This work was supported by a SC INBRE grant from the National Institute of General Medical Science - NIH (P20GM103499 to R.G.) and grants CA555536 &#38; CA154664 from the National Cancer Institute to P.H.H. This program was supported in part by a grant to the College of Charleston from the Howard Hughes Medical Institute through the Pre-college &#38; Undergraduate Science Education Program and by grants from the National Center for Research Resources (5 P20 RR016461) and the National Institute of General Medical Sciences (8 P20 GM103499) from the National Institutes of Health.

1. Culture and metabolic labeling
<ol>
	<li>Poke once the center of the cap of a sterile 1.5 mL micro-centrifuge tubes with a 18-gauge needle to allow proper aeration. Inoculate 500 &#181;L of supplemented sterile 7H9 broth with 5 &#181;L of M. smegmatis from a starter culture grown overnight12. 
	NOTE: The recipe for one liter of 7H9 broth is: 4.7 g Commercial 7H9 powder, 2 mL Glycerol, 1 mL Tween 80, 0.85 g NaCl, 5 g Albumin, 2 g Dextrose, H2O (to bring total volume to 1 L).
	<ol>
		<li>(CAUTION) Following standard radioprotection practices, spike the culture media with 20 &#181;Ci/mL of [32P] Na2HPO4. Grow bacteria at 37 &#176;C and 1,200 rpm agitation, in a shaker incubator placed behind a 9-mm thick acrylic shield.</li>
	</ol>
	</li>
	<li>At midlog phase (O.D.600 nm ~0.5), transfer the entire culture into a 2-mL screw-cap tube and pellet radioactive bacteria at room temperature by centrifuging for 2 min at 10,000 x g. Collect supernatant containing unincorporated radioactive orthophosphate in appropriate waste container.</li>
</ol>
2. Preparation of total RNAs
NOTE: Total RNAs are extracted from bacterial pellets using a commercial RNA extraction reagent (containing guanidinium thiocyanate, phenol and chloroform) following the manufacturer&#39;s protocol.
<ol>
	<li>Add 1 mL of commercial RNA extraction reagent and approximately 200 &#181;L of glass beads onto the pellet. Cap the tube securely and disrupt the bacterial in a homogenizer for 2 min under maximum agitation, (setting number five on chosen instrument (see the Table of Materials)).</li>
	<li>Centrifuge sample at 12,000 x g for 10 min at 4 &#176;C. Transfer the supernatant to a new 2-mL tube and discard the beads appropriately. Add 0.2 mL of chloroform and shake tube vigorously by hand for 15 s. Centrifuge at 12,000 x g for 15 min at 4 &#176;C.</li>
	<li>Collect the aqueous phase of the sample into a new tube by angling the tube at 45&#176;. Avoid drawing any of the interphase or organic layer. Add 2 &#181;L of colored precipitant and 0.5 mL of 100% isopropanol. Shake the tube vigorously by hand for 5 s. Centrifuge at 12,000 x g for 10 min at 4&#176;C.</li>
	<li>Remove the supernatant from the tube and discard appropriately as the liquid fraction may contain traces of radioactivity. Air dry pellet for 5 min then resuspend in 200 &#181;L of 2X saline-sodium citrate (SSC), 0.1% (w/v) sodium dodecyl sulfate (SDS) final. 
	NOTE: The composition of stock 20 X SSC is 3.0 M NaCl, 0.3 M sodium citrate, pH 7.0.</li>
</ol>
3. Preparation of 96 well printer plates
NOTE: tRNA microarrays are manually printed with forty two 70-mer DNA oligonucleotides complementary to the 3&#39; end of each M. smegmatis tRNA (terminal CCA excluded) using an eight-pin arrayer. The sequences of the DNA oligonucleotide probes as well as the probe layout in the well-plate and the array are provided (Supplementary File 1- sheet 1 to 3 respectively).
<ol>
	<li>Design DNA probes by first retrieving tRNA sequences or tRNA encoding genes from tRNA databases such as the Genomic tRNA Database13. Trim conserved 3&#39; end CCA if encoded. Reverse complement the resulting sequence. Order probe based on the first 70 nucleotides.</li>
	<li>Resuspend dry DNA probes in water. Adjust probes concentration to 100 &#181;M. In a 96 well-plate, prepare 120 &#181;L of 50 &#181;M oligos in 3X SSC, 0.01% (w/v) SDS final (dilute 60 &#181;L of stock probes in individual well with 60 &#181;L of 6X SSC , 0.01% (w/v) SDS.</li>
	<li>Cover plate with tin foil to prevent evaporation or contamination, freeze immediately and keep at -20 &#176;C until needed.</li>
</ol>
4. Array printing
<ol>
	<li>Thaw the 96-well plate at room temperature (takes approximately 20 min).</li>
	<li>Label amine-coated glass slides with a diamond pen. Place slides into indexing unit. Follow the grid placements and do as follows.
	<ol>
		<li>Carefully dip the replicator pins in the wells.</li>
		<li>Gently print the array on the glass slides, using minimal pressure (you will feel a small resistance). Continue printing without cleaning the arrayer until finished with block A.</li>
	</ol>
	</li>
	<li>When ready to move on to the next block, follow the washing procedure described below.
	<ol>
		<li>Dip replicator in the 5% bleach and gently shake.</li>
		<li>Press replicator into absorbent paper.</li>
		<li>Dip replicator in the distilled water, gently shake, and press into paper. Repeat this step once.</li>
		<li>Dip replicator in isopropanol, gently shake, and press into the paper.</li>
		<li>Dry the replicator on the fan for about 20 s before moving on to the next block of the 96-well plate. Continue to desired number of prints.</li>
	</ol>
	</li>
	<li>Allow the slides to dry then crosslink the oligos to the slide using a 254-nm UV crosslinker.
	<ol>
		<li>Set the energy level to 999,990 &#181;J/cm2.</li>
		<li>Put the slides face up on a clean surface in the crosslinker. Press &#34;start&#34;.</li>
	</ol>
	</li>
	<li>Block the arrays overnight in 450 mL of blocking solution on a magnetic stirrer, at room temperature and under slow agitation. Collect and reuse blocking solution up to four times. 
	NOTE: The recipe for the blocking solution is: 125 mM phosphate buffer (NaH2PO4/Na2HPO4-) pH 7.2, 2.25% SDS (w/v), 0.5 mM EDTA, 0.5X SSC, 1% BSA (w/v).</li>
	<li>Wash the slides 2 times for 5 min at room temperature in 500 mL of distilled water. Dry the slides by centrifuging for 10 s at room temperature in a microarray centrifuge. Store arrays in a dry and dark place for up to 6 months.</li>
</ol>
5. Array hybridization
<ol>
	<li>Prior to hybridization rinse slides in boiling water and dry by centrifugation (as in 4.6).</li>
	<li>Place array inside a hybridization cassette and load radiolabeled RNA sample.</li>
	<li>Run the automated hybridization-washing station for maximum reproducibility.
	<ol>
		<li>Program steps as following. Condition gaskets for 2 min at 75 &#176;C. Introduce probe at 60 &#176;C. 
		Denature probes and samples 5 min at 90 &#176;C. Hybridize samples for 3 h at 60 &#176;C.
		<ol>
			<li>Wash slides at 50 &#176;C twice with 2X SSC, 0.1% (w/v) SDS, flow 10 s and hold 20 s. Wash slides at 42 &#176;C twice with 0.1X SSC, 0.1% SDS, flow 10 s and hold 20 s. Wash slides at 42 &#176;C twice with 0.1 X SSC, flow 10 s and hold 20 s.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Dry slides by centrifugation (as in 4.6).</li>
</ol>
6. Array quantification
<ol>
	<li>Wrap slides using a thin plastic film. Check slides for radioactive signal using a Geiger counter on its most sensitive setting. Expose slides onto a storage phosphor screen in an exposure cassette at room temperature for 10 to 90 h depending on signal strength. 
	NOTE: As sensitivity of Geiger counters vary from one instrument to another, exposure times must be optimized empirically.</li>
	<li>Scan slide at 50 &#181;m resolution using a phosphorimager. Quantify and background-subtract radioactivity intensities at each probe spot using the free Image J software upgraded with a microarray profiler.</li>
	<li>Organize and process data using an electronic spreadsheet. Generate heat maps using the conditional formatting tool. Represent for example each probe signal as a fraction (expressed in &#8240;) of the total probe signal.</li>
</ol>

<ol>
	<li>Emilsson, V., Kurland, C. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Growth+rate+dependence+of+transfer+RNA+abundance+in+Escherichia+coli.">Growth rate dependence of transfer RNA abundance in Escherichia coli.</a> EMBO J. 9 (13), 4359-4366 (1990).</li><li>Dittmar, K. A., Goodenbour, J. M., Pan, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tissue-specific+differences+in+human+transfer+RNA+expression.">Tissue-specific differences in human transfer RNA expression.</a> PLoS Genet. 2 (12), e221 (2006).</li><li>Pavon-Eternod, M., Gomes, S., Geslain, R., Dai, Q., Rosner, M. R., Pan, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=tRNA+over-expression+in+breast+cancer+and+functional+consequences.">tRNA over-expression in breast cancer and functional consequences.</a> Nucleic Acids Res. 37 (21), 7268-7280 (2009).</li><li>Gieg&#233;, R., J&#252;hling, F., P&#252;tz, J., Stadler, P., Sauter, C., Florentz, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structure+of+transfer+RNAs:+similarity+and+variability.">Structure of transfer RNAs: similarity and variability.</a> Wiley Interdiscip Rev RNA. 3 (1), 37-61 (2012).</li><li>Machnicka, M. A., Olchowik, A., Grosjean, H., Bujnicki, 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=Distribution+and+frequencies+of+post-transcriptional+modifications+in+tRNAs.">Distribution and frequencies of post-transcriptional modifications in tRNAs.</a> RNA Biol. 11 (12), 1619-1629 (2014).</li><li>Torres, A. G., Pi&#241;eyro, D., Rodr&#237;guez-Escrib&#224;, M., Camacho, N., Reina, O., Saint-L&#233;ger, A., Filonava, L., Batlle, E., Ribas de Pouplana, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Inosine+modifications+in+human+tRNAs+are+incorporated+at+the+precursor+tRNA+level.">Inosine modifications in human tRNAs are incorporated at the precursor tRNA level.</a> Nucleic Acids Res. 43 (10), 5145-5157 (2015).</li><li>Cognat, V., Deragon, J. M., Vinogradova, E., Salinas, T., Remacle, C., Mar&#233;chal-Drouard, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=On+the+evolution+and+expression+of+Chlamydomonas+reinhardtii+nucleus-encoded+transfer+RNA+genes.">On the evolution and expression of Chlamydomonas reinhardtii nucleus-encoded transfer RNA genes.</a> Genetics. 179 (1), 113-123 (2008).</li><li>Zheng, G., Qin, Y., Clark, W. C., Dai, Q., Yi, C., He, C., 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=Efficient+and+quantitative+high-throughput+tRNA+sequencing.">Efficient and quantitative high-throughput tRNA sequencing.</a> Nat Methods. 12 (9), 835-837 (2015).</li><li>Grelet, S., McShane, A., Hok, E., Tomberlin, J., Howe, P. H., Geslain, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=SPOt:+A+novel+and+streamlined+microarray+platform+for+observing+cellular+tRNA+levels.">SPOt: A novel and streamlined microarray platform for observing cellular tRNA levels.</a> PLoS One. 12 (5), e0177939 (2017).</li><li>Eriani, G., Karam, J., Jacinto, J., Morris Richard, E., Geslain, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=MIST,+a+Novel+Approach+to+Reveal+Hidden+Substrate+Specificity+in+Aminoacyl-tRNA+Synthetases.">MIST, a Novel Approach to Reveal Hidden Substrate Specificity in Aminoacyl-tRNA Synthetases.</a> PLoS One. 10 (6), e0130042 (2015).</li><li>Grelet, S., McShane, A., Geslain, R., Howe, P. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pleiotropic+Roles+of+Non-Coding+RNAs+in+TGF-&#946;-Mediated+Epithelial-Mesenchymal+Transition+and+Their+Functions+in+Tumor+Progression.">Pleiotropic Roles of Non-Coding RNAs in TGF-&#946;-Mediated Epithelial-Mesenchymal Transition and Their Functions in Tumor Progression.</a> Cancers. 9 (7), (2017).</li><li>Belanger, A. E., Hatfull, G. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Exponential-phase+glycogen+recycling+is+essential+for+growth+of+Mycobacterium+smegmatis.">Exponential-phase glycogen recycling is essential for growth of Mycobacterium smegmatis.</a> J Bacteriol. 181 (21), 6670-6678 (1999).</li><li>Chan, P. P., Lowe, T. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=GtRNAdb:+A+database+of+transfer+RNA+genes+detected+in+genomic+sequence.">GtRNAdb: A database of transfer RNA genes detected in genomic sequence.</a> Nucl. Acids Res. 37 (Database issue), D93-D97 (2009).</li><li>Schmidt, C. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Effect+of+Radioactive+Phosphorus+upon+a+Suspension+of+Escherichia+coli.">The Effect of Radioactive Phosphorus upon a Suspension of Escherichia coli.</a> J Bacteriol. 55 (5), 705-710 (1948).</li></ol>

No conflict of interest declared.

Beta particle emissions are known bacteriostatic and bactericidal agents14, however radiations in the tested range have no significant impact on cell fitness. Scintillation counting showed that the radioactivity is incorporated into 25% of total-cell extracts and subsequently, 1% of purified total RNAs.
The probes&#39; identical sizes, comparable melting temperature and GC content, along with a uniform protocol for macroarray spotting, hybridization and quantification allows for unbiased measurement of tRNA levels directly from spot signals.
SPOt is reproducible and specific. Its large dynamic range and easily adjustable threshold allows profiling low abundant species, such as tRNAs associated with polysomes, simply by prolonging array exposure times9. After the initial investment for the necessary equipment, the running cost per sample, including consumables, averages $15 per samples.
SPOt is applicable to any organism whose genome is available for probe design. Model organisms that are grown in vitro are ideal candidates for metabolic labeling. As mammalian genomes often encode many isodecoders (tRNAs that share identical anticodons but display small differences in their body sequences) probes need to be partially degenerated to preserve homogenous hybridization of close tRNA species. Finally, adherent mammalian cells yield typically lower amounts of total RNA compared to organisms grown in suspension such as M. smegmatis, so cultures need to be substantially scaled up.

Cellular tRNA levels fluctuate according to conditions such as cell type, environment, and stress1,2,3. SPOt, Streamlined Platform for Observing tRNA, is an original, reliable, and straightforward technique that allows fast and precise quantification of transfer RNA levels in laboratory-grown organisms.
tRNAs have remarkably stable secondary and tertiary structures4. They also display numerous post-transcriptional modifications5. These features represent significant structural and sequence roadblocks biasing or sometimes preventing direct and reproducible tRNA profiling using standard benchmark RNA quantification techniques6. Research groups around the world were forced to develop creative but often convoluted techniques to assess cellular tRNA levels. Some of these methods include: (1) two-dimensional electrophoretic separation of metabolically labeled tRNAs combined with methodical spot assignment by Northern blot1; (2) individual quantification by Northern blot using carefully standardized radioactive DNA probes7; (3) post-extraction labeling with cyanine fluorochromes followed by microarray analysis3, and (4) in vitro stripping of tRNA modifications using recombinant demodification enzymes combined with reverse transcription and subsequent high-throughput sequencing8.
SPOt is a simple and original combination of two standard and straightforward approaches: (1) RNA body labeling, which consists in the synthesis, in growing organisms, of radioactive total RNAs and (2) tRNA macroarrays, a systematic and miniaturized genomic tool optimized for tRNA segregation.
Samples are streamlined from living organisms to the quantification platform. They are directly analyzed after extraction and not processed any further which significantly limits biases compared to techniques requiring post-extraction amplification or enzymatic treatments. SPOt is versatile and can be easily combined to polysome fractionation to identify and quantify tRNA subpopulations that are physically associated with translating ribosomes.
The protocol presented here is optimized for Mycobacterium smegmatis, and it was also successfully used to profile tRNAs in Escherichia coli9, Saccharomyces cerevisiae10, mouse, and human cell cultures11.

<table>
	<tbody>
		<tr>
			<td>Glass slide indexing system</td>
			<td>V&#38;P Scientific, Inc.</td>
			<td>VP 470</td>
			<td></td>
		</tr>
		<tr>
			<td>Glass slide arrayer replicator</td>
			<td>V&#38;P Scientific, Inc.</td>
			<td>VP 478</td>
			<td></td>
		</tr>
		<tr>
			<td>96 well microplate indexing system</td>
			<td>V&#38;P Scientific, Inc.</td>
			<td>VP 472</td>
			<td></td>
		</tr>
		<tr>
			<td>Wash and blot station</td>
			<td>V&#38;P Scientific, Inc.</td>
			<td>VP 475</td>
			<td></td>
		</tr>
		<tr>
			<td>Replicator pin dryer</td>
			<td>V&#38;P Scientific, Inc.</td>
			<td>VP 474</td>
			<td></td>
		</tr>
		<tr>
			<td>Amine coated slides</td>
			<td>Molecular Devices</td>
			<td>K2615</td>
			<td></td>
		</tr>
		<tr>
			<td>Hybridizer / Automated hybridization and washing station</td>
			<td>Digilab</td>
			<td>Hyb10022</td>
			<td></td>
		</tr>
		<tr>
			<td>Shaker incubator</td>
			<td>Eppendorf Themomixer</td>
			<td>05-400-200</td>
			<td></td>
		</tr>
		<tr>
			<td>Screw cap 2 ml tubes</td>
			<td>Thermo Scientific</td>
			<td>21-403-201</td>
			<td></td>
		</tr>
		<tr>
			<td>[32P] Na2HPO4</td>
			<td>Perkin Elmer</td>
			<td>NEX011001MC</td>
			<td></td>
		</tr>
		<tr>
			<td>Guanidinium thiocyanate-phenol-chloroform (Trizol)</td>
			<td>Invitrogen</td>
			<td>15596026</td>
			<td></td>
		</tr>
		<tr>
			<td>0.5 mm glass beads</td>
			<td>Research Products International Corp.</td>
			<td>9831</td>
			<td></td>
		</tr>
		<tr>
			<td>Mini bead mill</td>
			<td>VWR</td>
			<td>25-020</td>
			<td></td>
		</tr>
		<tr>
			<td>Storage phosphore screen</td>
			<td>Fujifilm</td>
			<td>BAS-IP SR 0813</td>
			<td></td>
		</tr>
		<tr>
			<td>Phosphorimager</td>
			<td>GE Healthcare</td>
			<td>Typhoon FLA7000</td>
			<td></td>
		</tr>
		<tr>
			<td>DNA oligonucleotides</td>
			<td>IDT</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>UV crosslinker</td>
			<td>Spectroline</td>
			<td>Select series 254 nm</td>
			<td></td>
		</tr>
		<tr>
			<td>Microarray centrifuge</td>
			<td>Arrayit Corporation</td>
			<td>MHC110V</td>
			<td></td>
		</tr>
		<tr>
			<td>Mycobacterium smegmatis</td>
			<td>ATCC</td>
			<td>700084</td>
			<td></td>
		</tr>
		<tr>
			<td>Single-use needles</td>
			<td>BD (Becton Dickinson)</td>
			<td>305185</td>
			<td></td>
		</tr>
		<tr>
			<td>2 ml centrifuge tube</td>
			<td>Fisherbrand</td>
			<td>14-666-317</td>
			<td></td>
		</tr>
		<tr>
			<td>Precipitant (GlucoBlue)</td>
			<td>Invitrogen</td>
			<td>AM9516</td>
			<td></td>
		</tr>
		<tr>
			<td>7H9 broth</td>
			<td>Difco</td>
			<td>271310</td>
			<td></td>
		</tr>
		<tr>
			<td>Chloroform</td>
			<td>Fisher Chemicals</td>
			<td>C298-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Isopropanol</td>
			<td>Fisher Chemicals</td>
			<td>A451-4</td>
			<td></td>
		</tr>
		<tr>
			<td>20 X SSC</td>
			<td>Lonza</td>
			<td>51205</td>
			<td></td>
		</tr>
		<tr>
			<td>SDS</td>
			<td>Fisher Bioreagents</td>
			<td>BP166-100</td>
			<td></td>
		</tr>
		<tr>
			<td>hybridisation cassette</td>
			<td>GE Healthcare</td>
			<td>63-0035-44</td>
			<td></td>
		</tr>
		<tr>
			<td>Glycerol</td>
			<td>Fisher Scientific</td>
			<td>BP229-1</td>
			<td></td>
		</tr>
		<tr>
			<td>Tween 80</td>
			<td>Amresco</td>
			<td>M126-100ML</td>
			<td></td>
		</tr>
		<tr>
			<td>NaCl</td>
			<td>Fisher Scientific</td>
			<td>BP358-212</td>
			<td></td>
		</tr>
		<tr>
			<td>Albumin</td>
			<td>Spectrum Chemicals</td>
			<td>A3611</td>
			<td></td>
		</tr>
		<tr>
			<td>Dextrose</td>
			<td>Fisher Chemicals</td>
			<td>D16-1</td>
			<td></td>
		</tr>
		<tr>
			<td>EDTA (Ethylenediaminetetraacetic Acid)</td>
			<td>Fisher Bioreagents</td>
			<td>BP2482-500</td>
			<td></td>
		</tr>
		<tr>
			<td>0.5 M Phosphate buffer pH 7.2</td>
			<td>Alfa Aesar</td>
			<td>AAJ63974AP</td>
			<td></td>
		</tr>
	</tbody>
</table>

metabolic labeling and profiling of transfer rnas using macroarrays

Transfer RNAs (tRNA) are abundant short non-coding RNA species that are typically 76 to 90 nucleotides in length. tRNAs are directly responsible for protein synthesis by translating codons in mRNA into amino acid sequences. tRNAs were long considered as house-keeping molecules that lacked regulatory functions. However, a growing body of evidence indicates that cellular tRNA levels fluctuate in correspondence to varying conditions such as cell type, environment, and stress. The fluctuation of tRNA expression directly influences gene translation, favoring or repressing the expression of particular proteins. Ultimately comprehending the dynamic of protein synthesis requires the development of methods able to deliver high-quality tRNA profiles. The method that we present here is named SPOt, which stands for Streamlined Platform for Observing tRNA. SPOt consists of three steps starting with metabolic labeling of cell cultures with radioactive orthophosphate, followed by guanidinium thiocyanate-phenol-chloroform extraction of radioactive total RNAs and finally hybridization on in-house printed macroarrays. tRNA levels are estimated by quantifying the radioactivity intensities at each probe spot. In the protocol presented here we profile tRNAs in Mycobacterium smegmatis mc2155, a nonpathogenic bacterium often used as a model organism to study tuberculosis.

Three independent biological replicates show that, under the tested growth conditions, all M. smegmatis tRNAs are expressed above background level (Figure 1). In this particular experiment, the observed standard deviation for each probe is comprised between 2% (Arg (TCT)) and 22% (Cys (GCA)) with a median at 5% (Figure 1). False changes between replicates are significantly influenced by factors such as array preparation and hybridization. High reproducibility is achieved through careful and consistent array printing as well as automated sample hybridization. There is a 5-fold difference between tRNA Ile (GAT) and tRNA (Val (TAC), the highest and lowest abundant species respectively. SPOt shows that the expression of tRNA isoacceptors is not uniform. Isoacceptors are species that hold the same amino acid but display different anticodon sequences and therefore decode different codons on mRNAs. For example, all Alanine isoacceptors are expressed at similar levels, whereas the highest and lowest Arginine accepting tRNAs differ by 3-fold.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/56898/56898fig1.jpg" /> 
Figure 1: Representative tRNA macroarray results. (A) Scanned bacterial, mouse and Human macroarrays. M. smegmatis arrays use only 43 probes instead of 48 for mouse and Human. As a consequence, the bacterial array displays 40 empty spots (probes are replicated eight times on each array) that blend with the background. Most of them are clustered in the upper left corner. (B) Histogram and heatmap representations of tRNA profiles in M. smegmatis under optimal growth conditions. Probe signals are the average of three independent experiments (including bacterial growth, metabolic labeling, extraction and array hybridization) and are expressed as per thousand values of total tRNAs. Standard deviations for the three replicates are indicated as error bars and shades of orange on the histogram and heatmap respectively. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56898/56898fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Metabolic Labeling and Profiling of Transfer RNAs Using Macroarrays at JoVE.com

Metabolic Labeling and Profiling of Transfer RNAs Using Macroarrays

We describe an original transfer RNA analysis platform named SPOt (Streamlined Platform for Observing tRNA). SPOt simultaneously measures cellular levels of all tRNAs in biological samples, in only three steps, and in less than 24 hours.

Transfer RNAs (tRNA) are abundant short non-coding RNA species that are typically 76 to 90 nucleotides in length. tRNAs are directly responsible for ...

metabolic-labeling-and-profiling-of-transfer-rnas-using-macroarrays

Nanyang Technological University

Research

JoVE Journal

Genetics

5.8K Views.  College of Charleston. We describe an original transfer RNA analysis platform named SPOt (Streamlined Platform for Observing tRNA). SPOt simultaneously measures cellular levels of all tRNAs in biological samples, in only three steps, and in less than 24 hours.

Video: Metabolic Labeling and Profiling of Transfer RNAs Using Macroarrays

Single-cell Gene Expression Profiling Using FACS and qPCR with Internal Standards

Gene expression measurements from bulk populations of cells can obscure the considerable transcriptomic variation of individual cells within those populations. Single-cell gene expression measurements can help assess the role of noise in gene expression, identify correlations in the expression of pairs of genes, and reveal subpopulations of cells that respond differently to a stimulus. Here, we describe a procedure to measure the expression of up to 96 genes in single mammalian cells isolated from a population growing in tissue culture. Cells are sorted into lysis buffer by fluorescence-activated cell sorting (FACS), and the mRNA species of interest are reverse-transcribed and amplified. Gene expression is then measured using a microfluidic real-time PCR machine, which performs up to 96 qPCR assays on up to 96 samples at a time. We also describe the generation and use of PCR amplicon standards to enable the estimation of the absolute number of each transcript. Compared with other methods of measuring gene expression in single cells, this approach allows for the quantification of more distinct transcripts than RNA FISH at a lower cost than RNA-Seq.

We describe a method to sort single mammalian cells and to quantify the expression of up to 96 target genes of interest in each cell. This method includes the use of internal qPCR standards to enable the estimation of absolute transcript counts.

Gene expression measurements from bulk populations of cells can obscure the considerable transcriptomic variation of individual cells within those ...

Sequence-specific and Selective Recognition of Double-stranded RNAs over Single-stranded RNAs by Chemically Modified Peptide Nucleic Acids

RNAs are emerging as important biomarkers and therapeutic targets. Thus, there is great potential in developing chemical probes and therapeutic ligands for the recognition of RNA sequence and structure. Chemically modified Peptide Nucleic Acid (PNA) oligomers have been recently developed that can recognize RNA duplexes in a sequence-specific manner. PNAs are chemically stable with a neutral peptide-like backbone. PNAs can be synthesized relatively easily by the manual Boc-chemistry solid-phase peptide synthesis method. PNAs are purified by reverse-phase HPLC, followed by molecular weight characterization by matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF). Non-denaturing polyacrylamide gel electrophoresis (PAGE) technique facilitates the imaging of the triplex formation, because carefully designed free RNA duplex constructs and PNA bound triplexes often show different migration rates. Non-denaturing PAGE with ethidium bromide post staining is often an easy and informative technique for characterizing the binding affinities and specificities of PNA oligomers. Typically, multiple RNA hairpins or duplexes with single base pair mutations can be used to characterize PNA binding properties, such as binding affinities and specificities. 2-Aminopurine is an isomer of adenine (6-aminopurine); the 2-aminopurine fluorescence intensity is sensitive to local structural environment changes, and is suitable for the monitoring of triplex formation with the 2-aminopurine residue incorporated near the PNA binding site. 2-Aminopurine fluorescence titration can also be used to confirm the binding selectivity of modified PNAs towards targeted double-stranded RNAs (dsRNAs) over single-stranded RNAs (ssRNAs). UV-absorbance-detected thermal melting experiments allow the measurement of the thermal stability of PNA-RNA duplexes and PNA&#183;RNA2 triplexes. Here, we describe the synthesis and purification of PNA oligomers incorporating modified residues, and describe biochemical and biophysical methods for characterization of the recognition of RNA duplexes by the modified PNAs.

We report the protocols for the synthesis and purification of Peptide Nucleic Acid (PNA) oligomers incorporating modified residues. The biochemical and biophysical methods for the characterization of the recognition of RNA duplexes by the modified PNAs are described.

RNAs are emerging as important biomarkers and therapeutic targets. Thus, there is great potential in developing chemical probes and therapeutic ligands ...

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 ...

Methodology for Accurate Detection of Mitochondrial DNA Methylation

Quantification of DNA methylation can be achieved using bisulfite sequencing, which takes advantage of the property of sodium bisulfite to convert unmethylated cytosine into uracil, in a single-stranded DNA context. Bisulfite sequencing can be targeted (using PCR) or performed on the whole genome and provides absolute quantification of cytosine methylation at the single base-resolution. Given the distinct nature of nuclear- and mitochondrial DNA, notably in the secondary structure, adaptions of bisulfite sequencing methods for investigating cytosine methylation in mtDNA should be made. Secondary and tertiary structure of mtDNA can indeed lead to bisulfite sequencing artifacts leading to false-positives due to incomplete denaturation poor access of bisulfite to single-stranded DNA. Here, we describe a protocol using an enzymatic digestion of DNA with BamHI coupled with bioinformatic analysis pipeline to allow accurate quantification of cytosine methylation levels in mtDNA. In addition, we provide guidelines for designing the bisulfite sequencing primers specific to mtDNA, in order to avoid targeting undesirable NUclear MiTochondrial segments (NUMTs) inserted into the nuclear genome.

Here, we present a protocol to allow accurate quantification of mitochondrial DNA (mtDNA) methylation. In this protocol, we describe an enzymatic digestion of DNA with BamHI coupled with a bioinformatic analysis pipeline which can be used to avoid overestimation of mtDNA methylation levels caused by the secondary structure of mtDNA.

Quantification of DNA methylation can be achieved using bisulfite sequencing, which takes advantage of the property of sodium bisulfite to convert ...

Tissue-specific miRNA Expression Profiling in Mouse Heart Sections Using In Situ Hybridization

micro-RNAs (miRNAs) are single-stranded RNA transcripts that bind to messenger RNAs (mRNAs) and inhibit their translation or promote their degradation. To date, miRNAs have been implicated in a large number of biological and disease processes, which has signified the need for the reliable detection methods of miRNA transcripts. Here, we describe a detailed protocol for digoxigenin-labeled (DIG) Locked Nucleic Acid (LNA) probe-based miRNA detection, combined with protein immunostaining on mouse heart sections. First, we performed an in situ hybridization technique using the probe to identify miRNA-182 expression in heart sections from control and cardiac hypertrophy mice. Next, we performed immunostaining for cardiac Troponin T (cTnT) protein, on the same sections, to co-localize miRNA-182 with the cardiomyocyte cells. Using this protocol, we were able to detect miRNA-182 through an alkaline phosphatase based colorimetric assay, and cTnT through fluorescent staining. This protocol can be used to detect the expression of any miRNA of interest through DIG-labeled LNA probes, and relevant protein expression on mouse heart tissue sections.

Tissue-specific miRNA Expression Profiling in Mouse Heart Sections Using In Situ Hybridization

micro-RNAs (miRNAs) are short and highly homologous RNA sequences, serving as post-transcriptional regulators of messenger RNAs (mRNAs). Current miRNA detection methods vary in sensitivity and specificity. We describe a protocol that combines in situ hybridization and immunostaining for concurrent detection of miRNA and protein molecules on mouse heart tissue sections.

micro-RNAs (miRNAs) are single-stranded RNA transcripts that bind to messenger RNAs (mRNAs) and inhibit their translation or promote their degradation. To ...

Saccharomyces cerevisiae Metabolic Labeling with 4-thiouracil and the Quantification of Newly Synthesized mRNA As a Proxy for RNA Polymerase II Activity

Global defects in RNA polymerase II transcription might be overlooked by transcriptomic studies analyzing steady-state RNA. Indeed, the global decrease in mRNA synthesis has been shown to be compensated by a simultaneous decrease in mRNA degradation to restore normal steady-state levels. Hence, the genome-wide quantification of mRNA synthesis, independently from mRNA decay, is the best direct reflection of RNA polymerase II transcriptional activity. Here, we discuss a method using non-perturbing metabolic labeling of nascent RNAs in Saccharomyces cerevisiae (S. cerevisiae). Specifically, the cells are cultured for 6 min with a uracil analog, 4-thiouracil, and the labeled newly transcribed RNAs are purified and quantified to determine the synthesis rates of all individual mRNA. Moreover, using labeled Schizosaccharomyces pombe cells as internal standard allows comparing mRNA synthesis in different S. cerevisiae strains. Using this protocol and fitting the data with a dynamic kinetic model, the corresponding mRNA decay rates can be determined.

Saccharomyces cerevisiae Metabolic Labeling with 4-thiouracil and the Quantification of Newly Synthesized mRNA As a Proxy for RNA Polymerase II Activity

The protocol described here is based on the genome-wide quantification of newly synthesized mRNA purified from yeast cells labeled with 4-thiouracil. This method allows to measure mRNA synthesis uncoupled from mRNA decay and, thus, provides an accurate measurement of RNA polymerase II transcription.

Global defects in RNA polymerase II transcription might be overlooked by transcriptomic studies analyzing steady-state RNA. Indeed, the global decrease in ...

Cell Based Assays of SINEUP Non-coding RNAs That Can Specifically Enhance mRNA Translation

Targeted-protein enhancement is of importance not only for the study of biological processes but also for therapeutic and biotechnological applications. Here, we present a method to selectively up-regulate protein expression of desired genes in cultured cells by means of synthetic antisense non-coding RNAs known as SINEUPs. This positive control of gene expression is at the post-transcriptional level and exerted by an inverted short interspersed nuclear element (SINE) repeat at the 3&#697; end of SINEUPs that comprises its effector domain (ED). SINEUPs can specifically bind to any protein-coding mRNA of choice through its binding domain (BD), a region designed to complement the sequence within the 5&#697; untranslated region (5&#697; UTR) and around the start codon of the mRNA. Target-specific SINEUPs designed in this manner are transfected to cultured cells, and protein and RNA are extracted for downstream analyses, generally 24-48 h post-transfection. SINEUP-induced protein up-regulation is detected by Western-blot analysis and RNA expression is measured using real-time quantitative reverse transcription PCR. We have observed that BD design is critical for achieving optimum SINEUP activity and that testing different BD sizes and positions with respect to the start codon of the target mRNA is recommended. Therefore, we describe here a semi-automated high-throughput imaging method based on fluorescence detection that can be implemented to target mRNA fused with green fluorescent protein (GFP). SINEUPs specifically enhance translation within normal physiological range of the cell, without altering the target transcript level. This method has been successfully employed against a range of endogenous and exogenous targets, in a wide variety of human, mouse, and insect cell lines along with in vivo systems. Moreover, SINEUPs have been reported to increase antibody production and work as an RNA therapeutic against haploinsufficient genes. The versatile and modular nature of SINEUPs makes them a suitable tool for gene-specific translational control.

SINEUPs are synthetic antisense non-coding RNAs, which contain a binding domain (BD) and an effector domain (ED) and up-regulate translation of target mRNA. Here, we describe detection methods for SINEUPs in cultured cell lines, analysis of their translation-promoting activity by Western-blot and a semi-automated high throughput imaging system.

Targeted-protein enhancement is of importance not only for the study of biological processes but also for therapeutic and biotechnological applications. ...

Overexpressing Long Noncoding RNAs Using Gene-activating CRISPR

Long noncoding RNA (lncRNA) biology is a new and exciting field of research, with the number of publications from this field growing exponentially since 2007. These studies have confirmed that lncRNAs are altered in almost all diseases. However, studying the functional roles for lncRNAs in the context of disease remains difficult due to the lack of protein products, tissue-specific expression, low expression levels, complexities in splice forms, and lack of conservation among species. Given the species-specific expression, lncRNA studies are often restricted to human research contexts when studying disease processes. Since lncRNAs function at the molecular level, one way to dissect lncRNA biology is to either remove the lncRNA or overexpress the lncRNA and measure cellular effects. In this article, a written and visualized protocol to overexpress lncRNAs in vitro is presented. As a representative experiment, an lncRNA associated with inflammatory bowel disease, Interferon Gamma Antisense 1 (IFNG-AS1), is shown to be overexpressed in a Jurkat T-cell model. To accomplish this, the activating clustered regularly interspaced short palindromic repeats (CRISPR) technique is used to enable overexpression at the endogenous genomic loci. The activating CRISPR technique targets a set of transcription factors to the transcriptional start site of a gene, enabling a robust overexpression of multiple lncRNA splice forms. This procedure will be broken down into three steps, namely (i) guide RNA (gRNA) design and vector construction, (ii) virus generation and transduction, and (iii) colony screening for overexpression. For this representative experiment, a greater than 20-fold enhancement in IFNG-AS1 in Jurkat T cells was observed.

Traditional cDNA-based overexpression techniques have a limited applicability for the overexpression of long noncoding RNAs due to their multiple splice forms with potential functionality. This review reports a protocol using CRISPR technology to overexpress multiple splice variants of a long noncoding RNA.

Long noncoding RNA (lncRNA) biology is a new and exciting field of research, with the number of publications from this field growing exponentially since ...

Identification of Circular RNAs using RNA Sequencing

Circular RNAs (circRNAs) are a class of non-coding RNAs involved in functions including micro-RNA (miRNA) regulation, mediation of protein-protein interactions, and regulation of parental gene transcription. In classical next generation RNA sequencing (RNA-seq), circRNAs are typically overlooked as a result of poly-A selection during construction of mRNA libraries, or are found at very low abundance, and are therefore difficult to isolate and detect. Here, a circRNA library construction protocol was optimized by comparing library preparation kits, pre-treatment options and various total RNA input amounts. Two commercially available whole transcriptome library preparation kits, with and without RNase R pre-treatment, and using variable amounts of total RNA input (1 to 4 &#181;g), were tested. Lastly, multiple tissue types; including liver, lung, lymph node, and pancreas; as well as multiple brain regions; including the cerebellum, inferior parietal lobe, middle temporal gyrus, occipital cortex, and superior frontal gyrus; were compared to evaluate circRNA abundance across tissue types. Analysis of the generated RNA-seq data using six different circRNA detection tools (find_circ, CIRI, Mapsplice, KNIFE, DCC, and CIRCexplorer) revealed that a stranded total RNA library preparation kit with RNase R pre-treatment and 4 &#181;g RNA input is the optimal method for identifying the highest relative number of circRNAs. Consistent with previous findings, the highest enrichment of circRNAs was observed in brain tissues compared to other tissue types.

Circular RNAs (circRNAs) are non-coding RNAs that may have roles in transcriptional regulation and mediating interactions between proteins. Following assessment of different parameters for construction of circRNA sequencing libraries, a protocol was compiled utilizing stranded total RNA library preparation with RNase R pre-treatment and is presented here.

Circular RNAs (circRNAs) are a class of non-coding RNAs involved in functions including micro-RNA (miRNA) regulation, mediation of protein-protein ...

Improving Small RNA-seq: Less Bias and Better Detection of 2'-O-Methyl RNAs

The study of small RNAs (sRNAs) by next-generation sequencing (NGS) is challenged by bias issues during library preparation. Several types of sRNA such as plant microRNAs (miRNAs) carry a 2&#39;-O-methyl (2&#39;-OMe) modification at their 3&#39;&#160;terminal nucleotide. This modification adds another difficulty as it inhibits 3&#39;&#160;adapter ligation. We previously demonstrated that modified versions of the &#39;TruSeq (TS)&#39;&#160;protocol have less bias and an improved detection of 2&#39;-OMe RNAs. Here we describe in detail protocol &#39;TS5&#39;, which showed the best overall performance. TS5 can be followed either using homemade reagents or reagents from the TS kit, with equal performance.

We present a detailed small RNA library reparation protocol with less bias than standard methods and an increased sensitivity for 2&#39;-O-methyl RNAs. This protocol can be followed using homemade reagents to save cost or using kits for convenience.

The study of small RNAs (sRNAs) by next-generation sequencing (NGS) is challenged by bias issues during library preparation. Several types of sRNA such as ...