Name: photobleaching assays (frap &amp; flip) to measure chromatin protein dynamics in living embryonic stem cells
Uploaded: 2011-06-29T12:00:00
Description: Watch this Scientific Journal Video about Photobleaching Assays FRAP & FLIP to Measure Chromatin Protein Dynamics in Living Embryonic Stem Cells at JoVE.com

We thank members of the Meshorer lab, especially Shai Melcer, Adi Alajem, Edupuganti Raghu Ram, Badi Sri Sailaja, Anna Mattout and Alva Biran, for critical comments and for trouble-shooting photobleaching experiments on a daily basis. EM is a Joseph H. and Belle R. Braun Senior Lecturer in Life Sciences and is supported by the Israel Science Foundation (ISF 943/09), the Israel Ministry of Health (6007) the European Union (IRG-206872 and 238176), the Israel Cancer Research Foundation, the Internal Applicative Medical Grants of the Hebrew University and the Israel Psychobiology Institute.

1. Plating the ES Cells
T = 0 hrs 
MEF plating
<ol>
 <li>Coat the live imaging 8-well &mu;-Slides (ibidi; Munich, Germany) with gelatin or in chambered cover glasses (Lab-Tek; Rochester, NY) or in glass-bottom culture dishes (MatTek; Ashland, MA). Leave for 5-30 min and aspirate away the free gelatin.</li>
 <li>Seed 22,000 MEFs/well in 250 &mu;l total volume of DMEM [supplemented with 10% fetal bovine serum (FBS)]. Allow cells to grow in a tissue culture incubator (37&deg;C, 5% CO2).</li...

<ol>
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Unlike most available techniques, which involve purified chromatin from cell populations or fixed cells, FRAP experiments follow changes in chromatin protein dynamics in living cells. We found chromatin protein dynamics to be a good indicator for chromatin plasticity. However, because it requires fusing the gene of interest with GFP, the addition of the fluorescent tag can interfere with the protein's function. Thus, prior to proceeding with FRAP, the fusion protein must be rigorously tested to ensure it has the same pro...

<table border="1">
 <tbody>
 <tr>
 <th>Name of the reagent</th>
 <th>Company</th>
 <th>Catalogue number</th>
 </tr>
 <tr>
 <td>DMEM</td>
 <td>Sigma</td>
 <td>D5671</td>
 </tr>
 <tr>
 <td>Gelatin</td>
 <td>Merck</td>
 <td>1.04078</td>
 </tr>
 <tr>
 <td>Opti-MEM</td>
 <td>Gibco</td>
 <td>31985</td>
 </tr>
 <tr>
 <td>TransIT-LT1</td>
 <td>Mirus</td>
 <td>MIR2300</td>
 </tr>
 <tr>
 <td>8-well &mu;-Slides</td>
 <td>ibidi</td>
 <td>80826</td>
 </tr>
 </tbody>
</table>

photobleaching assays (frap &amp; flip) to measure chromatin protein dynamics in living embryonic stem cells

Fluorescence Recovery After Photobleaching (FRAP) and Fluorescence Loss In Photobleaching (FLIP) enable the study of protein dynamics in living cells with good spatial and temporal resolution. Here we describe how to perform FRAP and FLIP assays of chromatin proteins, including H1 and HP1, in mouse embryonic stem (ES) cells. In a FRAP experiment, cells are transfected, either transiently or stably, with a protein of interest fused with the green fluorescent protein (GFP) or derivatives thereof (YFP, CFP, Cherry, etc.). In the transfected, fluorescing cells, an intense focused laser beam bleaches a relatively small region of interest (ROI). The laser wavelength is selected according to the fluorescent protein used for fusion. The laser light irreversibly bleaches the fluorescent signal of molecules in the ROI and, immediately following bleaching, the recovery of the fluorescent signal in the bleached area - mediated by the replacement of the bleached molecules with the unbleached molecules - is monitored using time lapse imaging. The generated fluorescence recovery curves provide information on the protein's mobility. If the fluorescent molecules are immobile, no fluorescence recovery will be observed. In a complementary approach, Fluorescence Loss in Photobleaching (FLIP), the laser beam bleaches the same spot repeatedly and the signal intensity is measured elsewhere in the fluorescing cell. FLIP experiments therefore measure signal decay rather than fluorescence recovery and are useful to determine protein mobility as well as protein shuttling between cellular compartments. Transient binding is a common property of chromatin-associated proteins. Although the major fraction of each chromatin protein is bound to chromatin at any given moment at steady state, the binding is transient and most chromatin proteins have a high turnover on chromatin, with a residence time in the order of seconds. These properties are crucial for generating high plasticity in genome expression1. Photobleaching experiments are therefore particularly useful to determine chromatin plasticity using GFP-fusion versions of chromatin structural proteins, especially in ES cells, where the dynamic exchange of chromatin proteins (including heterochromatin protein 1 (HP1), linker histone H1 and core histones) is higher than in differentiated cells2,3.

Watch this Scientific Journal Video about Photobleaching Assays FRAP & FLIP to Measure Chromatin Protein Dynamics in Living Embryonic Stem Cells at JoVE.com

Photobleaching Assays FRAP & FLIP to Measure Chromatin Protein Dynamics in Living Embryonic Stem Cells

We describe photobleaching methods including Fluorescence Recovery After Photobleaching (FRAP) and Fluorescence Loss In Photobleaching (FLIP) to monitor chromatin protein dynamics in embryonic stem (ES) cells. Chromatin protein dynamics, which is considered to be one of the means to study chromatin plasticity, is enhanced in pluripotent cells.

Photobleaching Assays (FRAP &amp; FLIP) to Measure Chromatin Protein Dynamics in Living Embryonic Stem Cells

Fluorescence Recovery After Photobleaching (FRAP) and Fluorescence Loss In Photobleaching (FLIP) enable the study of protein dynamics in living cells with ...

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