Name: use of the pyrimidine analog, 5-iodo-2&prime;-deoxyuridine (idu) with cell cycle markers to establish cell cycle phases in a mass cytometry platform
Uploaded: 2021-10-22T13:00:00
Description: Watch this Scientific Journal Video about Use of the Pyrimidine Analog, 5-Iodo-2â€²-Deoxyuridine IdU with Cell Cycle Markers to Establish Cell Cycle Phases in a Mass Cytometry Platform at JoVE.com

The authors would like to thank the efforts of Palak Sekhri, Hussam Alkhalaileh, Hsiaochi Chang, and Justin Lyeberger for their experimental support. This work was supported by the Pelotonia Fellowship Program. Any opinions, findings, and conclusions expressed in this material are those of the author(s) and do not necessarily reflect those of the Pelotonia Fellowship Program.&#34;

1. Preparation of IdU stocks
<ol>
	<li>Dissolve 5-iodo-2&#8217;-deoxyuridine (IdU) in DMSO to a concentration of 50 mM. Sterile filter, aliquot into 10-50 &#181;L tubes, and store at -80 &#176;C</li>
	<li>Remove IdU from the freezer, and thaw at room temperature. Dilute IdU in RPMI-1640 to make a working solution at a final concentration of 1 mM. Pipette up and down or vortex to mix.
	<ol>
		<li>Typically, dilute the concentrated IdU into the media in which the cells are being cultured (e.g. DMEM, IMDM, etc.) or have d...

<ol>
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R., Fantl, W. J., Nolan, G. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single-cell+mass+cytometry+adapted+to+measurements+of+the+cell+cycle.">Single-cell mass cytometry adapted to measurements of the cell cycle.</a> Cytometry A. 81 (7), 552-566 (2012).</li><li>Raval, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reversibility+of+Defective+Hematopoiesis+Caused+by+Telomere+Shortening+in+Telomerase+Knockout+Mice.">Reversibility of Defective Hematopoiesis Caused by Telomere Shortening in Telomerase Knockout Mice.</a> PLoS One. 10 (7), 0131722 (2015).</li><li>Behbehani, G. 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=Mass+Cytometric+Functional+Profiling+of+Acute+Myeloid+Leukemia+Defines+Cell-Cycle+and+Immunophenotypic+Properties+That+Correlate+with+Known+Responses+to+Therapy.">Mass Cytometric Functional Profiling of Acute Myeloid Leukemia Defines Cell-Cycle and Immunophenotypic Properties That Correlate with Known Responses to Therapy.</a> Cancer Discovery. 5 (9), 988-1003 (2015).</li><li>Kimmey, S. C., Borges, L., Baskar, R., Bendall, S. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Parallel+analysis+of+tri-molecular+biosynthesis+with+cell+identity+and+function+in+single+cells.">Parallel analysis of tri-molecular biosynthesis with cell identity and function in single cells.</a> Nature Communications. 10 (1), 1185 (2019).</li><li>Rabinovitch, P. S., Kubbies, M., Chen, Y. C., Schindler, D., Hoehn, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=BrdU-Hoechst+flow+cytometry:+a+unique+tool+for+quantitative+cell+cycle+analysis.">BrdU-Hoechst flow cytometry: a unique tool for quantitative cell cycle analysis.</a> Experimental Cell Research. 174 (2), 309-318 (1988).</li><li>Rahman, A. H., Tordesillas, L., Berin, M. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Heparin+reduces+nonspecific+eosinophil+staining+artifacts+in+mass+cytometry+experiments.">Heparin reduces nonspecific eosinophil staining artifacts in mass cytometry experiments.</a> Cytometry A. 89 (6), 601-607 (2016).</li><li>McCarthy, R. L., Duncan, A. D., Barton, M. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sample+Preparation+for+Mass+Cytometry+Analysis.">Sample Preparation for Mass Cytometry Analysis.</a> Journal of Visualized Experiments. (122), e54394 (2017).</li><li>Behbehani, G. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Immunophenotyping+by+Mass+Cytometry.">Immunophenotyping by Mass Cytometry.</a> Methods in Molecular Biology. 2032, 31-51 (2019).</li><li>Leipold, M. D., Maecker, H. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mass+cytometry:+protocol+for+daily+tuning+and+running+cell+samples+on+a+CyTOF+mass+cytometer.">Mass cytometry: protocol for daily tuning and running cell samples on a CyTOF mass cytometer.</a> Journal of Visualized Experiments. (69), e4398 (2012).</li><li>Finck, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Normalization+of+mass+cytometry+data+with+bead+standards.">Normalization of mass cytometry data with bead standards.</a> Cytometry A. 83 (5), 483-494 (2013).</li><li>Kotecha, N., Krutzik, P. O., Irish, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Web-based+analysis+and+publication+of+flow+cytometry+experiments.">Web-based analysis and publication of flow cytometry experiments.</a> Current Protocols in Cytometry. , 17 (2010).</li><li>Devine, R. D., Sekhri, P., Behbehani, G. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+storage+time+and+temperature+on+cell+cycle+analysis+by+mass+cytometry.">Effect of storage time and temperature on cell cycle analysis by mass cytometry.</a> Cytometry A. 93 (11), 1141-1149 (2018).</li><li>Campos, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Expression+of+immunological+markers+on+leukemic+cells+before+and+after+cryopreservation+and+thawing.">Expression of immunological markers on leukemic cells before and after cryopreservation and thawing.</a> Cryobiology. 25 (1), 18-22 (1988).</li><li>Kadic, E., Moniz, R. J., Huo, Y., Chi, A., Kariv, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+cryopreservation+on+delineation+of+immune+cell+subpopulations+in+tumor+specimens+as+determinated+by+multiparametric+single+cell+mass+cytometry+analysis.">Effect of cryopreservation on delineation of immune cell subpopulations in tumor specimens as determinated by multiparametric single cell mass cytometry analysis.</a> BMC Immunology. 18 (1), 6 (2017).</li><li>Shabihkhani, M., 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=The+procurement,+storage,+and+quality+assurance+of+frozen+blood+and+tissue+biospecimens+in+pathology,+biorepository,+and+biobank+settings.">The procurement, storage, and quality assurance of frozen blood and tissue biospecimens in pathology, biorepository, and biobank settings.</a> Clinical Biochemistry. 47 (4-5), 258-266 (2014).</li></ol>

The examples presented here demonstrate how to use an MCM platform to analyze cell cycle distribution. It has also been demonstrated that cell cycle analysis is sensitive to experimental conditions such as time and temperature, which is an important consideration researchers must take when considering MCM for their cell cycle analysis14. Samples left in storage for a short period of time, no longer than an hour, will have IdU incorporation comparable to their normal state. Samples in a closed syst...

Mass cytometry enables detection of approximately 40 parameters by taking advantage of the high resolution and quantitative nature of mass spectroscopy. Metal-labeled antibodies are used instead of fluorophore conjugated antibodies that allow for a higher number of channels and produce minimal spillover1,2. MCM has advantages and disadvantages in regard to cell cycle analysis in comparison to flow cytometry. One major advantage of MCM is that the large number of parameters enables the simultaneous measurement of cell cycle state across a large number of immunophenotypically distinct T-cell types in highly heterogeneous samples. MCM has been successfully used to measure the cell cycle state during normal hematopoiesis in human bone marrow3 and transgenic murine models of telomerase deficiency4. Analysis of cell cycle state in acute myeloid leukemia (AML) showed that cell cycle correlated to known responses to clinical therapies, providing an in vivo insight into functional characteristics that can inform therapy selections5. A second advantage of mass cytometric cell cycle analysis is the ability to measure a large number of other functional markers that may be correlated with cell cycle state. Recent work has been able to correlate protein and RNA synthesis with cell cycle state through the use of IdU and metal tagged antibodies to BRU and rRNA6. This kind of highly parametric analysis measuring cell cycle state across numerous populations in a continuum of differentiation would be nearly impossible with current flow cytometry technology. The major disadvantage of MCM is the lack of comparable DNA or RNA stains as those used in fluorescent flow cytometry (e.g., DAPI, Hoechst, Pyronin Y, etc.). Fluorescent dyes can give relatively precise measurements of DNA and RNA content, but this precision is only possible due to the changes in the fluorescent properties of these dyes that occur upon intercalation between nucleotide bases. MCM analysis is thus unable to measure DNA or RNA content with similar precision. Instead, mass cytometric cell cycle analysis relies on measurements of proteins related to cell cycle state such as cyclin B1, phosphorylated retinoblastoma protein (pRb), and phosphorylated Histone H3 (pHH3) combined with direct measurement of the iodine atom from IdU incorporation into S-phase cells. These two measurement approaches yield highly similar results during normal cellular proliferation, but can potentially be discordant when cell cycle progression is disrupted.
Measurement of the number of cells in each cell cycle phase is important in understanding normal cell cycle development as well as cell cycle disruption, which is commonly observed in cancers and immunological diseases. MCM provides reliable measurement of extracellular and intracellular factors using metal-tagged antibodies; however, measurement of the S-phase was limited as the iridium-based DNA intercalator was unable to differentiate between 2N and 4N DNA. In order to define cell cycle phases, Behbehani developed a method that utilizes IdU with a mass of 127, which falls within the range of the mass cytometer and allows direct measurement of cells in S-phase3. This direct measurement circumvents the need for secondary antibodies or use of DNA denaturing agents such as acid or DNase. In conjunction with intracellular cycling markers, it allows high resolution of cell cycle distribution in experimental models.
This protocol adapts cell cycle measurements from common flow cytometry protocols for MCM. Our methods provide a convenient and simple way to include cell cycle parameters. IdU incorporation of in vitro samples requires only 10 to 15 minutes of incubation at 37 &#176;C, which is shorter than most BrdU staining protocols that recommend incubation times of several hours3,7. IdU and BrdU incorporated samples can be fixed using a proteomic stabilizer and then stored for some time in a -80 &#176;C freezer. This allows large numbers of IdU stained samples to be archived for batch analysis without reduction in sample quality.

<table>
	<tbody>
		<tr>
			<td>Bovine Serum Albumin (BSA)</td>
			<td>Sigma</td>
			<td>A3059</td>
			<td>Component of CSM</td>
		</tr>
		<tr>
			<td>Centrifuge</td>
			<td>Thermo Scientific</td>
			<td>75-217-420</td>
			<td>Sample centrifugation</td>
		</tr>
		<tr>
			<td>Cleaved-PARP (D214)</td>
			<td>BD Biosciences</td>
			<td>F21-852</td>
			<td>Identification of apoptotic cells</td>
		</tr>
		<tr>
			<td>Cyclin B1</td>
			<td>BD Biosciences</td>
			<td>GNS-1</td>
			<td>G2 Resolution</td>
		</tr>
		<tr>
			<td>Dimethylsulfoxide (DMSO)</td>
			<td>Sigma</td>
			<td>D2650</td>
			<td>Cryopreservative</td>
		</tr>
		<tr>
			<td>EQ Four Element Calibration Beads</td>
			<td>Fluidigm</td>
			<td>201078</td>
			<td>Internal metal standard for CyTOF performance</td>
		</tr>
		<tr>
			<td>FACS Tube w/ mesh strainer</td>
			<td>Corning</td>
			<td>08-771-23</td>
			<td>Cell strainer to remove clumps/debris before CyTOF run</td>
		</tr>
		<tr>
			<td>Fetal Bovine Serum (FBS)</td>
			<td>VWR</td>
			<td>97068-085</td>
			<td>Cell culture growth supplement</td>
		</tr>
		<tr>
			<td>Helios</td>
			<td>Fluidigm</td>
			<td></td>
			<td>CyTOF System/Platform</td>
		</tr>
		<tr>
			<td>Heparin</td>
			<td>Sigma</td>
			<td>H3393</td>
			<td>Staining additive to prevent non-specific staining</td>
		</tr>
		<tr>
			<td>IdU (5-Iodo-2&#8242;-deoxyuridine)</td>
			<td>Sigma</td>
			<td>I7125</td>
			<td>Incorporates in S-phase</td>
		</tr>
		<tr>
			<td>Ki-67</td>
			<td>eBiosciences</td>
			<td>SolA15</td>
			<td>Confirmation of G0/G1</td>
		</tr>
		<tr>
			<td>MaxPar Multi Label Kit</td>
			<td>Fluidigm</td>
			<td>201300</td>
			<td>Metal labeling kit, attaches metals to antibodies</td>
		</tr>
		<tr>
			<td>Microplate Shaker</td>
			<td>Thermo Scientific</td>
			<td>88880023</td>
			<td>Mixing samples during staining</td>
		</tr>
		<tr>
			<td>Paraformaldehyde (PFA)</td>
			<td>Electron Microscopy Services</td>
			<td>15710</td>
			<td>Fixative</td>
		</tr>
		<tr>
			<td>pentamethylcyclopentadienyl-Ir(III)-dipyridophenazine</td>
			<td>Fluidigm</td>
			<td>201192</td>
			<td>Cell identification during CyTOF acquisition</td>
		</tr>
		<tr>
			<td>p-H2AX (S139)</td>
			<td>Millipore</td>
			<td>JBW301</td>
			<td>Detection of DNA damage</td>
		</tr>
		<tr>
			<td>p-HH3 (S28)</td>
			<td>Biolegend</td>
			<td>HTA28</td>
			<td>M-phase Resolution</td>
		</tr>
		<tr>
			<td>Phosphate Buffered Saline (PBS)</td>
			<td>Gibco</td>
			<td>14190-144</td>
			<td>Wash solution for cell culture and component of fixative solution</td>
		</tr>
		<tr>
			<td>p-Rb (S807/811)</td>
			<td>BD Biosciences</td>
			<td>J112906</td>
			<td>G0/G1 Resolution</td>
		</tr>
		<tr>
			<td>Proteomic Stabilizer</td>
			<td>SmartTube Inc</td>
			<td>PROT1</td>
			<td>Sample fixative</td>
		</tr>
		<tr>
			<td>RPMI 1640</td>
			<td>Gibco</td>
			<td>21870-076</td>
			<td>Cell culture growth medium</td>
		</tr>
		<tr>
			<td>Sodium Azide</td>
			<td>Acros Organics</td>
			<td>AC447810250</td>
			<td>Component of CSM/Antibody buffer, biocide</td>
		</tr>
	</tbody>
</table>

use of the pyrimidine analog, 5-iodo-2&prime;-deoxyuridine (idu) with cell cycle markers to establish cell cycle phases in a mass cytometry platform

The regulation of cell cycle phase is an important aspect of cellular proliferation and homeostasis. Disruption of the regulatory mechanisms governing the cell cycle is a feature of a number of diseases, including cancer. Study of the cell cycle necessitates the ability to define the number of cells in each portion of cell cycle progression as well as to clearly delineate between each cell cycle phase. The advent of mass cytometry (MCM) provides tremendous potential for high throughput single cell analysis through direct measurements of elemental isotopes, and the development of a method to measure the cell cycle state by MCM further extends the utility of MCM. Here we describe a method that directly measures 5-iodo-2&#8242;-deoxyuridine (IdU), similar to 5-bromo-2&#180;-deoxyuridine (BrdU), in an MCM system. Use of this IdU-based MCM provides several advantages. First, IdU is rapidly incorporated into DNA during its synthesis, allowing reliable measurement of cells in the S-phase with incubations as short as 10-15 minutes. Second, IdU is measured without the need for secondary antibodies or the need for DNA degradation. Third, IdU staining can be easily combined with measurement of cyclin B1, phosphorylated retinoblastoma protein (pRb), and phosphorylated histone H3 (pHH3), which collectively provides clear delineation of the five cell cycle phases. Combination of these cell cycle markers with the high number of parameters possible with MCM allow combination with numerous other metrics.

Utilizing HL-60 cells and a human bone marrow aspirate it is possible to show how experimental conditions can affect cell cycle distribution and analysis. First, the gating strategy must be established to demonstrate how the cell cycle phases are derived. In Figure 1 we show the establishment of the singlet gate, which is important in separating cellular debris and doublets, establishing a single cell population. For cell lines the singlet gate is all that is needed to move onto cell cycle a...

Watch this Scientific Journal Video about Use of the Pyrimidine Analog, 5-Iodo-2â€²-Deoxyuridine IdU with Cell Cycle Markers to Establish Cell Cycle Phases in a Mass Cytometry Platform at JoVE.com

Use of the Pyrimidine Analog, 5-Iodo-2&amp;#8242;-Deoxyuridine IdU with Cell Cycle Markers to Establish Cell Cycle Phases in a Mass Cytometry Platform

This protocol adapts cell cycle measurements for use in a mass cytometry platform. With the multi-parameter capabilities of mass cytometry, direct measurement of iodine incorporation allows identification of cells in S-phase while intracellular cycling markers enable characterization of each cell cycle state in a range of experimental conditions.

Use of the Pyrimidine Analog, 5-Iodo-2&prime;-Deoxyuridine (IdU) with Cell Cycle Markers to Establish Cell Cycle Phases in a Mass Cytometry Platform

The regulation of cell cycle phase is an important aspect of cellular proliferation and homeostasis. Disruption of the regulatory mechanisms governing the ...

This protocol allows us to examine the cell cycle at the single cell level using the mass cytometer, and this enables several novel research and clinical studies to be performed. The main advantage of this technique is its simplicity. IdU is added directly to the cells and there is no need for further treatment or antibodies.We've used this technique to investigate the cell cycle state in patients with acute myeloid leukemia within the stem and progenitor cell compartments. And this demonstrated that the cell cycle properties of these specific cell types may correlate with the clinical outcome of patients with these diseases. This technique can be useful for understanding growth properties of rare cancer cells and understanding the proliferation of immune cell subsets.Before and after adding IdU to the cell samples, maintain the cells in the growth conditions of interest. In this case, a humidified 37 degrees Celsius incubator at 5%CO2 to label the cells with IdU, dilute the concentrated IdU stock solution one to 50 into the growth media of the cells. Then transfer the samples into a biosafety hood and add 10 microliters of one millimolar IdU to every one milliliter of cells.Return the cells to the incubator for 10 to 15 minutes before transferring the samples to individual conical tubes. Collect the cells by centrifugation in 15 milliliter conical tubes and resuspend the pellets in 200 microliters of PBS per tube. If needed, label the cells with an appropriate live/dead stain to mark the dead cells.Following live/dead stain, quenched the cells with media washed with CSM before fixing the cells with 25 microliters of 16%paraformaldehyde. After a 10 minute incubation at room temperature, collect the cells by centrifugation. Add five to 15 milliliters of CSM and centrifuge again.Resuspend the pellets in 500 microliters of cell staining medium supplemented with 10%dimethyl sulfoxide. Then transfer the cells into smaller tubes to store them in negative 80 degrees Celsius. To normalize the for their cell cycle analysis, import the files into an appropriate flow cytometry analysis software program and create a biaxial plot of the event length versus 191 iridium.The cells will form a distinct bright iridium high population. Change the event length scale to make the cells appear more prominent. Then create a singlet gate to exclude 50 to 60%of the doublets and debris and set the residual and offset Gaussian parameters to remove any remaining doublets and debris.To set the S-phase gate, create a biaxial plot of IdU versus a proliferation marker. The S-phase IdU positive cells will form a distinct population. For G0/G1, and G2/M gating, establish the gates on an IdU versus Cyclin B1 plot.The G0/G1 phase will be Cyclin B1 low, IdU negative, and the G2/M phase will be Cyclin B1 high, IdU negative. To gate for specific cell types, plot only the S-phase cells on the Cyclin B1 versus IdU graph to help establish the separation between G0/G1 phase and G2/M phase cells. Draw a gate around the Cyclin B1 high population.In some cases, this can be difficult to discern but the level of Cyclin B1 of approximately top 5%of the S-phase population is typically the breakpoint between the G0/G1 and G2/M phase gates. The cells residing within the previous gate will be the G2/M phase population, while the remainder will be the G0/G1 phase population. To establish the G0 phase population, create a phosphorylated retinoblastoma protein versus IdU plot.The G0 phase will be represented by a phosphorylated retinoblastoma protein low, IdU negative population. As the active cycling population will demonstrate a high phosphorylated retinoblastoma protein and IdU incorporation, the G0 phase gate can be drawn on this boundary as it typically expresses at two distinct populations. If the G0 gate is difficult to define, make the S-phase population the active population and draw a gate incorporating the top 90 to 100%of the phosphorylated retinoblastoma protein high population.The phosphorylated retinoblastoma protein low population outside of the gate is typically the G0 population, while the G0/G1 cells with pRb levels that fall in this gate are G1 cells. For M-phase gating, create an IdU versus phosphorylated histone H3 by axial plot. The M-phase phase will be observed as the very small fraction of cells within the phosphorylated histone H3 population.The cells in the G2/M population with lower levels of pHH3 are the G2 cells. If IdU incorporation failed or was not possible, define the cycling and not cycling cell fractions using Ki67 and phosphorylated retinoblastoma protein. The double positive population will represent the active cycling population correlating to the G1, S, G2, and M-phases.The the double low population will represent the not cycling population correlating to the G0 phase. Once all of the gates have been established, export the numerical values from the gates. The percentages in each cycle can be achieved by subtracting the single populations from the combined populations to generate numerical values for each individual cell cycle phase for subsequent graphing and statistical analyze.The establishment of the singlet gate is important for separating the cellular debris and doublets to allow isolation of the single cell population. Cell cycle analysis of the single cells can then be performed. IdU labeling and thus downstream cell cycle analysis can significantly be affected by time and temperature.For example, cells that remain too long in enclosed vessels or in transport between locations will have reduced S-phase fractions and that will not be accurate for cell cycle analysis. Cell samples held for short periods of an hour or less still demonstrate a normal cell cycle distribution, indicating that a quick transport may not negatively impact the analysis. Cryopreserved cells may require a long equilibration period before the cells return to active cell cycling, which may still not reflect the pre-cryopreservation cell cycle state.Different cell types may also be differentially affected by maintenance conditions. For example, in this human bone marrow sample, the T-cells demonstrated a reduction in cell numbers compared to monoblasts from the same sample. Another benefit of mass cytometry is the ability to discriminate cells in cell cycle arrest or that have an abnormal cell cycle distribution.A major advantage of this technique is it is easily compatible with other mass cytometry measurements such as surface phenotyping, chromatin structure, intracellular cytokine stimulate, which can be correlated with cell cycle state. We've used this technique to study immune cell exhaustion, senescence, and to show that the response to chemotherapy in patients with acute leukemia may correlate with the cell cycle properties of the leukemia cells.

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High-Throughput Robotically Assisted Isolation of Temperature-sensitive Lethal Mutants in Chlamydomonas reinhardtii

Systematic identification and characterization of genetic perturbations have proven useful to decipher gene function and cellular pathways. However, the conventional approaches of permanent gene deletion cannot be applied to essential genes. We have pioneered a unique collection of ~70 temperature-sensitive (ts) lethal mutants for studying cell cycle regulation in the unicellular green algae Chlamydomonas reinhardtii1. These mutations identify essential genes, and the ts alleles can be conditionally inactivated by temperature shift, providing valuable tools to identify and analyze essential functions. Mutant collections are much more valuable if they are close to comprehensive, since scattershot collections can miss important components. However, this requires the efficient collection of a large number of mutants, especially in a wide-target screen. Here, we describe a robotics-based pipeline for generating ts lethal mutants and analyzing their phenotype in Chlamydomonas. This technique can be applied to any microorganism that grows on agar. We have collected over 3000 ts mutants, probably including mutations in most or all cell-essential pathways, including about 200 new candidate cell cycle mutations. Subsequent molecular and cellular characterization of these mutants should provide new insights in plant cell biology; a comprehensive mutant collection is an essential prerequisite to ensure coverage of a broad range of biological pathways. These methods are integrated with downstream genetics and bioinformatics procedures for efficient mapping and identification of the causative mutations that are beyond the scope of this manuscript.

High-Throughput Robotically Assisted Isolation of Temperature-sensitive Lethal Mutants in Chlamydomonas reinhardtii

Temperature-sensitive (ts) lethal mutants are valuable tools to identify and analyze essential functions. Here we describe methods to generate and classify ts lethal mutants in high throughput.

Systematic identification and characterization of genetic perturbations have proven useful to decipher gene function and cellular pathways. However, the ...

Rearing and Double-stranded RNA-mediated Gene Knockdown in the Hide Beetle, Dermestes maculatus

Advances in genomics have raised the possibility of probing biodiversity at an unprecedented scale. However, sequence alone will not be informative without tools to study gene function. The development and sharing of detailed protocols for the establishment of new model systems in laboratories, and for tools to carry out functional studies, is thus crucial for leveraging the power of genomics. Coleoptera (beetles) are the largest clade of insects and occupy virtually all types of habitats on the planet. In addition to providing ideal models for fundamental research, studies of beetles can have impacts on pest control as they are often pests of households, agriculture, and food industries. Detailed protocols for rearing and maintenance of D. maculatus laboratory colonies and for carrying out dsRNA-mediated interference in D. maculatus are presented. Both embryonic and parental RNAi procedures-including apparatus set up, preparation, injection, and post-injection recovery-are described. Methods are also presented for analyzing embryonic phenotypes, including viability, patterning defects in hatched larvae, and cuticle preparations for unhatched larvae. These assays, together with in situ hybridization and immunostaining for molecular markers, make D. maculatus an accessible model system for basic and applied research. They further provide useful information for establishing procedures in other emerging insect model systems.

Rearing and Double-stranded RNA-mediated Gene Knockdown in the Hide Beetle, Dermestes maculatus

Here, we present protocols for rearing an intermediate-germ beetle, Dermestes maculatus (D. maculatus) in the lab. We also share protocols for embryonic and parental RNAi and methods for analyzing embryonic phenotypes to study gene function in this species.

Advances in genomics have raised the possibility of probing biodiversity at an unprecedented scale. However, sequence alone will not be informative ...

Detection of Copy Number Alterations Using Single Cell Sequencing

Detection of genomic changes at single cell resolution is important for characterizing genetic heterogeneity and evolution in normal tissues, cancers, and microbial populations. Traditional methods for assessing genetic heterogeneity have been limited by low resolution, low sensitivity, and/or low specificity. Single cell sequencing has emerged as a powerful tool for detecting genetic heterogeneity with high resolution, high sensitivity and, when appropriately analyzed, high specificity. Here we provide a protocol for the isolation, whole genome amplification, sequencing, and analysis of single cells. Our approach allows for the reliable identification of megabase-scale copy number variants in single cells. However, aspects of this protocol can also be applied to investigate other types of genetic alterations in single cells.

Single cell sequencing is an increasingly popular and accessible tool for addressing genomic changes at high resolution. We provide a protocol that uses single cell sequencing to identify copy number alterations in single cells.

Detection of genomic changes at single cell resolution is important for characterizing genetic heterogeneity and evolution in normal tissues, cancers, and ...

Using a Fluorescent PCR-capillary Gel Electrophoresis Technique to Genotype CRISPR/Cas9-mediated Knockout Mutants in a High-throughput Format

The development of programmable genome-editing tools has facilitated the use of reverse genetics to understand the roles specific genomic sequences play in the functioning of cells and whole organisms. This cause has been tremendously aided by the recent introduction of the CRISPR/Cas9 system-a versatile tool that allows researchers to manipulate the genome and transcriptome in order to, among other things, knock out, knock down, or knock in genes in a targeted manner. For the purpose of knocking out a gene, CRISPR/Cas9-mediated double-strand breaks recruit the non-homologous end-joining DNA repair pathway to introduce the frameshift-causing insertion or deletion of nucleotides at the break site. However, an individual guide RNA may cause undesirable off-target effects, and to rule these out, the use of multiple guide RNAs is necessary. This multiplicity of targets also means that a high-volume screening of clones is required, which in turn begs the use of an efficient high-throughput technique to genotype the knockout clones. Current genotyping techniques either suffer from inherent limitations or incur high cost, hence rendering them unsuitable for high-throughput purposes. Here, we detail the protocol for using fluorescent PCR, which uses genomic DNA from crude cell lysate as a template, and then resolving the PCR fragments via capillary gel electrophoresis. This technique is accurate enough to differentiate one base-pair difference between fragments and hence is adequate in indicating the presence or absence of a frameshift in the coding sequence of the targeted gene. This precise knowledge effectively precludes the need for a confirmatory sequencing step and allows users to save time and cost in the process. Moreover, this technique has proven to be versatile in genotyping various mammalian cells of various tissue origins targeted by guide RNAs against numerous genes, as shown here and elsewhere.

The genotyping technique described here, which couples fluorescent polymerase chain reaction (PCR) to capillary gel electrophoresis, allows for high-throughput genotyping of nuclease-mediated knockout clones. It circumvents limitations faced by other genotyping techniques and is more cost effective than sequencing methods.

The development of programmable genome-editing tools has facilitated the use of reverse genetics to understand the roles specific genomic sequences play ...

Studying Cell Cycle-regulated Gene Expression by Two Complementary Cell Synchronization Protocols

The gene expression program of the cell cycle represents a critical step for understanding cell cycle-dependent processes and their role in diseases such as cancer. Cell cycle-regulated gene expression analysis depends on cell synchronization into specific phases. Here we describe a method utilizing two complementary synchronization protocols that is commonly used for studying periodic variation of gene expression during the cell cycle. Both procedures are based on transiently blocking the cell cycle in one defined point. The synchronization protocol by hydroxyurea (HU) treatment leads to cellular arrest in late G1/early S phase, and release from HU-mediated arrest provides a cellular population uniformly progressing through S and G2/M. The synchronization protocol by thymidine and nocodazole (Thy-Noc) treatment blocks cells in early mitosis, and release from Thy-Noc mediated arrest provides a synchronized cellular population suitable for G1 phase and S phase-entry studies. Application of both procedures requires monitoring of the cell cycle distribution profiles, which is typically performed after propidium iodide (PI) staining of the cells and flow cytometry-mediated analysis of DNA content. We show that the combined use of two synchronization protocols is a robust approach to clearly determine the transcriptional profiles of genes that are differentially regulated in the cell cycle (i.e. E2F1 and E2F7), and consequently to have a better understanding of their role in cell cycle processes. Furthermore, we show that this approach is useful for the study of mechanisms underlying drug-based therapies (i.e. mitomycin C, an anticancer agent), because it allows to discriminate genes that are responsive to the genotoxic agent from those solely affected by cell cycle perturbations imposed by the agent.

We report two cell synchronization protocols that provide a context for studying events related to specific phases of the cell cycle. We show that this approach is useful for analyzing the regulation of specific genes in an unperturbed cell cycle or upon exposure to agents affecting the cell cycle.

The gene expression program of the cell cycle represents a critical step for understanding cell cycle-dependent processes and their role in diseases such ...

Profiling DNA Replication Timing Using Zebrafish as an In Vivo Model System

DNA replication timing is an important cellular characteristic, exhibiting significant relationships with chromatin structure, transcription, and DNA mutation rates. Changes in replication timing occur during development and in cancer, but the role replication timing plays in development and disease is not known. Zebrafish were recently established as an in vivo model system to study replication timing. Here is detailed the protocols for using the zebrafish to determine DNA replication timing. After sorting cells from embryos and adult zebrafish, high-resolution genome-wide DNA replication timing patterns can be constructed by determining changes in DNA copy number through analysis of next generation sequencing data. The zebrafish model system allows for evaluation of the replication timing changes that occur in vivo throughout development, and can also be used to assess changes in individual cell types, disease models, or mutant lines. These methods will enable studies investigating the mechanisms and determinants of replication timing establishment and maintenance during development, the role replication timing plays in mutations and tumorigenesis, and the effects of perturbing replication timing on development and disease.

Profiling DNA Replication Timing Using Zebrafish as an In Vivo Model System

Zebrafish were recently used as an in vivo model system to study DNA replication timing during development. Here is detailed the protocols for using zebrafish embryos to profile replication timing. This protocol can be easily adapted to study replication timing in mutants, individual cell types, disease models, and other species.

DNA replication timing is an important cellular characteristic, exhibiting significant relationships with chromatin structure, transcription, and DNA ...

Candidate Gene Testing in Clinical Cohort Studies with Multiplexed Genotyping and Mass Spectrometry

Complex diseases are often underpinned by multiple common genetic variants that contribute to disease susceptibility. Here, we describe a cost-effective tag single nucleotide polymorphism (SNP) approach using a multiplexed genotyping assay with mass spectrometry, to investigate gene pathway associations in clinical cohorts. We investigate the food allergy candidate locus Interleukin13 (IL13) as an example. This method efficiently maximizes the coverage by taking advantage of shared linkage disequilibrium (LD) within a region. Selected LD SNPs are then designed into a multiplexed assay, enabling up to 40 different SNPs to be analyzed simultaneously, boosting cost-effectiveness. Polymerase chain reaction (PCR) is used to amplify the target loci, followed by single nucleotide extension, and the amplicons are then measured using matrix-assisted laser desorption/ionization-time of flight(MALDI-TOF) mass spectrometry. The raw output is analyzed with the genotype calling software, using stringent quality control definitions and cut-offs, and high probability genotypes are determined and output for data analysis.

Identification of genetic variants contributing to complex human disease allows us to identify novel mechanisms. Here, we demonstrate a multiplex genotyping approach to candidate genes or gene pathway analysis that maximizes the coverage at low cost and is amenable to cohort-based studies.

Complex diseases are often underpinned by multiple common genetic variants that contribute to disease susceptibility. Here, we describe a cost-effective ...

A Combinatorial Single-cell Approach to Characterize the Molecular and Immunophenotypic Heterogeneity of Human Stem and Progenitor Populations

Immunophenotypic characterization and molecular analysis have long been used to delineate heterogeneity and define distinct cell populations. FACS is inherently a single-cell assay, however prior to molecular analysis, the target cells are often prospectively isolated in bulk, thereby losing single-cell resolution. Single-cell gene expression analysis provides a means to understand molecular differences between individual cells in heterogeneous cell populations. In bulk cell analysis an overrepresentation of a distinct cell type results in biases and occlusions of signals from rare cells with biological importance. By utilizing FACS index sorting coupled to single-cell gene expression analysis, populations can be investigated without the loss of single-cell resolution while cells with intermediate cell surface marker expression are also captured, enabling evaluation of the relevance of continuous surface marker expression. Here, we describe an approach that combines single-cell reverse transcription quantitative PCR (RT-qPCR) and FACS index sorting to simultaneously characterize the molecular and immunophenotypic heterogeneity within cell populations.
In contrast to single-cell RNA sequencing methods, the use of qPCR with specific target amplification allows for robust measurements of low-abundance transcripts with fewer dropouts, while it is not confounded by issues related to cell-to-cell variations in read depth. Moreover, by directly index-sorting single-cells into lysis buffer this method, allows for cDNA synthesis and specific target pre-amplification to be performed in one step as well as for correlation of subsequently derived molecular signatures with cell surface marker expression. The described approach has been developed to investigate hematopoietic single-cells, but have also been used successfully on other cell types.
In conclusion, the approach described herein allows for sensitive measurement of mRNA expression for a panel of pre-selected genes with the possibility to develop protocols for subsequent prospective isolation of molecularly distinct subpopulations.

Bulk gene expression measurements cloud individual cell differences in heterogeneous cell populations. Here, we describe a protocol for how single-cell gene expression analysis and index sorting by Florescence Activated Cell Sorting (FACS) can be combined to delineate heterogeneity and immunophenotypically characterize molecularly distinct cell populations.

Immunophenotypic characterization and molecular analysis have long been used to delineate heterogeneity and define distinct cell populations. FACS is ...

Using In Vitro and In-cell SHAPE to Investigate Small Molecule Induced Pre-mRNA Structural Changes

In the process of drug development of RNA-targeting small molecules, elucidating the structural changes upon their interactions with target RNA sequences is desired. We herein provide a detailed in vitro and in-cell selective 2&#39;-hydroxyl acylation analyzed by primer extension (SHAPE) protocol to study the RNA structural change in the presence of an experimental drug for spinal muscular atrophy (SMA), survival of motor neuron (SMN)-C2, and in exon 7 of the pre-mRNA of the SMN2 gene. In in vitro SHAPE, an RNA sequence of 140 nucleotides containing SMN2 exon 7 is transcribed by T7 RNA polymerase, folded in the presence of SMN-C2, and subsequently modified by a mild 2&#39;-OH acylation reagent, 2-methylnicotinic acid imidazolide (NAI). This 2&#39;-OH-NAI adduct is further probed by a 32P-labeled primer extension and resolved by polyacrylamide gel electrophoresis (PAGE). Conversely, 2&#39;-OH acylation in in-cell SHAPE takes place in situ with SMN-C2 bound cellular RNA in living cells. The pre-mRNA sequence of exon 7 in the SMN2 gene, along with SHAPE-induced mutations in the primer extension, was then amplified by PCR and subject to next-generation sequencing. Comparing the two methodologies, in vitro SHAPE is a more cost-effective method and does not require computational power to visualize results. However, the in vitro SHAPE-derived RNA model sometimes deviates from the secondary structure in a cellular context, likely due to the loss of all interactions with RNA-binding proteins. In-cell SHAPE does not need a radioactive material workplace and yields a more accurate RNA secondary structure in the cellular context. Furthermore, in-cell SHAPE is usually applicable for a larger range of RNA sequences (~1,000 nucleotides) by utilizing next-generation sequencing, compared to in vitro SHAPE (~200 nucleotides) that usually relies on PAGE analysis. In case of exon 7 in SMN2 pre-mRNA, the in vitro and in-cell SHAPE derived RNA models are similar to each other.

Detailed protocols for both in vitro and in-cell selective 2&#39;-hydroxyl acylation analyzed by primer extension (SHAPE) experiments to determine the secondary structure of pre-mRNA sequences of interest in the presence of an RNA-targeting small molecule are presented in this article.

In the process of drug development of RNA-targeting small molecules, elucidating the structural changes upon their interactions with target RNA sequences ...

The Use of Mouse Mammary Tumor Cells in an In Vitro Invasion Assay as a Measure of Oncogenic Cell Behavior

The in vitro invasion assay uses a protein-rich matrix in a Boyden chamber to measure the ability of cultured cells to pass through the matrix and a porous membrane in a process analogous to the initial steps of cancer cell metastasis. The tested cells can be altered for the gene expression or treated with inhibitors to test for changes in the invasion potential. This experiment tests the aggressive phenotype of the mouse mammary tumor cells to discover and characterize the potential oncogenes that promote cell invasion. This technique, however, can be versatile and adapted to many different applications. The experiment itself can be done in one day and the results are acquired by light microscopy in less than a day. The results include counts of the number of invading cells for comparison and analysis. The in vitro invasion assay is a rapid, inexpensive, and clear-cut method for determining cell behavior in a culture that can be used as an initial assessment before more involved in vivo assays.

The in vitro cell invasion assay is used to measure the potential of cancer metastasis by quantifying the cellular potential for invasion and migration using cell culture inserts containing protein matrix. Cells are challenged to migrate through the protein matrix and a porous membrane, towards a chemoattractant, and then quantified by light microscopy.

The in vitro invasion assay uses a protein-rich matrix in a Boyden chamber to measure the ability of cultured cells to pass through the matrix and a ...