National Institutes of Health grant R01 CA149976 (N.A.S) supported this work.

All procedures must be performed in accordance with institutional animal use and care guidelines. The procedure was developed for the analysis of murine hematopoietic stem and progenitor cells (HSCs and HPs), but can be adapted for the analysis of other cell populations.
1. Flow Cytometry Isolation of Murine HSCs and HPs
<ol>
	<li>Harvest murine bone marrow cells as described in the literature6. 
	NOTE: In data presented in Figure 1 and Figure 2, bone marrow was harvested from C57BL/6J mice.</li>
	<li>Perform lineage depletion of bone marrow cells using a mouse lineage depletion kit, following the manufacturer&#39;s instructions.</li>
	<li>Incubate the cells with antibodies against the cell surface markers of interest as described7. In the experiments shown in Figure 1 and Figure 2, antibodies to Sca-1, Kit, Flt3, and lineage (Lin) markers Mac1, Gr1, CD3e, B220, and Ter119 are used.</li>
	<li>Sort 2,000 - 20,000 Lin- Sca1+Kit+ Flt3- cells (HSCs) or Lin-Sca1-Kit+ cells (HPs) into 1.5 mL Eppendorf tubes containing 0.1 mL of phosphate buffered saline (PBS) with 2% fetal bovine serum (FBS). 
	NOTE: For the data shown in Figure 1 and Figure 2, cells were sorted using a Flow Cytometer with a 70 &#181;M nozzle. The maximum collection volume is 1.4 mL.</li>
</ol>
2. Sample Preparation
NOTE: This step is critical. Process the sample very carefully. When removing the supernatant, be very careful not to disturb the cell pellet.
<ol>
	<li>Centrifuge the 1.5 mL tubes containing sorted cells in a swinging bucket rotor at 4 &#176;C, 500 x g, for 5 min. Remove all but approximately 100 &#181;L of the supernatant from the cell pellet very gently using a pipette and a 20 &#181;L pipet tip. Do not disturb the pellet.
	<ol>
		<li>If the sample contains fewer than 5,000 cells, and the total volume of the sorted sample is less than 0.2 mL, transfer the cells first to low binding 0.2 mL PCR tubes before centrifugation.</li>
		<li>If sample contains fewer than 5,000 cells and volume is more than 0.2 mL, spin the cells down with a centrifuge at 4 &#176;C, 500 x g, for 5 min, and remove all but 200 &#181;L of the supernatant. Re-suspend the pelleted cells in the remaining 200 &#181;L of supernatant, then transfer the cells to the 0.2 mL PCR tubes and spin down again. Remove all but 20 - 30 &#181;L from the pellet after the second spin and re-suspend cells.</li>
	</ol>
	</li>
	<li>Resuspend the cells in the supernatant left in the tube. If necessary,add additional PBS in 2% FBS/PBS (you can also use 2% bovine serum albumin (BSA)/PBS, or PBS alone) to obtain a concentration 5 x104 to 5 x 105 cells/mL. 
	NOTE: Use the cell counts collected by cytometry to estimate the volume used to suspend cells.</li>
	<li>Use 2 - 5 &#181;L of the re-suspended cells to determine an accurate cell concentration using an automated cell counter (following the manufacturer&#39;s instructions) or a hemocytometer9.</li>
	<li>Transfer a volume of re-suspended cells containing the desired number of cells to new 1.5 mL tubes. For the experiment in Figure 1, 2,000, 1,000, or 500 HSCs or HPs were transferred. The desired number of cells depends on the strength of the signal obtained by Western blot, and is determined empirically. Perform the transfer using a 20 &#181;L or 100 &#181;L Eppendorf pipette tip.</li>
	<li>Centrifuge the cells in a swinging bucket rotor at 4 &#176;C, 500 x g, for 5 min.</li>
	<li>To generate 100x stock solutions, dissolve proteasome and phosphatase inhibitors in DMSO according to the manufacturer&#39;s instructions.</li>
	<li>Prepare 2x Laemmli sample buffer by diluting the 4x Laemmli sample buffer provided by the manufacturer with an equivalent amount of distilled water. Add an appropriate amount of the 100x stock of proteasome and phosphatase inhibitors to obtain a final concentration of 2x inhibitors in 2x Laemmli sample buffer. 
	NOTE: The 2x Laemmli sample buffer can be made in advance, but the proteasome and phosphatase inhibitors should be added immediately before adding the 2x Laemmli sample buffer (plus inhibitors) to the cell pellet to lyse the cells, as described in the following step.</li>
	<li>Carefully remove a portion of the supernatant from the cell pellet, and to the supernatant remaining in the tube with the cell pellet, add an equal volume of 2x Laemmli sample buffer plus proteasome and phosphatase inhibitors to achieve a final concentration of 500 cells/&#181;L in 1x Laemmli sample buffer. 
	NOTE: For example, if you transfer 2,000 cells in a total volume of 20 &#181;L to a tube in Step 2.5, after centrifuging the cells (Step 2.6) you should remove 18 &#181;L of the supernatant from the pellet, and to the 2 &#181;L of supernatant that is remaining add an equal volume (2 &#181;L) of 2x Laemmli sample buffer to achieve a final concentration of 500 cells/&#181;L in 1x Laemmli sample buffer.</li>
	<li>Resuspend the pellet to generate the lysate as soon as possible. At this point, the samples can be immediately electrophoresed through SDS-PAGE gels, or can be snap frozen in liquid N2 and stored at -80 &#176;C for future use.</li>
</ol>
3. Electrophoresis
<ol>
	<li>Heat the lysates in a heat block at 95 &#176;C or in boiling water for 5 min.</li>
	<li>Electrophorese 1 - 40 &#181;L of the lysates (containing from 500 up to 20,000 cell equivalents) through SDS-PAGE gels at 100V using standard protocols10. 
	NOTE: The volume of lysate loaded into the gel is determined by the number of cells needed to generate the desirable signal, and will depend on the abundance of the protein of interest, and the quality of the antibody. The data in Figure 1 were obtained with 2,000, 1,000, and 500 cell equivalents of lysate. The width of the well should be in the range of 3 mm to 1.5 mm. 1.5 mm teeth can be cut from a commercially available comb with wider teeth using scissors.</li>
</ol>
4. Transfer and Block
NOTE: Perform a Western blot following standard protocols11. The steps are briefly outlined here:
<ol>
	<li>Pretreat a polyvinylidene difluoride (PVDF) membrane with methanol for 10 s, then wash the membrane briefly with distilled water.</li>
	<li>Transfer the protein from the SDS-PAGE gel to the membrane following the instructions in the manual provided by the manufacturer of the transfer apparatus.</li>
	<li>Following transfer, block the membrane with 2 mL of 5% bovine serum albumin (BSA) in PBST (PBS with 0.1% Tween) overnight at 4 &#176;C following standard protocols11.</li>
</ol>
5. Antibody Labeling
<ol>
	<li>Incubate the membrane with antibodies on a shaker overnight at 4 &#176;C using antibody dilutions recommended by the vendor. 
	NOTE: In the Table of Materials, antibodies, which we have validated for HSCs and HPs and the corresponding antibody dilutions, are shown. Perform the antibody labeling using standard procedures8.</li>
</ol>
6. Detection
<ol>
	<li>Wash the membrane 3 times, 5 min for each wash in PBST at room temperature.</li>
	<li>Incubate the membrane with 2 mL of enhanced chemiluminescence buffer for 1 min at room temperature. Detect the signals using an imaging system following the manufacturer&#39;s instructions, or autoradiography film and film processor.</li>
</ol>

<ol>
	<li>Krutzik, P. O., Clutter, M. R., 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=Coordinate+analysis+of+murine+immune+cell+surface+markers+and+intracellular+phosphoproteins+by+flow+cytometry.">Coordinate analysis of murine immune cell surface markers and intracellular phosphoproteins by flow cytometry.</a> J Immunol. 175 (4), 2357-2365 (2005).</li><li>Du, 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=Signaling+profiling+at+the+single-cell+level+identifies+a+distinct+signaling+signature+in+murine+hematopoietic+stem+cells.">Signaling profiling at the single-cell level identifies a distinct signaling signature in murine hematopoietic stem cells.</a> Stem Cells. 30 (7), 1447-1454 (2012).</li><li>Signer, R. A., Magee, J. A., Salic, A., Morrison, S. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Haematopoietic+stem+cells+require+a+highly+regulated+protein+synthesis+rate.">Haematopoietic stem cells require a highly regulated protein synthesis rate.</a> Nature. 509 (7498), 49-54 (2014).</li><li>Wang, 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=A+differentiation+checkpoint+limits+hematopoietic+stem+cell+self-renewal+in+response+to+DNA+damage.">A differentiation checkpoint limits hematopoietic stem cell self-renewal in response to DNA damage.</a> Cell. 148 (5), 1001-1014 (2012).</li><li>Hoshii, T., 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=mTORC1+is+essential+for+leukemia+propagation+but+not+stem+cell+self-renewal.">mTORC1 is essential for leukemia propagation but not stem cell self-renewal.</a> J Clin Invest. 122 (6), 2114-2129 (2012).</li><li>Signer, R. 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=The+rate+of+protein+synthesis+in+hematopoietic+stem+cells+is+limited+partly+by+4E-BPs.">The rate of protein synthesis in hematopoietic stem cells is limited partly by 4E-BPs.</a> Genes Dev. 30 (15), 1698-1703 (2016).</li><li>Cai, X., 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=Runx1+deficiency+decreases+ribosome+biogenesis+and+confers+stress+resistance+to+hematopoietic+stem+and+progenitor+cells.">Runx1 deficiency decreases ribosome biogenesis and confers stress resistance to hematopoietic stem and progenitor cells.</a> Cell Stem Cell. , (2015).</li><li>Loven, 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=Revisiting+global+gene+expression+analysis.">Revisiting global gene expression analysis.</a> Cell. 151 (3), 476-482 (2012).</li><li>JoVE Science Education Database. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Using+a+Hemoacytometer+to+Count+Cells.">Using a Hemoacytometer to Count Cells.</a> Basic Methods in Cellular and Molecular Biology. , (2017).</li><li>JoVE Science Education Database. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Separating+Protein+with+SDS-PAGE.">Separating Protein with SDS-PAGE.</a> Basic Methods in Cellular and Molecular Biology. , (2017).</li><li>JoVE Science Education Database. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Western+Blot.">The Western Blot.</a> Basic Methods in Cellular and Molecular Biology. , (2017).</li><li>Jackson, R. J., Hellen, C. U., Pestova, T. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+mechanism+of+eukaryotic+translation+initiation+and+principles+of+its+regulation.">The mechanism of eukaryotic translation initiation and principles of its regulation.</a> Nat Rev Mol Cell Biol. 11 (2), 113-127 (2010).</li><li>Eaton, S. 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=A+guide+to+modern+quantitative+fluorescent+western+blotting+with+troubleshooting+strategies.">A guide to modern quantitative fluorescent western blotting with troubleshooting strategies.</a> J Vis Exp. (93), e52099 (2014).</li></ol>

The authors have no conflict of interests to declare.

Western Blotting is a common technique for detecting specific proteins and the activation of signaling pathways in tissues or cells. By introducing small adjustments to a commonly used procedure, we were able to routinely detect 15 different proteins (Table of Materials) in 15,000 HSCs, and in some cases in as few as 500 HSCs. The most critical steps in this protocol are: 1) accurately counting the cells, 2) minimizing the number of transfers between tubes, and 3) lysing the cells directly with Laemmli s...

Hematopoietic stem cells (HSCs) are self-renewing cells that can give rise to all blood lineages. They are relatively rare cells in the bone marrow, rendering biochemical analyses difficult. Approaches suitable for analyzing rare cells, such as flow cytometry, have been extremely useful for quantifying relative amounts of cell surface markers and intracellular proteins. However, the analysis of intracellular proteins necessitates the use of cell permeabilization procedures to enable antibody access, and not all cell surface epitopes survive these procedures1,2. In addition, antibodies that discriminate between different protein isoforms or cleavage products are not often available for flow cytometry, and therefore investigators still rely on Western blots for certain types of analyses.
Western blot analysis of cell lysates is a routine procedure in most laboratories. Cells can be purified under native conditions that preserve the epitopes of cell surface molecules, and cell lysates can subsequently be prepared and analyzed. However, the analysis of proteins in rare primary cell populations by Western blot can require euthanizing large numbers of animals to obtain enough cells. By making small adjustments to several steps, a conventional Western blotting protocol was able to detect proteins in relatively small numbers of HSCs (500 - 15,000, depending on the protein of interest). The adjustments include accurately counting the cells, carefully handling the cell pellet, reducing transfers of cells between tubes to minimize cell loss, and lysing a defined number of cells with a concentrated loading buffer containing proteasome and phosphatase inhibitors. Many published reports include Western blots obtained with 20,000 or more HSCs3,4,5,6,7; this simple procedure will reduce the number of cells and experimental animals required to produce equivalent data by between 4 and 40 fold. The protocol is designed to normalize results on a per cell basis, rather than to an internal control. This enables detection of overall reductions in protein levels that can be overlooked if data are normalized to an internal control. The importance of normalizing on a per cell basis was described for the analysis of gene expression data8, and the same principle applies to quantifying proteins by Western blot. This optimized protocol should be useful for anyone needing to analyze small numbers of cells.

<table>
	<tbody>
		<tr>
			<td>sodium dodecyl sulfate (SDS)</td>
			<td>Fisher Scientific</td>
			<td>BP166-500</td>
			<td>&#160;SDS-PAGE</td>
		</tr>
		<tr>
			<td>TEMED</td>
			<td>Fisher Scientific</td>
			<td>BP150-20</td>
			<td>&#160;SDS-PAGE</td>
		</tr>
		<tr>
			<td>30% Acrylamidel Bis solution</td>
			<td>Bio-Rad</td>
			<td>1610158</td>
			<td>&#160;SDS-PAGE</td>
		</tr>
		<tr>
			<td>1.5M Tris-HCl pH8.8</td>
			<td>TEKNOVA</td>
			<td>T1588</td>
			<td>&#160;SDS-PAGE</td>
		</tr>
		<tr>
			<td>1.0M Tris-HCl pH6.8</td>
			<td>TEKNOVA</td>
			<td>T1068</td>
			<td>&#160;SDS-PAGE</td>
		</tr>
		<tr>
			<td>Ammonium Persulfate</td>
			<td>Fisher Scientific</td>
			<td>BP179-25</td>
			<td>&#160;SDS-PAGE</td>
		</tr>
		<tr>
			<td>mini-protean 3 comb</td>
			<td>Bio-Rad</td>
			<td>1653360</td>
			<td>&#160;SDS-PAGE</td>
		</tr>
		<tr>
			<td> 
			Mini-PROTEAN Tetra Cell</td>
			<td>Bio-Rad</td>
			<td>1658005EDU&#160;</td>
			<td>&#160;SDS-PAGE</td>
		</tr>
		<tr>
			<td>&#160;Transfer System</td>
			<td>Bio-Rad</td>
			<td>1704155EDU</td>
			<td>transfer</td>
		</tr>
		<tr>
			<td>PowerPac HC Power Supply</td>
			<td>Bio-Rad</td>
			<td>1645052EDU&#160;</td>
			<td>electrophoresis</td>
		</tr>
		<tr>
			<td>Imaging System</td>
			<td>Bio-Rad</td>
			<td>1708195&#160;</td>
			<td>signal detection</td>
		</tr>
		<tr>
			<td>4x Laemmli Sample Buffer</td>
			<td>Bio-Rad</td>
			<td>1610747EDU&#160;</td>
			<td>sample preparation</td>
		</tr>
		<tr>
			<td>10x Tris/Glycine/SDS Electrophoresis Buffer</td>
			<td>Bio-Rad</td>
			<td>1610732EDU&#160;</td>
			<td>electrophoresis</td>
		</tr>
		<tr>
			<td>2-Mercaptoethanol</td>
			<td>Bio-Rad</td>
			<td>1610710EDU</td>
			<td>sample preparation</td>
		</tr>
		<tr>
			<td>&#160;RTA Mini PVDF Transfer Kit, for 40 blots</td>
			<td>Bio-Rad</td>
			<td>1704272&#160;</td>
			<td>transfer</td>
		</tr>
		<tr>
			<td>Protease Inhibitor Cocktail</td>
			<td>Sigma</td>
			<td>11697498001</td>
			<td>sample preparation</td>
		</tr>
		<tr>
			<td>Phosphatase Inhibitor Cocktailrs</td>
			<td>Gold Biotechnology</td>
			<td>GB-450-1</td>
			<td>sample preparation</td>
		</tr>
		<tr>
			<td>EIF4G</td>
			<td>Cell signaling</td>
			<td>2469</td>
			<td>WB antibody, validated in 1000 cells 
			antibody concentration: 1:1000 
			reference(figure): Fig2</td>
		</tr>
		<tr>
			<td>p-Rps6</td>
			<td>Cell signaling</td>
			<td>4858</td>
			<td>WB antibody,validated in 1000 cells 
			antibody concentration: 1:1000 
			reference(figure): Fig2</td>
		</tr>
		<tr>
			<td>actin(HRP conjugated)</td>
			<td>abcam</td>
			<td>ab49900</td>
			<td>WB antibody,validated in 500 cells 
			antibody concentration: 1:5000 
			reference(figure): Fig1, Fig2</td>
		</tr>
		<tr>
			<td>LC-3</td>
			<td>Abcam</td>
			<td>ab48394</td>
			<td>WB antibody,validated in 15000 cells 
			antibody concentration: 1:1000 
			reference(figure): ref5 (Fig5)</td>
		</tr>
		<tr>
			<td>S6</td>
			<td>Cell Signaling</td>
			<td>2317</td>
			<td>WB antibody,validated in 15000 cells 
			antibody concentration: 1:1000 
			reference(figure): ref5 (Fig4)</td>
		</tr>
		<tr>
			<td>4EBP1</td>
			<td>Cell Signaling</td>
			<td>9644</td>
			<td>WB antibody, validated in 15000 cells 
			antibody concentration: 1:1000 
			reference(figure): ref5 (Fig4)</td>
		</tr>
		<tr>
			<td>p-4EBP1</td>
			<td>Cell Signaling</td>
			<td>2855</td>
			<td>WB antibody,validated in 15000 cells 
			antibody concentration: 1:1000 
			reference(figure): ref5 (Fig4)</td>
		</tr>
		<tr>
			<td>TSC2</td>
			<td>Cell Signaling</td>
			<td>4308</td>
			<td>WB antibody,validated in 15000 cells 
			antibody concentration: 1:1000 
			reference(figure): ref5 (Fig4)</td>
		</tr>
		<tr>
			<td>HSP90</td>
			<td>Cell Signaling</td>
			<td>4877</td>
			<td>WB antibody,validated in 15000 cells 
			antibody concentration: 1:1000 
			reference(figure): ref5 (Fig5)</td>
		</tr>
		<tr>
			<td>PTEN</td>
			<td>Cell Signaling</td>
			<td>9188</td>
			<td>WB antibody,validated in 15000 cells 
			antibody concentration: 1:1000 
			reference(figure): ref5 (FigS1)</td>
		</tr>
		<tr>
			<td>mTOR</td>
			<td>Cell Signaling</td>
			<td>2983</td>
			<td>WB antibody,validated in 15000 cells 
			antibody concentration: 1:1000 
			reference(figure): ref5 (FigS1)</td>
		</tr>
		<tr>
			<td>p-mTOR</td>
			<td>Cell Signaling</td>
			<td>5536</td>
			<td>WB antibody,validated in 15000 cells 
			antibody concentration: 1:1000 
			reference(figure): ref5 (FigS1)</td>
		</tr>
		<tr>
			<td>PP2AB</td>
			<td>Cell Signaling</td>
			<td>4953</td>
			<td>WB antibody,validated in 15000 cells 
			antibody concentration: 1:1000 
			reference(figure): ref5 (FigS1)</td>
		</tr>
		<tr>
			<td>p-AMPKa</td>
			<td>Cell Signaling</td>
			<td>2535</td>
			<td>WB antibody,validated in 15000 cells 
			antibody concentration: 1:1000 
			reference(figure): ref5 (FigS1)</td>
		</tr>
		<tr>
			<td>actin</td>
			<td>Santa Cruz</td>
			<td>sc-47778</td>
			<td>WB antibody,validated in 15000 cells 
			antibody concentration: 1:3000 
			reference(figure): ref5 (Fig4)</td>
		</tr>
		<tr>
			<td>lineage depletion kit (mouse)</td>
			<td>Miltenyi Biotec</td>
			<td>130-090-858</td>
			<td>hematopoietic stem and progenitor cells purification</td>
		</tr>
		<tr>
			<td>LS columns</td>
			<td>Miltenyi Biotec</td>
			<td>130-041-305</td>
			<td>hematopoietic stem and progenitor cells purification</td>
		</tr>
		<tr>
			<td>SCF</td>
			<td>PeproTech</td>
			<td>250-03</td>
			<td>phosphorylation stimulation</td>
		</tr>
		<tr>
			<td>APC-Cy7 c-kit antibody</td>
			<td>ThermoFisher</td>
			<td>A15423</td>
			<td>cell sorting</td>
		</tr>
		<tr>
			<td>anti-B220</td>
			<td>ThermoFisher</td>
			<td>48-0452-82</td>
			<td>cell sorting</td>
		</tr>
		<tr>
			<td>anti-CD3e</td>
			<td>ThermoFisher</td>
			<td>48-0031-82</td>
			<td>cell sorting</td>
		</tr>
		<tr>
			<td>anti-Mac1</td>
			<td>ThermoFisher</td>
			<td>48-0112-82</td>
			<td>cell sorting</td>
		</tr>
		<tr>
			<td>anti-Gr1</td>
			<td>ThermoFisher</td>
			<td>48-5931-82</td>
			<td>cell sorting</td>
		</tr>
		<tr>
			<td>anti-Ter119</td>
			<td>ThermoFisher</td>
			<td>48-5921-82</td>
			<td>cell sorting</td>
		</tr>
		<tr>
			<td>Spacer Plates with 1.0 mm Integrated Spacers</td>
			<td>Bio-Rad</td>
			<td>1653311</td>
			<td>&#160;SDS-PAGE</td>
		</tr>
		<tr>
			<td>BSA</td>
			<td>Research Products International</td>
			<td>A30075</td>
			<td>membrane blocking</td>
		</tr>
		<tr>
			<td>serum</td>
			<td>Atlanta Biologicals</td>
			<td>A12450</td>
			<td>medium supplement</td>
		</tr>
		<tr>
			<td>cell counter</td>
			<td>Invitrogen</td>
			<td>AMQAF1000</td>
			<td>cell counting</td>
		</tr>
		<tr>
			<td>hemocytometer</td>
			<td>ThermoFisher</td>
			<td>&#160;S17040</td>
			<td>cell counting</td>
		</tr>
		<tr>
			<td>flim</td>
			<td>Denville Scientific</td>
			<td>E3012</td>
			<td>signal detection</td>
		</tr>
		<tr>
			<td>medical film processor</td>
			<td>Konica</td>
			<td>SRC-101A</td>
			<td>signal detection</td>
		</tr>
		<tr>
			<td>Supersignal West Femto Maximum Sensitivity Substrate</td>
			<td>Therom Scientific</td>
			<td>34096</td>
			<td>signal detection</td>
		</tr>
		<tr>
			<td>Allegra X-15R Centrifuge (Rotor SX4750A)</td>
			<td>Beckman Coulter</td>
			<td>X-15R</td>
			<td>sample preparation</td>
		</tr>
		<tr>
			<td>BLUEstain protein ladder</td>
			<td>Gold Biotechnology</td>
			<td>P007-500</td>
			<td>electrophoresis</td>
		</tr>
		<tr>
			<td>cell sorter</td>
			<td>BD</td>
			<td>FACSAria II</td>
			<td>sample preparation</td>
		</tr>
		<tr>
			<td>Incublock</td>
			<td>Denville Scientific</td>
			<td>I0510</td>
			<td>electrophoresis</td>
		</tr>
	</tbody>
</table>

a western blotting protocol for small numbers of hematopoietic stem cells

Hematopoietic stem cells (HSCs) are rare cells, with the mouse bone marrow containing only ~25,000 phenotypic long term repopulating HSCs. A Western blotting protocol was optimized and suitable for the analysis of small numbers of HSCs (500 - 15,000 cells). Phenotypic HSCs were purified, accurately counted, and directly lysed in Laemmli sample buffer. Lysates containing equal numbers of cells were analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), and the blot was prepared and processed following standard Western blotting protocols. Using this protocol, 2,000 - 5,000 HSCs can be routinely analyzed, and in some cases data can be obtained from as few as 500 cells, compared to the 20,000 to 40,000 cells reported in most publications. This protocol should be generally applicable to other hematopoietic cells, and enables the routine analysis of small numbers of cells using standard laboratory procedures.

Representative results from 500 - 2,000 purified HSCs and HPs are shown in Figure 1 and Figure 2. The &#946;-actin signal in Figure 1 can be detected from as few as 500 HSCs and HPs purified from the bone marrow of one mouse. Note that loading the lysates into 1.5 mm wells produced a much stronger signal from 500 HPs than loading into 3.0 mm wells. Figure 2 is a Western ...

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A Western Blotting Protocol for Small Numbers of Hematopoietic Stem Cells

A standard Western blotting protocol was optimized for analyzing as few as 500 hematopoietic stem or progenitor cells. Optimization involves careful handling of the cell sample, limiting transfers between tubes, and directly lysing the cells in Laemmli sample buffer.

Hematopoietic stem cells (HSCs) are rare cells, with the mouse bone marrow containing only ~25,000 phenotypic long term repopulating HSCs. A Western ...

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Research

JoVE Journal

Biochemistry

10.3K Views.  Cincinnati Children's Hospital Medical Center. A standard Western blotting protocol was optimized for analyzing as few as 500 hematopoietic stem or progenitor cells. Optimization involves careful handling of the cell sample, limiting transfers between tubes, and directly lysing the cells in Laemmli sample buffer.

Video: A Western Blotting Protocol for Small Numbers of Hematopoietic Stem Cells

Method for Identifying Small Molecule Inhibitors of the Protein-protein Interaction Between HCN1 and TRIP8b

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are expressed ubiquitously throughout the brain, where they function to regulate the excitability of neurons. The subcellular distribution of these channels in pyramidal neurons of hippocampal area CA1 is regulated by tetratricopeptide repeat-containing Rab8b interacting protein (TRIP8b), an auxiliary subunit. Genetic knockout of HCN pore forming subunits or TRIP8b, both lead to an increase in antidepressant-like behavior, suggesting that limiting the function of HCN channels may be useful as a treatment for Major Depressive Disorder (MDD). Despite significant therapeutic interest, HCN channels are also expressed in the heart, where they regulate rhythmicity. To circumvent off-target issues associated with blocking cardiac HCN channels, our lab has recently proposed targeting the protein-protein interaction between HCN and TRIP8b in order to specifically disrupt HCN channel function in the brain. TRIP8b binds to HCN pore forming subunits at two distinct interaction sites, although here the focus is on the interaction between the tetratricopeptide repeat (TPR) domains of TRIP8b and the C terminal tail of HCN1. In this protocol, an expanded description of a method for purifying TRIP8b and executing a high throughput screen to identify small molecule inhibitors of the interaction between HCN and TRIP8b, is described. The method for high throughput screening utilizes a Fluorescence Polarization (FP) -based assay to monitor the binding of a large TRIP8b fragment to a fluorophore-tagged eleven amino acid peptide corresponding to the HCN1 C terminal tail. This method allows &#39;hit&#39; compounds to be identified based on the change in the polarization of emitted light. Validation assays are then performed to ensure that &#39;hit&#39; compounds are not artifactual.

The interaction between HCN channels and their auxiliary subunit has been identified as a therapeutic target in Major Depressive Disorder. Here, a fluorescence polarization-based method for identifying small molecule inhibitors of this protein-protein interaction, is presented.

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are expressed ubiquitously throughout the brain, where they function to regulate the ...

Using Scaffold Liposomes to Reconstitute Lipid-proximal Protein-protein Interactions In Vitro

Studies of integral membrane proteins in vitro are frequently complicated by the presence of a hydrophobic transmembrane domain. Further complicating these studies, reincorporation of detergent-solubilized membrane proteins into liposomes is a stochastic process where protein topology is impossible to enforce. This paper offers an alternative method to these challenging techniques that utilizes a liposome-based scaffold. Protein solubility is enhanced by deletion of the transmembrane domain, and these amino acids are replaced with a tethering moiety, such as a His-tag. This tether interacts with an anchoring group (Ni2+ coordinated by nitrilotriacetic acid (NTA(Ni2+)) for His-tagged proteins), which enforces a uniform protein topology at the surface of the liposome. An example is presented wherein the interaction between Dynamin-related protein 1 (Drp1) with an integral membrane protein, Mitochondrial Fission Factor (Mff), was investigated using this scaffold liposome method. In this work, we have demonstrated the ability of Mff to efficiently recruit soluble Drp1 to the surface of liposomes, which stimulated its GTPase activity. Moreover, Drp1 was able to tubulate the Mff-decorated lipid template in the presence of specific lipids. This example demonstrates the effectiveness of scaffold liposomes using structural and functional assays and highlights the role of Mff in regulating Drp1 activity.

Using Scaffold Liposomes to Reconstitute Lipid-proximal Protein-protein Interactions In Vitro

This paper describes a method for assessing the interactions and assemblies of integral membrane proteins in vitro with various partner factors in a lipid-proximal environment.

Studies of integral membrane proteins in vitro are frequently complicated by the presence of a hydrophobic transmembrane domain. Further complicating ...

SorLA and CLC:CLF-1-dependent Downregulation of CNTFR&#945; as Demonstrated by Western Blotting, Inhibition of Lysosomal Enzymes, and Immunocytochemistry

The heterodimeric cytokine Cardiotrophin-like Cytokine:Cytokine-like Factor-1 (CLC:CLF-1) targets the glycosylphosphatidylinositol (GPI)-anchored CNTFR&#945; to form a trimeric complex that subsequently recruits glycoprotein 130/Leukemia Inhibitory Factor Receptor-&#946; (gp130/LIFR&#946;) for signaling. Both CLC and CNTFR&#945; are necessary for signaling but so far CLF-1 has only been known as a putative facilitator of CLC secretion. However, it has recently been shown that CLF-1 contains three binding sites: one for CLC; one for CNTFR&#945; (that may promote assembly of the trimeric complex); and one for the endocytic receptor sorLA. The latter site provides high affinity binding of CLF-1, CLC:CLF-1, as well as the trimeric (CLC:CLF-1:CNTFR&#945;) complex to sorLA, and in sorLA-expressing cells the soluble ligands CLF-1 and CLC:CLF-1 are rapidly taken up and internalized. In cells co-expressing CNTFR&#945; and sorLA, CNTFR&#945; first binds CLC:CLF-1 to form a membrane-associated trimeric complex, but it also connects to sorLA via the free sorLA-binding site in CLF-1. As a result, CNTFR&#945;, which has no capacity for endocytosis on its own, is tugged along and internalized by the sorLA-mediated endocytosis of CLC:CLF-1.
The present protocol describes the experimental procedures used to demonstrate i) the sorLA-mediated and CLC:CLF-1-dependent downregulation of surface-membrane CNTFR&#945; expression; ii) sorLA-mediated endocytosis and lysosomal targeting of CNTFR&#945;; and iii) the lowered cellular response to CLC:CLF-1-stimulation upon sorLA-mediated downregulation of CNTFR&#945;.

The present protocol describes how Western blotting and immunocytochemistry combined with inhibition of lysosomal enzymes can be used to demonstrate the downregulation of Ciliary Neurotrophic Factor Receptor-&#945; (CNTFR&#945;), which is conveyed by the interaction between Cytokine-like Factor-1 (CLF-1) and the endocytic receptor sorLA.

The heterodimeric cytokine Cardiotrophin-like Cytokine:Cytokine-like Factor-1 (CLC:CLF-1) targets the glycosylphosphatidylinositol (GPI)-anchored ...

Dissipative Microgravimetry to Study the Binding Dynamics of the Phospholipid Binding Protein Annexin A2 to Solid-supported Lipid Bilayers Using a Quartz Resonator

The dissipative quartz crystal microbalance technique is a simple and label-free approach to measure simultaneously the mass uptake and viscoelastic properties of the absorbed/immobilized mass on sensor surfaces, allowing the measurements of the interaction of proteins with solid-supported surfaces, such as lipid bilayers, in real-time and with a high sensitivity. Annexins are a highly conserved group of phospholipid-binding proteins that interact reversibly with the negatively charged headgroups via the coordination of calcium ions. Here, we describe a protocol that was employed to quantitatively analyze the binding of annexin A2 (AnxA2) to planar lipid bilayers prepared on the surface of a quartz sensor. This protocol is optimized to obtain robust and reproducible data and includes a detailed step-by-step description. The method can be applied to other membrane-binding proteins and bilayer compositions.

Here, we present an experimental protocol that can be employed to determine the binding affinities and mode of interaction of label-free phospholipid-binding protein annexin A2 with immobilized solid-supported bilayers (SLB) by simultaneously measuring the mass uptake and the viscoelastic properties of the protein annexin A2.

The dissipative quartz crystal microbalance technique is a simple and label-free approach to measure simultaneously the mass uptake and viscoelastic ...

Robust Comparison of Protein Levels Across Tissues and Throughout Development Using Standardized Quantitative Western Blotting

Western blotting is a technique that is commonly used to detect and quantify protein expression. Over the years, this technique has led to many advances in both basic and clinical research. However, as with many similar experimental techniques, the outcome of Western blot analyses is easily influenced by choices made in the design and execution of the experiment. Specific housekeeping proteins have traditionally been used to normalize protein levels for quantification, however, these have a number of limitations and have therefore been increasingly criticized over the past few years. Here, we describe a detailed protocol that we have developed to allow us to undertake complex comparisons of protein expression variation across different tissues, mouse models (including disease models), and developmental timepoints. By using a fluorescent total protein stain and introducing the use of an internal loading standard, it is possible to overcome existing limitations in the number of samples that can be compared within experiments and systematically compare protein levels across a range of experimental conditions. This approach expands the use of traditional western blot techniques, thereby allowing researchers to better explore protein expression across different tissues and samples.

This method describes a robust and reproducible approach for the comparison of protein levels in different tissues and at different developmental timepoints using a standardized quantitative western blotting approach.

Western blotting is a technique that is commonly used to detect and quantify protein expression. Over the years, this technique has led to many advances ...

A Semi-High-Throughput Adaptation of the NADH-Coupled ATPase Assay for Screening Small Molecule Inhibitors

ATPase enzymes utilize the free energy stored in adenosine triphosphate to catalyze a wide variety of endergonic biochemical processes in vivo that would not occur spontaneously. These proteins are crucial for essentially all aspects of cellular life, including metabolism, cell division, responses to environmental changes and movement. The protocol presented here describes a nicotinamide adenine dinucleotide (NADH)-coupled ATPase assay that has been adapted to semi-high throughput screening of small molecule ATPase inhibitors. The assay has been applied to cardiac and skeletal muscle myosin II's, two actin-based molecular motor ATPases, as a proof of principle. The hydrolysis of ATP is coupled to the oxidation of NADH by enzymatic reactions in the assay. First, the ADP generated by the ATPase is regenerated to ATP by pyruvate kinase (PK). PK catalyzes the transition of phosphoenolpyruvate (PEP) to pyruvate in parallel. Subsequently, pyruvate is reduced to lactate by lactate dehydrogenase (LDH), which catalyzes the oxidation of NADH in parallel. Thus, the decrease in ATP concentration is directly correlated to the decrease in NADH concentration, which is followed by change to the intrinsic fluorescence of NADH. As long as PEP is available in the reaction system, the ADP concentration remains very low, avoiding inhibition of the ATPase enzyme by its own product. Moreover, the ATP concentration remains nearly constant, yielding linear time courses. The fluorescence is monitored continuously, which allows for easy estimation of the quality of data and helps to filter out potential artifacts (e.g., arising from compound precipitation or thermal changes).

A nicotinamide adenine dinucleotide (NADH)-coupled ATPase assay has been adapted to semihigh throughput screening of small molecule myosin inhibitors. This kinetic assay is run in a 384-well microplate format with total reaction volumes of only 20 &#181;L per well. The platform should be applicable to virtually any ADP producing enzyme.

ATPase enzymes utilize the free energy stored in adenosine triphosphate to catalyze a wide variety of endergonic biochemical processes in vivo that would ...

A Rapidly Incremented Tethered-Swimming Maximal Protocol for Cardiorespiratory Assessment of Swimmers

Incremental exercise testing is the standard means of assessing cardiorespiratory capacity of endurance athletes. While the maximal rate of oxygen consumption is typically used as the criterion measurement in this regard, two metabolic breakpoints that reflect changes in the dynamics of lactate production/consumption as the work rate is increased are perhaps more relevant for endurance athletes from a functional standpoint. Exercise economy, which represents the rate of oxygen consumption relative to performance of submaximal work, is also an important parameter to measure for endurance-athlete assessment. Ramp incremental tests comprising a gradual but rapid increase in work rate until the limit of exercise tolerance is reached are useful for determining these parameters. This type of test is typically performed on a cycle ergometer or treadmill because there is a need for precision with respect to work-rate incrementation. However, athletes should be tested while performing the mode of exercise required for their sport. Consequently, swimmers are typically assessed during free-swimming incremental tests where such precision is difficult to achieve. We have recently suggested that stationary swimming against a load that is progressively increased (incremental tethered swimming) can serve as a &#34;swim ergometer&#34; by allowing sufficient precision to accommodate a gradual but rapid loading pattern that reveals the aforementioned metabolic breakpoints and exercise economy. However, the degree to which the peak rate of oxygen consumption achieved during such a protocol approximates the maximal rate that is measured during free swimming remains to be determined. In the present article, we explain how this rapidly incremented tethered-swimming protocol can be employed to assess the cardiorespiratory capacity of a swimmer. Specifically, we explain how assessment of a short-distance competitive swimmer using this protocol revealed that his rate of oxygen uptake was 30.3 and 34.8 mL&#8729;min-1&#8729;kg-1BM at his gas-exchange threshold and respiratory compensation point, respectively.

As opposed to measurement during free swimming, which presents inherent challenges and limitations, determination of important parameters of cardiorespiratory function for swimmers can be made using a more feasible and easier to administer tethered-swimming rapidly incremented protocol with gas exchange and ventilatory data collection.

Incremental exercise testing is the standard means of assessing cardiorespiratory capacity of endurance athletes. While the maximal rate of oxygen ...

Stepwise Dosing Protocol for Increased Throughput in Label-Free Impedance-Based GPCR Assays

Label-free impedance-based assays are increasingly used to non-invasively study ligand-induced GPCR activation in cell culture experiments. The approach provides real-time cell monitoring with a device-dependent time resolution down to several tens of milliseconds and it is highly automated. However, when sample numbers get high (e.g., dose-response studies for various different ligands), the cost for the disposable electrode arrays as well as the available time resolution for sequential well-by-well recordings may become limiting. Therefore, we here present a serial agonist addition protocol which has the potential to significantly increase the output of label-free GPCR assays. Using the serial agonist addition protocol, a GPCR agonist is added sequentially in increasing concentrations to a single cell layer while continuously monitoring the sample&#39;s impedance (agonist mode). With this serial approach, it is now possible to establish a full dose-response curve for a GPCR agonist from just one single cell layer. The serial agonist addition protocol is applicable to different GPCR coupling types, Gq Gi/0 or Gs and it is compatible with recombinant and endogenous expression levels of the receptor under study. Receptor blocking by GPCR antagonists is assessable as well (antagonist mode).

This protocol demonstrates real-time recording of full dose-response relationships for agonist-induced GPCR activation from a single cell layer grown on a single microelectrode using label-free impedance measurements. The new dosing scheme significantly increases throughput without loss in time resolution.

Label-free impedance-based assays are increasingly used to non-invasively study ligand-induced GPCR activation in cell culture experiments. The approach ...

A High-Throughput Enzyme-Coupled Activity Assay to Probe Small Molecule Interaction with the dNTPase SAMHD1

Sterile alpha motif and HD domain-containing protein 1 (SAMHD1) is a pivotal regulator of intracellular deoxynucleoside triphosphate (dNTP) pools, as this enzyme can hydrolyze dNTPs into their corresponding nucleosides and inorganic triphosphates. Due to its critical role in nucleotide metabolism, its association to several pathologies, and its role in therapy resistance, intense research is currently being carried out for a better understanding of both the regulation and cellular function of this enzyme. For this reason, development of simple and inexpensive high-throughput amenable methods to probe small molecule interaction with SAMHD1, such as allosteric regulators, substrates, or inhibitors, is vital. To this purpose, the enzyme-coupled malachite green assay is a simple and robust colorimetric assay that can be deployed in a 384-microwell plate format allowing the indirect measurement of SAMHD1 activity. As SAMHD1 releases the triphosphate group from nucleotide substrates, we can couple a pyrophosphatase activity to this reaction, thereby producing inorganic phosphate, which can be quantified by the malachite green reagent through the formation of a phosphomolybdate malachite green complex. Here, we show the application of this methodology to characterize known inhibitors of SAMHD1 and to decipher the mechanisms involved in SAMHD1 catalysis of non-canonical substrates and regulation by allosteric activators, exemplified by nucleoside-based anticancer drugs. Thus, the enzyme-coupled malachite green assay is a powerful tool to study SAMHD1, and furthermore, could also be utilized in the study of several enzymes which release phosphate species.

SAMHD1 is a deoxynucleoside triphosphate triphosphohydrolase with critical roles in human health and disease. Here we present a versatile enzyme-coupled SAMHD1 activity assay, deployed in a 384-well microplate format, that allows for the evaluation of small molecules and nucleotide analogues as SAMHD1 substrates, activators, and inhibitors.

Sterile alpha motif and HD domain-containing protein 1 (SAMHD1) is a pivotal regulator of intracellular deoxynucleoside triphosphate (dNTP) pools, as this ...

RIBO-seq in Bacteria: a Sample Collection and Library Preparation Protocol for NGS Sequencing

The ribosome profiling technique (RIBO-seq) is currently the most effective tool for studying the process of protein synthesis in vivo. The advantage of this method, in comparison to other approaches, is its ability to monitor translation by precisely mapping the position and number of ribosomes on a mRNA transcript.
In this article, we describe the consecutive stages of sample collection and preparation for RIBO-seq method in bacteria, highlighting the details relevant to the planning and execution of the experiment.
Since the RIBO-seq relies on intact ribosomes and related mRNAs, the key step is rapid inhibition of translation and adequate disintegration of cells. Thus, we suggest filtration and flash-freezing in liquid nitrogen for cell harvesting with an optional pretreatment with chloramphenicol to arrest translation in bacteria. For the disintegration, we propose grinding frozen cells with mortar and pestle in the presence of aluminum oxide to mechanically disrupt the cell wall. In this protocol, sucrose cushion or a sucrose gradient ultracentrifugation for monosome purification is not required. Instead, mRNA separation using polyacrylamide gel electrophoresis (PAGE) followed by the ribosomal footprint excision (28-30 nt band) is applied and provides satisfactory results. This largely simplifies the method as well as reduces the time and equipment requirements for the procedure. For library preparation, we recommend using the commercially available small RNA kit for Illumina sequencing from New England Biolabs, following manufacturer&#39;s guidelines with some degree of optimization.
The resulting cDNA libraries present appropriate quantity and quality required for next generation sequencing (NGS). Sequencing of the libraries prepared according to the described protocol results in 2 to 10 mln uniquely mapped reads per sample providing sufficient data for comprehensive bioinformatic analysis. The protocol we present is quick and relatively easy and can be performed with standard laboratory equipment.

Here we describe the stages of sample collection and preparation for RIBO-seq in bacteria. Sequencing of the libraries prepared according to these guidelines results in sufficient data for comprehensive bioinformatic analysis. The protocol we present is simple, uses standard laboratory equipment and takes seven days from lysis to obtaining libraries.

The ribosome profiling technique (RIBO-seq) is currently the most effective tool for studying the process of protein synthesis in vivo. The advantage of ...