRE&prime;s activity becomes visible in the form of the encoded reporter protein. P-element mediated transgenesis in the fruit fly species Drosophila (D.) melanogaster7 has been used for decades to introduce reporter transgenes into this model organism, though the genomic placement of transgenes is random. Hence, reporter gene activity is strongly influenced by the local chromatin and gene environment, limiting CRE comparisons to being qualitative. In recent years, the phiC31 based integration system was adapted for use in D. melanogaster to insert transgenes into specific genome landing sites8-10. This capability has made the quantitative measurement of gene and, relevant here, CRE activity11-13 feasible. The production of transgenic fruit flies can be outsourced, including phiC31-based integration, eliminating the need to purchase expensive equipment and/or have proficiency at specialized transgene injection protocols. 
Here, we present a general protocol to quantitatively evaluate a CRE&prime;s activity, and show how this approach can be used to measure the effects of an introduced mutation on a CRE&prime;s activity and to compare the activities of orthologous CREs. Although the examples given are for a CRE active during fruit fly metamorphosis, the approach can be applied to other developmental stages, fruit fly species, or model organisms. Ultimately, a more widespread use of this approach to study CREs should advance an understanding of regulatory logic and how logic can vary and evolve.

Quantitative Comparison of cis-Regulatory Element CRE Activities in Transgenic Drosophila melanogaster

Phenotypic variation for traits can result from mutations in cis-regulatory element (CRE) sequences that control gene expression patterns. Methods derived for use in Drosophila melanogaster can quantitatively compare the levels of spatial and temporal patterns of gene expression mediated by modified or naturally occurring CRE variants.

Gene expression patterns are specified by cis-regulatory element (CRE) sequences, which are also called enhancers or cis-regulatory modules. A typical CRE ...

A Quantitative Fitness Analysis Workflow

Quantitative Fitness Analysis (QFA) is an experimental and computational workflow for comparing fitnesses of microbial cultures grown in parallel1,2,3,4. QFA can be applied to focused observations of single cultures but is most useful for genome-wide genetic interaction or drug screens investigating up to thousands of independent cultures. The central experimental method is the inoculation of independent, dilute liquid microbial cultures onto solid agar plates which are incubated and regularly photographed. Photographs from each time-point are analyzed, producing quantitative cell density estimates, which are used to construct growth curves, allowing quantitative fitness measures to be derived. Culture fitnesses can be compared to quantify and rank genetic interaction strengths or drug sensitivities. The effect on culture fitness of any treatments added into substrate agar (e.g. small molecules, antibiotics or nutrients) or applied to plates externally (e.g. UV irradiation, temperature) can be quantified by QFA.
The QFA workflow produces growth rate estimates analogous to those obtained by spectrophotometric measurement of parallel liquid cultures in 96-well or 200-well plate readers. Importantly, QFA has significantly higher throughput compared with such methods. QFA cultures grow on a solid agar surface and are therefore well aerated during growth without the need for stirring or shaking.
QFA throughput is not as high as that of some Synthetic Genetic Array (SGA) screening methods5,6. However, since QFA cultures are heavily diluted before being inoculated onto agar, QFA can capture more complete growth curves, including exponential and saturation phases3. For example, growth curve observations allow culture doubling times to be estimated directly with high precision, as discussed previously1.
Here we present a specific QFA protocol applied to thousands of S. cerevisiae cultures which are automatically handled by robots during inoculation, incubation and imaging. Any of these automated steps can be replaced by an equivalent, manual procedure, with an associated reduction in throughput, and we also present a lower throughput manual protocol. The same QFA software tools can be applied to images captured in either workflow.
We have extensive experience applying QFA to cultures of the budding yeast S. cerevisiae but we expect that QFA will prove equally useful for examining cultures of the fission yeast S. pombe and bacterial cultures.

Quantitative Fitness Analysis (QFA) is a complementary series of experimental and computational methods for estimating microbial culture fitnesses. QFA estimates the effect of genetic mutations, drugs or other applied treatments on microbe growth. Experiments scaling from focussed analysis of single cultures to thousands of parallel cultures can be designed.

Quantitative Fitness Analysis (QFA) is an experimental and computational workflow for comparing fitnesses of microbial cultures grown in parallel1,2,3,4. ...

Using SecM Arrest Sequence as a Tool to Isolate Ribosome Bound Polypeptides

Extensive research has provided ample evidences suggesting that protein folding in the cell is a co-translational process1-5. However, the exact pathway that polypeptide chain follows during co-translational folding to achieve its functional form is still an enigma. In order to understand this process and to determine the exact conformation of the co-translational folding intermediates, it is essential to develop techniques that allow the isolation of RNCs carrying nascent chains of predetermined sizes to allow their further structural analysis.
SecM (secretion monitor) is a 170 amino acid E. coli protein that regulates expression of the downstream SecA (secretion driving) ATPase in the secM-secA operon6. Nakatogawa and Ito originally found that a 17 amino acid long sequence (150-FSTPVWISQAQGIRAGP-166) in the C-terminal region of the SecM protein is sufficient and necessary to cause stalling of SecM elongation at Gly165, thereby producing peptidyl-glycyl-tRNA stably bound to the ribosomal P-site7-9. More importantly, it was found that this 17 amino acid long sequence can be fused to the C-terminus of virtually any full-length and/or truncated protein thus allowing the production of RNCs carrying nascent chains of predetermined sizes7. Thus, when fused or inserted into the target protein, SecM stalling sequence produces arrest of the polypeptide chain elongation and generates stable RNCs both in vivo in E. coli cells and in vitro in a cell-free system. Sucrose gradient centrifugation is further utilized to isolate RNCs.
The isolated RNCs can be used to analyze structural and functional features of the co-translational folding intermediates. Recently, this technique has been successfully used to gain insights into the structure of several ribosome bound nascent chains10,11. Here we describe the isolation of bovine Gamma-B Crystallin RNCs fused to SecM and generated in an in vitro translation system.

We describe here a technique that is now routinely used to isolate stably bound ribosome nascent chain complexes (RNCs). This technique takes advantage of the discovery that a 17 amino acid long SecM "arrest sequence" can halt translation elongation in a prokaryotic (E. coli) system, when inserted into (or fused to the C-terminus) of virtually any protein.

Extensive research has provided ample evidences suggesting that protein folding in the cell is a co-translational process1-5. However, the exact pathway ...

Quantitative Immunofluorescence Assay to Measure the Variation in Protein Levels at Centrosomes

Centrosomes are small but important organelles that serve as the poles of mitotic spindle to maintain genomic integrity or assemble primary cilia to facilitate sensory functions in cells. The level of a protein may be regulated differently at centrosomes than at other .cellular locations, and the variation in the centrosomal level of several proteins at different points of the cell cycle appears to be crucial for the proper regulation of centriole assembly. We developed a quantitative fluorescence microscopy assay that measures relative changes in the level of a protein at centrosomes in fixed cells from different samples, such as at different phases of the cell cycle or after treatment with various reagents. The principle of this assay lies in measuring the background corrected fluorescent intensity corresponding to a protein at a small region, and normalize that measurement against the same for another protein that does not vary under the chosen experimental condition. Utilizing this assay in combination with BrdU pulse and chase strategy to study unperturbed cell cycles, we have quantitatively validated our recent observation that the centrosomal pool of VDAC3 is regulated at centrosomes during the cell cycle, likely by proteasome-mediated degradation specifically at centrosomes.

Here, a novel quantitative fluorescence assay is developed to measure changes in the level of a protein specifically at centrosomes by normalizing that protein&#8217;s fluorescence intensity to that of an appropriate internal standard.

Centrosomes are small but important organelles that serve as the poles of mitotic spindle to maintain genomic integrity or assemble primary cilia to ...

Method for Measuring the Activity of Deubiquitinating Enzymes in Cell Lines and Tissue Samples

The ubiquitin-proteasome system has recently been implicated in various pathologies including neurodegenerative diseases and cancer. In light of this, techniques for studying the regulatory mechanism of this system are essential to elucidating the cellular and molecular processes of the aforementioned diseases. The use of hemagglutinin derived ubiquitin probes outlined in this paper serves as a valuable tool for the study of this system. This paper details a method that enables the user to perform assays that give a direct visualization of deubiquitinating enzyme activity. Deubiquitinating enzymes control proteasomal degradation and share functional homology at their active sites, which allows the user to investigate the activity of multiple enzymes in one assay. Lysates are obtained through gentle mechanical cell disruption and incubated with active site directed probes. Functional enzymes are tagged with the probes while inactive enzymes remain unbound. By running this assay, the user obtains information on both the activity and potential expression of multiple deubiquitinating enzymes in a fast and easy manner. The current method is significantly more efficient than using individual antibodies for the predicted one hundred deubiquitinating enzymes in the human cell.

The current protocol details a method for measuring the activity of functionally homologous deubiquitinating enzymes. Specialized probes covalently modify the enzyme and allow for detection. This method holds the potential to identify new therapeutic targets.

The ubiquitin-proteasome system has recently been implicated in various pathologies including neurodegenerative diseases and cancer. In light of this, ...

Employing Digital Droplet PCR to Detect BRAF V600E Mutations in Formalin-fixed Paraffin-embedded Reference Standard Cell Lines

ddPCR is a highly sensitive PCR method that utilizes a water-oil emulsion system. Using a droplet generator, an extracted nucleic acid sample is partitioned into ~20,000 nano-sized, water-in-oil droplets, and PCR amplification occurs in individual droplets. The ddPCR approach is in identifying sequence mutations, copy number alterations, and select structural rearrangements involving targeted genes. Here, we demonstrate the use of ddPCR as a powerful technique for precisely quantitating rare BRAF V600E mutations in FFPE reference standard cell lines, which is helpful in identifying individuals with cancer. In conclusion, ddPCR technique offers the potential to precisely profile the specific rare mutations in different genes in various types of FFPE samples.

The goal of this video is to demonstrate how to perform&#160;automated DNA extraction from formalin-fixed paraffin-embedded (FFPE) reference standard cell lines and digital droplet PCR&#160;(ddPCR) analysis to detect rare mutations in a clinical setting. Detecting mutations in FFPE samples demonstrates the clinical utility of ddPCR in FFPE samples.

ddPCR is a highly sensitive PCR method that utilizes a water-oil emulsion system. Using a droplet generator, an extracted nucleic acid sample is ...

Immunofluorescence Analysis of Endogenous and Exogenous Centromere-kinetochore Proteins

"Centromeres" and "kinetochores" refer to the site where chromosomes associate with the spindle during cell division. Direct visualization of centromere-kinetochore proteins during the cell cycle remains a fundamental tool in investigating the mechanism(s) of these proteins. Advanced imaging methods in fluorescence microscopy provide remarkable resolution of centromere-kinetochore components and allow direct observation of specific molecular components of the centromeres and kinetochores. In addition, methods of indirect immunofluorescent (IIF) staining using specific antibodies are crucial to these observations. However, despite numerous reports about IIF protocols, few discussed in detail problems of specific centromere-kinetochore proteins.1-4 Here we report optimized protocols to stain endogenous centromere-kinetochore proteins in human cells by using paraformaldehyde fixation and IIF staining. Furthermore, we report protocols to detect Flag-tagged exogenous CENP-A proteins in human cells subjected to acetone or methanol fixation. These methods are useful in detecting and quantifying endogenous centromere-kinetochore proteins and Flag-tagged CENP-A proteins, including those in human cells.

Here we report protocols to detect endogenous and exogenous centromere-kinetochore proteins in human cells and quantify these protein levels at centromeres-kinetochores by indirect immunofluorescent staining through the use of fixation (paraformaldehyde, acetone, or methanol fixation).

"Centromeres" and "kinetochores" refer to the site where chromosomes associate with the spindle during cell division. Direct visualization of ...

Gap Junctional Intercellular Communication: A Functional Biomarker to Assess Adverse Effects of Toxicants and Toxins, and Health Benefits of Natural Products

This protocol describes a scalpel loading-fluorescent dye transfer (SL-DT) technique that measures intercellular communication through gap junction channels, which is a major intercellular process by which tissue homeostasis is maintained. Interruption of gap junctional intercellular communication (GJIC) by toxicants, toxins, drugs, etc. has been linked to numerous adverse health effects. Many genetic-based human diseases have been linked to mutations in gap junction genes. The SL-DT technique is a simple functional assay for the simultaneous assessment of GJIC in a large population of cells. The assay involves pre-loading cells with a fluorescent dye by briefly perturbing the cell membrane with a scalpel blade through a population of cells. The fluorescent dye is then allowed to traverse through gap junction channels to neighboring cells for a designated time. The assay is then terminated by the addition of formalin to the cells. The spread of the fluorescent dye through a population of cells is assessed with an epifluorescence microscope and the images are analyzed with any number of morphometric software packages that are available, including free software packages found on the public domain. This assay has also been adapted for in vivo studies using tissue slices from various organs from treated animals. Overall, the SL-DT assay can serve a broad range of in vitro pharmacological and toxicological needs, and can be potentially adapted for high throughput set-up systems with automated fluorescence microscopy imaging and analysis to elucidate more samples in a shorter time.

This protocol describes a scalpel loading-fluorescent dye transfer technique that measures intercellular communication through gap junction channels. Gap junctional intercellular communication is a major cellular process by which tissue homeostasis is maintained and disruption of this cell signaling has adverse health effects.

This protocol describes a scalpel loading-fluorescent dye transfer (SL-DT) technique that measures intercellular communication through gap junction ...

Comparison of Three Different Methods for Determining Cell Proliferation in Breast Cancer Cell Lines

Measuring cell proliferation can be performed by a number of different methods, each with varying levels of sensitivity, reproducibility and compatibility with high-throughput formatting. This protocol describes the use of three different methods for measuring cell proliferation in vitro including conventional hemocytometer counting chamber, a luminescence-based assay that utilizes the change in the metabolic activity of viable cells as a measure of the relative number of cells, and a multi-mode cell imager that measures cell number using a counting algorithm. Each method presents its own advantages and disadvantages for the measurement of cell proliferation, including time, cost and high-throughput compatibility. This protocol demonstrates that each method could accurately measure cell proliferation over time, and was sensitive to detect growth at differing cellular densities. Additionally, measurement of cell proliferation using a cell imager was able to provide further information such as morphology, confluence and allowed for a continual monitoring of cell proliferation over time. In conclusion, each method is capable of measuring cell proliferation, but the chosen method is user-dependent.

This protocol describes the use of three different methods for analyzing cell proliferation in breast cancer cell lines. This includes the use of conventional cell counting, luminescence-based cell viability, and cell counting through the use of a cell imager. Each offers advantages for the reproducible measurement of cell proliferation.

Measuring cell proliferation can be performed by a number of different methods, each with varying levels of sensitivity, reproducibility and compatibility ...