Name: a simple fluorescence-based reporter assay to identify cellular components required for ricin toxin a chain (rta) trafficking in yeast
Uploaded: 2017-12-15T15:00:00
Description: Watch this Scientific Journal Video about A Simple Fluorescence-based Reporter Assay to Identify Cellular Components Required for Ricin Toxin A Chain RTA Trafficking in Yeast at JoVE.com

Parts of this study were kindly supported by a grant from the Deutsche Forschungsgemeinschaft (SFB 1027, A6).

NOTE: An overview of the general experimental workflow is depicted in Figure 1.
Caution: RTA is highly toxic for humans. Safety lab permission S2 (biosafety level 2 equivalent) is needed. Please wear gloves during the entire experiment.
1. Heterologous Expression of His-tagged RTA in Escherichia coli
<ol>
	<li>Transform E. coli cells with the expression plasmid pET24-RTA(His)6 or the empty vector pET24a<su...

<ol>
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K., 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+comprehensive+strategy+enabling+high-resolution+functional+analysis+of+the+yeast+genome.">A comprehensive strategy enabling high-resolution functional analysis of the yeast genome.</a> Nat Methods. 5 (8), 711-718 (2008).</li><li>Jablonowski, D., Schaffrath, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Zymocin,+a+composite+chitinase+and+tRNase+killer+toxin+from+yeast.">Zymocin, a composite chitinase and tRNase killer toxin from yeast.</a> Biochem Soc Trans. 35 (Pt 6), 1533-1537 (2007).</li><li>Jablonowski, D., Schaffrath, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Saccharomyces+cerevisiae+RNA+polymerase+II+is+affected+by+Kluyveromyces+lactis+zymocin.">Saccharomyces cerevisiae RNA polymerase II is affected by Kluyveromyces lactis zymocin.</a> J Biol Chem. 277 (29), 26276-26280 (2002).</li><li>Jablonowski, D., Frohloff, F., Fichtner, L., Stark, M. 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When performing the above protocol, we recommend the following suggestions to achieve a successful outcome of the experiment.
For heterologous protein expression, it is important to not exceed the IPTG concentration of 1 mM. IPTG concentrations &#62;1 mM inhibit promoter-induced RTA expression and lead to lower toxin yields. Furthermore, cells should not be cultivated at temperatures higher than 28 &#176;C to prevent inclusion body formation, inefficient folding, and toxin inactivation. RTA ex...

Patients suffering from infections by toxin producing bacteria represent a severe medical and financial burden for each social health care system, in particular since efficient therapeutic treatments are still largely missing. To develop new therapeutic strategies, the complex intoxication mechanisms of medically relevant A/B toxins such as cholera toxin, Shiga toxin, or ricin need to be fully understood at the molecular level based on novel powerful assays that have to be implemented.
In recent years, several studies attempted to analyze A/B toxin transport in yeast and mammalian cells by using time-consuming and cost-intensive methods such as radioactive toxin labeling1,2 as well as siRNA-based screening approaches3. In some cases, toxin trafficking has been visualized in vivo by fluorescence microscopy after chemical and/or genetic coupling of individual toxin subunits with fluorophores, quantum dots, or fluorescent proteins4,5. Unfortunately, such modifications often lead to inactive and/or altered natural properties of the toxins. Another elegant way to indirectly answer a wide variety of scientific questions is the use of reporter systems based on enzymes such as lacZ, luciferase, or fluorescent proteins (e.g. GFP or Discosoma sp. red fluorescent protein (dsRed)).
In this manuscript, a simple protocol is described which identifies cellular components required for the intracellular transport of extracellularly applied RTA in S. cerevisiae. Thereby, a fluorescence-reporter plasmid containing an N-terminal ER-import signal followed by GFP acts as a protein biosynthesis sensor, which indirectly measures RTA-mediated protein translation inhibition by GFP fluorescence emission after in vivo translation6. In case that RTA endocytosis and/or intracellular trafficking is negatively (or positively) affected in a particular yeast deletion mutant compared to wild-type, this can be detected through an increase (or decrease) in GFP fluorescence emission6.
So far, all methods analyzing RTA transport in yeast cells were restricted to the ER-to-cytosol retro-translocation process of RTA. In such an artificial system, RTA containing an ER import signal is expressed from an inducible promoter resulting in a suicidal phenotype1,7. Although the cell binding B-subunit of ricin is likewise missing in the experimental setup described in this manuscript and, thus, does not fully represent the natural situation of ricin holotoxin intoxication8, toxin transport from the plasma membrane through the Golgi apparatus to the ER can be closely mimicked with this novel assay. Interestingly, the preliminary results obtained in the pilot study indicate that the trafficking pathways used by RTA reveal striking similarities with the intoxication route of ricin holotoxin.
In summary, the described method can be used to determine the specific role of selected cellular proteins in RTA endocytosis and trafficking in yeast. Furthermore, this experimental setup might be easily adapted to other ribosome inactivating toxins produced and secreted from various yeast and bacterial species such as zymocin or Shiga toxin.

<table>
	<tbody>
		<tr>
			<td>Bacterial and yeast strains</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>E coli BL21 DE3(Gold)</td>
			<td>Aligent Technologies</td>
			<td>230130</td>
			<td></td>
		</tr>
		<tr>
			<td>S. cerevisiae BY4742</td>
			<td>Euroscarf</td>
			<td>Y10000</td>
			<td></td>
		</tr>
		<tr>
			<td>S. cerevisiae BY4742 deletion mutants</td>
			<td>Dharmacon</td>
			<td>YSC1054</td>
			<td>whole collection</td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Plasmids used in this protocol</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>pET24a(+) (Novagen)</td>
			<td>Millipore</td>
			<td>69772-3</td>
			<td></td>
		</tr>
		<tr>
			<td>pET-RTA(His6)</td>
			<td>Becker et al. (2016)3</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Reagents</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Zymolyase 20T</td>
			<td>USBio</td>
			<td>Z1000.250</td>
			<td>lytic enzyme for cell wall removal</td>
		</tr>
		<tr>
			<td>LB broth medium</td>
			<td>Thermo Scientific</td>
			<td>10855021</td>
			<td>15 g agar was added for plate production</td>
		</tr>
		<tr>
			<td>YNB</td>
			<td>Thermo Scientific</td>
			<td>DF0335-15-9</td>
			<td></td>
		</tr>
		<tr>
			<td>Ammonium sulfate</td>
			<td>Sigma-Aldrich</td>
			<td>A4418-100G</td>
			<td></td>
		</tr>
		<tr>
			<td>Yeast drop-out mix supplemts without leucine</td>
			<td>Sigma-Aldrich</td>
			<td>Y1376-20G</td>
			<td></td>
		</tr>
		<tr>
			<td>Agar</td>
			<td>Sigma-Aldrich</td>
			<td>05040-100G</td>
			<td></td>
		</tr>
		<tr>
			<td>D-glucose</td>
			<td>Sigma-Aldrich</td>
			<td>G8270-100G</td>
			<td></td>
		</tr>
		<tr>
			<td>DTT</td>
			<td>Sigma-Aldrich</td>
			<td>10197777001</td>
			<td></td>
		</tr>
		<tr>
			<td>D-raffinose</td>
			<td>Sigma-Aldrich</td>
			<td>83400-25G</td>
			<td></td>
		</tr>
		<tr>
			<td>D-sorbitol</td>
			<td>Sigma-Aldrich</td>
			<td>S1876-1KG</td>
			<td></td>
		</tr>
		<tr>
			<td>D-galactose</td>
			<td>Sigma-Aldrich</td>
			<td>G0750-10MG</td>
			<td></td>
		</tr>
		<tr>
			<td>G418</td>
			<td>Thermo Scientific</td>
			<td>11811031</td>
			<td></td>
		</tr>
		<tr>
			<td>IPTG</td>
			<td>Sigma-Aldrich</td>
			<td>I6758-1G</td>
			<td></td>
		</tr>
		<tr>
			<td>Imidazole</td>
			<td>Roth</td>
			<td>3899.1</td>
			<td></td>
		</tr>
		<tr>
			<td>PAGE ruler prestained</td>
			<td>Fermentas</td>
			<td>26616</td>
			<td>protein ladder used for Western analysis</td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Material for RTA purification, desalting and reader measurements</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Spectrophotometer Ultrospec 2100 pro</td>
			<td>Amersham</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Soniprep 150</td>
			<td>MSE</td>
			<td></td>
			<td>old model, other models available</td>
		</tr>
		<tr>
			<td>Fluoroskan Ascent</td>
			<td>Thermo Scientific</td>
			<td>5210470</td>
			<td>old model, not available anymore</td>
		</tr>
		<tr>
			<td>&#196;KTAPurifier</td>
			<td>Thermo Scientific</td>
			<td>28406266</td>
			<td>Product is discontinued and replaced</td>
		</tr>
		<tr>
			<td>HisTRAP HP column</td>
			<td>GE Healthcare</td>
			<td>17-5248-02</td>
			<td></td>
		</tr>
		<tr>
			<td>HiTRAP desalting column</td>
			<td>GE Healthcare</td>
			<td>11-0003-29</td>
			<td></td>
		</tr>
		<tr>
			<td>Midisart sterile filter</td>
			<td>Sartorius</td>
			<td>16534K</td>
			<td>0.2 &#181;m pore size</td>
		</tr>
		<tr>
			<td>BCA protein assay kit</td>
			<td>Pierce</td>
			<td>23225</td>
			<td></td>
		</tr>
		<tr>
			<td>660 nm assay kit</td>
			<td>Thermo Scientific</td>
			<td>22660</td>
			<td></td>
		</tr>
		<tr>
			<td>96 well plates</td>
			<td>Thermo Scientific</td>
			<td>260860</td>
			<td></td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Antibodies (optional)</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Anti-Tetra-His</td>
			<td>Qiagen</td>
			<td>34670</td>
			<td>primary antibody; 1:1,000 dilution</td>
		</tr>
		<tr>
			<td>Anti-mouse-HRP</td>
			<td>Sigma-Aldrich</td>
			<td>A9044-2ML</td>
			<td>secondary antibody, 1:10,000 dilution</td>
		</tr>
	</tbody>
</table>

a simple fluorescence-based reporter assay to identify cellular components required for ricin toxin a chain (rta) trafficking in yeast

Bacterial and plant A/B toxins exploit the natural trafficking pathways in eukaryotic cells to reach their intracellular target(s) in the cytosol and to ultimately kill. Such A/B toxins generally consist of an enzymatically active Asubunit (e.g., ricin toxin A (RTA)) and one or more cell binding Bsubunit(s), which are responsible for toxin binding to specific cell surface receptors. Our current knowledge of how A/B toxins are capable of efficiently intoxicating cells helped scientists to understand fundamental cellular mechanisms, like endocytosis and intracellular protein sorting in higher eukaryotic cells. From a medical point of view, it is likewise important to identify the major toxin trafficking routes to find adequate treatment solutions for patients or to eventually develop therapeutic toxin-based applications for cancer therapy.
Since genome-wide analyses of A/B toxin trafficking in mammalian cells is complex, time-consuming, and expensive, several studies on A/B toxin transport have been performed in the yeast model organism Saccharomyces cerevisiae. Despite being less complex, fundamental cellular processes in yeast and higher eukaryotic cells are similar and very often results obtained in yeast can be transferred to the mammalian situation.
Here, we describe a fast and easy to use reporter assay to analyze the intracellular trafficking of RTA in yeast. An essential advantage of the new assay is the opportunity to investigate not only RTA retro-translocation from the endoplasmic reticulum (ER) into the cytosol, but rather endocytosis and retrograde toxin transport from the plasma membrane into the ER. The assay makes use of a reporter plasmid that allows indirect measurement of RTA toxicity through fluorescence emission of the green fluorescent protein (GFP) after in vivo translation. Since RTA efficiently prevents the initiation of protein biosynthesis by 28S rRNA depurination, this assay allows the identification of host cell proteins involved in intracellular RTA transport through the detection of changes in fluorescence emission.

The general workflow of the protocol described in this manuscript is illustrated in Figure 1, roughly summarizing the single steps for successful RTA purification and the subsequent GFP reporter assay experiment. A more detailed description of each individual step can be found in the protocol. Figure 2 illustrates the expected result of a successful RTA purification by affinity chromatography (Figure 2A</stro...

Watch this Scientific Journal Video about A Simple Fluorescence-based Reporter Assay to Identify Cellular Components Required for Ricin Toxin A Chain RTA Trafficking in Yeast at JoVE.com

A Simple Fluorescence-based Reporter Assay to Identify Cellular Components Required for Ricin Toxin A Chain RTA Trafficking in Yeast

In the manuscript, we describe the use of a yeast-based fluorescence reporter assay to identify cellular components involved in the trafficking and killing processes of the cytotoxic A subunit of the plant toxin ricin (RTA).

A Simple Fluorescence-based Reporter Assay to Identify Cellular Components Required for Ricin Toxin A Chain (RTA) Trafficking in Yeast

Bacterial and plant A/B toxins exploit the natural trafficking pathways in eukaryotic cells to reach their intracellular target(s) in the cytosol and to ...

The overall goal of this simple fluorescence-based reporter assay is to screen for cellular components required for proper trafficking of ricin toxin A or RTA chain in the yeast model organism. This method can help to answer key questions concerning the intercellular transport of ribosome in activating a B toxin. In our case, the cytotoxic subunit of the plain toxin ricin from the plasma membrane into the cytosome.The main advantage of this assay is the opportunity to analyze the effect of an individual yeast gene on RTA transport in a fast and inexpensive way. Begin this protocol with cell transformation as detailed in the text protocol. Inoculate five milliliters of LB kanamycin medium with cells containing RTA expression plasmid or the empty vector.Incubate the cells at 37 degrees Celsius and 220 RPM for 24 hours. Supplement one liter of LB kanamycin medium with five milliliters of preculture. Then incubate the cells at 37 degrees Celsius and 220 RPM until cells have reached an optical density at 600 nanometers of 0.8 to 1.0.Thereafter, reduce the culture temperature to 28 degrees Celsius. Induce RTA expression of the E.Coli by adding IPTG to a final concentration of one millimolar. After 3.5 hours at 28 degrees Celsius and 220 RPM, harvest the cells by centrifugation at 10, 000 g and four degrees Celsius for 10 minutes.Then wash the pellet with five milliliters of binding buffer and pellet at 10, 000 g and four degrees Celsius for 10 minutes. After repeating the wash once, re-suspend the pellet in five milliliters of binding buffer. Sonicate the cells on ice using five cycles of a 15 second pulse and a 30 second pause.After centrifuging the cell licate at 21, 000 g and four degrees Celsius for 15 minutes, filter the supernatant using a sterile syringe filter system. Use an automated purification system, equipped with a five milliliter, nickel-based affinity column to purify the HIS-tagged RTA fraction from the sterile filtered E.Coli supernatant. In general, use an allusion speed of one milliliter per minute and cool the whole purification system to prevent non-efficient toxin binding and loss of toxin activity.Briefly equilibrate the affinity column with 20 milliliters of binding buffer to remove the storage buffer. Then apply the sterile, filtered supernatant onto the affinity column using a syringe. Wash the column with 25 to 35 milliliters of binding buffer to remove the unbound proteins from the column.Perform the washing step until the UV absorbents at 280 nanometers is close to the initial UV value. Then elute the bound RTA fraction with 20 to 35 milliliters of elution buffer and keep the sample on ice. It's important to start the RTA fraction sampling shortly after the UV, 280 value increases and stop the RTA fraction sampling when it reaches the original base line again.To desalt the eluded RTA fraction, replace the affinity column of the purification system with the desalting column and equilibrate the column with 20 milliliters of 0.8 molar sorbitol. Apply the eluded RTA fraction to the column via a syringe. Wash the column with 100 milliliters of 0.8 molar sorbitol and dilute the desalted RTA fraction in a 15 milliliter tube as soon as the UV absorption starts to increase.To avoid salt contamination, stop at the fraction sampling directly when conductance increases. Store the Eluded RTA fraction at four degrees Celsius. After transforming the yeast as described in the text protocol, pick three different yeast clones from each plate.Inoculate the clones in 100 milliliters of lucine dropout raffinose medium at 220 RPM and 30 degrees Celsius to an optical density at 600 nanometers of 1.0 to 2.0. Centrifuge the cells at 25 degrees Celsius for five minutes at 10, 000 g. After washing the cells twice with five milliliters of sterile water, re-suspend the cells in 50 milliliters of spheroplasting buffer.Incubate the 50 milliliter culture at 100 RPM and 30 degrees Celsius for 90 minutes. Following centrifugation at 400 g and four degrees Celsius for 10 minutes, wash the cells twice with five milliliters of stabilized lucine drop out raffinose medium. Then re-suspend the cells in five milliliters of the same medium to use the cells directly for the GFP reporter assay measurements.Seed out the yeast cell spheroplasts into 96 well plates. To each well, add 70 microliters of stabilized lucine drop out raffinose medium, containing the negative control, expressing the empty vector or purified RTA in a final RTA concentration of five micromolar. Add 70 microliters of stabilized lucine drop out medium to each of the remaining wells to bring their total volume to 270 microliters.For a positive control for protein inhibition, add 70 microliters of 0.8 molar sorbitol stabilized G418 solution, as G418 prevents GFP expression in yeast. Immediately add 30 microliters of stabilized galactose solution to induce GFP expression. Prepare an additional negative control by adding 30 microliters of stabilized lucine drop out raffinose medium instead of 30%galactose.After finishing sample preparation, put the 96 well plate in a fluorescence reader and prepare for measurement using the 475, 509 nanometer filter set required for GFP fluorescence detection. Perform measurements at 30 degrees Celsius 120 RPM and a shaking diameter of one millimeter over a time window of 20 hours with measuring intervals of 10 minutes. Shown here is a representative purification graph of the affinity chromatography of RTA and the empty vector control.The blue peak in the black box represents the bound RTA fraction. As shown in the black box, no proteins are eluded from the column in the negative control. Shown here is a desalting diagram of an affinity purified RTA fraction.The diagram shows the separation of the RTA protein fraction and the salt fraction. Coomassie staining results after successful purification and desalting show cell lysate or purified samples of different RTA variants. Unmodified RTA was used in this study.To validate the fluorescence spaced reporter assay, relative GFP fluorescence of wild type yeast spheroplasts was measured under induced and noninduced conditions after 20 hours of GFP induction. Relative GFP fluorescence was also analyzed in the presence of RTA, G418, or the negative control. Relative GFP fluorescence was also measured for selected mutants in which corresponding proteins are known to be involved and not involved in RTA trafficking in yeast.The dotted line represented a significance threshold. Once the RTA expression and purification is mastered, the results of the fluorescence report assay can be received in one day. Additionally, this method paves the way for researchers in the field of ribosome inactivating of B toxins to study their intoxication roots in a eucaryotic model organism yeast.

a-simple-fluorescence-based-reporter-assay-to-identify-cellular

Research

JoVE Journal

Biology

Pyrosequencing: A Simple Method for Accurate Genotyping

Pharmacogenetic research benefits first-hand from the abundance of information provided by the completion of the Human Genome Project. With such a tremendous amount of data available comes an explosion of genotyping methods. Pyrosequencing(R) is one of the most thorough yet simple methods to date used to analyze polymorphisms. It also has the ability to identify tri-allelic, indels, short-repeat polymorphisms, along with determining allele percentages for methylation or pooled sample assessment. In addition, there is a standardized control sequence that provides internal quality control. This method has led to rapid and efficient single-nucleotide polymorphism evaluation including many clinically relevant polymorphisms. The technique and methodology of Pyrosequencing is explained.


Pyrosequencing(R) is one of the most thorough yet simple methods to date used to analyze polymorphisms. This method has led to rapid and efficient single-nucleotide polymorphism evaluation including many clinically relevant polymorphisms. The technique and methodology of Pyrosequencing is explained.

Pharmacogenetic research benefits first-hand from the abundance of information provided by the completion of the Human Genome Project. With such a ...

A Fluorescence Microscopy Assay for Monitoring Mitophagy in the Yeast Saccharomyces cerevisiae

Autophagy is important for turnover of cellular components under a range of different conditions. It serves an essential homeostatic function as well as a quality control mechanism that can target and selectively degrade cellular material including organelles1-4. For example, damaged or redundant mitochondria (Fig. 1), not disposed of by autophagy, can represent a threat to cellular homeostasis and cell survival. In the yeast, Saccharomyces cerevisiae, nutrient deprivation (e.g., nitrogen starvation) or damage can promote selective turnover of mitochondria by autophagy in a process termed mitophagy 5-9.
We describe a simple fluorescence microscopy approach to assess autophagy. For clarity we restrict our description here to show how the approach can be used to monitor mitophagy in yeast cells. The assay makes use of a fluorescent reporter, Rosella, which is a dual-emission biosensor comprising a relatively pH-stable red fluorescent protein linked to a pH-sensitive green fluorescent protein. The operation of this reporter relies on differences in pH between the vacuole (pH ~ 5.0-5.5) and mitochondria (pH ~ 8.2) in living cells. Under growing conditions, wild type cells exhibit both red and green fluorescence distributed in a manner characteristic of the mitochondria. Fluorescence emission is not associated with the vacuole. When subjected to nitrogen starvation, a condition which induces mitophagy, in addition to red and green fluorescence labeling the mitochondria, cells exhibit the accumulation of red, but not green fluorescence, in the acidic vacuolar lumen representing the delivery of mitochondria to the vacuole. Scoring cells with red, but not green fluorescent vacuoles can be used as a measure of mitophagic activity in cells5,10-12.

A Fluorescence Microscopy Assay for Monitoring Mitophagy in the Yeast Saccharomyces cerevisiae

A robust approach to monitor the delivery of organelles to the acidic lumen of the yeast vacuole for degradation and recycling is described. The method relies on the specific labeling of target organelles with a genetically encoded dual-emission fluorescence pH-biosensor, and visualization of individual cells using fluorescence microscopy.

Autophagy is important for turnover of cellular components under a range of different conditions. It serves an essential homeostatic function as well as a ...

RNAi Screening to Identify Postembryonic Phenotypes in C. elegans

C. elegans has proven to be a valuable model system for the discovery and functional characterization of many genes and gene pathways1. More sophisticated tools and resources for studies in this system are facilitating continued discovery of genes with more subtle phenotypes or roles. 
Here we present a generalized protocol we adapted for identifying C. elegans genes with postembryonic phenotypes of interest using RNAi2. This procedure is easily modified to assay the phenotype of choice, whether by light or fluorescence optics on a dissecting or compound microscope. This screening protocol capitalizes on the physical assets of the organism and molecular tools the C. elegans research community has produced. As an example, we demonstrate the use of an integrated transgene that expresses a fluorescent product in an RNAi screen to identify genes required for the normal localization of this product in late stage larvae and adults. First, we used a commercially available genomic RNAi library with full-length cDNA inserts. This library facilitates the rapid identification of multiple candidates by RNAi reduction of the candidate gene product. Second, we generated an integrated transgene that expresses our fluorecently tagged protein of interest in an RNAi-sensitive background. Third, by exposing hatched animals to RNAi, this screen permits identification of gene products that have a vital embryonic role that would otherwise mask a post-embryonic role in regulating the protein of interest. Lastly, this screen uses a compound microscope equipped for single cell resolution.

RNAi Screening to Identify Postembryonic Phenotypes in C. elegans

We describe a sensitized method to identify postembryonic regulators of protein expression and localization in C. elegans using an RNAi-based genomic screen and an integrated transgene that expresses a functional, fluorescently tagged protein.

C. elegans has proven to be a valuable model system for the discovery and functional characterization of many genes and gene pathways1. More sophisticated ...

Modified Yeast-Two-Hybrid System to Identify Proteins Interacting with the Growth Factor Progranulin

Progranulin (PGRN), also known as granulin epithelin precursor (GEP), is a 593-amino-acid autocrine growth factor. PGRN is known to play a critical role in a variety of physiologic and disease processes, including early embryogenesis, wound healing 1, inflammation 2, 3, and host defense 4. PGRN also functions as a neurotrophic factor 5, and mutations in the PGRN gene resulting in partial loss of the PGRN protein cause frontotemporal dementia 6, 7. Our recent studies have led to the isolation of PGRN as an important regulator of cartilage development and degradation 8-11. Although PGRN, discovered nearly two decades ago, plays crucial roles in multiple physiological and pathological conditions, efforts to exploit the actions of PGRN and understand the mechanisms involved have been significantly hampered by our inability to identify its binding receptor(s). To address this issue, we developed a modified yeast two-hybrid (MY2H) approach based on the most commonly used GAL4 based 2-hybrid system. Compared with the conventional yeast two-hybrid screen, MY2H dramatically shortens the screen process and reduces the number of false positive clones. In addition, this approach is reproducible and reliable, and we have successfully employed this system in isolating the binding proteins of various baits, including ion channel 12, extracellular matrix protein 10, 13, and growth factor14. In this paper, we describe this MY2H experimental procedure in detail using PGRN as an example that led to the identification of TNFR2 as the first known PGRN-associated receptor 14, 15.

We have modified the conventional yeast two-hybrid screening, an effective genetic tool in identifying protein interaction. This modification markedly shortens the process, reduces the workload, and most importantly, reduces the number of false positives. In addition, this approach is reproducible and reliable.

Progranulin (PGRN), also known as granulin epithelin precursor (GEP), is a 593-amino-acid autocrine growth factor. PGRN is known to play a critical role ...

Isolation of Ribosome Bound Nascent Polypeptides in vitro to Identify Translational Pause Sites Along mRNA

The rate of translational elongation is non-uniform. mRNA secondary structure, codon usage and mRNA associated proteins may alter ribosome movement on the messagefor review see 1. However, it's now widely accepted that synonymous codon usage is the primary cause of non-uniform translational elongation rates1. Synonymous codons are not used with identical frequency. A bias exists in the use of synonymous codons with some codons used more frequently than others2. Codon bias is organism as well as tissue specific2,3. Moreover, frequency of codon usage is directly proportional to the concentrations of cognate tRNAs4. Thus, a frequently used codon will have higher multitude of corresponding tRNAs, which further implies that a frequent codon will be translated faster than an infrequent one. Thus, regions on mRNA enriched in rare codons (potential pause sites) will as a rule slow down ribosome movement on the message and cause accumulation of nascent peptides of the respective sizes5-8. These pause sites can have functional impact on the protein expression, mRNA stability and protein foldingfor review see 9. Indeed, it was shown that alleviation of such pause sites can alter ribosome movement on mRNA and subsequently may affect the efficiency of co-translational (in vivo) protein folding1,7,10,11. To understand the process of protein folding in vivo, in the cell, that is ultimately coupled to the process of protein synthesis it is essential to gain comprehensive insights into the impact of codon usage/tRNA content on the movement of ribosomes along mRNA during translational elongation.
Here we describe a simple technique that can be used to locate major translation pause sites for a given mRNA translated in various cell-free systems6-8. This procedure is based on isolation of nascent polypeptides accumulating on ribosomes during in vitro translation of a target mRNA. The rationale is that at low-frequency codons, the increase in the residence time of the ribosomes results in increased amounts of nascent peptides of the corresponding sizes. In vitro transcribed mRNA is used for in vitro translational reactions in the presence of radioactively labeled amino acids to allow the detection of the nascent chains. In order to isolate ribosome bound nascent polypeptide complexes the translation reaction is layered on top of 30% glycerol solution followed by centrifugation. Nascent polypeptides in polysomal pellet are further treated with ribonuclease A and resolved by SDS PAGE. This technique can be potentially used for any protein and allows analysis of ribosome movement along mRNA and the detection of the major pause sites. Additionally, this protocol can be adapted to study factors and conditions that can alter ribosome movement and thus potentially can also alter the function/conformation of the protein.

Isolation of Ribosome Bound Nascent Polypeptides in vitro to Identify Translational Pause Sites Along mRNA

A technique to identify translational pause sites on mRNA is described. This procedure is based on isolation of nascent polypeptides accumulating on ribosomes during in vitro translation of a target mRNA, followed by the size analysis of the nascent chains using a denaturing gel electrophoresis.

The rate of translational elongation is non-uniform. mRNA secondary structure, codon usage and mRNA associated proteins may alter ribosome movement on the ...

An Explant Assay for Assessing Cellular Behavior of the Cranial Mesenchyme

The central nervous system is derived from the neural plate that undergoes a series of complex morphogenetic movements resulting in formation of the neural tube in a process known as neurulation. During neurulation, morphogenesis of the mesenchyme that underlies the neural plate is believed to drive neural fold elevation. The cranial mesenchyme is comprised of the paraxial mesoderm and neural crest cells. The cells of the cranial mesenchyme form a pourous meshwork composed of stellate shaped cells and intermingling extracellular matrix (ECM) strands that support the neural folds. During neurulation, the cranial mesenchyme undergoes stereotypical rearrangements resulting in its expansion and these movements are believed to provide a driving force for neural fold elevation. However, the pathways and cellular behaviors that drive cranial mesenchyme morphogenesis remain poorly studied. Interactions between the ECM and the cells of the cranial mesenchyme underly these cell behaviors. Here we describe a simple ex vivo explant assay devised to characterize the behaviors of these cells. This assay is amendable to pharmacological manipulations to dissect the signaling pathways involved and live imaging analyses to further characterize the behavior of these cells. We present a representative experiment demonstrating the utility of this assay in characterizing the migratory properties of the cranial mesenchyme on a variety of ECM components.

The cranial mesenchyme undergoes dramatic morphogenic movements that likely provides a driving force for elevation of the neural folds1,2. Here we describe a simple ex vivo explant assay to characterize the cellular behaviors of the cranial mesenchyme during neurulation. This assay has numerous applications including being amenable to pharmacological manipulations and live imaging analyses.

The central nervous system is derived from the neural plate that undergoes a series of complex morphogenetic movements resulting in formation of the ...

A Quantitative Assay to Study Protein:DNA Interactions, Discover Transcriptional Regulators of Gene Expression, and Identify Novel Anti-tumor Agents

Many DNA-binding assays such as electrophoretic mobility shift assays (EMSA), chemiluminescent assays, chromatin immunoprecipitation (ChIP)-based assays, and multiwell-based assays are used to measure transcription factor activity. However, these assays are nonquantitative, lack specificity, may involve the use of radiolabeled oligonucleotides, and may not be adaptable for the screening of inhibitors of DNA binding. On the other hand, using a quantitative DNA-binding enzyme-linked immunosorbent assay (D-ELISA) assay, we demonstrate nuclear protein interactions with DNA using the RUNX2 transcription factor that depend on specific association with consensus DNA-binding sequences present on biotin-labeled oligonucleotides. Preparation of cells, extraction of nuclear protein, and design of double stranded oligonucleotides are described. Avidin-coated 96-well plates are fixed with alkaline buffer and incubated with nuclear proteins in nucleotide blocking buffer. Following extensive washing of the plates, specific primary antibody and secondary antibody incubations are followed by the addition of horseradish peroxidase substrate and development of the colorimetric reaction. Stop reaction mode or continuous kinetic monitoring were used to quantitatively measure protein interaction with DNA. We discuss appropriate specificity controls, including treatment with non-specific IgG or without protein or primary antibody. Applications of the assay are described including its utility in drug screening and representative positive and negative results are discussed.

We developed a quantitative DNA-binding, ELISA-based assay to measure transcription factor interactions with DNA. High specificity for the RUNX2 protein was achieved with a consensus DNA-recognition oligonucleotide and specific monoclonal antibody. Colorimetric detection with an enzyme-coupled antibody substrate reaction was monitored in real time.

Many DNA-binding assays such as electrophoretic mobility shift assays (EMSA), chemiluminescent assays, chromatin immunoprecipitation (ChIP)-based assays, ...

A Fluorescence-based Exonuclease Assay to Characterize DmWRNexo, Orthologue of Human Progeroid WRN Exonuclease, and Its Application to Other Nucleases

WRN exonuclease is involved in resolving DNA damage that occurs either during DNA replication or following exposure to endogenous or exogenous genotoxins. It is likely to play a role in preventing accumulation of recombinogenic intermediates that would otherwise accumulate at transiently stalled replication forks, consistent with a hyper-recombinant phenotype of cells lacking WRN. In humans, the exonuclease domain comprises an N-terminal portion of a much larger protein that also possesses helicase activity, together with additional sites important for DNA and protein interaction. By contrast, in Drosophila, the exonuclease activity of WRN (DmWRNexo) is encoded by a distinct genetic locus from the presumptive helicase, allowing biochemical (and genetic) dissection of the role of the exonuclease activity in genome stability mechanisms. Here, we demonstrate a fluorescent method to determine WRN exonuclease activity using purified recombinant DmWRNexo and end-labeled fluorescent oligonucleotides. This system allows greater reproducibility than radioactive assays as the substrate oligonucleotides remain stable for months, and provides a safer and relatively rapid method for detailed analysis of nuclease activity, permitting determination of nuclease polarity, processivity, and substrate preferences.

Exonucleases play critical roles in ensuring genome stability. Loss of WRN exonuclease function results in premature aging. Studying substrates and other requirements of the nuclease in vitro can help elucidate its role in vivo. Here we demonstrate a rapid and reproducible fluorescence-based assay to measure its nuclease activity.

WRN exonuclease is involved in resolving DNA damage that occurs either during DNA replication or following exposure to endogenous or exogenous genotoxins. ...

Filtration Isolation of Nucleic Acids:  A Simple and Rapid DNA Extraction Method

FINA, filtration isolation of nucleic acids, is a novel extraction method which utilizes vertical filtration via a separation membrane and absorbent pad to extract cellular DNA from whole blood in less than 2 min. The blood specimen is treated with detergent, mixed briefly and applied by pipet to the separation membrane. The lysate wicks into the blotting pad due to capillary action, capturing the genomic DNA on the surface of the separation membrane. The extracted DNA is retained on the membrane during a simple wash step wherein PCR inhibitors are wicked into the absorbent blotting pad. The membrane containing the entrapped DNA is then added to the PCR reaction without further purification. This simple method does not require laboratory equipment and can be easily implemented with inexpensive laboratory supplies. Here we describe a protocol for highly sensitive detection and quantitation of HIV-1 proviral DNA from 100 &#181;l whole blood as a model for early infant diagnosis of HIV that could readily be adapted to other genetic targets.

We describe here a simple and rapid paper-based DNA extraction method of HIV proviral DNA from whole blood detected by quantitative PCR. This protocol can be extended for use in detecting other genetic markers or using alternative amplification methods.

FINA, filtration isolation of nucleic acids, is a novel extraction method which utilizes vertical filtration via a separation membrane and absorbent pad ...

Using Microfluidic Devices to Measure Lifespan and Cellular Phenotypes in Single Budding Yeast Cells

Budding yeast Saccharomyces cerevisiae is an important model organism in aging research. Genetic studies have revealed many genes with conserved effects on the lifespan across species. However, the molecular causes of aging and death remain elusive. To gain a systematic understanding of the molecular mechanisms underlying yeast aging, we need high-throughput methods to measure lifespan and to quantify various cellular and molecular phenotypes in single cells. Previously, we developed microfluidic devices to track budding yeast mother cells throughout their lifespan while flushing away newborn daughter cells. This article presents a method for preparing microfluidic chips and for setting up microfluidic experiments. Multiple channels can be used to simultaneously track cells under different conditions or from different yeast strains. A typical setup can track hundreds of cells per channel and allow for high-resolution microscope imaging throughout the lifespan of the cells. Our method also allows detailed characterization of the lifespan, molecular markers, cell morphology, and the cell cycle dynamics of single cells. In addition, our microfluidic device is able to trap a significant amount of fresh mother cells that can be identified by downstream image analysis, making it possible to measure the lifespan with higher accuracy.

This article presents a protocol optimized for the production of microfluidic chips and the setup of microfluidic experiments to measure the lifespan and cellular phenotypes of single yeast cells.

Budding yeast Saccharomyces cerevisiae is an important model organism in aging research. Genetic studies have revealed many genes with conserved effects ...