This work was partially supported by NIH R00HD082686. We thank the Endocrine Society Summer Research Fellowship to H.S.Z. We also thank Dr. Yuan Kang for breeding and maintaining the mouse colony.

All performed animal experiments followed the protocols approved by the Institutional Animal Care and Use Committees (IACUC) at Auburn University.
NOTE: The following protocol uses one testis (about 100 mg) at P28 from Gli1-CreERT2; NuTRAP mice (Mus musculus). Volumes of reagents may need to be adjusted based on the types of samples and the number of tissues.
1. Tissue collection
<ol>
	<li>Euthanize the mice using a CO2 chamber, sanitize the abdomen surface with 70% ethanol.</li>
	<li>Open the lower abdomen with scissors and remove the testes.&#160;Use liquid nitrogen&#160;(LN2) to snap-freeze the testes immediately.</li>
	<li>Store samples in the vapor phase of LN2 until use.</li>
</ol>
2. Reagents and beads preparation
<ol>
	<li>Prepare the homogenization stock solution: Add 50 mM Tris (pH 7.4), 12 mM MgCl2, 100 mM KCl, 1% NP-40, and 1 mg/mL heparin. Store the solution at 4 &#176;C until use (up to 1 month).</li>
	<li>Prepare the homogenization working buffer from the stock solution (step 2.1) freshly before use: Add DTT (final concentration: 1 mM), cycloheximide (final concentration: 100 &#181;g/mL), recombinant ribonuclease (final concentration: 200 units/mL), and protease inhibitor cocktail (final concentration: 1x) to the homogenization stock solution to make the required amount of the homogenization working buffer. Store the freshly prepared working buffer on ice until use.</li>
	<li>Prepare the low-salt and the high-salt wash buffers:
	<ol>
		<li>To prepare low-salt wash buffer mix 50 mM Tris (pH 7.4), 12 mM MgCl2, 100 mM KCl, and 1% NP-40. Add DTT (final concentration: 1 mM) and cycloheximide (final concentration: 100 &#181;g/mL) before use.</li>
		<li>To prepare high-salt wash buffer mix 50 mM Tris (pH 7.4), 12 mM MgCl2, 300 mM KCl, 1% NP-40. Add DTT (final concentration: 2 mM) and Cycloheximide (final concentration: 100 &#181;g/mL) before use.</li>
	</ol>
	</li>
	<li>Prepare protein G beads (Table of Materials):
	<ol>
		<li>Each sample will need 50 &#181;L of protein G beads. Place the required amount of beads in a 1.5 mL centrifuge tube and separate the beads from the solution using a magnetic rack by leaving the tube on the rack for 30-60 s.</li>
		<li>Remove the supernatant by pipetting. Wash the beads three times with 1 mL of ice-cold low-salt wash buffer each time.</li>
	</ol>
	</li>
</ol>
3. Tissue lysis and homogenization
<ol>
	<li>Add 2 mL of ice-cold homogenization working buffer (freshly prepared from step 2.2) to a glass tissue grinder set. Quickly place the frozen sample into the grinder and homogenize the tissue with 30 strokes on ice using a loose pestle.</li>
	<li>Transfer the homogenate to a 2 mL round-bottom tube and centrifuge at 12,000 x g for 10 min at 4 &#176;C.</li>
	<li>Transfer the supernatant to a new 2 mL tube. Save 100 &#181;L to a 1.5 mL tube as the &#34;input&#34;.</li>
	<li>Incubate the supernatant in the 2 mL tube with the anti-GFP antibody (5 &#181;g/mL; 1:400) at 4 &#176;C on an end-over-end rotator (24 rpm) overnight.</li>
</ol>
4. Immunoprecipitation
<ol>
	<li>Transfer the homogenate/antibody mixture to a new 2 mL round-bottom tube containing the washed protein G beads from step 2.4. Incubate at 4 &#176;C on an end-over-end rotator (24 rpm) for 2 h.</li>
	<li>Separate the magnetic beads from the supernatant using a magnet rack. Save the supernatant as the &#34;negative fraction&#34;. The negative fraction contains (1) RNAs in EGFP-negative cells and (2) RNAs in EGFP-positive cells that are not bound to ribosomes.</li>
	<li>Add 1 mL of high-salt wash buffer to the beads and briefly vortex the tube to wash the beads. Place the tube in a magnet rack.</li>
	<li>Remove the wash buffer. Repeat the washing step two more times. The beads now contain the beads-ribosome-RNA complex from EGFP-positive cells.</li>
</ol>
5. RNA extraction
NOTE: The following steps are adapted from the RNA isolation kit (Table of Materials). Treat each fraction (i.e., input, positive, and negative) as an independent sample and isolate RNAs independently.
<ol>
	<li>Incubate the beads from step 4.4 with 50 &#181;L of Extraction Buffer (from the RNA isolation kit) in a thermomixer (42 &#176;C, 500 rpm) for 30 min to release RNAs from beads.</li>
	<li>Separate the beads with a magnet rack, transfer the supernatant which contains the beads-ribosome-RNA complex to a 1.5 mL tube.</li>
	<li>Centrifuge the tube at 3000 x g for 2 min, then pipette the supernatant to a new 1.5 mL tube. This tube contains the &#34;positive fraction&#34; of the TRAP step. 
	NOTE: For the input and the negative fractions, extract RNA from 25 &#181;L of samples using 1 mL of Extraction Buffer. Incubate in a thermomixer (42 &#176;C, 500 rpm) for 30 min.</li>
	<li>Pre-condition the RNA purification column: Pipette 250 &#181;L of Conditioning Buffer onto the purification column. Incubate for 5 min at room temperature (RT). Centrifuge the column at 16,000 x g for 1 min.</li>
	<li>Pipet&#160;equal volume of 70% EtOH into the&#160;supernatant from step 5.3 (around 50 &#181;L of 70% EtOH for the positive fraction and 1 mL of 70% EtOH for the input and the negative fractions). Mix well by pipetting up and down.</li>
	<li>Pipette the mixture into the column from step 5.4.</li>
	<li>Centrifuge the column at 100 x g for 2 min to allow RNA binding to the membrane in the column, then continue centrifuge at 16,000 x g for 30 s immediately. Discard the flow-through. 
	NOTE: For the input and the negative fractions, add 250 &#181;L of the mixture to the column each time. Repeat steps 5.6 and 5.7 until all mixtures are used.</li>
	<li>Pipette 100 &#181;L of Wash Buffer 1 (W1) into the column and centrifuge at 8,000 x g for 1 min. Discard the flow-through.</li>
	<li>Pipette 75 &#181;L of DNase solution mix directly into the purification column membrane. Incubate at RT for 15 min.</li>
	<li>Pipette 40 &#181;L of W1 into the column and centrifuge at 8,000 x g for 30 s. Discard the flow-through.</li>
	<li>Pipette 100 &#181;L of Wash Buffer 2 (W2) into the column and centrifuge at 8,000 x g for 1 min. Discard the flow-through.</li>
	<li>Pipette 100 &#181;L of W2 into the column and centrifuge at 16,000 x g for 2 min. Discard the flow-through. Re-centrifuge the same column at 16,000 x g for 1 min to remove all traces of wash buffer prior to the elution step.</li>
	<li>Transfer the column to a new 1.5 mL microcentrifuge tube.</li>
	<li>Pipette 12 &#181;L of RNase-free water directly onto the membrane of the purification column. The pipet tip should not touch the membrane. Incubate at RT for 1 min and centrifuge at 1000 x g for 1 min. Then continue centrifugation at 16,000 x g for 1 min to elute the RNA.</li>
</ol>
6. RNA concentration and quality
<ol>
	<li>Use a bioanalyzer to assess the quality and quantity of the extracted RNA10.</li>
</ol>
7. Storage and further analysis
<ol>
	<li>Store the RNA at -80 &#176;C (up to 1 year) until further analysis (e.g., microarray, quantitative PCR (qPCR), and RNA-seq, etc.). 
	NOTE: For details of the qPCR analysis, including cDNA synthesis, refer to Lyu et al.11. Primers for qPCR are listed in the Table of Materials.</li>
</ol>

<ol>
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B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neuronal+subtypes+and+diversity+revealed+by+single-nucleus+RNA+sequencing+of+the+human+brain.">Neuronal subtypes and diversity revealed by single-nucleus RNA sequencing of the human brain.</a> Science. 352 (6293), 1586-1590 (2016).</li><li>Heiman, M., Kulicke, R., Fenster, R. J., Greengard, P., Heintz, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cell+type-specific+mRNA+purification+by+translating+ribosome+affinity+purification+(TRAP).">Cell type-specific mRNA purification by translating ribosome affinity purification (TRAP).</a> Nature Protocols. 9 (6), 1282-1291 (2014).</li><li>Bertin, B., Renaud, Y., Aradhya, R., Jagla, K., Junion, G. J. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=TRAP-rc,+translating+ribosome+affinity+purification+from+rare+cell+populations+of+Drosophila+embryos.">TRAP-rc, translating ribosome affinity purification from rare cell populations of Drosophila embryos.</a> Journal of Visualized Experiments: JoVE. (103), e52985 (2015).</li><li>Thellmann, M., Andersen, T. G., Vermeer, J. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Translating+ribosome+affinity+purification+(trap)+to+investigate+Arabidopsis+thaliana+root+development+at+a+cell+type-specific+scale.">Translating ribosome affinity purification (trap) to investigate Arabidopsis thaliana root development at a cell type-specific scale.</a> Journal of Visualized Experiments: JoVE. 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H., Pervolarakis, N., Nee, K., Kessenbrock, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Experimental+considerations+for+single-cell+rna+sequencing+approaches.">Experimental considerations for single-cell rna sequencing approaches.</a> Frontiers in Cell and Development Biology. 6, 108 (2018).</li><li>Chucair-Elliott, A. J., 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=Inducible+cell-specific+mouse+models+for+paired+epigenetic+and+transcriptomic+studies+of+microglia+and+astroglia.">Inducible cell-specific mouse models for paired epigenetic and transcriptomic studies of microglia and astroglia.</a> Communications Biology. 3 (1), 693 (2020).</li><li>Barsoum, I., Yao, H. 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The authors declare no conflict of interest.

The usefulness of the whole-tissue transcriptome analysis could be dampened, especially when studying complex heterogeneous tissues. How to obtain cell-type-specific RNAs becomes an urgent need to unleash the powerful RNA-seq technique. The isolation of cell-type-specific RNAs usually relies on the collection of a specific type of cells using micromanipulation, fluorescent-activated cell sorting (FACS), or laser capture microdissection (LCM)18. Other modern high-throughput single-cell collection m...

High-throughput approaches, including RNA sequencing (RNA-seq) and microarray, have made it possible to interrogate gene expression profiles at the genome-wide level. For complex tissues such as the heart, brain, and testis, the cell-type-specific data will provide more details comparing the use of RNAs from the whole tissue1,2,3. To overcome the impact of cellular heterogeneity, the Translating Ribosome Affinity Purification (TRAP) method has been developed since early 2010s4. TRAP is able to isolate ribosome-bound RNAs from specific cell types without tissue dissociation. This method has been used for translatome (mRNAs that are being recruited to the ribosome for translation) analysis in different organisms, including targeting an extremely rare population of muscle cells in Drosophila embryos5, studying different root cells in the model plant Arabidopsis thaliana6, and performing transcriptome analysis of endothelial cells in mammals7.
TRAP requires a genetic modification to tag the ribosome of a model organism. Evan Rosen and colleagues recently developed a mouse model called Nuclear tagging and Translating Ribosome Affinity Purification (NuTRAP) mouse8, which has been available through the Jackson Laboratory since 2017. By crossing with a Cre mouse line, researchers can use this NuTRAP mouse model to isolate ribosome-bound RNAs and cell nuclei from Cre-expressing cells without cell sorting. In Cre-expressing cells that also carry the NuTRAP allele, the EGFP/L10a tagged ribosome allows the isolation of translating mRNAs using affinity pulldown assays. At the same cell, the biotin ligase recognition peptide (BLRP)-tagged nuclear membrane, which is also mCherry positive, allows the nuclear isolation by using affinity- or fluorescence-based purification. The same research team also generated a similar mouse line in which the nuclear membrane is labeled only with mCherry without biotin8. These two genetically modified mouse lines give access to characterize paired epigenomic and transcriptomic profiles of specific types of cells in interest.
The hedgehog (Hh) signaling pathway plays a critical role in tissue development9. GLI1, a member of the GLI family, acts as a transcriptional activator and mediates the Hh signaling. Gli1+ cells can be found in many hormone-secreting organs, including the adrenal gland and the testis. To isolate cell-type-specific DNAs and RNAs from Gli1+ cells using the NuTRAP mouse model, Gli1-CreERT2 mice were crossed with the NuTRAP mice. Shh-CreERT2 mice were also crossed with the NuTRAP mice aim to isolate sonic hedgehog (Shh) expressing cells. The following protocol shows how to use Gli1-CreERT2;NuTRAP mice to isolate ribosome-bound RNAs from Gli1+ cells in adult mouse testes.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Actb</td>
			<td>eurofins</td>
			<td>qPCR primers</td>
			<td>ATGGAGGGGAATACAGCCC / TTCTTTGCAGCTCCTTCGTT (forward primer/reverse primer)</td>
		</tr>
		<tr>
			<td>Bioanalyzer</td>
			<td>Agilent</td>
			<td>2100 Bioanalyzer Instrument</td>
			<td></td>
		</tr>
		<tr>
			<td>cOmplete Mini EDTA-free Protease Inhibitor Cocktail</td>
			<td>Millipore</td>
			<td>11836170001</td>
			<td></td>
		</tr>
		<tr>
			<td>cycloheximide</td>
			<td>Millipore</td>
			<td>239764-100MG</td>
			<td></td>
		</tr>
		<tr>
			<td>Cyp11a1</td>
			<td>eurofins</td>
			<td>qPCR primers</td>
			<td>CTGCCTCCAGACTTCTTTCG / TTCTTGAAGGGCAGCTTGTT (forward primer/reverse primer)</td>
		</tr>
		<tr>
			<td>dNTP</td>
			<td>Thermo Fisher Scientific</td>
			<td>R0191</td>
			<td></td>
		</tr>
		<tr>
			<td>DTT, Dithiothreitol</td>
			<td>Thermo Fisher Scientific</td>
			<td>P2325</td>
			<td></td>
		</tr>
		<tr>
			<td>DynaMag-2 magnet</td>
			<td>Thermo Fisher Scientific</td>
			<td>12321D</td>
			<td></td>
		</tr>
		<tr>
			<td>Falcon tubes 15 mL</td>
			<td>VWR</td>
			<td>89039-666</td>
			<td></td>
		</tr>
		<tr>
			<td>GFP antibody</td>
			<td>Abcam</td>
			<td>ab290</td>
			<td></td>
		</tr>
		<tr>
			<td>Glass grinder set</td>
			<td>DWK Life Sciences</td>
			<td>357542</td>
			<td></td>
		</tr>
		<tr>
			<td>heparin</td>
			<td>BEANTOWN CHEMICAL</td>
			<td>139975-250MG</td>
			<td></td>
		</tr>
		<tr>
			<td>Hsd3b</td>
			<td>eurofins</td>
			<td>qPCR primers</td>
			<td>GACAGGAGCAGGAGGGTTTGTG / CACTGGGCATCCAGAATGTCTC (forward primer/reverse primer)</td>
		</tr>
		<tr>
			<td>KCl</td>
			<td>Biosciences</td>
			<td>R005</td>
			<td></td>
		</tr>
		<tr>
			<td>MgCl2</td>
			<td>Biosciences</td>
			<td>R004</td>
			<td></td>
		</tr>
		<tr>
			<td>Microcentrifuge tubes 2 mL</td>
			<td>Thermo Fisher Scientific</td>
			<td>02-707-354</td>
			<td></td>
		</tr>
		<tr>
			<td>Mouse Clariom S Assay microarrays</td>
			<td>Thermo Fisher Scientific</td>
			<td></td>
			<td>Microarray service</td>
		</tr>
		<tr>
			<td>NP-40</td>
			<td>Millipore</td>
			<td>492018-50 Ml</td>
			<td></td>
		</tr>
		<tr>
			<td>oligo (dT)20</td>
			<td>Invitrogen</td>
			<td>18418020</td>
			<td></td>
		</tr>
		<tr>
			<td>PicoPure RNA Isolation Kit</td>
			<td>Thermo Fisher Scientific</td>
			<td>KIT0204</td>
			<td></td>
		</tr>
		<tr>
			<td>Protein G Dynabead</td>
			<td>Thermo Fisher Scientific</td>
			<td>10003D</td>
			<td></td>
		</tr>
		<tr>
			<td>RNase-free water</td>
			<td>growcells</td>
			<td>NUPW-0500</td>
			<td></td>
		</tr>
		<tr>
			<td>RNaseOUT Recombinant Ribonuclease Inhibitor</td>
			<td>Thermo Fisher Scientific</td>
			<td>10777019</td>
			<td></td>
		</tr>
		<tr>
			<td>Sox9</td>
			<td>eurofins</td>
			<td>qPCR primers</td>
			<td>TGAAGAACGGACAAGCGGAG / CTGAGATTGCCCAGAGTGCT (forward primer/reverse primer</td>
		</tr>
		<tr>
			<td>Superscript IV reverse transcriptase</td>
			<td>Invitrogen</td>
			<td>18090050</td>
			<td></td>
		</tr>
		<tr>
			<td>SYBR Green PCR Master Mix</td>
			<td>Thermo Fisher Scientific</td>
			<td>4309155</td>
			<td></td>
		</tr>
		<tr>
			<td>Sycp3</td>
			<td>eurofins</td>
			<td>qPCR primers</td>
			<td>GAATGTGTTGCAGCAGTGGGA /GAACTGCTCGTGTATCTGTTTGA (forward primer/reverse primer)</td>
		</tr>
		<tr>
			<td>Tris</td>
			<td>Alfa Aesar</td>
			<td>J62848</td>
			<td></td>
		</tr>
	</tbody>
</table>

isolate cell-type-specific rnas from snap-frozen heterogeneous tissue samples without cell sorting

Cellular heterogeneity poses challenges to understanding the function of complex tissues at a transcriptome level. Using cell-type-specific RNAs avoids potential pitfalls caused by the heterogeneity of tissues and unleashes the powerful transcriptome analysis. The protocol described here demonstrates how to use the Translating Ribosome Affinity Purification (TRAP) method to isolate ribosome-bound RNAs from a small amount of EGFP-expressing cells in a complex tissue without cell sorting. This protocol is suitable for isolating cell-type-specific RNAs using the recently available NuTRAP mouse model and could also be used to isolate RNAs from any EGFP-expressing cells.

Gli1-CreERT2 mouse (Jackson Lab Stock Number: 007913) were first crossed with the NuTRAP reporter mouse (Jackson Lab Stock Number: 029899) to generate double-mutant mice. Mice carrying both genetically engineered gene alleles (i.e., Gli1-CreERT2&#160;and NuTRAP) were injected with tamoxifen once a day, every other day, for three injections. Tissue samples were collected on the 7th day after the 1st day of the injection. Immunofluorescence analysis sho...

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Isolate Cell-Type-Specific RNAs from Snap-Frozen Heterogeneous Tissue Samples without Cell Sorting

This protocol aims to isolate cell-type-specific translating ribosomal mRNAs using the NuTRAP mouse model.

Cellular heterogeneity poses challenges to understanding the function of complex tissues at a transcriptome level. Using cell-type-specific RNAs avoids ...

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2.1K Views.  Auburn University. This protocol aims to isolate cell-type-specific translating ribosomal mRNAs using the NuTRAP mouse model.

Video: Isolate Cell-Type-Specific RNAs from Snap-Frozen Heterogeneous Tissue Samples without Cell Sorting

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

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

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

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

Fluorescence Activated Cell Sorting of Plant Protoplasts

High-resolution, cell type-specific analysis of gene expression greatly enhances understanding of developmental regulation and responses to environmental stimuli in any multicellular organism. In situ hybridization and reporter gene visualization can to a limited extent be used to this end but for high resolution quantitative RT-PCR or high-throughput transcriptome-wide analysis the isolation of RNA from particular cell types is requisite. Cellular dissociation of tissue expressing a fluorescent protein marker in a specific cell type and subsequent Fluorescence Activated Cell Sorting (FACS) makes it possible to collect sufficient amounts of material for RNA extraction, cDNA synthesis/amplification and microarray analysis.
An extensive set of cell type-specific fluorescent reporter lines is available to the plant research community. In this case, two marker lines of the Arabidopsis thaliana root are used: PSCR::GFP (endodermis and quiescent center) and PWOX5::GFP (quiescent center). Large numbers (thousands) of seedlings are grown hydroponically or on agar plates and harvested to obtain enough root material for further analysis. Cellular dissociation of plant material is achieved by enzymatic digestion of the cell wall. This procedure makes use of high osmolarity-induced plasmolysis and commercially available cellulases, pectinases and hemicellulases to release protoplasts into solution.
FACS of GFP-positive cells makes use of the visualization of the green versus the red emission spectra of protoplasts excited by a 488 nm laser. GFP-positive protoplasts can be distinguished by their increased ratio of green to red emission. Protoplasts are typically sorted directly into RNA extraction buffer and stored for further processing at a later time.
This technique is revealed to be straightforward and practicable. Furthermore, it is shown that it can be used without difficulty to isolate sufficient numbers of cells for transcriptome analysis, even for very scarce cell types (e.g. quiescent center cells). Lastly, a growth setup for Arabidopsis seedlings is demonstrated that enables uncomplicated treatment of the plants prior to cell sorting (e.g. for the cell type-specific analysis of biotic or abiotic stress responses). Potential supplementary uses for FACS of plant protoplasts are discussed.

A method for isolating specific cell types from plant material is demonstrated. This technique employs transgenic marker lines expressing fluorescent proteins in particular cell types, cellular dissociation and Fluorescence Activated Cell Sorting. Additionally, a growth setup is established here that facilitates treatment of Arabidopsis thaliana seedlings prior to cell sorting.

High-resolution, cell type-specific analysis of gene expression greatly enhances understanding of developmental regulation and responses to environmental ...

Investigating Tissue- and Organ-specific Phytochrome Responses using FACS-assisted Cell-type Specific Expression Profiling in Arabidopsis thaliana

Light mediates an array of developmental and adaptive processes throughout the life cycle of a plant. Plants utilize light-absorbing molecules called photoreceptors to sense and adapt to light. The red/far-red light-absorbing phytochrome photoreceptors have been studied extensively. Phytochromes exist as a family of proteins with distinct and overlapping functions in all higher plant systems in which they have been studied1. Phytochrome-mediated light responses, which range from seed germination through flowering and senescence, are often localized to specific plant tissues or organs2. Despite the discovery and elucidation of individual and redundant phytochrome functions through mutational analyses, conclusive reports on distinct sites of photoperception and the molecular mechanisms of localized pools of phytochromes that mediate spatial-specific phytochrome responses are limited. We designed experiments based on the hypotheses that specific sites of phytochrome photoperception regulate tissue- and organ-specific aspects of photomorphogenesis, and that localized phytochrome pools engage distinct subsets of downstream target genes in cell-to-cell signaling. We developed a biochemical approach to selectively reduce functional phytochromes in an organ- or tissue-specific manner within transgenic plants. Our studies are based on a bipartite enhancer-trap approach that results in transactivation of the expression of a gene under control of the Upstream Activation Sequence (UAS) element by the transcriptional activator GAL43. The biliverdin reductase (BVR) gene under the control of the UAS is silently maintained in the absence of GAL4 transactivation in the UAS-BVR parent4. Genetic crosses between a UAS-BVR transgenic line and a GAL4-GFP enhancer trap line result in specific expression of the BVR gene in cells marked by GFP expression4. BVR accumulation in Arabidopsis plants results in phytochrome chromophore deficiency in planta5-7. Thus, transgenic plants that we have produced exhibit GAL4-dependent activation of the BVR gene, resulting in the biochemical inactivation of phytochrome, as well as GAL4-dependent GFP expression. Photobiological and molecular genetic analyses of BVR transgenic lines are yielding insight into tissue- and organ-specific phytochrome-mediated responses that have been associated with corresponding sites of photoperception4, 7, 8. Fluorescence Activated Cell Sorting (FACS) of GFP-positive, enhancer-trap-induced BVR-expressing plant protoplasts coupled with cell-type-specific gene expression profiling through microarray analysis is being used to identify putative downstream target genes involved in mediating spatial-specific phytochrome responses. This research is expanding our understanding of sites of light perception, the mechanisms through which various tissues or organs cooperate in light-regulated plant growth and development, and advancing the molecular dissection of complex phytochrome-mediated cell-to-cell signaling cascades.

Investigating Tissue- and Organ-specific Phytochrome Responses using FACS-assisted Cell-type Specific Expression Profiling in Arabidopsis thaliana

The molecular basis of spatial-specific phytochrome responses is being investigated using transgenic plants that exhibit tissue- and organ-specific phytochrome deficiencies. The isolation of specific cells exhibiting induced phytochrome chromophore depletion by Fluorescence-Activated Cell Sorting followed by microarray analyses is being utilized to identify genes involved in spatial-specific phytochrome responses.

Light mediates an array of developmental and adaptive processes throughout the life cycle of a plant. Plants utilize light-absorbing molecules called ...

Quantitation of &gamma;H2AX Foci in Tissue Samples

DNA double-strand breaks (DSBs) are particularly lethal and genotoxic lesions, that can arise either by endogenous (physiological or pathological) processes or by exogenous factors, particularly ionizing radiation and radiomimetic compounds. Phosphorylation of the H2A histone variant, H2AX, at the serine-139 residue, in the highly conserved C-terminal SQEY motif, forming &gamma;H2AX, is an early response to DNA double-strand breaks1. This phosphorylation event is mediated by the phosphatidyl-inosito 3-kinase (PI3K) family of proteins, ataxia telangiectasia mutated (ATM), DNA-protein kinase catalytic subunit and ATM and RAD3-related (ATR)2. Overall, DSB induction results in the formation of discrete nuclear &gamma;H2AX foci which can be easily detected and quantitated by immunofluorescence microscopy2. Given the unique specificity and sensitivity of this marker, analysis of &gamma;H2AX foci has led to a wide range of applications in biomedical research, particularly in radiation biology and nuclear medicine. The quantitation of &gamma;H2AX foci has been most widely investigated in cell culture systems in the context of ionizing radiation-induced DSBs. Apart from cellular radiosensitivity, immunofluorescence based assays have also been used to evaluate the efficacy of radiation-modifying compounds. In addition, &gamma;H2AX has been used as a molecular marker to examine the efficacy of various DSB-inducing compounds and is recently being heralded as important marker of ageing and disease, particularly cancer3. Further, immunofluorescence-based methods have been adapted to suit detection and quantitation of &gamma;H2AX foci ex vivo and in vivo4,5. Here, we demonstrate a typical immunofluorescence method for detection and quantitation of &gamma;H2AX foci in mouse tissues.

Quantitation of &#947;H2AX Foci in Tissue Samples

Quantitation of DNA double-strand breaks on the basis of &gamma;H2AX foci has become an invaluable tool, particularly in radiation biology, for the evaluation of tissue radiosensitivity and effects of radiation modifying compounds. Here we demonstrate the use of an immunofluorescence assay for quantitation of &gamma;H2AX foci in tissue samples.

DNA double-strand breaks (DSBs) are particularly lethal and genotoxic lesions, that can arise either by endogenous (physiological or pathological) ...

Heterokaryon Technique for Analysis of Cell Type-specific Localization

A significant number of proteins are regulated by subcellular trafficking or nucleocytolasmic shuttling. These proteins display a diverse array of cellular functions including nuclear import/export of RNA and protein, transcriptional regulation, and apoptosis. Interestingly, major cellular reorganizations including cell division, differentiation and transformation, often involve such activities3,4,8,10. The detailed study of these proteins and their respective regulatory mechanisms can be challenging as the stimulation for these localization changes can be elusive, and the movements themselves can be quite dynamic and difficult to track. Studies involving cellular oncogenesis, for example, continue to benefit from understanding pathways and protein activities that differ between normal primary cells and transformed cells6,7,11,12. As many proteins show altered localization during transformation or as a result of transformation, methods to efficiently characterize these proteins and the pathways in which they participate stand to improve the understanding of oncogenesis and open new areas for drug targeting.
Here we present a method for the analysis of protein trafficking and shuttling activity between primary and transformed mammalian cells. This method combines the generation of heterokaryon fusions with fluorescence microscopy to provide a flexible protocol that can be used to detect steady-state or dynamic protein localizations. As shown in Figure 1, two separate cell types are transiently transfected with plasmid constructs bearing a fluoroprotein gene attached to the gene of interest. After expression, the cells are fused using polyethylene glycol, and protein localizations may then be imaged using a variety of methods. The protocol presented here is a fundamental approach to which specialized techniques may be added.

A flexible and efficient method for the characterization of cell type-specific protein localization and nucleocytoplasmic shuttling is described. This heterokaryon approach uses fluorescently-labeled fusion proteins to image protein localizations after cell fusion. The protocol is amenable to steady-state localizations or more dynamic determinations based on live cell imaging.

A significant number of proteins are regulated by subcellular trafficking or nucleocytolasmic shuttling.  These proteins display a diverse array of ...

Genotyping of Plant and Animal Samples without Prior DNA Purification

The Direct PCR approach facilitates PCR amplification directly from small amounts of unpurified samples, and is demonstrated here for several plant and animal tissues (Figure 1). Direct PCR is based on specially engineered Thermo Scientific Phusion and Phire DNA Polymerases, which include a double-stranded DNA binding domain that gives them unique properties such as high tolerance of inhibitors.
PCR-based target DNA detection has numerous applications in plant research, including plant genotype analysis and verification of transgenes. PCR from plant tissues traditionally involves an initial DNA isolation step, which may require expensive or toxic reagents. The process is time consuming and increases the risk of cross contamination1, 2. Conversely, by using Thermo Scientific Phire Plant Direct PCR Kit the target DNA can be easily detected, without prior DNA extraction. In the model demonstrated here, an example of derived cleaved amplified polymorphic sequence analysis (dCAPS)3,4 is performed directly from Arabidopsis plant leaves. dCAPS genotyping assays can be used to identify single nucleotide polymorphisms (SNPs) by SNP allele-specific restriction endonuclease digestion3. 
Some plant samples tend to be more challenging when using Direct PCR methods as they contain components that interfere with PCR, such as phenolic compounds. In these cases, an additional step to remove the compounds is traditionally required2,5. Here, this problem is overcome by using a quick and easy dilution protocol followed by Direct PCR amplification (Figure 1). Fifteen year-old oak leaves are used as a model for challenging plants as the specimen contains high amounts of phenolic compounds including tannins. 
Gene transfer into mice is broadly used to study the roles of genes in development, physiology and human disease. The use of these animals requires screening for the presence of the transgene, usually with PCR. Traditionally, this involves a time consuming DNA isolation step, during which DNA for PCR analysis is purified from ear, tail or toe tissues6,7. However, with the Thermo Scientific Phire Animal Tissue Direct PCR Kit transgenic mice can be genotyped without prior DNA purification. In this protocol transgenic mouse genotyping is achieved directly from mouse ear tissues, as demonstrated here for a challenging example where only one primer set is used for amplification of two fragments differing greatly in size.

The Direct PCR approach presented here facilitates PCR amplification directly from small amounts of unpurified plant and animal tissue.

The Direct PCR approach facilitates PCR amplification directly from small amounts of unpurified samples, and is demonstrated here for several plant and ...

Optimized Staining and Proliferation Modeling Methods for Cell Division Monitoring using Cell Tracking Dyes

Fluorescent cell tracking dyes, in combination with flow and image cytometry, are powerful tools with which to study the interactions and fates of different cell types in vitro and in vivo.1-5 Although there are literally thousands of publications using such dyes, some of the most commonly encountered cell tracking applications include monitoring of:
<ol>
	<li>stem and progenitor cell quiescence, proliferation and/or differentiation6-8</li>
	<li>antigen-driven membrane transfer9 and/or precursor cell proliferation3,4,10-18 and</li>
	<li>immune regulatory and effector cell function1,18-21.</li>
</ol>
Commercially available cell tracking dyes vary widely in their chemistries and fluorescence properties but the great majority fall into one of two classes based on their mechanism of cell labeling. "Membrane dyes", typified by PKH26, are highly lipophilic dyes that partition stably but non-covalently into cell membranes1,2,11. "Protein dyes", typified by CFSE, are amino-reactive dyes that form stable covalent bonds with cell proteins4,16,18. Each class has its own advantages and limitations. The key to their successful use, particularly in multicolor studies where multiple dyes are used to track different cell types, is therefore to understand the critical issues enabling optimal use of each class2-4,16,18,24.
The protocols included here highlight three common causes of poor or variable results when using cell-tracking dyes. These are:
<ol>
	<li>Failure to achieve bright, uniform, reproducible labeling. This is a necessary starting point for any cell tracking study but requires attention to different variables when using membrane dyes than when using protein dyes or equilibrium binding reagents such as antibodies.</li>
	<li>Suboptimal fluorochrome combinations and/or failure to include critical compensation controls. Tracking dye fluorescence is typically 102 - 103 times brighter than antibody fluorescence. It is therefore essential to verify that the presence of tracking dye does not compromise the ability to detect other probes being used.</li>
	<li>Failure to obtain a good fit with peak modeling software. Such software allows quantitative comparison of proliferative responses across different populations or stimuli based on precursor frequency or other metrics. Obtaining a good fit, however, requires exclusion of dead/dying cells that can distort dye dilution profiles and matching of the assumptions underlying the model with characteristics of the observed dye dilution profile.</li>
</ol>
Examples given here illustrate how these variables can affect results when using membrane and/or protein dyes to monitor cell proliferation.

Successful use of cell tracking dyes to monitor immune cell function and proliferation involves several critical steps. We describe methods for: 1) obtaining bright, uniform, reproducible label-ing with membrane dyes; 2) selecting fluorochromes and data acquisition conditions; and 3) choosing a model to quantify cell proliferation based on dye dilution.

Fluorescent cell tracking dyes, in combination with flow and image cytometry, are powerful tools with which to study the interactions and fates of ...

Isolation of Small Noncoding RNAs from Human Serum

The analysis of RNA and its expression is a common feature in many laboratories. Of significance is the emergence of small RNAs like microRNAs, which are found in mammalian cells. These small RNAs are potent gene regulators controlling vital pathways such as growth, development and death and much interest has been directed at their expression in bodily fluids. This is due to their dysregulation in human diseases such as cancer and their potential application as serum biomarkers. However, the analysis of miRNA expression in serum may be problematic. In most cases the amount of serum is limiting and serum contains low amounts of total RNA, of which small RNAs only constitute 0.4-0.5%1. Thus the isolation of sufficient amounts of quality RNA from serum is a major challenge to researchers today. In this technical paper, we demonstrate a method which uses only 400 &#181;l of human serum to obtain sufficient RNA for either DNA arrays or qPCR analysis. The advantages of this method are its simplicity and ability to yield high quality RNA. It requires no specialized columns for purification of small RNAs and utilizes general reagents and hardware found in common laboratories. Our method utilizes a Phase Lock Gel to eliminate phenol contamination while at the same time yielding high quality RNA. We also introduce an additional step to further remove all contaminants during the isolation step. This protocol is very effective in isolating yields of total RNA of up to 100 ng/&#181;l from serum but can also be adapted for other biological tissues.

This protocol describes a method for extracting small RNAs from human serum. We have used this method to isolate microRNAs from cancer serum for use in DNA arrays and also singleplex quantitative PCR. The protocol utilizes phenol and guanidinium thiocyanate reagents with modifications to yield high quality RNA.

The analysis of RNA and its expression is a common feature in many laboratories. Of significance is the emergence of small RNAs like microRNAs, which are ...

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

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

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

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

Magnetic-Activated Cell Sorting Strategies to Isolate and Purify Synovial Fluid-Derived Mesenchymal Stem Cells from a Rabbit Model

Mesenchymal stem cells (MSCs) are the main cell source for cell-based therapy. MSCs from articular cavity synovial fluid could potentially be used for cartilage tissue engineering. MSCs from synovial fluid (SF-MSCs) have been considered promising candidates for articular regeneration, and their potential therapeutic benefit has made them an important research topic of late. SF-MSCs from the knee cavity of the New Zealand white rabbit can be employed as an optimized translational model to assess human regenerative medicine. By means of CD90-based magnetic activated cell sorting (MACS) technologies, this protocol successfully obtains rabbit SF-MSCs (rbSF-MSCs) from this rabbit model and further fully demonstrates the MSC phenotype of these cells by inducing them to differentiate to osteoblasts, adipocytes, and chondrocytes. Therefore, this approach can be applied in cell biology research and tissue engineering using simple equipment and procedures.

This article presents a simple and economic protocol for the straightforward isolation and purification of mesenchymal stem cells from New Zealand white rabbit synovial fluid.

Mesenchymal stem cells (MSCs) are the main cell source for cell-based therapy. MSCs from articular cavity synovial fluid could potentially be used for ...