Name: isolation and characterization of single cells from zebrafish embryos
Uploaded: 2016-03-12T15:00:00
Description: Watch this Scientific Journal Video about Isolation and Characterization of Single Cells from Zebrafish Embryos at JoVE.com

We thank Dr. C. Geoffrey Burns for fish stock. The authors are grateful to UNC Flow Cytometry Core Facility, UNC-CGIBD AAC core for resources enabling this project, and the ZAC facility for animal care. L.S. is supported by NIH T32 grant HL069768-13 (PI, Nobuyo Maeda). N.F. is supported by NSF Graduate Research Fellowship NSF-DGE-1144081. This study was supported by NIH P30DK034987 grant (to UNC Advanced Analytics Core), American Heart Association Scientist Development Grant 13SDG17060010 and Ellison Medical Foundation New Scholar Grant AG-NS-1064-13 (to Dr. Qian), and NIH R00 HL109079 grant (to Dr. Liu).

This protocol requires the use of live, adult zebrafish to produce embryos. The embryos are harvested for tissue collection. It is essential to obtain approval from appropriate ethics review boards to conduct this experiment.
1. Obtain Staged Embryos
<ol>
	<li>The day before the experiment, prepare healthy, adult zebrafish for breeding. Place one male and one female on opposite sides of a clear divider in a breeding tank.</li>
	<li>Repeat 1.1 for as many breeding tanks as necessary for suffi...

<ol>
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The method described herein uses expression of a fluorescent protein under control of a cell-type specific promoter to enrich a population of cardiac progenitor cells from zebrafish embryos for use in microfluidic assisted single cell capture system to assess expression of a subset of cardiac genes in single cells. Provided that FACS laser excitation and emission capabilities are compatible with the fluorophore(s) of choice, this method can be used for any fluorescent reporter line. Many zebrafish reporter lines are alre...

Most current studies of cell and molecular biology are based on population averages. However, important biological events may be masked by these traditional population-based analyses since minor populations can play major roles in biological processes and disease outcome. Understanding gene expression in heterogeneous populations at the single cell level can (and has) lead to relevant biological and clinical insights1,2. Of concern to embryonic development studies, in a larger population of cells, progenitor cells are often underrepresented, making it challenging to detect subtle changes in gene expression that ultimately initiate cell fate decisions3. Similarly, a single cell type may have different expression profiles in response to the microenvironment4. For example, resident endothelial cells in the same organ or in different organs (e.g., aorta or kidney) exhibit significant heterogeneity despite sharing common morphological and functional features5. In addition, cancer cells populating the same tumor can also have varying molecular profiles or mutations at the single cell level6.
In model systems, transcriptomics in single cells has successfully identified new cell populations, characterized intermediate states that occur during cell differentiation, and revealed differential cellular responses to stimuli7,8,9. Such insights would have been masked in conventional population-based studies. Zebrafish embryos are a tremendously under-utilized source of stem, progenitor, and differentiating cells for exploring questions of single cell heterogeneity and molecular regulation of cellular identities during development. Their highly stereotyped, ex vivo development and ease of genetic manipulation make them an excellent model system for this approach10,11. Specifically, a major limitation to interpretation of single cell gene expression data is that reliable identification of novel intermediate cell states during development requires very careful timing of tissue collection9. This is necessary to ensure that heterogeneity between captured cells represents heterogeneity within a tissue at a single time point rather than heterogeneity in gene expression presented by age-dependent cell differentiation. Compared to mice, zebrafish embryo development may be precisely synchronized across a large number of embryos12. Additionally, with large clutch sizes, zebrafish embryos can be used as an abundant source of stem and progenitor cells.
This protocol describes a method to isolate cells from zebrafish embryos and capture single cells using a commercially available integrated microfluidics circuit (IFC) chip and autoprep system for qRT-PCR gene expression analysis. This protocol can be rapidly transferrable to any high throughput multiplexing assays including whole transcriptome sequencing that allows more comprehensive analysis of cellular heterogeneity13. It also offers several advantages to traditional gene expression assays. The single cell isolation protocol yields high viability after FACS, which decreases the proportion of compromised cells that are included in downstream applications. By using an IFC, captured cells may be directly observed to evaluate capture rates and assess cell health morphologically. In addition, this protocol is broadly applicable to the zebrafish research community, requiring only a labeled transgenic fish line and access to microfluidic cell capture technologies.
As proof of principle, single cells derived from cardiac progenitors were isolated and captured on an IFC chip, and then the relative abundance of cardiac differentiation markers was measured by qRT-PCR. Gene expression analysis at the single cell level demonstrates that cardiac progenitors coexist with their differentiating progeny. The insight gained from single-cell profiling of cardiac progenitors may shed light on the heterogeneity in gene expression patterns among cardiac progenitor cells during vertebrate development, which may have been masked in traditional population-based analyses.

<table border="0" cellpadding="0" cellspacing="0" width="816">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Supplies</td>
			<td style="width:111px;"></td>
			<td style="width:103px;"></td>
			<td style="width:388px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Dumont #5 forceps</td>
			<td style="width:111px;">Fine Science Tools</td>
			<td style="width:103px;">11254-20</td>
			<td>For removing the chorion from embryos</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Microcentrifuge tube 2 mL</td>
			<td style="width:111px;">GeneMate</td>
			<td style="width:103px;">C-3261-1</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">40 um cell strainer</td>
			<td style="width:111px;">Biobasic</td>
			<td style="width:103px;">SP104151</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">35 mm culture dish</td>
			<td style="width:111px;">Falcon</td>
			<td align="right" style="width:103px;">351008</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">FACS tubes topped with 35 um cell strainer</td>
			<td style="width:111px;">Falcon</td>
			<td align="right" style="width:103px;">352235</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">P1000 and tips</td>
			<td style="width:111px;">Rainin</td>
			<td align="right" style="width:103px;">17005089</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">P20 and tips</td>
			<td style="width:111px;">Rainin</td>
			<td align="right" style="width:103px;">17005091</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">IFC chip manufacturer&#39;s protocol</td>
			<td style="width:111px;">Fluidigm</td>
			<td style="width:103px;">100-6117</td>
			<td>Version 100-6117 E1 was used in representative experiment</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Wide bore pastuer glass pippette</td>
			<td style="width:111px;">VWR</td>
			<td style="width:103px;">14673-010</td>
			<td>For transferring embryos</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Adult wild type zebrafish</td>
			<td style="width:111px;">N/A</td>
			<td style="width:103px;"></td>
			<td>We used AB line</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Adult transgenic zebrafish</td>
			<td style="width:111px;">N/A</td>
			<td style="width:103px;"></td>
			<td>We used Tg(nkx2.5:ZsYellow)</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Name</td>
			<td style="width:111px;">Company</td>
			<td style="width:103px;">Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Reagents for cell dissociation</td>
			<td style="width:111px;"></td>
			<td style="width:103px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Double distilled water</td>
			<td style="width:111px;">N/A</td>
			<td style="width:103px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Instant Ocean Sea Salt</td>
			<td style="width:111px;">Instant Ocean</td>
			<td style="width:103px;">SS15-10</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">NaCl</td>
			<td style="width:111px;">FisherScientific</td>
			<td style="width:103px;">S271-3</td>
			<td>make stock in water and use for de-yolking buffer</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">KCl</td>
			<td style="width:111px;">Sigma Aldrich</td>
			<td style="width:103px;">P5405</td>
			<td>make stock in water and use for de-yolking buffer</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">NaHCO3</td>
			<td style="width:111px;">Sigma Aldrich</td>
			<td style="width:103px;">S6014</td>
			<td>make stock in water and use for de-yolking buffer</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Leibovitz&#39;s L-15</td>
			<td style="width:111px;">Gibco</td>
			<td style="width:103px;">21083-027</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">FBS</td>
			<td style="width:111px;">FisherScientific</td>
			<td style="width:103px;">03-600-511</td>
			<td>Heat inactivate; any brand of FBS should be fine</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Cell Dissociation Reagent 1 -TrypLE</td>
			<td style="width:111px;">Life Technologies</td>
			<td style="width:103px;">12605-010</td>
			<td>Store at room temperature.</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Cell Dissociation Reagent 2 - FACSmax</td>
			<td style="width:111px;">Genlantis</td>
			<td style="width:103px;">T200100</td>
			<td>Store -20; thaw on ice; bring to room temp before use</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">pronase (optional)</td>
			<td style="width:111px;">Sigma</td>
			<td style="width:103px;">P5147</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">L/D Dye - Sytox Blue</td>
			<td style="width:111px;">Life Technologies</td>
			<td style="width:103px;">S34857</td>
			<td>Any live/dead stain suitable for flow cytometry will work</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Trypan Blue</td>
			<td style="width:111px;">Gibco</td>
			<td style="width:103px;">15250-061</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Name</td>
			<td style="width:111px;">Company</td>
			<td style="width:103px;">Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Reagents for IFC plate use and qRT-PCR</td>
			<td style="width:111px;"></td>
			<td style="width:103px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Gene-specific probes</td>
			<td style="width:111px;"></td>
			<td style="width:103px;"></td>
			<td>Probes will vary by experiment</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">TaqMan Probe ef1a</td>
			<td style="width:111px;">Life Technologies</td>
			<td>Dr03432748_m1</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">TaqMan Probe gata4</td>
			<td style="width:111px;">Life Technologies</td>
			<td>Dr03443262_g1</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">TaqMan Probe nk2-5</td>
			<td style="width:111px;">Life Technologies</td>
			<td>Dr03074126_m1</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">TaqMan Probe myl7</td>
			<td style="width:111px;">Life Technologies</td>
			<td>Dr03105700_m1</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">TaqMan Probe vmhc</td>
			<td style="width:111px;">Life Technologies</td>
			<td>Dr03431136_m1</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">TaqMan Probe isl1</td>
			<td style="width:111px;">Life Technologies</td>
			<td>Dr03425734_m1</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">TaqMan Gene Expression Master Mix</td>
			<td style="width:111px;">Life Technologies</td>
			<td align="right" style="width:103px;">4369016</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Reagents listed in IFC manufacturer&#39;s protocol</td>
			<td style="width:111px;"></td>
			<td style="width:103px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">C1 Reagent Kit</td>
			<td style="width:111px;">Fluidigm</td>
			<td style="width:103px;">100-5319</td>
			<td>Reagents for loading cells onto IFC plate</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Ambion Single Cell-to-CTTM</td>
			<td style="width:111px;">Life Technologies</td>
			<td align="right" style="width:103px;">4458237</td>
			<td>Reagents for reverse transcription and pre-amplification steps</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Molecular Biology Quality Water</td>
			<td style="width:111px;">Corning</td>
			<td style="width:103px;">46-000CM</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">C1 IFC for PreAmp (5-10 um)</td>
			<td style="width:111px;">Fluidigm</td>
			<td style="width:103px;">100-5757</td>
			<td>IFC plate for small cells</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Name</td>
			<td style="width:111px;">Company</td>
			<td style="width:103px;">Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Equipment</td>
			<td style="width:111px;"></td>
			<td style="width:103px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">C1 AutoPrep machine</td>
			<td style="width:111px;">Fluidigm</td>
			<td style="width:103px;">100-5477</td>
			<td>For IFC plate use</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Hemocytometer&#160;</td>
			<td style="width:111px;">Sigma Aldrich</td>
			<td style="width:103px;">Z359629</td>
			<td>For counting cells and assessing cell size</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Dissecting microscope</td>
			<td style="width:111px;"></td>
			<td style="width:103px;"></td>
			<td>For removing embryos from chorion</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Tissue culture microscope</td>
			<td style="width:111px;"></td>
			<td style="width:103px;"></td>
			<td>For assessing single cell digestion</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">FACS machine</td>
			<td style="width:111px;"></td>
			<td style="width:103px;"></td>
			<td>For isolating cells of interest</td>
		</tr>
	</tbody>
</table>

isolation and characterization of single cells from zebrafish embryos

The zebrafish (Danio rerio) is a powerful model organism to study vertebrate development. Though many aspects of zebrafish embryonic development have been described at the morphological level, little is known about the molecular basis of cellular changes that occur as the organism develops. With recent advancements in microfluidics and multiplexing technologies, it is now possible to characterize gene expression in single cells. This allows for investigation of heterogeneity between individual cells of specific cell populations to identify and classify cell subtypes, characterize intermediate states that occur during cell differentiation, and explore differential cellular responses to stimuli. This study describes a protocol to isolate viable, single cells from zebrafish embryos for high throughput multiplexing assays. This method may be rapidly applied to any zebrafish embryonic cell type with fluorescent markers. An extension of this method may also be used in combination with high throughput sequencing technologies to fully characterize the transcriptome of single cells. As proof of principle, the relative abundance of cardiac differentiation markers was assessed in isolated, single cells derived from nkx2.5 positive cardiac progenitors. By evaluation of gene expression at the single cell level and at a single time point, the data support a model in which cardiac progenitors coexist with differentiating progeny. The method and work flow described here is broadly applicable to the zebrafish research community, requiring only a labeled transgenic fish line and access to microfluidics technologies.

As proof of principle, gene expression was assessed to explore differentiation dynamics during cardiac development. In zebrafish, cardiac progenitors arise from a mesodermal population of cells that migrate to the anterior lateral plate mesoderm where they fuse to form the linear heart tube. Prior to fusion, cardiac progenitors begin to express the transcription factor nkx2.5 (NK2 homeobox 5), which is thought to be the earliest specific marker of cardiac progenitors16,17</s...

Watch this Scientific Journal Video about Isolation and Characterization of Single Cells from Zebrafish Embryos at JoVE.com

Isolation and Characterization of Single Cells from Zebrafish Embryos

This protocol describes a method for isolating single cells from zebrafish embryos, enriching for cells of interest, capturing zebrafish cells in microfluidic based single cell multiplex systems, and assessing gene expression from single cells.

The zebrafish (Danio rerio) is a powerful model organism to study vertebrate development. Though many aspects of zebrafish embryonic development have been ...

The overall goal of this experiment is to isolate single cells from early stage zebrafish embryos for their capture in a microfluidic-based single-cell multiplex system to assess the gene expression of individual cells. This method can help answer key questions in the developmental biology field, such as what transcriptional changes do cells undergo during specification and differentiation. The main advantage of this technique is that it is an unbiased approach for revealing the heterogeneity that is masked in conventional population-based techniques.Generally, individuals new to this technique will struggle because generating the viable preparations of single cells is technically challenging but essential for downstream analysis. Once mastered, processing the whole embryo samples into single lysed cells on an integrated microfluidic chip can be completed in six hours if steps are performed properly. While attempting this procedure, it's important to remember to make sure that only single cells are captured on the microfluidic device.After breeding adult wild-type and transgenic zebrafish, collect embryos at 15-minute intervals according to facility and institution-approved standard operating procedures. At least two hours later, transfer 100 to 300 fertilized embryos from a single timepoint into a new Petri dish containing fresh egg water. And use fine forceps to manually remove the chorion from each embryo.Next, use a wide bore glass pipette to transfer the embryos into a 2-milliliter microcentrifuge tube in a minimum volume of egg water. When all of the embryos have been transferred, replace the water with 1 milliliter of ice cold egg water and submerge the tube in ice for 20 minutes. After the euthanization, use a wide bore glass pipette to remove the supernatant.And a P-1000 pipette to add fresh egg water to the embryos two times. After the second wash, replace the egg water with 1 milliliter of de-yolking buffer and use a P-1000 pipette to triturate the embryos eight to 12 times until the yolk is dissolved and only the bodies of the embryos are visible. Collect the tissue by centrifugation.Then, use the pipette to gently remove the supernatant without disturbing the tissue pellet, and re-suspend the cells in 1 milliliter of fresh egg water. After washing the embryos two more times, re-suspend the pellet in 1 milliliter of room temperature cell dissociation reagent-1. Then place the tube on its side for a 10-minute incubation at room temperature.With gentle trituration every two to three minutes to prevent clumping. At the end of the incubation, spin down the cells again and re-suspend the pellet in 1 milliliter of cell dissociation reagent-2. Incubate the cells horizontally at room temperature for another five to 15 minutes with gentle trituration every two to three minutes.Every five minutes, dilute 2 microliters of supernatant in 18 microliters of FACS buffer, and dispense the cells as a droplet onto a cell culture dish. Place a coverslip over the sample and use a tissue culture microscope to assess the digestion progression at 10 and 20x magnifications. When the preparation appears to be a mix of primarily single cells with some small and large cell clusters and a few mostly intact embryo bodies, spin down the cells and re-suspend the pellet in 1 milliliter of cold FACS buffer.Next, wet a 40-micron cell strainer with FACS buffer. And filter the cells through the strainer into a 35-millimeter cell culture dish. After spinning down the cells again, re-suspend the pellet in 100 microliters of FACS buffer, and count the number of viable cells by Trypan blue exclusion.Next, dilute the sample to 5 times 10 to the 6th cells per milliliter. And reserve 10 to 20%of the cells for the unstained control. Stain the rest of the cells with a fluorescent live/dead discrimination dye.Then wet a 35-micron cell strainer capped FACS tube with 20 microliters of FACS buffer, and add the cells to the strainer, collecting them by gravity. Using the illustrated gating strategy, sort the single live cells expressing the fluorescent marker. Verifying the gating with the double-labled cells.Sort 2, 000 to 4, 000 cells from the population of interest into 5 microliters of cold FACS buffer in a microcentrifuge tube on ice. Then transfer 1 microliter of the sorted cells into a new FACS tube with 100 microliters of FACS sorting buffer and a 1 to 1, 000 dilution of live/dead stain. And run the cell sample using the sorting gates to assess the post sort viability.Next, load 1 microliter of cells diluted in 9 microliters of FACS buffer onto a hemocytometer to determine the cell concentration and average diameter. Now select an integrated microfluidic circuit, or IFC chip, of the appropriate size for the average cell diameter of the sample, and prime the fluidics according to the manufacturer's instructions. Load the cells onto the plate according to the manufacturer's instructions, and load the plate into a compatible fluidic machine.Then run an appropriate cell loading script for the IFC chip to push the cells into the capture lanes. To confirm that the cells are lodged in the capture sites, mount the plate on a microscope equipped with a plate adapter and obtain brightfield and fluorescence images of each capture site at a 10x magnification. The cells can then be processed for downstream assessment of their target gene expression by QRT-PCR.At the 18-somite stage, fluorescence microscopy can be used to verify the ZsYellow expression of the embryos. After sorting, cells with a range of diameters are obtained. The IFC plate can be used to capture cells with a diameter of interest.For example, in this experiment, cells five to 10 micrometers in diameter. As expected, the sorted and captured cells from 18-hour post-fertilization embryos expressed the ZsYellow fluorescent marker. Here, QRT-PCR was used to assess the relative gene expression of specific genes of interest in 40 single cells from cell capture sites on an IFC plate.Since the range of cycle threshold values for the housekeeping gene was too broad for comparing gene expression between samples and many cycle threshold values exceeded 30, The values were visualized as a heat map. Comparing across samples, a substantial heterogeneity in gene expression was observed in this experiment. With cells classified as Types 1 through 5 based on their gene expression pattern.Once mastered, processing the whole embryo samples into single lysed cells on an integrated microfluidic chip can be completed in six hours if the steps are performed properly. While attempting this procedure, it's important to remember that only single cells are captured on the microfluidic chip. Following this procedure, other methods like high-throughput single cell sequencing can be performed to fully characterize the transcriptomes of single cells.After its development, this technique paved the way for researchers in the field of developmental biology for exploring cellular heterogeneity in early developing embryos. After watching this video, you should have a good understanding of how to isolate single cells from zebrafish embryos, capture single cells in a microfluidic base single-cell multiplex system and assess the gene expression of individual cells.

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