We would like to thank Dr. Garry Nolan from Stanford University for providing the Phoenix GP packaging cell line for the production of retroviral particles. We thank Dr. Roger Tsien at University of California San Diego for providing td Tomato. We would also like to thank the San Diego State University Flow Cytometry Core Facility for their service and help.

1. Preparation of Mammalian Cells, Viral Production and Transduction for Genetic Barcoding
<ol>
	<li>Plate 2.5 x 106 adherent cells in a 10 cm plate (or around 50-60% confluency) one day prior to transfection in Dulbecco&#8217;s modified eagle medium (DMEM) with 10% fetal calf serum (FCS). For retroviral production use packaging cell-line of choice such as Phoenix-GP (a kind gift from Gary Nolan, Stanford University). 
	NOTE: The packaging cell line stably expresses Gag and Pol proteins for retroviral particle formation in trans. Make sure cells are healthy and adhered to the plate in a monolayer, prior to transfection.</li>
	<li>24 hr later, prepare the DNA transfection mixture.
	<ol>
		<li>To 125 &#956;l of serum-free DMEM add 3 &#956;g Vesicular Stomatitis Virus Envelope glycoprotein vector (pCI-VSVg) and 3 &#956;g of transfer vector carrying the fluorescent protein gene of interest. Mix and add 15 &#956;l of polyethylimine (2 mg/ml).</li>
		<li>Incubate mixture at room temperature for 15 min and add to cells drop-wise. 
		NOTE: Polyethylimine is added to the homogenous DNA mixture as transfection reagent for the formation of polyplexes. In order to obtain viral particles carrying different fluorescent protein markers, perform each transfection independently with the marker of choice. Remember that the retroviral transfer vector is around 7 kb in length and cannot be packaged if above 10 kb.</li>
	</ol>
	</li>
	<li>Incubate plates at 37 &#176;C. In order to increase viral production place plates at 30 &#176;C or 32 &#176;C instead. 
	NOTE: 24 hr post transfection media can be replaced with 7 ml of fresh media, and although this may improve cell health it may decrease viral load in the supernatant.</li>
	<li>48 hr post transfection collect the supernatant-containing viral particles and filter with a 0.45 &#956;M polytetrafluoroethylene filter. Use freshly collected viral supernatant for transduction. Otherwise keep supernatant in aliquots at -80 &#176;C and avoid freeze-thaw. Remember that viral titer will decrease probably up to 50% with each freezing-thawing cycle.</li>
	<li>Plate cell line of choice 24 hr prior to transduction if adherent, or immediately before transduction if non-adherent. Seed 2.0 x 105 to 3.0 x 105 adherent cells (here Huh 7.5.1 and HEK 293T) or 5.0 x 105 to 1 x 106 non-adherent cells (here SupT1) per well in a 6-well plate. 
	NOTE: Make sure to calibrate the number of cells to be seeded prior to transduction, especially so for adherent cells, so cells achieve a confluency of around 60% at the time of transduction.</li>
	<li>Add 5 &#956;g/ml Polybrene (hexadimethrene bromide) to seeded cells and then add previously collected viral supernatant to obtain around 20-40% infection (here 2 ml). 
	NOTE: The MOI or percentage of infection is mostly arbitrary, as sorting will allow to amplify any subpopulation of cells. Obviously, a higher rate of infection eases and speeds up the process of amplification.</li>
	<li>Transduce cells by centrifugation in a hanging bucket rotor at 1,500 x g for 120 min at 32 &#176;C. Resuspend non-adherent cells with fresh media prior to incubation. For adherent cells, replace with fresh media 24 hr post-transduction. 
	NOTE: It is recommended to seal the plates prior to centrifugation with parafilm to avoid spilling over. To increase genetically barcoded cell diversity, transduce cells with viral particles carrying different fluorescent proteins (obtained from step 1.4). When choosing fluorescent markers, make sure they are compatible with the instrumentation and they have distinguishable fluorescent parameters.</li>
</ol>
2. Selection and Amplification of Genetically Barcoded Cells
<ol>
	<li>Analyze transduced mammalian cells by flow cytometry at least 72 hr post transduction to quantitate the percentage rate of transduction. Use a comparable non-transduced cell line as negative control. 
	NOTE: As sorting will be used to purify individual barcoded cell populations, a high percentage rate of initial transduction, while not necessary, should speed up the process of amplification.</li>
	<li>Utilize the cell-sorter of choice to obtain the cells that express the protein of interest.
	<ol>
		<li>For that purpose, ensure the gates are properly set in the right channels.
		<ol>
			<li>To do so use the same na&#239;ve cell line as negative control and set the parameter/channel voltage so that the negative population is below the value of 103 on each fluorescent axis. Determine gating for positive fluorescence as events that appear above that of the negative control for each fluorescent channel.</li>
		</ol>
		</li>
		<li>Be aware that each instrument may vary and the correct voltage for determining gating should be adjusted accordingly, making positive and negative controls imperative in every experimental setup.
		<ol>
			<li>For fluorescence detection in this experimental setup use the FITC channel (530/30 band pass filter proceeded by a 502 long pass filter) for eGFP, the PE channel (585/42 band pass filter proceeded by a 556 long pass filter) for td Tomato, and the APC channel (660/20 band pass filter) for E2 Crimson. 
			NOTE: The 488 nm laser excites eGFP and td Tomato while E2 Crimson is excited by the 633 nm laser.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Sort into 15 ml conical tubes with 1 ml of 100% FCS. 
	NOTE: The process of sorting fluorescent cell populations is not compulsory as one can directly proceed with the sort of individual clones (see below). Sorting tight populations based on chosen fluorescence ensures a backup population for future selection of individual clones. Keep in mind that individual cells are at times difficult to grow while a large population of cells can be easily frozen, and then thawed and amplified at a later stage.</li>
	<li>Spin down the sorted populations in a hanging bucket rotor centrifuge at 524 g at 32 &#176;C for 5 min to pellet cells. Re-suspend in 1 ml of fresh media, and re-plate cells so that cell confluency is below 60% to allow growth and division for at least two days.
	<ol>
		<li>For example, plate adherent cells at around 3 x 105 cells in 2 ml of media per well in a 6-well plate and 2 x 106 cells in 2 ml of media in a 6 cm plate. Use DMEM for adherent cells and RPMI for non-adherent cells (or any specified medium if required). Place plated cells in an incubator at 37 &#176;C for several days to allow amplification.</li>
	</ol>
	</li>
</ol>
3. Obtain Clonal Populations of Genetically Barcoded Cells at Different Intensities
<ol>
	<li>Obtain clonal populations from cells originally transduced (step 1.7) or from the sorted population (step 2.3). 
	NOTE: This will ensure equal or similar level of fluorescent protein expression among all the cells within the population (a tight population with a small CV in mean fluorescence intensity of up to 40%).
	<ol>
		<li>For that purpose, sort single cells into 96-well plates with an automated cell deposition unit (ACDU). Set gates for sorting according to populations of interest. Ensure gates are set at least one log-scale apart to obtain distinguishable populations when choosing cells at different fluorescent intensities. For the procedure shown here, use the same flow cytometry experimental set up as the one described in step 2.2.</li>
	</ol>
	</li>
	<li>Amplify individual clones in an incubator at 37 &#176;C for at least 2 weeks. Through the process of amplification analyze the cells under the microscope to ensure that growing populations arise from individual cells and not from more than one. 
	NOTE: Remember that the sorter will place one cell per well on average, and while some wells may not have any cell at all, others may have more than one.
	<ol>
		<li>To ensure that a population arises from one cell only, be extremely gentle with the plate and never disturb the wells by pipetting. Observe the plate, well by well, under the microscope. 
		NOTE: While individual cells may at times be difficult to identify, once they start dividing they will be easily recognizable.</li>
		<li>Be aware that often cells &#8216;clump&#8217; along the edges. Discard those wells where multiple clonal populations can be observed and keep those that have one tight population. 
		NOTE: It is advisable to transfer those into larger plates for amplification.</li>
	</ol>
	</li>
	<li>Screen the putative clonal populations by analyzing them by flow cytometry. Compare them to a negative control utilizing the same flow cytometry experimental setup.
	<ol>
		<li>Analyze only a percentage of the sample and keep the rest as backup. Choose the most distinctly separate populations based on average intensity and tightness of the population. Amplify them as needed or freeze stocks in freezing media with 20% glycerol at -80 &#176;C for short periods of time or liquid nitrogen for longer. 
		NOTE: Remember that a &#8216;true&#8217; clonal population should have a very tight fluorescence pattern.</li>
	</ol>
	</li>
</ol>
4. Ensure Multiplexing Capabilities for High Throughput Screening (HTS)
<ol>
	<li>Combine as many distinct clonal populations as needed that can be further utilized in a multiplexed format. Choose clones with distinguishable absorption/emission spectra and/or different intensities. If a 96-well plate format is used, which is suitable for HTS, seed 50,000 cells in 200 &#956;l per well. 
	NOTE: Keep in mind that the number of cells is only an estimate and may change based on cell-type and whether it is adherent or not.</li>
	<li>Analyze the sample using flow cytometry to ensure that each of the independent established fluorescent cell lines can be distinguished from each other. Prior to the analysis prepare negative and single color controls to set parameters and compensation values. 
	NOTE: Setting the parameters to clearly distinguish the mixed populations will enable them to be further utilized in a multiplexed format.</li>
</ol>
5. Adapt Genetically Barcoded Cell Lines to the Biological Application of Choice
<ol>
	<li>Transduce established genetically barcoded cell lines with viral particles that contain the assay elements of choice, as described here in Stolp et al., 201359. Remember that the assay of choice should occupy an additional and distinguishable fluorescent channel and thus it is to be transferred to the appropriate barcoded cell line. 
	NOTE: Each barcoded cell line can bear a different assay.</li>
	<li>Sort genetically fluorescent barcoded cells for those that contain assay elements. 
	NOTE: Assay elements can be engineered coupled to a tag or fluorescent protein (as a fusion or through an internal ribosome entry site) for straightforward detection through western blotting, flow cytometry or microscopy. The system utilized in this protocol relies on HA epitope surface expression alone, or with additional FLAG epitope expression.
	<ol>
		<li>Stain the clonal populations containing the assay with HA and APC-fluorescently coupled antibodies. Then analyze the clonal populations with anti-FLAG and FITC-conjugated antibody staining.</li>
		<li>To track back the assay, analyze or &#8216;decode&#8217; the populations in the appropriate channel where the distinct genetically barcoded cell lines can be distinguished. Here, decode the nature of the substrate by analyzing in the PE channel for td Tomato detection.</li>
	</ol>
	</li>
</ol>

The authors have nothing to disclose.

Here two well-established procedures have been combined; genetic engineering through retroviral technology and detection of fluorescent proteins utilizing flow cytometry. Fluorescent protein-based genetic barcoding for the production of unique cell lines provides a robust and simple way for multiplexed applications. Generating genetically engineered barcoded cells through retroviral technology, is initially a lengthy process, but allows one to obtain, once established, a reliable and stable source of cell material. The n...

Technologies such as fluorescence spectroscopy, fluorescence microscopy and flow cytometry, all rely on fluorescence, a property widely exploited in biochemical, biomedical, and chemical applications. Fluorescence, whether intrinsic or through labeling, has been exploited for the analysis of protein expression patterns and profiles, cell fate, protein interactions and biological functions1-9, and through fluorescence/F&#246;rster resonance energy transfer for the detection of biomolecule interactions and conformational changes10-13. Since the isolation of the Aequorea victoria green fluorescent protein (GFP)14, the discovery of additional naturally occurring fluorescent proteins from other cnidarians, particularly corals, has largely increased the number of existing fluorescent proteins with distinguishable excitation/emission spectra. These, together with the introduction of mutations in their genes15-19, have further expanded the possibilities, obtaining a true palette of fluorescent proteins available to scientists that exploit microscopy, flow cytometry and other fluorescence-based technologies for their research.
In parallel, although independently, the development of retroviral technology has drastically facilitated the stable expression of ectopic genetic information in mammalian cells20-23. It is thus not surprising that this technology has been used to transfer genes of fluorescent proteins into a broad number of cell types and tissues24-28 or for production of transgenic animals29-31. Following the nature of retroviruses, the genetic information of the ectopic fluorescent protein is introduced within the genome of the cell32 and the cell becomes fluorescent `for ever&#180;. This property has allowed tracking of cell fate, or of a single cell within a population of cells. The now fluorescent cell has thus acquired its own biosignature and can be defined as barcoded. Its unique biosignature identifies it from other cells, and importantly, distinguishes it from cells genetically manipulated to express different fluorescent proteins with distinguishable absorption/emission spectra. Biological applications such as the tracking of reprogramming factors toward pluripotency33, the analysis of subnuclear factors for the elucidation of nucleolar localization34, the construction of fluorescent reporter plasmids for transcriptional studies35 or the genetic labeling of neurons for the study of neuronal network architecture36, are just four examples of the many that have exploited different fluorescent protein genes for the same experimental setup.
Flow cytometry has been broadly utilized for the analysis of biological processes at the single cell level, such as gene expression, cell cycle, apoptosis, and signaling through phosphorylation37-43.The stable expression of fluorescent protein genes in mammalian cells has further enhanced the utility of flow cytometry for cell analysis38,44 and ligand-receptor interactions45. Enhanced capabilities have allowed flow cytometry to become a widely utilized methodology for high-throughput and high-content screening46. Despite the now expanded number of fluorometers and robotics technologies that can couple plate reader systems, imaging and flow cytometry, there seems to be a lack in experimental design that can exploit and fit these enhanced technological capabilities.
Fast, reliable, simple and robust cell-based methodologies are drastically needed for multiplexed applications that further enhance high-throughput capacity. This is especially true in the field of drug discovery where engineering cell-based assays in a multiplexed format can enhance the power of high-throughput screening39,47-50. Multiplexing, as it allows simultaneous analyses in one sample, further enhances high-throughput capabilities51-54. Fluorescent genetic barcoding not only allows for elegant multiplexing, but also, once engineered, circumvents the need of time consuming protocols, reduces costs accompanied with antibodies, beads and stains39,52,55, and can reduce the number of screens required for high-throughput applications. We have recently described how retroviral technology can enhance multiplexing through fluorescent genetic barcoding for biological applications, by expressing an assay previously developed to monitor HIV-1 protease activity56,57 with different clinically prevalent variants58. The methodology is explained in a more descriptive manner focusing on how to select and amplify genetically fluorescent barcoded cells and how to produce panels of clonal populations expressing distinct fluorescent proteins and/or different fluorescence intensities. Panels of cell populations distinguishable based on their fluorescent characteristics enhance multiplexed capabilities, which can be further exploited in combination with cell-based assays that tackle different biological questions. The protocol also describes how to engineer a panel of barcoded cells bearing one of the cell-based assays previously developed in the laboratory, as example59. This protocol is thus not intended to show the well-established retroviral/lentiviral technology for genetic transfer, the value of fluorescent proteins or the applications of flow cytometry60,48 but rather to show the enhancing power of combining the three for multiplexed applications.

<table border="0" cellpadding="0" cellspacing="0" width="1138">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:345px;">Name of Material/ Equipment</td>
			<td style="width:160px;">Company</td>
			<td style="width:119px;">Catalog Number</td>
			<td style="width:515px;">Comments/Description</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:345px;">10mL syringes</td>
			<td style="width:160px;">BD&#160;&#160;</td>
			<td>309604</td>
			<td>used for filtering the virus</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">0.45&#181;m plytetrafluoroethylen filter</td>
			<td style="width:160px;">pall corporation</td>
			<td>4219</td>
			<td>used for filtering the virus</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:345px;">DMEM (Dulbecco&#39;s Modified Eagle Medium)</td>
			<td style="width:160px;">Corning</td>
			<td style="width:119px;">45000-304</td>
			<td>cell growth media for HEK 293T cells</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">PEI (Polyethylenimine)</td>
			<td style="width:160px;">poly sciences</td>
			<td>23966-2</td>
			<td>&#160;2mg/mL concentration used</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:345px;">Hanging bucket centrifuge (refrigerated)</td>
			<td style="width:160px;">Eppendorf&#160;</td>
			<td style="width:119px;">5805 000.017</td>
			<td>used for spin infection</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:345px;">PBS (phosphate buffered saline)</td>
			<td style="width:160px;">Corning</td>
			<td>21-040-CV</td>
			<td>used for washing of cells</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:345px;">Polybrene (hexadimethreen bromide)</td>
			<td style="width:160px;">Sigma-Aldrich</td>
			<td>107689</td>
			<td>Used to increase viral infection efficiency.&#160; Used at a 5&#181;g/mL concentration.&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:345px;">FACSAria</td>
			<td style="width:160px;">BD Biosciences</td>
			<td style="width:119px;"></td>
			<td>instrument used for sorting cell populations</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:345px;">FACSCanto</td>
			<td style="width:160px;">BD Biosciences</td>
			<td style="width:119px;"></td>
			<td>instrument used for cell analysis</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:345px;">Phoenix-GP</td>
			<td style="width:160px;">Gift from Gary Nolan</td>
			<td style="width:119px;"></td>
			<td>cell line used to produced retroviral particles</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:345px;">Fetal calf serum</td>
			<td style="width:160px;">Mediatech</td>
			<td>MT35015CV&#160;</td>
			<td>used for cell growth and sorting</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:345px;">&#160;SupT1 cells</td>
			<td style="width:160px;">ATCC</td>
			<td>CRL-1942</td>
			<td>Human T lymphoblasts</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:345px;">HEK 293T cells</td>
			<td style="width:160px;">ATCC</td>
			<td>CRL-11268</td>
			<td>Human Embryonic Kidney cells that also contain the SV40 large T-antigen</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:345px;">RPMI 1640</td>
			<td style="width:160px;">Corning</td>
			<td>10-040-CV</td>
			<td>cell growth media for SupT1 cells</td>
		</tr>
	</tbody>
</table>

genetic barcoding with fluorescent proteins for multiplexed applications

Fluorescent proteins, fluorescent dyes and fluorophores in general have revolutionized the field of molecular cell biology. In particular, the discovery of fluorescent proteins and their genes have enabled the engineering of protein fusions for localization, the analysis of transcriptional activation and translation of proteins of interest, or the general tracking of individual cells and cell populations. The use of fluorescent protein genes in combination with retroviral technology has further allowed the expression of these proteins in mammalian cells in a stable and reliable manner. Shown here is how one can utilize these genes to give cells within a population of cells their own biosignature. As the biosignature is achieved with retroviral technology, cells are barcoded &#180;indefinitely&#180;. As such, they can be individually tracked within a mixture of barcoded cells and utilized in more complex biological applications. The tracking of distinct populations in a mixture of cells is ideal for multiplexed applications such as discovery of drugs against a multitude of targets or the activation profile of different promoters. The protocol describes how to elegantly develop and amplify barcoded mammalian cells with distinct genetic fluorescent markers, and how to use several markers at once or one marker at different intensities. Finally, the protocol describes how the cells can be further utilized in combination with cell-based assays to increase the power of analysis through multiplexing.

Multiplexing fluorescent genetically barcoded cells for the purpose of biological applications can only be achieved once individual clonal populations have been generated. Multiplexing is most effective when barcoded populations have clear distinct fluorescent characteristics with minimal spectral overlap. The example shown in Figure 1 with clonal populations of mammalian SupT1 cells illustrates that barcoded cells with mCherry and cyano fluorescent protein (CFP) can be easily analyzed simultaneously wit...

Watch this Scientific Journal Video about Genetic Barcoding with Fluorescent Proteins for Multiplexed Applications at JoVE.com

Genetic Barcoding with Fluorescent Proteins for Multiplexed Applications

Since the discovery of the green fluorescent protein gene, fluorescent proteins have impacted molecular cell biology. This protocol describes how expression of distinct fluorescent proteins through genetic engineering is used for barcoding individual cells. The procedure enables tracking distinct populations in a cell mixture, which is ideal for multiplexed applications.

Fluorescent proteins, fluorescent dyes and fluorophores in general have revolutionized the field of molecular cell biology. In particular, the discovery ...

genetic-barcoding-with-fluorescent-proteins-for-multiplexed

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JoVE Journal

Biology

9.2K Views.  San Diego State University. Since the discovery of the green fluorescent protein gene, fluorescent proteins have impacted molecular cell biology. This protocol describes how expression of distinct fluorescent proteins through genetic engineering is used for barcoding individual cells. The procedure enables tracking distinct populations in a cell mixture, which is ideal for multiplexed applications. 

Video: Genetic Barcoding with Fluorescent Proteins for Multiplexed Applications

Labeling Stem Cells with Fluorescent Dyes for non-invasive Detection with Optical Imaging

Optical imaging (OI) is an easy, fast and inexpensive tool for in vivo monitoring of new stem cell based therapies. The technique is based on ex vivo labeling of stem cells with a fluorescent dye, subsequent intravenous injection of the labeled cells and visualization of their accumulation in specific target organs or pathologies. The presented technique demonstrates how we label human mesenchymal stem cells (hMSC) by simple incubation with the lipophilic fluorescent dye DiD (C67H103CIN2O3S) and how we label human embryonic stem cells (hESC) with the FDA approved fluorescent dye Indocyanine Green (ICG). The uptake mechanism is via adherence and diffusion of the lypophilic dye across the phospholipid cell membrane bilayer. The labeling efficiency is usually improved if the cells are incubated with the dye in serum-free media as opposed to incubation in serum-containing media. Furthermore, the addition of the transfection agent Protamine Sulfate significantly improves contrast agent uptake.

This video shows techniques for labeling of human embryonic stem cells and mesenchymal stem cells with fluorescent dyes. This technique can be used for an in vivo tracking of transplanted stem cells with optical imaging and for histopathological correlations with fluorescence microscopy.

Optical imaging (OI) is an easy, fast and inexpensive tool for in vivo monitoring of new stem cell based therapies. The technique is based on ex vivo ...

Method for Culture of Early Chick Embryos ex vivo (New Culture)

The chick embryo is a valuable tool in the study of early embryonic development. Its transparency, accessibility and ease of manipulation, make it an ideal tool for studying  the formation and patterning of brain, neural tube, somite and heart primordia. Applications of chick embryo culture include electroporation of DNA or RNA constructs in order to analyze gene function, grafts of growth factor coated beads such as FGFs and BMPs , as well as whole mount in situ hybridization and immunohistochemistry. This video demonstrates the different steps in chick embryo culture; First, the embryo is explanted in saline. Then, the embryo is centered on a glass ring. The membranes surrounding the embryo are lifted along the walls of the ring. The ring is then placed in a culture dish containing a pool of albumine. The culture dish is sealed and placed in a humid chamber, where the embryo is cultured for up to 24 hrs. Finally, the embryo is removed from the ring, fixed and processed for further applications. A troubleshooting guide is also presented.

Method for Culture of Early Chick Embryos ex vivo New Culture

This video demonstrates New culture, a method by which chick embryos are cultured outside the egg for up to 24 hr. This method enables one to study early development (primitive streak to 14 som.), a period corresponding to E7-9 in mouse. Applications of this technique include electroporation, in situ hybridization and immunohistochemistry.

The chick embryo is a valuable tool in the study of early embryonic development. Its transparency, accessibility and ease of manipulation, make it an ...

Double Whole Mount in situ Hybridization of Early Chick Embryos

The chick embryo is a valuable tool in the study of early embryonic development. Its transparency, accessibility and ease of manipulation, make it an ideal tool for studying  gene expression in brain, neural tube, somite and heart primordia formation. This video demonstrates the different steps in 2-color whole mount in situ hybridization; First, the embryo is dissected from the egg and fixed in paraformaldehyde. Second, the embryo is processed for prehybridization. The embryo is then hybridized with two different probes, one coupled to DIG, and one coupled to FITC.  Following overnight hybridization, the embryo is incubated with DIG coupled antibody. Color reaction for DIG substrate is performed, and the region of interest appears blue. The embryo is then incubated with FITC coupled antibody. The embryo is processed for color reaction with FITC, and the region of interest appears red. Finally, the embryo is fixed and processed for phtograph and sectioning. A troubleshooting guide is also presented.

This video demonstrates 2-color whole mount in situ hybridization, a method by which the spatial and temporal expression pattern of 2 different genes can be visualized in young chick embryos. This method was originally introduced by David Wilkinson, Domingos Henrique, Phil Ingham and David Ish -Horowicz.

Genetic Studies of Human DNA Repair Proteins Using Yeast as a Model System 

Understanding the roles of human DNA repair proteins in genetic pathways is a formidable challenge to many researchers. Genetic studies in mammalian systems have been limited due to the lack of readily available tools including defined mutant genetic cell lines, regulatory expression systems, and appropriate selectable markers. To circumvent these difficulties, model genetic systems in lower eukaryotes have become an attractive choice for the study of functionally conserved DNA repair proteins and pathways. We have developed a model yeast system to study the poorly defined genetic functions of the Werner syndrome helicase-nuclease (WRN) in nucleic acid metabolism. Cellular phenotypes associated with defined genetic mutant backgrounds can be investigated to clarify the cellular and molecular functions of WRN through its catalytic activities and protein interactions. The human WRN gene and associated variants, cloned into DNA plasmids for expression in yeast, can be placed under the control of a regulatory plasmid element. The expression construct can then be transformed into the appropriate yeast mutant background, and genetic function assayed by a variety of methodologies. Using this approach, we determined that WRN, like its related RecQ family members BLM and Sgs1, operates in a Top3-dependent pathway that is likely to be important for genomic stability. This is described in our recent publication [1] at <a href="http://www.impactaging.com">www.impactaging.com</a>. Detailed methods of specific assays for genetic complementation studies in yeast are provided in this paper.

Genetic Studies of Human DNA Repair Proteins Using Yeast as a Model System

Genetic studies in yeast can be employed to investigate the molecular and cellular functions of human genes in cellular DNA metabolism. Methods are described for the genetic characterization of the human WRN gene product defective in the premature aging disorder Werner syndrome in functionally conserved pathways using yeast as a tractable model system.

Understanding the roles of human DNA repair proteins in genetic pathways is a formidable challenge to many researchers.  Genetic studies in mammalian ...

Fluorescent Labeling of COS-7 Expressing SNAP-tag Fusion Proteins for Live Cell Imaging

SNAP-tag and CLIP-tag protein labeling systems enable the specific, covalent attachment of molecules, including fluorescent dyes, to a protein of interest in live cells. These systems offer a broad selection of fluorescent substrates optimized for a range of imaging instrumentation. Once cloned and expressed, the tagged protein can be used with a variety of substrates for numerous downstream applications without having to clone again. There are two steps to using this system: cloning and expression of the protein of interest as a SNAP-tag fusion, and labeling of the fusion with the SNAP-tag substrate of choice. The SNAP-tag is a small protein based on human O6-alkylguanine-DNA-alkyltransferase (hAGT), a DNA repair protein. SNAP-tag labels are dyes conjugated to guanine or chloropyrimidine leaving groups via a benzyl linker. In the labeling reaction, the substituted benzyl group of the substrate is covalently attached to the SNAP-tag. CLIP-tag is a modified version of SNAP-tag, engineered to react with benzylcytosine rather than benzylguanine derivatives. When used in conjunction with SNAP-tag, CLIP-tag enables the orthogonal and complementary labeling of two proteins simultaneously in the same cells.

SNAP-tag and CLIP-tag protein labeling systems enable the specific, covalent attachment of molecules, including fluorescent dyes, to a protein of interest in live cells. Once cloned and expressed, the tagged protein can be used with a variety of substrates for numerous downstream applications without having to clone again.

SNAP-tag and CLIP-tag protein labeling systems enable the specific, covalent attachment of molecules, including fluorescent dyes, to a protein of interest ...

Closed System Cell Culture Protocol Using HYPERStack Vessels with Gas Permeable Material Technology

Large volume adherent cell culture is currently standardized on stacked plate cell growth products when microcarrier beads are not an optimal choice. HYPERStack vessels allow closed system scale up from the current stacked plate products and delivers >2.5X more cells in the same volumetric footprint. The HYPERStack vessels function via gas permeable material which allows gas exchange to occur, therefore eliminating the need for internal headspace within a vessel. The elimination of headspace allows the compartment where cell growth occurs to be minimized to reduce space, allowing more layers of cell growth surface area within the same volumetric footprint.
For many applications such as cell therapy or vaccine production, a closed system is required for cell growth and harvesting. The HYPERStack vessel allows cell and reagent addition and removal via tubing from media bags or other methods.
This protocol will explain the technology behind the gas permeable material used in the HYPERStack vessels, gas diffusion results to meet the metabolic needs of cells, closed system cell growth protocols, and various harvesting methods.

An Introduction into the technology, protocol and handling of the Corning HYPERStack Vessels and accessories used for high yield adherent cell culture. The protocol will show how to use the closed system vessels for increasing cell harvesting over current stacked plate products.

Large volume adherent cell culture is currently standardized on stacked plate cell growth products when microcarrier beads are not an optimal choice.   ...

Absolute Quantum Yield Measurement of Powder Samples

Measurement of fluorescence quantum yield has become an important tool in the search for new solutions in the development, evaluation, quality control and research of illumination, AV equipment, organic EL material, films, filters and fluorescent probes for bio-industry.
Quantum yield is calculated as the ratio of the number of photons absorbed, to the number of photons emitted by a material. The higher the quantum yield, the better the efficiency of the fluorescent material.
For the measurements featured in this video, we will use the Hitachi F-7000 fluorescence spectrophotometer equipped with the Quantum Yield measuring accessory and Report Generator program. All the information provided applies to this system. 
Measurement of quantum yield in powder samples is performed following these steps:
<ol>
 <li>Generation of instrument correction factors for the excitation and emission monochromators. This is an important requirement for the correct measurement of quantum yield. It has been performed in advance for the full measurement range of the instrument and will not be shown in this video due to time limitations.</li>
 <li>Measurement of integrating sphere correction factors. The purpose of this step is to take into consideration reflectivity characteristics of the integrating sphere used for the measurements.</li>
 <li>Reference and Sample measurement using direct excitation and indirect excitation.</li>
 <li>Quantum Yield calculation using Direct and Indirect excitation. Direct excitation is when the sample is facing directly the excitation beam, which would be the normal measurement setup. However, because we use an integrating sphere, a portion of the emitted photons resulting from the sample fluorescence are reflected by the integrating sphere and will re-excite the sample, so we need to take into consideration indirect excitation. This is accomplished by measuring the sample placed in the port facing the emission monochromator, calculating indirect quantum yield and correcting the direct quantum yield calculation.</li>
 <li>Corrected quantum yield calculation.</li>
 <li>Chromaticity coordinates calculation using Report Generator program.</li>
</ol>
The Hitachi F-7000 Quantum Yield Measurement System offer advantages for this
application, as follows:
<ul>
 <li>High sensitivity (S/N ratio 800 or better RMS). Signal is the Raman band of water measured under the following conditions: Ex wavelength 350 nm, band pass Ex and Em 5 nm, response 2 sec), noise is measured at the maximum of the Raman peak. High sensitivity allows measurement of samples even with low quantum yield. Using this system we have measured quantum yields as low as 0.1 for a sample of salicylic acid and as high as 0.8 for a sample of magnesium tungstate.</li>
 <li>Highly accurate measurement with a dynamic range of 6 orders of magnitude allows for measurements of both sharp scattering peaks with high intensity, as well as broad fluorescence peaks of low intensity under the same conditions. </li>
 <li>High measuring throughput and reduced light exposure to the sample, due to a high scanning speed of up to 60,000 nm/minute and automatic shutter function. </li>
 <li>Measurement of quantum yield over a wide wavelength range from 240 to 800 nm.</li>
 <li>Accurate quantum yield measurements are the result of collecting instrument spectral response and integrating sphere correction factors before measuring the sample.</li>
 <li>Large selection of calculated parameters provided by dedicated and easy to use software.
</li>
</ul> 
During this video we will measure sodium salicylate in powder form which is known to have a quantum yield value of 0.4 to 0.5.

In this video we will demonstrate measuring and calculating absolute quantum yield and chromaticity coordinates directly in powder samples using the Hitachi F-7000 Quantum Yield Measuring System.

Measurement of fluorescence quantum yield has become an important tool in the search for new solutions in the development, evaluation, quality control and ...

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