Name: an in vivo crosslinking approach to isolate protein complexes from drosophila embryos
Uploaded: 2014-04-23T21:00:00
Description: Watch this Scientific Journal Video about An in vivo Crosslinking Approach to Isolate Protein Complexes From Drosophila Embryos at JoVE.com

We thank Jordan Davis, Yanyan Lin, Eric Schadler and Jimiao Zheng for their technical help with this study. This work was supported by NSF CAREER grant MCB-1054962 to A.L.A.

1. Preparing Large Apple Juice-agar Plates
<ol>
	<li>To make 4 plates, add 375 ml H2O, 11.25 g fly agar and a stir bar to a 1,000&#160;ml flask. This is Mix A. Autoclave Mix A with the flask lid loosely capped on one 30 min-sterilization cycle for liquid goods.</li>
	<li>Add 125 ml apple juice, 12.5 g table sugar and a stir bar to a 500&#160;ml beaker. This is Mix B. Heat Mix B on a heated platform while stirring and maintain the temperature at approximately 70 &#176;C until the autoclaving of Mix A is finis...

<ol>
	<li>Landt, S. G., 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=ChIP-seq+guidelines+and+practices+of+the+ENCODE+and+modENCODE+consortia.">ChIP-seq guidelines and practices of the ENCODE and modENCODE consortia.</a> Genome research. 22, 1813-1831 (2012).</li><li>Murigneux, V., Sauliere, J., Roest Crollius, H., Le Hir, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transcriptome-wide+identification+of+RNA+binding+sites+by+CLIP-seq.">Transcriptome-wide identification of RNA binding sites by CLIP-seq.</a> Methods. , (2013).</li><li>Sutherland, B. W., Toews, J., Kast, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Utility+of+formaldehyde+cross-linking+and+mass+spectrometry+in+the+study+of+protein-protein+interactions.">Utility of formaldehyde cross-linking and mass spectrometry in the study of protein-protein interactions.</a> Journal of mass spectrometry : JMS. 43, 699-715 (2008).</li><li>Creed, T. M., Loganathan, S. N., Varonin, D., Jackson, C. A., Arkov, A. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Novel+role+of+specific+Tudor+domains+in+Tudor-Aubergine+protein+complex+assembly+and+distribution+during+Drosophila+oogenesis.">Novel role of specific Tudor domains in Tudor-Aubergine protein complex assembly and distribution during Drosophila oogenesis.</a> Biochemical and biophysical research communications. 402, 384-389 (2010).</li><li>Arkov, A. L., Wang, J. Y., Ramos, A., Lehmann, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+role+of+Tudor+domains+in+germline+development+and+polar+granule+architecture.">The role of Tudor domains in germline development and polar granule architecture.</a> Development. 133, 4053-4062 (2006).</li><li>Boswell, R. E., Ptudor Mahowald, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=a+gene+required+for+assembly+of+the+germ+plasm+in+Drosophila+melanogaster.">a gene required for assembly of the germ plasm in Drosophila melanogaster.</a> Cell. 43, 97-104 (1985).</li><li>Thomson, T., Lasko, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Drosophila+tudor+is+essential+for+polar+granule+assembly+and+pole+cell+specification,+but+not+for+posterior+patterning.">Drosophila tudor is essential for polar granule assembly and pole cell specification, but not for posterior patterning.</a> Genesis. 40, 164-170 (2004).</li><li>Arkov, A. L., Ramos, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Building+RNA-protein+granules:+insight+from+the+germline.">Building RNA-protein granules: insight from the germline.</a> Trends in cell biology. 20, 482-490 (2010).</li><li>Gao, M., Arkov, A. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Next+generation+organelles:+Structure+and+role+of+germ+granules+in+the+germline.">Next generation organelles: Structure and role of germ granules in the germline.</a> Molecular reproduction and development. , (2012).</li><li>Liu, H., 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=Structural+basis+for+methylarginine-dependent+recognition+of+Aubergine+by+Tudor.">Structural basis for methylarginine-dependent recognition of Aubergine by Tudor.</a> Genes &amp; development. 24, 1876-1881 (2010).</li><li>Liu, N., Han, H., Lasko, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vasa+promotes+Drosophila+germline+stem+cell+differentiation+by+activating+mei-P26+translation+by+directly+interacting+with+a+(U)-rich+motif+in+its+3.">Vasa promotes Drosophila germline stem cell differentiation by activating mei-P26 translation by directly interacting with a (U)-rich motif in its 3.</a> UTR. Genes &amp; development. 23, 2742-2752 (2009).</li><li>Matthews, K. A., Goldstein, L. S. B., Fyrberg, E. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Drosophila+melanogaster:+Practical+Uses+in+Cell+and+Molecular+Biology.">Drosophila melanogaster: Practical Uses in Cell and Molecular Biology.</a> Methods in Cell Biology. 44, 13-32 (1995).</li><li>Sambrook, J., Russell, D. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Molecular cloning: A laboratory manual. , (2001).</li><li>Thomson, T., Liu, N., Arkov, A., Lehmann, R., Lasko, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isolation+of+new+polar+granule+components+in+Drosophila+reveals+P+body+and+ER+associated+proteins.">Isolation of new polar granule components in Drosophila reveals P body and ER associated proteins.</a> Mechanisms of development. 125, 865-873 (2008).</li><li>Vasilescu, J., Guo, X., Kast, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+of+protein-protein+interactions+using+in+vivo+cross-linking+and+mass+spectrometry.">Identification of protein-protein interactions using in vivo cross-linking and mass spectrometry.</a> Proteomics. 4, 3845-3854 (2004).</li><li>Klockenbusch, C., Kast, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optimization+of+formaldehyde+cross-linking+for+protein+interaction+analysis+of+non-tagged+integrin+beta1.">Optimization of formaldehyde cross-linking for protein interaction analysis of non-tagged integrin beta1.</a> J Biomed Biotechnol. 2010, 9275-9285 (2010).</li><li>Nowak, D. E., Tian, B., Brasier, A. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Two-step+cross-linking+method+for+identification+of+NF-kappaB+gene+network+by+chromatin+immunoprecipitation.">Two-step cross-linking method for identification of NF-kappaB gene network by chromatin immunoprecipitation.</a> Biotechniques. 39, 715-725 (2005).</li><li>Zeng, P. Y., Vakoc, C. R., Chen, Z. C., Blobel, G. A., Berger, S. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vivo+dual+cross-linking+for+identification+of+indirect+DNA-associated+proteins+by+chromatin+immunoprecipitation.">In vivo dual cross-linking for identification of indirect DNA-associated proteins by chromatin immunoprecipitation.</a> Biotechniques. 41, 694 (2006).</li><li>Liu, N., Dansereau, D. A., Lasko, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fat+facets+interacts+with+vasa+in+the+Drosophila+pole+plasm+and+protects+it+from+degradation.">Fat facets interacts with vasa in the Drosophila pole plasm and protects it from degradation.</a> Current biology : CB. 13, 1905-1909 (2003).</li></ol>

Formaldehyde has been commonly used as a crosslinking reagent for identifying protein-protein and protein-nucleic acid interactions. Its good solubility and cell membrane permeability, together with the compatibility with downstream mass spectrometry procedures, make formaldehyde an ideal candidate agent for intracellular crosslinking applications3,15-17. In particular, it was successfully used to identify mRNAs associated with Vasa, a critical germ cell RNA helicase in Drosophila11. In add...

Isolation of multisubunit protein assemblies and DNA- or RNA-protein complexes is performed to identify protein complexes, genomic loci recognized by DNA-binding regulatory proteins or RNA targets of RNA binding proteins. Different methods allow genome-wide identification of DNA sites recognized by transcription factors or chromatin proteins (ChIP-seq)1 and RNA targets associated with a given RNA-binding protein (CLIP-seq)2. The libraries of RNA-derived cDNAs or DNA targets are then deeply sequenced. These methods use chemical or UV-induced cross-linking to stabilize the complexes followed by immunoprecipitation (IP) with an antibody against a protein component of the studied complex.
During development of an organism, many protein complexes form transiently. Therefore, it is crucial to analyze the composition and function of these complexes in vivo to understand the molecular mechanisms that control development. Such an in vivo analysis would be superior to in vitro approach since it is virtually impossible to reproduce native concentrations of the interacting components and cellular biochemical environment in vitro. Here we demonstrate an in vivo approach that we successfully use to isolate large protein complexes from Drosophila embryos. In this method, protein complexes in the living embryos are crosslinked with a low concentration of formaldehyde and subsequently protein complexes of interest are isolated by IP with an antibody against a known component of the complexes followed by gel purification of the complexes and mass spectrometry analysis to identify unknown complex components. Since formaldehyde is able to permeate the cell membrane and has a crosslinking range of 2.3-2.7 &Aring;3, protein complexes can be crosslinked in vivo and the complex components are likely to be close to each other. In this article we describe this method using the isolation of Tudor (Tud) protein complex as an example. Tud is a germline protein which is essential for germline development4-7. This protein contains 11 Tud domains known to interact with methylated arginines or lysines of other polypeptides8-10.
Previously, we have generated a transgenic Drosophila line which expresses HA-tagged functional Tud5 and therefore, specific anti-HA antibody is used to pull down Tud complex after crosslinking.
In addition to protein-protein crosslinks, formaldehyde can generate nucleic acid-protein crosslinks and is used in ChIP-seq experiments. Furthermore, in Drosophila, in vivo crosslinking with formaldehyde has allowed the identification of an RNA target of Vasa RNA helicase protein11.
While in this article we describe a method for in vivo crosslinking and purification of protein complexes from Drosophila embryos, this method can be adapted for other organisms and tissues.

<table border="0" cellpadding="0" cellspacing="0" width="858">
	<tbody>
		<tr height="84">
			<td height="84" style="height:84px;width:216px;">Drosophila agar</td>
			<td style="width:235px;">Lab Scientific (http://www.labscientific.com/)</td>
			<td style="width:119px;">FLY-8020-1</td>
			<td style="width:289px;">Do not autoclave the water and agar mix for prolonged period of time as it will cause the apple juice plates to become fragile</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Methyl 4-hydroxybenzoate</td>
			<td style="width:235px;">Sigma (http://www.sigmaaldrich.com/united-states.html)</td>
			<td style="width:119px;">H5501</td>
			<td style="width:289px;">Other name: TEGOSEPT</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Population cage</td>
			<td style="width:235px;">Flystuff (http://www.flystuff.com/)</td>
			<td style="width:119px;">59-104</td>
			<td style="width:289px;"></td>
		</tr>
		<tr height="84">
			<td height="84" style="height:84px;width:216px;">Fine nylon mesh</td>
			<td style="width:235px;">Flystuff (http://www.flystuff.com/)</td>
			<td style="width:119px;">57-102</td>
			<td style="width:289px;">When making the collection basket, cut the mesh slightly larger than the opening of the falcon tube cap to ensure a tight seal</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Dounce homogenizer</td>
			<td style="width:235px;">Sigma (http://www.sigmaaldrich.com/united-states.html)</td>
			<td style="width:119px;">D8938-1SET</td>
			<td style="width:289px;">Chill the homogenizer on ice and prerinse with cold lysis buffer before use to prevent protein degradation</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Protease inhibitor cocktail&#160;</td>
			<td style="width:235px;">Roche (http://www.rocheusa.com/portal/usa)</td>
			<td style="width:119px;">4693132001</td>
			<td style="width:289px;">PBS could be used to prepare concentrated protease inhibitor stock solution</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Anti-HA agarose beads</td>
			<td style="width:235px;">MBL international (http://www.mblintl.com/)</td>
			<td style="width:119px;">561-8</td>
			<td style="width:289px;">The kit also includes HA-peptide and spin columns</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">HA-peptide</td>
			<td style="width:235px;">MBL international (http://www.mblintl.com/)</td>
			<td style="width:119px;">561-8</td>
			<td style="width:289px;">Prepare to 2 mg/ml with PBS&#160;</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Spin Column</td>
			<td style="width:235px;">MBL international (http://www.mblintl.com/)</td>
			<td style="width:119px;">561-8</td>
			<td style="width:289px;">Spin columns are included as part of the kit</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Isopropanol</td>
			<td style="width:235px;">Fisher Scientific (www.fishersci.com/&#8206;)</td>
			<td style="width:119px;">BP26324</td>
			<td style="width:289px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Triton X-100</td>
			<td style="width:235px;">Fisher Scientific (www.fishersci.com/&#8206;)</td>
			<td style="width:119px;">BP151-500</td>
			<td style="width:289px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Heptane</td>
			<td style="width:235px;">Fisher Scientific (www.fishersci.com/&#8206;)</td>
			<td style="width:119px;">H350-4</td>
			<td style="width:289px;"></td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">PBS</td>
			<td style="width:235px;">Invitrogen (https://www.lifetechnologies.com/us/en/home.html)</td>
			<td style="width:119px;">AM9625</td>
			<td style="width:289px;">Dilute from 10 X to 1 X with nanopure water before use</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Formaldehyde</td>
			<td style="width:235px;">Fisher Scientific (www.fishersci.com/&#8206;)</td>
			<td style="width:119px;">BP531-500</td>
			<td style="width:289px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Glycine</td>
			<td style="width:235px;">BioRad (www.bio-rad.com/&#8206;)</td>
			<td style="width:119px;">161-0724</td>
			<td style="width:289px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">SDS</td>
			<td style="width:235px;">BioRad (www.bio-rad.com/&#8206;)</td>
			<td style="width:119px;">161-0301</td>
			<td style="width:289px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Urea</td>
			<td style="width:235px;">BioRad (www.bio-rad.com/&#8206;)</td>
			<td style="width:119px;">161-0730</td>
			<td style="width:289px;"></td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Phenylmethanesulfonyl fluoride</td>
			<td style="width:235px;">Sigma (http://www.sigmaaldrich.com/united-states.html)</td>
			<td style="width:119px;">P7626-1G</td>
			<td style="width:289px;">Prepare 200 mM stock solution in isopropanol then dilute to working concentration of 2 mM in lysis buffer</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">IGEPAL CA-630</td>
			<td style="width:235px;">Sigma (http://www.sigmaaldrich.com/united-states.html)</td>
			<td style="width:119px;">I8896-50ML</td>
			<td style="width:289px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Tween 20</td>
			<td style="width:235px;">Fisher Scientific (www.fishersci.com/&#8206;)</td>
			<td style="width:119px;">BP337-100</td>
			<td style="width:289px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">15-ml tubes</td>
			<td style="width:235px;">USA Scientific (http://www.usascientific.com/)</td>
			<td style="width:119px;">1475-0511</td>
			<td style="width:289px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Bleach</td>
			<td style="width:235px;">Clorox brand</td>
			<td style="width:119px;"></td>
			<td style="width:289px;">Dilute with equal volume of nanopure water to make 50% bleach</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">50-ml tubes</td>
			<td style="width:235px;">BD Biosciences (http://www.bdbiosciences.com/home.jsp)</td>
			<td style="width:119px;">352098</td>
			<td style="width:289px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">Top layer sieve</td>
			<td style="width:235px;">Fisher Scientific (www.fishersci.com/&#8206;)</td>
			<td style="width:119px;">04-884-1AK</td>
			<td style="width:289px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">Bottom layer sieve</td>
			<td style="width:235px;">Fisher Scientific (www.fishersci.com/&#8206;)</td>
			<td style="width:119px;">04-884-1BA</td>
			<td style="width:289px;"></td>
		</tr>
	</tbody>
</table>

an in vivo crosslinking approach to isolate protein complexes from drosophila embryos

Many cellular processes are controlled by multisubunit protein complexes. Frequently these complexes form transiently and require native environment to assemble. Therefore, to identify these functional protein complexes, it is important to stabilize them in vivo before cell lysis and subsequent purification. Here we describe a method used to isolate large bona fide protein complexes from Drosophila embryos. This method is based on embryo permeabilization and stabilization of the complexes inside the embryos by in vivo crosslinking using a low concentration of formaldehyde, which can easily cross the cell membrane. Subsequently, the protein complex of interest is immunopurified followed by gel purification and analyzed by mass spectrometry. We illustrate this method using purification of a Tudor protein complex, which is essential for germline development. Tudor is a large protein, which contains multiple Tudor domains - small modules that interact with methylated arginines or lysines of target proteins. This method can be adapted for isolation of native protein complexes from different organisms and tissues.

The effectiveness of the crosslinking and the successful purification of the crosslinked Tud protein complex were analyzed by SDS-PAGE on a 3% - 7% step gel (illustrated in Figure 1) followed by western blot (Figure 2).
The purpose of using the 3% - 7% step gel is based on the effective separation of crosslinked Tud protein complex from the remaining uncrosslinked Tud protein and concentration of the complex. Under our in vivo crosslinking conditions ...

Watch this Scientific Journal Video about An in vivo Crosslinking Approach to Isolate Protein Complexes From Drosophila Embryos at JoVE.com

An in vivo Crosslinking Approach to Isolate Protein Complexes From Drosophila Embryos

Multi-component protein complexes play crucial roles during cellular function and development. Here we describe a method used to isolate native protein complexes from Drosophila embryos after in vivo crosslinking followed by purification of the crosslinked complexes for subsequent structure-function analysis.

An in vivo Crosslinking Approach to Isolate Protein Complexes From Drosophila Embryos

Many cellular processes are controlled by multisubunit protein complexes. Frequently these complexes form transiently and require native environment to ...

an-vivo-crosslinking-approach-to-isolate-protein-complexes-from

Research

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Biology

Preparation of Neuronal Cultures from Midgastrula Stage Drosophila Embryos

This video illustrates the procedure for making primary neuronal cultures from midgastrula stage Drosophila embryos. The methods for collecting embryos and their dechorionation using bleach are demonstrated. Using a glass pipet attached to a mouth suction tube, we illustrate the removal of all cells from single embryos. The method for dispersing cells from each embyro into a small (5 l) drop of medium on an uncoated glass coverslip is demonstrated. A view through the microscope at 1 hour after plating illustrates the preferred cell density. Most of the cells that survive when grown in defined medium are neuroblasts that divide one or more times in culture before extending neuritic processes by 12-24 hours. A view through the microscope illustrates the level of neurite outgrowth and branching expected in a healthy culture at 2 days in vitro. The cultures are grown in a simple bicarbonate based defined medium, in a 5% CO2 incubator at 22-24&deg;C. Neuritic processes continue to elaborate over the first week in culture and when they make contact with neurites from neighboring cells they often form functional synaptic connections. Neurons in these cultures express voltage-gated sodium, calcium, and potassium channels and are electrically excitable. This culture system is useful for studying molecular genetic and environmental factors that regulate neuronal differentiation, excitability, and synapse formation/function.

This video demonstrates the preparation of primary neuronal cultures from midgastrula stage Drosophila embryos. Views of live cultures show cells 1 hour after plating and differentiated neurons after 2 days of growth in a bicarbonate-based defined medium. The neurons are electrically excitable and form synaptic connections.

This video illustrates the procedure for making primary neuronal cultures from midgastrula stage Drosophila embryos. The methods for collecting embryos ...

Microfabricated Post-Array-Detectors (mPADs): an Approach to Isolate Mechanical Forces

In this video, we will present our approach to measure cellular traction forces using a microfabricated array of posts.  Traction forces are generated through myosin-actin interactions and play an important role in our physiology.  During development, they enable cells to move from one location to the next in order to form the early structures of tissue.  Traction forces help in the healing processes.  They are necessary for the proper closure of wounds or the migration and crawling of leukocytes through our body.  These same forces can be detrimental to our health in the case of cancer metastasis or vascular growth towards a tumor.  The most common method by which to study cells in vitro has been to use a glass or polystyrene dish.  However, the rigidity of the substrates makes it impossible to physically measure cell traction forces, and there are relatively few methods to study traction forces.  Our lab has developed a technique to overcome these limitations.  The method is based on a vertical array of flexible cantilevers, the stiffness and size scale of which are such that individual cells spread across many cantilevers and deflect them in the process.  The pillars we use are 3 &mu;m in diameter, 10 &mu;m tall, and are configured in a regular array with 9 &mu;m center-to-center spacing.  But these physical dimensions can be readily varied to accommodate a variety of studies.  We start with a silicon master, but the final posts are made out of silicone rubber called poly (dimethyl siloxane), or PDMS.  We can measure the deflections under a microscope and calculate the magnitude and direction of traction forces required to produce the observed deflections.  We call these substrates microfabricated post-array-detectors, or mPADs.  Here, we will show you how we fabricate and use the mPADs to assess modulations of cellular contractility.

Microfabricated Post-Array-Detectors mPADs: an Approach to Isolate Mechanical Forces

In this video, we demonstrate how to fabricate and utilize microfabricated post array detectors (mPADs) to assess modulations of cellular contractility.

In this video, we will present our approach to measure cellular traction forces using a microfabricated array of posts.  Traction forces are generated ...

Visualizing Single Molecular Complexes In Vivo Using Advanced Fluorescence Microscopy

Full insight into the mechanisms of living cells can be achieved only by investigating the key processes that elicit and direct events at a cellular level. To date the shear complexity of biological systems has caused precise single-molecule experimentation to be far too demanding, instead focusing on studies of single systems using relatively crude bulk ensemble-average measurements. However, many important processes occur in the living cell at the level of just one or a few molecules; ensemble measurements generally mask the stochastic and heterogeneous nature of these events. Here, using advanced optical microscopy and analytical image analysis tools we demonstrate how to monitor proteins within a single living bacterial cell to a precision of single molecules and how we can observe dynamics within molecular complexes in functioning biological machines. The techniques are directly relevant physiologically. They are minimally-perturbative and non-invasive to the biological sample under study and are fully attuned for investigations in living material, features not readily available to other single-molecule approaches of biophysics. In addition, the biological specimens studied all produce fluorescently-tagged protein at levels which are almost identical to the unmodified cell strains ("genomic encoding"), as opposed to the more common but less ideal approach for generating significantly more protein than would occur naturally ('plasmid expression'). Thus, the actual biological samples which will be investigated are significantly closer to the natural organisms, and therefore the observations more relevant to real physiological processes.

Visualizing Single Molecular Complexes In Vivo Using Advanced Fluorescence Microscopy

Here we demonstrate the protocols for performing single-molecule fluorescence microscopy on living bacterial cells to enable functional molecular complexes to be detected, tracked and quantified.

Full insight into the mechanisms of living cells can be achieved only by investigating the key processes that elicit and direct events at a cellular ...

Isolation of Labile Multi-protein Complexes by in vivo Controlled Cellular Cross-Linking and Immuno-magnetic Affinity Chromatography

The dynamic nature of cellular machineries is frequently built on transient and/or weak protein associations. These low affinity interactions preclude stringent methods for the isolation and identification of protein networks around a protein of interest. The use of chemical crosslinkers allows the selective stabilization of labile interactions, thus bypassing biochemical limitations for purification. Here we present a protocol amenable for cells in culture that uses a homobifunctional crosslinker with a spacer arm of 12 &Aring;, dithiobis-(succinimidyl proprionate) (DSP). DSP is cleaved by reduction of a disulphide bond present in the molecule. Cross-linking combined with immunoaffinity chromatography of proteins of interest with magnetic beads allows the isolation of protein complexes that otherwise would not withstand purification. This protocol is compatible with regular western blot techniques and it can be scaled up for protein identification by mass spectrometry1.
Stephanie A. Zlatic and Pearl V. Ryder contributed equally to this work.

Isolation of Labile Multi-protein Complexes by in vivo Controlled Cellular Cross-Linking and Immuno-magnetic Affinity Chromatography

The cell permeable crosslinker DSP [dithiobis-(succinimidyl propionate)] stabilizes transient and labile interactions in vivo, which allows their isolation using stringent protein complex purification techniques. Here we present a technique for crosslinking cells grown in culture followed by isolation of protein complexes by immunoprecipitation.

The dynamic nature of cellular machineries is frequently built on transient and/or weak protein associations. These low affinity interactions preclude ...

In-vivo Centrifugation of Drosophila Embryos

A major strategy for purifying and isolating different types of intracellular organelles is to separate them from each other based on differences in buoyant density. However, when cells are disrupted prior to centrifugation, proteins and organelles in this non-native environment often inappropriately stick to each other. Here we describe a method to separate organelles by density in intact, living Drosophila embryos. Early embryos before cellularization are harvested from population cages, and their outer egg shells are removed by treatment with 50% bleach. Embryos are then transferred to a small agar plate and inserted, posterior end first, into small vertical holes in the agar. The plates containing embedded embryos are centrifuged for 30 min at 3000g. The agar supports the embryos and keeps them in a defined orientation. Afterwards, the embryos are dug out of the agar with a blunt needle. Centrifugation separates major organelles into distinct layers, a stratification easily visible by bright-field microscopy. A number of fluorescent markers are available to confirm successful stratification in living embryos. Proteins associated with certain organelles will be enriched in a particular layer, demonstrating colocalization. Individual layers can be recovered for biochemical analysis or transplantation into donor eggs. This technique is applicable for organelle separation in other large cells, including the eggs and oocytes of diverse species.

In-vivo Centrifugation of Drosophila Embryos

We describe a method to separate organelles by density in living Drosophila embryos. Embryos are embedded in agar and centrifuged. This technique yields reproducible separation of major organelles along the anterior-posterior embryo axis. This method facilitates colocalization experiments and yields organelle fractions for biochemical analysis and transplantation experiments.

A major strategy for purifying and isolating different types of intracellular organelles is to separate them from each other based on differences in ...

Imaging Protein-protein Interactions in vivo

Protein-protein interactions are a hallmark of all essential cellular processes. However, many of these interactions are transient, or energetically weak, preventing their identification and analysis through traditional biochemical methods such as co-immunoprecipitation. In this regard, the genetically encodable fluorescent proteins (GFP, RFP, etc.) and their associated overlapping fluorescence spectrum have revolutionized our ability to monitor weak interactions in vivo using F&ouml;rster resonance energy transfer (FRET)1-3. Here, we detail our use of a FRET-based proximity assay for monitoring receptor-receptor interactions on the endothelial cell surface.

Imaging Protein-protein Interactions in vivo

This protocol describes how to image protein-protein interactions using a FRET-based proximity assay.

Protein-protein interactions are a hallmark of all essential cellular processes. However, many of these interactions are transient, or energetically weak, ...

Upright Imaging of Drosophila Embryos

Several well-known morphogenetic gradients and cellular movements occur along the dorsal/ventral axis of the Drosophila embryo. However, the current techniques used to view such processes are somewhat limited. The following protocol describes a new technique for mounting fixed and labeled Drosophila embryos for coronal viewing with confocal imaging. This method consists of embedding embryos between two layers of glycerin jelly mounting media, and imaging jelly strips positioned upright. The first step for sandwiching the embryos is to make a thin bedding of glycerin jelly on a slide. Next, embryos are carefully aligned on this surface and covered with a second layer of jelly. After the second layer is solidified, strips of jelly are cut and flipped upright for imaging. Alternatives are described for visualizing the embryos depending upon the type of microscope stand to be used. Since all cells along the dorsal-ventral axis are imaged within a single confocal Z-plane, our method allows precise measurement and comparison of fluorescent signals without photobleaching or light scattering common to 3D reconstructions of longitudinally mounted embryos.

Upright Imaging of Drosophila Embryos

Here we present a mounting protocol for stained Drosophila embryos in an upright position that allows imaging of cross-sections using Confocal microscopy.

Several well-known morphogenetic gradients and cellular movements occur along the dorsal/ventral axis of the Drosophila embryo. However, the current ...

Primary Cell Cultures from Drosophila Gastrula Embryos

Here we describe a method for preparing and culturing primary cells dissociated from Drosophila gastrula embryos. In brief, a large amount of staged embryos from young and healthy flies are collected, sterilized, and then physically dissociated into a single cell suspension using a glass homogenizer. After being plated on culture plates or chamber slides at an appropriate density in culture medium, these cells can further differentiate into several morphologically-distinct cell types, which can be identified by their specific cell markers. Furthermore, we present conditions for treating these cells with double stranded (ds) RNAs to elicit gene knockdown. Efficient RNAi in Drosophila primary cells is accomplished by simply bathing the cells in dsRNA-containing culture medium. The ability to carry out effective RNAi perturbation, together with other molecular, biochemical, cell imaging analyses, will allow a variety of questions to be answered in Drosophila primary cells, especially those related to differentiated muscle and neuronal cells.

Primary Cell Cultures from Drosophila Gastrula Embryos

We provide a detailed protocol for preparing primary cells dissociated from Drosophila embryos. The ability to carry out the effective RNAi perturbation, together with other molecular, biochemical and cell imaging methods will allow a variety of questions to be addressed in Drosophila primary cells.

Here we describe a method for preparing and culturing primary cells dissociated from Drosophila gastrula embryos.   In brief, a large amount of staged ...

Imaging Cell Shape Change in Living Drosophila Embryos

The developing Drosophila melanogaster embryo undergoes a number of cell shape changes that are highly amenable to live confocal imaging. Cell shape changes in the fly are analogous to those in higher organisms, and they drive tissue morphogenesis. So, in many cases, their study has direct implications for understanding human disease (Table 1)1-5. On the sub-cellular scale, these cell shape changes are the product of activities ranging from gene expression to signal transduction, cell polarity, cytoskeletal remodeling and membrane trafficking. Thus, the Drosophila embryo provides not only the context to evaluate cell shape changes as they relate to tissue morphogenesis, but also offers a completely physiological environment to study the sub-cellular activities that shape cells.
The protocol described here is designed to image a specific cell shape change called cellularization. Cellularization is a process of dramatic plasma membrane growth, and it ultimately converts the syncytial embryo into the cellular blastoderm. That is, at interphase of mitotic cycle 14, the plasma membrane simultaneously invaginates around each of ~6000 cortically anchored nuclei to generate a sheet of primary epithelial cells. Counter to previous suggestions, cellularization is not driven by Myosin-2 contractility6, but is instead fueled largely by exocytosis of membrane from internal stores7. Thus, cellularization is an excellent system for studying membrane trafficking during cell shape changes that require plasma membrane invagination or expansion, such as cytokinesis or transverse-tubule (T-tubule) morphogenesis in muscle.
Note that this protocol is easily applied to the imaging of other cell shape changes in the fly embryo, and only requires slight adaptations such as changing the stage of embryo collection, or using "embryo glue" to mount the embryo in a specific orientation (Table 1)8-19. In all cases, the workflow is basically the same (Figure 1). Standard methods for cloning and Drosophila transgenesis are used to prepare stable fly stocks that express a protein of interest, fused to Green Fluorescent Protein (GFP) or its variants, and these flies provide a renewable source of embryos. Alternatively, fluorescent proteins/probes are directly introduced into fly embryos via straightforward micro-injection techniques9-10. Then, depending on the developmental event and cell shape change to be imaged, embryos are collected and staged by morphology on a dissecting microscope, and finally positioned and mounted for time-lapse imaging on a confocal microscope.

Imaging Cell Shape Change in Living Drosophila Embryos

Early development of the fruit fly, Drosophila melanogaster, is characterized by a number of cell shape changes that are well suited for imaging approaches. This article will describe basic tools and methods required for live confocal imaging of Drosophila embryos, and will focus on a cell shape change called cellularization.

The developing Drosophila melanogaster embryo undergoes a number of cell shape changes that are highly amenable to live confocal imaging.  Cell shape ...

Isolation and Purification of Kinesin from Drosophila Embryos

Motor proteins move cargos along microtubules, and transport them to specific sub-cellular locations. Because altered transport is suggested to underlie a variety of neurodegenerative diseases, understanding microtubule based motor transport and its regulation will likely ultimately lead to improved therapeutic approaches. Kinesin-1 is a eukaryotic motor protein which moves in an anterograde (plus-end) direction along microtubules (MTs), powered by ATP hydrolysis. Here we report a detailed purification protocol to isolate active full length kinesin from Drosophila embryos, thus allowing the combination of Drosophila genetics with single-molecule biophysical studies. Starting with approximately 50 laying cups, with approximately 1000 females per cup, we carried out overnight collections. This provided approximately 10 ml of packed embryos. The embryos were bleach dechorionated (yielding approximately 9 grams of embryos), and then homogenized. After disruption, the homogenate was clarified using a low speed spin followed by a high speed centrifugation. The clarified supernatant was treated with GTP and taxol to polymerize MTs. Kinesin was immobilized on polymerized MTs by adding the ATP analog, 5'-adenylyl imidodiphosphate at room temperature. After kinesin binding, microtubules were sedimented via high speed centrifugation through a sucrose cushion. The microtubule pellet was then re-suspended, and this process was repeated. Finally, ATP was added to release the kinesin from the MTs. High speed centrifugation then spun down the MTs, leaving the kinesin in the supernatant. This kinesin was subjected to a centrifugal filtration using a 100 KD cut off filter for further purification, aliquoted, snap frozen in liquid nitrogen, and stored at -80 &deg;C. SDS gel electrophoresis and western blotting was performed using the purified sample. The motor activity of purified samples before and after the final centrifugal filtration step was evaluated using an in vitro single molecule microtubule assay. The kinesin fractions before and after the centrifugal filtration showed processivity as previously reported in literature. Further experiments are underway to evaluate the interaction between kinesin and other transport related proteins.

Isolation and Purification of Kinesin from Drosophila Embryos

This is a protocol to isolate active full length Kinesin from Drosophila embryos for single-molecule biophysical studies. We show how to collect embryos, make the embryo lysate, and then polymerize microtubules (MTs). Kinesin is purified by immobilizing it on the MTs, spinning down the Kinesin-MT complexes, and then releasing the kinesin from the MTs via ATP addition.

Motor proteins move cargos along microtubules, and transport them to specific sub-cellular locations. Because altered transport is suggested to underlie a ...