This work was funded by a research grant from the Department of Biotechnology, Government of India (Grant No. BT/PR12568/BRB/10/1369/2015) to Nimisha Sharma. The authors thank Prof. Charles Hoffman (Boston College, USA) for the gift of the S. pombe cDNA library and Prof. Susan Forsburg for the yeast plasmids.

1.&#160;Transformation of the cDNA library into the query S. pombe mutant strain to screen for multicopy suppressors
NOTE: The Standard Lithium-Acetate method27 was followed to transform the S. pombe cDNA library into the query S. pombe ell1&#916;&#160;strain with a few modifications:
<ol>
	<li>Grow the S. pombe ell1&#916;&#160;strain at 32 &#176;C on a YE medium (Table 1) plate supplemented with 225 &#181;g/mL each of adenine, leucine, and uracil. Inoculate a loop full of inoculum of ell1&#916;&#160;strain from the above plate in 15-20 mL of YE medium supplemented with 225 &#181;g/mL each of adenine, leucine, and uracil. Incubate it overnight at 32 &#176;C with shaking (200-250 rpm).</li>
	<li>Next day, dilute the overnight culture in 100 mL of fresh YE medium with the desired supplements to an OD600 nm (optical density at 600 nm) of 0.3 and incubate it at 32 &#176;C with shaking at 200-250 rpm until the OD600 nm reaches mid-log phase.</li>
	<li>Divide the 100 mL culture into two 50 mL centrifuge tubes, followed by centrifugation at room temperature for 10 min at 4,000 &#215; g.</li>
	<li>Discard the supernatant and wash the cell pellet with 1 mL of sterile water, i.e., resuspend the cells in 1 mL of sterile water and centrifuge at 4,000 &#215; g for 5 min at room temperature.</li>
	<li>Discard the supernatant and wash each cell pellet with 1 mL of 1x LiAc-TE (100 mM lithium acetate, 10 mM Tris-HCl, 1 mM EDTA, pH 7.5) solution as described in step 1.4.</li>
	<li>Remove the supernatant and resuspend each cell pellet in 250 &#181;L of 1x LiAc-TE. Use these S. pombe competent cells (500 &#181;L) for transformation with the DNA of interest. Transfer 125 &#181;L of the competent cells into four different sterile microcentrifuge tubes for subsequent transformation steps.</li>
	<li>Boil carrier DNA from Salmon testes or herring sperm for 1 min and immediately place on ice. For each transformation, add 10 &#181;L of 10 mg/mL denatured, single-stranded carrier DNA to the microcentrifuge tube containing 125 &#181;L of the competent cells, followed by gentle mixing using a micropipette tip. Subsequently, add 50 &#181;g of the S. pombe cDNA library to the competent cells-carrier DNA mixture-containing microcentrifuge tube.</li>
	<li>Incubate the microcentrifuge tubes at room temperature for 10 min, and then add 260 &#181;L of polyethylene glycol-lithium acetate solution (40% [w/v] PEG 4,000, 100 mM lithium acetate, 10 mM Tris-HCl, 1 mM EDTA, pH 7.5) to the tubes and mix gently with the help of a micropipette tip.</li>
	<li>Incubate the microcentrifuge tubes containing the transformation mixture at 32 &#176;C for 2 h without shaking. Add 43 &#181;L of prewarmed dimethyl sulfoxide (DMSO) to the microcentrifuge tube and mix gently. Subsequently, expose the tubes to heat shock at 42 &#176;C for 5 min.</li>
	<li>Pellet the cells at 4,000 &#215; g for 5 min at room temperature. Discard the supernatant and remove the residual PEG- LiAc-TE solution with the help of a micropipette tip.</li>
	<li>Resuspend the cells in 100 &#181;L of sterile water and plate on one EMM2 (Table 1) plate (150 mm) with required supplements and 0.2 &#181;g/mL of 4-NQO.</li>
	<li>Incubate the plates at 32 &#176;C for 5-6 days to allow colonies to appear on the plates. Streak the obtained colonies on the same medium plate in the presence of 0.2 &#181;g/mL of 4-NQO and use for further screening.</li>
	<li>For one library transformation experiment, use 500 &#181;L of competent cells (125 &#181;L of competent cells x 4 microcentrifuge tubes) for transformation as described in steps 1.8 to 1.14 above.</li>
	<li>As a control, plate 1/10th of the transformation mixture on one EMM2 plate (150 mm) with required supplements, but lacking 4-NQO, to calculate the total number of library clones obtained after transformation of the library, and screen for isolation of the suppressor clones.</li>
</ol>
2.&#160;Test and validate the rescue/suppression of the phenotype associated with the query mutant strain by the putative suppressor
NOTE: Stress spot assays were carried out as described below to test and validate the rescue/suppression of the ell1 deletion-associated 4-NQO stress sensitivity by the putative suppressor(s).
<ol>
	<li>Add 100-200 &#181;L sterile water in each of the different wells of a sterile 96-well microtiter plate.</li>
	<li>Pick a small amount of inoculum from each of the different colonies obtained after cDNA library transformation on the plate containing 4-NQO using a sterile toothpick or a 20-200 &#956;L micropipette tip. Add the inoculum from each of the different colonies into separate independent wells of the microtiter plate containing 100-200 &#181;L of sterile water. Mix thoroughly.</li>
	<li>Spot 3 &#181;L of the cell suspension from each well onto EMM2 agar plates containing adenine (225 &#181;g/mL) and uracil (225 &#181;g/mL) but lacking leucine (the selectable auxotrophic marker present on the plasmid vector used for construction of the library used in this work). Add appropriate concentrations of 4-NQO to the plates as required.</li>
	<li>Incubate the plates at 32 &#176;C for 3-4 days to allow the cells to grow. Identify the colonies that show growth in the presence of different concentrations of 4-NQO as putative suppressors.</li>
	<li>To further validate the suppressors, grow the selected suppressors along with appropriate control strains overnight at 32 &#176;C with shaking (200-250 rpm) in EMM2 medium containing 225 &#181;g/mL each of adenine and uracil but lacking leucine.</li>
	<li>Next day, dilute the cells to an OD600 nm of 0.3 in fresh EMM2 medium and grow them at 32 &#176;C with shaking until mid-log phase (approximately OD600 nm of 0.6-0.8).</li>
	<li>Spot appropriate serial dilutions (1:10 or 1:5) of cultures on EMM2 plates with required supplements containing either 0.4 &#181;M 4-NQO or 0.01% MMS. For control, spot the strains on an EMM2 plate with required supplements but lacking any DNA-damaging agent.</li>
	<li>Incubate the plates at 32 &#176;C for 3-5 days to monitor growth. 
	NOTE: Suitable assays based on the phenotype associated with the query mutant strain should be used to test the rescue or suppression of the phenotype. For example, if suppressors of a cold-sensitive phenotype of a query mutant strain need to be identified, the assay for testing and validation of the suppressor clones would involve growing transformants at low temperature.</li>
	<li>Spot the mutant strains transformed with full-length gene of interest (Spell1 in this case) or empty vector as positive and negative controls, respectively, along with the library transformants.</li>
</ol>
3.&#160;Isolation of the plasmid from the S. pombe suppressor clones
NOTE: Plasmid isolation from S. pombe was carried out by following the protocol described in Fission yeast: a laboratory manual28 with a few modifications.
<ol>
	<li>Inoculate a single yeast colony in EMM2 medium containing 225 &#181;g/mL of adenine and uracil and grow the cells overnight at 32 &#176;C with shaking at 200-250 rpm. Next day, harvest 5 O.D. cells (i.e., 10 mL culture of O.D. 0.5) by centrifuging for 2 min at 4,000 &#215; g at room temperature.</li>
	<li>Remove the supernatant and resuspend the cell pellet in 0.2 mL of lysis buffer (2% Triton X-100, 1% SDS, 100 mM NaCl, 10 mM Tris HCl (pH 8.0), and 1 mM Na2EDTA).</li>
	<li>Add 0.2 mL of phenol:chloroform:isoamyl alcohol (25:24:1) and 0.3 g of acid-washed glass beads to the microcentrifuge tube. Vortex the microcentrifuge tube for 2 min at 4 &#176;C and incubate on ice for 1 min. Repeat this step 6x.</li>
	<li>Centrifuge the tube at 10,000 &#215; g for 15 min at room temperature. Transfer the upper aqueous layer to a fresh microcentrifuge tube and add 200 &#181;L of phenol:chloroform:isoamyl alcohol (25:24:1).</li>
	<li>Centrifuge the tube at 10,000 &#215; g for 10 min. Transfer the upper aqueous layer to a fresh tube and add two volumes of 100% ethanol (~400 &#181;L) and 1/10 volume of sodium acetate (3 M, pH 5.8) (~20 &#181;L) to the tube. Incubate the microcentrifuge tube -70 &#176;C for 1 h.</li>
	<li>Precipitate the DNA by centrifugation at 10,000 &#215; g for 15 min at 4 &#176;C and remove the supernatant. Wash the DNA pellet with 70% ethanol (~500 &#181;L) and keep it at room temperature to air-dry.</li>
	<li>Resuspend the DNA in 20 &#181;L of sterile water. Use 2-5 &#181;L of plasmid DNA for transformation of competent E. coli cells. 
	NOTE: Plasmid can also be isolated from yeast cells using any of the commercially available yeast plasmid isolation kits.</li>
</ol>
4.&#160;Identification of the gene encoded by the suppressor clone
<ol>
	<li>Transform the isolated yeast plasmids into E. coli Top10 strain [F-mcrA (mrr-hsdRMS-mcrBC) 80LacZM15 lacX74 recA1 ara139 (ara-leu)7697 galUgalKrpsL (StrR) endA1 nupG] using the standard protocol29 and spread the cells on LB (Luria Broth) plates with required antibiotics.</li>
	<li>Isolate the plasmid(s) from E. coli transformants using the standard alkaline lysis protocol29, and follow the appropriate combinations of restriction enzymes to check for the release of the insert DNA fragment by restriction digestion. 
	NOTE: Suppressor plasmid 84 was digested with BamHI restriction enzyme, and Suppressor plasmid 104 was digested with PstI/BamHI restriction enzymes.</li>
	<li>Retransform the plasmids showing insert release after restriction digestion in the ell1&#916;&#160;strain to check for their ability to rescue the genotoxic stress-sensitive phenotype of the ell1&#916;&#160;strain.</li>
	<li>Select the plasmid clones showing suppression of the genotoxic stress sensitivity and sequence the insert DNA fragment present in these plasmid clones using vector-specific forward and reverse primers. 
	NOTE: In this study, the adh1 promoter-specific universal forward primer (5&#39;CATTGGTCTTCCGCTCCG 3&#39;) was used30.</li>
	<li>To identify the gene responsible for the suppression, align the sequence obtained using NCBI nucleotide blast (https://blast.ncbi.nlm.nih.gov/Blast.cgi?PROGRAM=blastn&#38;BLAST_SPEC=GeoBlast&#38;PAGE_TYPE=BlastSearch) or Pombase sequence alignment tool (https://fungi.ensembl.org/Schizosaccharomyces_pombe/Tools/Blast?db=core). Select the sequence showing maximum alignment and identify it as the gene for the multicopy suppressor plasmid.</li>
</ol>

The authors have no conflicts of interest.

Yeasts have been widely used to investigate the basic biological processes and pathways that are evolutionarily conserved across eukaryotic organisms. The availability of genetic and genomic tools along with their amenability to various biochemical, genetic, and molecular procedures make yeasts an excellent model organism for genetic research34,35,36. Over the years, various genetic screens have been designed by yeast researcher...

Networks of genetic interactions provide functional information about genes and delineate pathways and biological processes that these genes may be involved in in vivo. In addition, they may also provide insights into how different genes interact with one another, resulting in a specific phenotype1,2,3. Over the years, a variety of genetic screens have been designed by researchers to answer fundamental biological questions and study human diseases. Screens for the identification of genetic interactions can be performed in multiple ways. Genetic interactions identified in different genetic screens can represent distinct mechanistic relationships between genes. Furthermore, studies have revealed that a common set of genetic interactions are shared by genes that encode proteins belonging to the same pathway or complex4,5. Thus, genetic interaction networks can be used to establish the functional organization in a cell, wherein genes sharing the most similar profiles belong to the same complex or pathway, those genes sharing somewhat less similar profiles belong to the same biological process, and those genes exhibiting overlapping but more diverse profiles reflect members belonging to the same cellular compartment6.
Genetic interaction screens based on dosage suppression (&#39;high-copy or multicopy suppression&#39;) are one of the commonly used approaches. These screens can be performed by transforming a query mutant strain with a high-copy-number genomic or cDNA library, followed by suitable assays/selection techniques to identify suppressing or enhancing genetic interactions7,8,9. To ensure a comprehensive genome-wide coverage, these screens have also been carried out by overexpressing a specific gene of interest in a collection of genome-wide loss-of-function mutant or by overexpressing a high-copy-number plasmid-encoded genomic or cDNA library in a loss-of-function query mutant9,10,11,12,13,14,15. The multicopy strategy could also work using a dominant/overexpression approach using a regulatable promoter.
The main advantages of using suppressor-based screens are that suppression of a preexisting phenotype in a mutant strain by another gene establishes a genetic relationship among these two gene products that may not have been demonstrated using other approaches. Second, it has been observed that the presence of a preexisting mutation sensitizes a particular pathway, allowing additional components of that pathway to be identified by the isolation of suppressors, which may have not been identified by more direct genetic selections. Moreover, this screen can be used to identify suppressors that have different mechanisms of suppression16. Suppressor interactions usually occur between genes that are functionally related and can be used to elucidate hierarchies in pathways. The exact underlying mechanism of suppression may differ based on several factors, including the type of query mutant used in the screen, experimental conditions, and the level of gene expression. One of the common dosage suppression mechanisms involves genes encoding products that function together in the same complex or in parallel in the same cellular/biological process. The results of such screens in simpler model organisms such as yeast can be extended to higher eukaryotic organisms since most fundamental biological pathways and processes are conserved across evolution.
These genetic screens can also be modified in several ways to answer different biological questions. For example, orthologous genes from different organisms that can suppress the phenotype of the query mutant strain can be identified. It has also been used to delineate potential resistance mechanisms and determine protein targets of novel antibacterial17,18, antifungal19,20, antiparasitic21, and anticancer22 compounds. This screen has also been exploited to identify suppressors of the activity of pharmaceutical drugs whose mechanism of action is not known. Thus, in principle, these multicopy suppressor screens can be optimized and used in a variety of applications in different organisms. Although most of the genetic screens employed by yeast researchers have been initially developed in S. cerevisiae, S. pombe has emerged as a complementary model system for&#160;carrying out various genetic screens and assays23. Moreover, genomic organization and biological&#160;processes in S. pombe, such as occurrence of introns in more genes, complexity of origins of DNA replication, centromere structure, organization of the cell cycle and presence of the RNAi&#160;machinery, show greater resemblance between S. pombe and higher eukaryotes23,24, underscoring&#160;the importance of designing and using genetic tools in S. pombe.
This paper describes a protocol for identifying genetic interactors based on &#39;dosage suppression&#39; of a loss-of-function mutant phenotype in S. pombe. The basis of this protocol is that it is a rapid and efficient method to screen a cDNA library overexpressing wild-type genes either on a multicopy plasmid and/or from a strong promoter. This protocol has four main steps: transformation of the library into a query mutant strain, selection of plasmid clones that suppress the desired phenotype of the query mutant strain, retrieving the plasmid(s) from these suppressor clones, and identification of the gene responsible for the suppression of the phenotype. As is true for any method based on the selection and identification of cDNAs from a library, the success of the screen is dependent on using a high-quality and high-complexity library as the screen can retrieve only those cDNA clones that are present in the library.
Using this protocol, we have successfully identified two novel suppressors of the genotoxic stress-sensitive phenotype of the query S. pombe ell1 null mutant. The ELL (Eleven Nineteen Lysine Rich Leukemia) family of transcription elongation factors suppress transient pausing of RNA polymerase II on DNA templates in in vitro biochemical assays and are conserved across various organisms, from fission yeast to humans25. Earlier work has provided evidence that an S. pombe ell1 null mutant shows genotoxic stress sensitivity in the presence of 4-nitroquinoline 1-oxide (4-NQO) and methyl methanesulfonate (MMS)26. Therefore, we transformed a S. pombe plasmid-encoded multicopy cDNA library into the query S. pombe ell1 null mutant and identified two putative clones that exhibited the ability to suppress the genotoxic stress sensitivity of the S. pombe ell1 null mutant in the presence of 4-NQO, a compound that induces DNA lesions. Subsequent sequencing of the insert present in the plasmid clones identified that the genes encoding rax2+ and osh6+ were responsible for suppressing the genotoxic stress sensitivity of ell1 null mutant when overexpressed in the ell1 null mutant.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>4-NQO</td>
			<td>Sigma</td>
			<td>N8141</td>
			<td></td>
		</tr>
		<tr>
			<td>Acetic Acid, glacial</td>
			<td>Sigma</td>
			<td>1371301000</td>
			<td></td>
		</tr>
		<tr>
			<td>Adenine Sulphate</td>
			<td>Himedia</td>
			<td>GRM033</td>
			<td></td>
		</tr>
		<tr>
			<td>Agar</td>
			<td>Himedia</td>
			<td>GRM026</td>
			<td></td>
		</tr>
		<tr>
			<td>Agarose</td>
			<td>Lonza</td>
			<td>50004L</td>
			<td></td>
		</tr>
		<tr>
			<td>Ammonium Chloride</td>
			<td>Himedia</td>
			<td>MB054</td>
			<td></td>
		</tr>
		<tr>
			<td>BamHI</td>
			<td>Fermentas</td>
			<td>ER0051</td>
			<td></td>
		</tr>
		<tr>
			<td>Biotin</td>
			<td>Himedia</td>
			<td>RM095</td>
			<td></td>
		</tr>
		<tr>
			<td>Boric Acid</td>
			<td>Himedia</td>
			<td>MB007</td>
			<td></td>
		</tr>
		<tr>
			<td>Calcium Chloride&#160;</td>
			<td>Sigma</td>
			<td>C4901</td>
			<td></td>
		</tr>
		<tr>
			<td>Chloroform:Isoamyl alcohol 24:1</td>
			<td>Sigma</td>
			<td>C0549</td>
			<td></td>
		</tr>
		<tr>
			<td>Citric Acid</td>
			<td>Himedia</td>
			<td>RM1023</td>
			<td></td>
		</tr>
		<tr>
			<td>Disodium hydrogen phospahte anhydrous</td>
			<td>Himedia</td>
			<td>GRM3960</td>
			<td></td>
		</tr>
		<tr>
			<td>single stranded DNA from Salmon testes</td>
			<td>Sigma</td>
			<td>D7656</td>
			<td></td>
		</tr>
		<tr>
			<td>EDTA disodium</td>
			<td>Sigma</td>
			<td>324503</td>
			<td></td>
		</tr>
		<tr>
			<td>Ferric Chloride Hexahydrate</td>
			<td>Himedia</td>
			<td>RM6353</td>
			<td></td>
		</tr>
		<tr>
			<td>Glucose</td>
			<td>Amresco</td>
			<td>188</td>
			<td></td>
		</tr>
		<tr>
			<td>Ionositol</td>
			<td>Himedia</td>
			<td>GRM102</td>
			<td></td>
		</tr>
		<tr>
			<td>Isopropanol</td>
			<td>Qualigen</td>
			<td>Q26897</td>
			<td></td>
		</tr>
		<tr>
			<td>Leucine</td>
			<td>Himedia</td>
			<td>GRM054</td>
			<td></td>
		</tr>
		<tr>
			<td>Lithium Acetatae</td>
			<td>Sigma</td>
			<td>517992</td>
			<td></td>
		</tr>
		<tr>
			<td>Magnesium Chloride Hexahydrate</td>
			<td>Himedia</td>
			<td>MB040</td>
			<td></td>
		</tr>
		<tr>
			<td>Molybdic Acid</td>
			<td>Himedia</td>
			<td>RM690</td>
			<td></td>
		</tr>
		<tr>
			<td>Nicotinic Acid</td>
			<td>Himedia</td>
			<td>CMS177</td>
			<td></td>
		</tr>
		<tr>
			<td>PEG, MW 4000</td>
			<td>Sigma</td>
			<td>81240</td>
			<td></td>
		</tr>
		<tr>
			<td>Pentothinic Acid</td>
			<td>Himedia</td>
			<td>TC159</td>
			<td></td>
		</tr>
		<tr>
			<td>Phenol</td>
			<td>Himedia</td>
			<td>MB082</td>
			<td></td>
		</tr>
		<tr>
			<td>Plasmid Extraction Kit</td>
			<td>Qiagen</td>
			<td>27104</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium Chloride</td>
			<td>Sigma</td>
			<td>P9541</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium hydrogen Pthallate</td>
			<td>Merc</td>
			<td>DDD7D670815</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium iodide</td>
			<td>Himedia</td>
			<td>RM1086</td>
			<td></td>
		</tr>
		<tr>
			<td>RNAse</td>
			<td>Fermentas</td>
			<td>EN0531</td>
			<td></td>
		</tr>
		<tr>
			<td>SDS</td>
			<td>Himedia</td>
			<td>GRM205</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Hydroxide</td>
			<td>Himedia</td>
			<td>GRM1183</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Sulphate</td>
			<td>Himedia</td>
			<td>RM1037</td>
			<td></td>
		</tr>
		<tr>
			<td>Tris free Base</td>
			<td>Himedia</td>
			<td>MB209</td>
			<td></td>
		</tr>
		<tr>
			<td>Uracil</td>
			<td>Himedia</td>
			<td>GRM264</td>
			<td></td>
		</tr>
		<tr>
			<td>Yeast Extract Powder</td>
			<td>Himedia</td>
			<td>RM668</td>
			<td></td>
		</tr>
		<tr>
			<td>Zinc Sulphate Heptahydrate</td>
			<td>Merc</td>
			<td>DJ9D692580</td>
			<td></td>
		</tr>
	</tbody>
</table>

genetic screen for identification of multicopy suppressors in schizosaccharomyces pombe

Identification of genetic interactions is a powerful tool to decipher the functions of gene(s) by providing insights into their functional relationships with other genes and organization into biological pathways and processes. Although the majority of the genetic screens were initially developed in Saccharomyces cerevisiae, a complementary platform for carrying out these genetic screens has been provided by Schizosaccharomyces pombe. One of the common approaches used to identify genetic interactions is by overexpression of clones from a genome-wide, high-copy-number plasmid library in a loss-of-function mutant, followed by selection of clones that suppress the mutant phenotype.
This paper describes a protocol for carrying out this &#39;multicopy suppression&#39;-based genetic screen in S. pombe. This screen has helped identify multicopy suppressor(s) of the genotoxic stress-sensitive phenotype associated with the absence of the Ell1 transcription elongation factor in S. pombe. The screen was initiated by transformation of the query ell1 null mutant strain with a high-copy-number S. pombe cDNA plasmid library and selecting the suppressors on EMM2 plates containing 4-nitroquinoline 1-oxide (4-NQO), a genotoxic stress-inducing compound. Subsequently, plasmid was isolated from two shortlisted suppressor colonies and digested by restriction enzymes to release the insert DNA. Plasmids releasing an insert DNA fragment were retransformed into the ell1 deletion strain to confirm the ability of these suppressor plasmid clones to restore growth of the ell1 deletion mutant in the presence of 4-NQO and other genotoxic compounds. Those plasmids showing a rescue of the deletion phenotype were sequenced to identify the gene(s) responsible for suppression of the ell1 deletion-associated genotoxic stress-sensitive phenotype.

Screening for multicopy suppressor(s) of ell1 deletion-associated genotoxic stress sensitivity in S. pombe 
We performed the genetic screen using the protocol described above to identify multicopy suppressors of the loss-of-function phenotype of the query ell1 deletion mutant strain. The growth-related sensitivity of the ell1 deletion strain observed in the presence of the 4-NQO genotoxic agent was adopted as the ...

Watch this Scientific Journal Video about Genetic Screen for Identification of Multicopy Suppressors in Schizosaccharomyces pombe at JoVE.com

Genetic Screen for Identification of Multicopy Suppressors in Schizosaccharomyces pombe

This work describes a protocol for a multicopy suppressor genetic screen in Schizosaccharomyces pombe. This screen uses a genome-wide plasmid library to identify suppressor clone(s) of a loss-of-function phenotype associated with a query mutant strain. Novel genetic suppressors of the ell1 null mutant were identified using this screen.

Genetic Screen for Identification of Multicopy Suppressors in Schizosaccharomyces pombe

Identification of genetic interactions is a powerful tool to decipher the functions of gene(s) by providing insights into their functional relationships ...

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1.7K Views.  University School of Biotechnology, G.G.S. Indraprastha University. This work describes a protocol for a multicopy suppressor genetic screen in Schizosaccharomyces pombe. This screen uses a genome-wide plasmid library to identify suppressor clone(s) of a loss-of-function phenotype associated with a query mutant strain. Novel genetic suppressors of the ell1 null mutant were identified using this screen.

Video: Genetic Screen for Identification of Multicopy Suppressors in Schizosaccharomyces pombe

Method for Culture of Early Chick Embryos ex vivo (New Culture)

The chick embryo is a valuable tool in the study of early embryonic development. Its transparency, accessibility and ease of manipulation, make it an ideal tool for studying  the formation and patterning of brain, neural tube, somite and heart primordia. Applications of chick embryo culture include electroporation of DNA or RNA constructs in order to analyze gene function, grafts of growth factor coated beads such as FGFs and BMPs , as well as whole mount in situ hybridization and immunohistochemistry. This video demonstrates the different steps in chick embryo culture; First, the embryo is explanted in saline. Then, the embryo is centered on a glass ring. The membranes surrounding the embryo are lifted along the walls of the ring. The ring is then placed in a culture dish containing a pool of albumine. The culture dish is sealed and placed in a humid chamber, where the embryo is cultured for up to 24 hrs. Finally, the embryo is removed from the ring, fixed and processed for further applications. A troubleshooting guide is also presented.

Method for Culture of Early Chick Embryos ex vivo New Culture

This video demonstrates New culture, a method by which chick embryos are cultured outside the egg for up to 24 hr. This method enables one to study early development (primitive streak to 14 som.), a period corresponding to E7-9 in mouse. Applications of this technique include electroporation, in situ hybridization and immunohistochemistry.

The chick embryo is a valuable tool in the study of early embryonic development. Its transparency, accessibility and ease of manipulation, make it an ...

Double Whole Mount in situ Hybridization of Early Chick Embryos

The chick embryo is a valuable tool in the study of early embryonic development. Its transparency, accessibility and ease of manipulation, make it an ideal tool for studying  gene expression in brain, neural tube, somite and heart primordia formation. This video demonstrates the different steps in 2-color whole mount in situ hybridization; First, the embryo is dissected from the egg and fixed in paraformaldehyde. Second, the embryo is processed for prehybridization. The embryo is then hybridized with two different probes, one coupled to DIG, and one coupled to FITC.  Following overnight hybridization, the embryo is incubated with DIG coupled antibody. Color reaction for DIG substrate is performed, and the region of interest appears blue. The embryo is then incubated with FITC coupled antibody. The embryo is processed for color reaction with FITC, and the region of interest appears red. Finally, the embryo is fixed and processed for phtograph and sectioning. A troubleshooting guide is also presented.

This video demonstrates 2-color whole mount in situ hybridization, a method by which the spatial and temporal expression pattern of 2 different genes can be visualized in young chick embryos. This method was originally introduced by David Wilkinson, Domingos Henrique, Phil Ingham and David Ish -Horowicz.

Method for Whole Mount Antibody Staining in Chick

The chick embryo is a valuable tool in the study of early embryonic development. Its transparency, accessibility and ease of manipulation, make it an ideal tool for studying antibody expression in developing brain, neural tube and somite. This video demonstrates the different steps in whole-mount antibody staining using HRP conjugated secondary antibodies; First, the embryo is dissected from the egg and fixed in paraformaldehyde. Second, endogenous peroxidase is inactivated; The embryo is then exposed to primary antibody. After several washes, the embryo is incubated with secondary antibody conjugated to HRP. Peroxidase activity is revealed using reaction with diaminobenzidine substrate. Finally, the embryo is fixed and processed for photography and sectioning. The advantage of this method over the use of fluorescent antibodies is that embryos can be processed for wax sectioning, thus enabling the study of antigen sites in cross section. This method was originally introduced by Jane Dodd and Tom Jessell 1.

This video demonstrates whole mount immunohistochemistry, a method by which the spatial and temporal expression pattern of an antigen can be visualized in young chick embryos. This method was originally introduced by Jane Dodd and Tom Jessell.

Assay for Neural Induction in the Chick Embryo

The chick embryo is a valuable tool in the study of early embryonic development. Its transparency, accessibility and ease of manipulation, make it an ideal tool for studying the formation and initial patterning of the nervous system. This video demonstrates how to graft organizer tissue into a host, a method by which Hensen s node (the organizer in the chick embryo) is grafted to a host competent ectoderm. The organizer graft instructs overlying na ve tissue to adopt a neural fate via neural inducing signals. This mechanism is referred to as neural induction, and constitutes the initial step in the formation of brain and spinal cord in amniotes. This method is essentially used for the characterization of putative neural inducing molecules in chick. This video demonstrates the different steps in the assay for neural induction; First, the donnor embryo is explanted and pinned on a dish. Then, the host embryo is prepared for New culture. The graft is excised and transplanted to the host area pellucida margin. The host is cultured for 18-22 hrs. The assembly is fixed and processed for further applications (e.g. in situ hybridization). This method was originally devised by Waddington 1,2 and Gallera 3,4.

Neural induction is the first step in the formation of the brain. It is a mechanism by which Hensen's node (organizer), instructs adjacent tissue to adopt a neural fate, i.e. to give rise to the nervous system. This video demonstrates an assay for neural induction in chick embryo.

Dissection of Hippocampal Dentate Gyrus from Adult Mouse

The hippocampus is one of the most widely studied areas in the brain because of its important functional role in memory processing and learning, its remarkable neuronal cell plasticity, and its involvement in epilepsy, neurodegenerative diseases, and psychiatric disorders. The hippocampus is composed of distinct regions; the dentate gyrus, which comprises mainly granule neurons, and Ammon's horn, which comprises mainly pyramidal neurons, and the two regions are connected by both anatomic and functional circuits. Many different mRNAs and proteins are selectively expressed in the dentate gyrus, and the dentate gyrus is a site of adult neurogenesis; that is, new neurons are continually generated in the adult dentate gyrus. To investigate mRNA and protein expression specific to the dentate gyrus, laser capture microdissection is often used. This method has some limitations, however, such as the need for special apparatuses and complicated handling procedures. In this video-recorded protocol, we demonstrate a dissection technique for removing the dentate gyrus from adult mouse under a stereomicroscope. Dentate gyrus samples prepared using this technique are suitable for any assay, including transcriptomic, proteomic, and cell biology analyses. We confirmed that the dissected tissue is dentate gyrus by conducting real-time PCR of dentate gyrus-specific genes, tryptophan 2,3-dioxygenase (TDO2) and desmoplakin (Dsp), and Ammon's horn enriched genes, Meis-related gene 1b (Mrg1b) and TYRO3 protein tyrosine kinase 3 (Tyro3). The mRNA expressions of TDO2 and Dsp in the dentate gyrus samples were detected at obviously higher levels, whereas Mrg1b and Tyro3 were lower levels, than those in the Ammon's horn samples. To demonstrate the advantage of this method, we performed DNA microarray analysis using samples of whole hippocampus and dentate gyrus. The mRNA expression of TDO2 and Dsp, which are expressed selectively in the dentate gyrus, in the whole hippocampus of alpha-CaMKII+/- mice, exhibited 0.037 and 0.10-fold changes compared to that of wild-type mice, respectively. In the isolated dentate gyrus, however, these expressions exhibited 0.011 and 0.021-fold changes compared to that of wild-type mice, demonstrating that gene expression changes in dentate gyrus can be detected with greater sensitivity. Taken together, this convenient and accurate dissection technique can be reliably used for studies focused on the dentate gyrus.

A dissection technique for removal of the dentate gyrus from adult mouse under a stereomicroscope was demonstrated in this video-recorded protocol.

The hippocampus is one of the most widely studied areas in the brain because of its important functional role in memory processing and learning, its ...

Rapid Genetic Analysis of Epithelial-Mesenchymal Signaling During Hair Regeneration

Hair follicle morphogenesis, a complex process requiring interaction between epithelia-derived keratinocytes and the underlying mesenchyme, is an attractive model system to study organ development and tissue-specific signaling. Although hair follicle development is genetically tractable, fast and reproducible analysis of factors essential for this process remains a challenge. Here we describe a procedure to generate targeted overexpression or shRNA-mediated knockdown of factors using lentivirus in a tissue-specific manner. Using a modified version of a hair regeneration model 5, 6, 11, we can achieve robust gain- or loss-of-function analysis in primary mouse keratinocytes or dermal cells to facilitate study of epithelial-mesenchymal signaling pathways that lead to hair follicle morphogenesis. We describe how to isolate fresh primary mouse keratinocytes and dermal cells, which contain dermal papilla cells and their precursors, deliver lentivirus containing either shRNA or cDNA to one of the cell populations, and combine the cells to generate fully formed hair follicles on the backs of nude mice. This approach allows analysis of tissue-specific factors required to generate hair follicles within three weeks and provides a fast and convenient companion to existing genetic models.

Tissue-specific analysis of a hair follicle regeneration model using lentivirus to mediate gain- or loss-of-function.

Hair follicle morphogenesis, a complex process requiring interaction between epithelia-derived keratinocytes and the underlying mesenchyme, is an ...

Imaging Cell Membrane Injury and Subcellular Processes Involved in Repair

The ability of injured cells to heal is a fundamental cellular process, but cellular and molecular mechanisms involved in healing injured cells are poorly understood. Here assays are described to monitor the ability and kinetics of healing of cultured cells following localized injury. The first protocol describes an end point based approach to simultaneously assess cell membrane repair ability of hundreds of cells. The second protocol describes a real time imaging approach to monitor the kinetics of cell membrane repair in individual cells following localized injury with a pulsed laser. As healing injured cells involves trafficking of specific proteins and subcellular compartments to the site of injury, the third protocol describes the use of above end point based approach to assess one such trafficking event (lysosomal exocytosis) in hundreds of cells injured simultaneously and the last protocol describes the use of pulsed laser injury together with TIRF microscopy to monitor the dynamics of individual subcellular compartments in injured cells at high spatial and temporal resolution. While the protocols here describe the use of these approaches to study the link between cell membrane repair and lysosomal exocytosis in cultured muscle cells, they can be applied as such for any other adherent cultured cell and subcellular compartment of choice.

The process of healing injured cells involves trafficking of specific proteins and subcellular compartments to the site of cell membrane injury. This protocol describes assays to monitor these processes.

The ability of injured cells to heal is a fundamental cellular process, but cellular and molecular mechanisms involved in healing injured cells are poorly ...

Rapid Identification of Chemical Genetic Interactions in Saccharomyces cerevisiae

Determining the mode of action of bioactive chemicals is of interest to a broad range of academic, pharmaceutical, and industrial scientists. Saccharomyces cerevisiae, or budding yeast, is a model eukaryote for which a complete collection of ~6,000 gene deletion mutants and hypomorphic essential gene mutants are commercially available. These collections of mutants can be used to systematically detect chemical-gene interactions, i.e. genes necessary to tolerate a chemical. This information, in turn, reports on the likely mode of action of the compound. Here we describe a protocol for the rapid identification of chemical-genetic interactions in budding yeast. We demonstrate the method using the chemotherapeutic agent 5-fluorouracil (5-FU), which has a well-defined mechanism of action. Our results show that the nuclear TRAMP RNA exosome and DNA repair enzymes are needed for proliferation in the presence of 5-FU, which is consistent with previous microarray based bar-coding chemical genetic approaches and the knowledge that 5-FU adversely affects both RNA and DNA metabolism. The required validation protocols of these high-throughput screens are also described.

Rapid Identification of Chemical Genetic Interactions in Saccharomyces cerevisiae

Here we present a cost-effective method for defining chemical-genetic interactions in budding yeast. The approach is built on fundamental techniques in yeast molecular biology and is well suited for the mechanistic interrogation of small to medium collections of chemicals and other media environments.

Determining the mode of action of bioactive chemicals is of interest to a broad range of academic, pharmaceutical, and industrial scientists. ...

DNA Electroporation, Isolation and Imaging of Myofibers

Mature muscle has a unique structure that is amenable to live cell imaging. Herein, we describe the experimental protocol for expressing fluorescently labeled proteins in the flexor digitorum brevis (FDB) muscle. Conditions have been optimized to provide a large number of high quality myofibers expressing the electroporated plasmid while minimizing muscle damage. The method employs fluorescent tags on various proteins. Combining this expression method with high resolution confocal microscopy permits live cell imaging, including imaging after laser-induced damage. Fluorescent dyes combined with imaging of fluorescently-tagged proteins provides information regarding the basic structure of muscle and its response to stimuli.

This protocol utilizes electroporation to introduce and express fluorescently labeled proteins in mouse muscle fibers. Following recovery after electroporation, fibers are isolated. Individual fibers are then imaged using high resolution confocal microscopy to visualize muscle structure.

Mature muscle has a unique structure that is amenable to live cell imaging. Herein, we describe the experimental protocol for expressing fluorescently ...

In Vivo Alkaline Comet Assay and Enzyme-modified Alkaline Comet Assay for Measuring DNA Strand Breaks and Oxidative DNA Damage in Rat Liver

Unrepaired DNA damage can lead to genetic instability, which in turn may enhance cancer development. Therefore, identifying potential DNA damaging agents is important for protecting public health. The in vivo alkaline comet assay, which detects DNA damage as strand breaks, is especially relevant for assessing the genotoxic hazards of xenobiotics, as its responses reflect the in vivo absorption, tissue distribution, metabolism and excretion (ADME) of chemicals, as well as DNA repair process. Compared to other in vivo DNA damage assays, the assay is rapid, sensitive, visual and inexpensive, and, by converting oxidative DNA damage into strand breaks using specific repair enzymes, the assay can measure oxidative DNA damage in an efficient and relatively artifact-free manner. Measurement of DNA damage with the comet assay can be performed using both acute and subchronic toxicology study designs, and by integrating the comet assay with other toxicological assessments, the assay addresses animal welfare requirements by making maximum use of animal resources. Another major advantage of the assays is that they only require a small amount of cells, and the cells do not have to be derived from proliferating cell populations. The assays also can be performed with a variety of human samples obtained from clinically or occupationally exposed individuals.

In Vivo Alkaline Comet Assay and Enzyme-modified Alkaline Comet Assay for Measuring DNA Strand Breaks and Oxidative DNA Damage in Rat Liver

The alkaline comet assay measures DNA strand breaks in eukaryotic cells. By adding an Endonuclease III or human 8-oxoguanine-DNA-N-glycosylase digestion step, the assay can efficiently detect oxidative DNA damage. We describe methods for using these assays to detect DNA damage in rat liver.

Unrepaired DNA damage can lead to genetic instability, which in turn may enhance cancer development. Therefore, identifying potential DNA damaging agents ...