This work was funded by the friends of Sophia Foundation (SSWO WAR-63).

All zebrafish husbandry and experiments were conducted according to the institutional guidelines of the Erasmus MC and Animal welfare legislation. The use of zebrafish larvae at 5 days post fertilization falls under the category of experiments that do not require formal ethical approval, as outlined by the Dutch regulations.
1. Obtaining 5 days post fertilization (dpf) wildtype and tg(phox2bb:GFP) larvae
<ol>
	<li>Set up breeding of wildtype zebrafish and collect 50 eggs in HEPES-buffered E3 medium (hereafter referred to as E3) in a 15 cm Petri dish. Use these fish as a negative control for fluorescence-activated cell sorting (FACs).</li>
	<li>Set up breeding of tg(phox2bb:GFP) zebrafish and collect approximately 300 eggs in E3 in a 15 cm Petri dish.</li>
	<li>Keep fertilized eggs in E3 (maximum 50 eggs/dish) on a 14 h/10 h light/dark cycle, in an incubator at 28.5 &#176;C.</li>
	<li>At 1 dpf, remove unfertilized eggs and let the fertilized ones develop to 5 dpf.</li>
	<li>Select tg(phox2bb:GFP) larvae at 1 dpf.</li>
</ol>
2. Wildtype whole larvae dissociation
<ol>
	<li>Anesthetize 5 dpf larvae with 0.016% Tricaine.</li>
	<li>Chop 30 zebrafish into small pieces using a razor blade in a Petri dish containing 1 mL of 10x trypsin-EDTA solution.</li>
	<li>Transfer the chopped zebrafish into a microcentrifuge tube with a total volume of 2 mL of 10x trypsin-EDTA solution and leave on ice for 3 h. Pipette up and down with a P1000 pipette every hour to stimulate dissociation.</li>
</ol>
3. Gut isolation
<ol>
	<li>Place 6-10 5 dpf larvae anesthetized with 0.016% Tricaine in a row, on a 1.8% agarose plate (0.45 g of agarose in 25 mL of E3), under a dissection microscope</li>
	<li>Put one insect pin in the head of the zebrafish.</li>
	<li>Remove all remaining E3 using a tissue.</li>
	<li>Isolate the intestine using another insect pin, without disturbing any other organs. Make sure that the yolk is removed (Supplementary Figure S1A).</li>
	<li>Once isolated, inspect the intestine and remove all non-intestinal material (e.g., skin, fat, liver) if needed.</li>
	<li>Collect the intestine with tweezers and place it in a microcentrifuge tube, containing phosphate-buffered saline (PBS) with 10% fetal calf serum (FCS), on ice. 
	&#8203;NOTE: A minimum of 244 intestines should be isolated, keeping the total dissection time at 3 h. This is feasible with two people working in parallel.</li>
</ol>
4. Gut dissociation
<ol>
	<li>Immediately after the dissection of all intestines, centrifuge the microcentrifuge tube at full speed (13,800 &#215; g) for 30 s.</li>
	<li>Remove the PBS/10% FCS but leave a small amount (~100 &#181;L) to prevent the intestines from drying out. Add 500 &#181;L of 2.17 mg/mL papain in HBSS containing CaCl2 and MgCl2, to dissociate cells.</li>
	<li>Activate papain with 2.5 &#181;L of cysteine (1 M).</li>
	<li>Incubate the guts in a water bath at 37 &#176;C for 10 min. Pipette up and down halfway (after 5 min) to stimulate enzymatic tissue digestion.</li>
	<li>Transfer cells into a FACS tube using a 35 &#181;m cell strainer, prewetted with 0.5 mL of PBS/10% FCS.</li>
	<li>Wash the strainer by adding a total of 2 mL of PBS/10% FCS in 0.5 mL steps.</li>
	<li>Centrifuge at 700 &#215; g for 5 min at 4 &#176;C.</li>
	<li>Remove the supernatant and resuspend the pellet in 300 &#181;L of PBS/10% FCS.</li>
	<li>Add 1 &#181;g/mL of 4&#39;,6-diamidino-2-phenylindole (DAPI) to label dead cells (1:1,000) and incubate for 5 min to allow their exclusion during FACS.</li>
</ol>
5. FACS enrichment
<ol>
	<li>Use the wildtype sample to set the gates of the sorted cell population by recording 3,000 cells on the flow cytometer (Supplementary Figure S1B-E).</li>
	<li>Use a 100 &#181;m nozzle, set sort precision on purity, and put the collection tube containing 200 &#181;L of PBS/5% FCS, in the FACS machine.</li>
	<li>Load the cell suspension of the guts and sort live (DAPI-negative), single cells into the collection tube (Figure 2C), by excluding doublets (Figure 2B) and dead cells (Figure 2C). 
	NOTE: For the tg(phox2bb) zebrafish, the proportion of GFP+ cells is only checked for reference, as all single live cells are sorted.</li>
	<li>Keep the collection tube on ice after cell sorting.</li>
	<li>Count the cell suspension with a hemocytometer, including a viability check with trypan blue. If the viability is at least 80%, continue with the next step.</li>
	<li>Cells are now ready to process for scRNAseq (i.e., 10x Genomics Chromium platform). Use approximately 20,000 cells per sample.</li>
</ol>

Processing Gut Cells from Zebrafish Larvae for Single-Cell RNA Sequencing

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Gastroenterology &amp; Hepatology. 9 (5), 286-294 (2012).</li><li>Obata, Y., Pachnis, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+effect+of+microbiota+and+the+immune+system+on+the+development+and+organization+of+the+enteric+nervous+system.">The effect of microbiota and the immune system on the development and organization of the enteric nervous system.</a> Gastroenterology. 151 (5), 836-844 (2016).</li><li>Heuckeroth, R. O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hirschsprung+disease+-+integrating+basic+science+and+clinical+medicine+to+improve+outcomes.">Hirschsprung disease - integrating basic science and clinical medicine to improve outcomes.</a> Nature Reviews. Gastroenterology &amp; Hepatology. 15 (3), 152-167 (2018).</li><li>Antonucci, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chronic+intestinal+pseudo-obstruction.">Chronic intestinal pseudo-obstruction.</a> World Journal of Gastroenterology. 14 (19), 2953-2961 (2008).</li><li>De Giorgio, R., Sarnelli, G., Corinaldesi, R., Stanghellini, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Advances+in+our+understanding+of+the+pathology+of+chronic+intestinal+pseudo-obstruction.">Advances in our understanding of the pathology of chronic intestinal pseudo-obstruction.</a> Gut. 53 (11), 1549-1552 (2004).</li><li>Bianco, F., 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=Enteric+neuromyopathies:+highlights+on+genetic+mechanisms+underlying+chronic+intestinal+pseudo-obstruction.">Enteric neuromyopathies: highlights on genetic mechanisms underlying chronic intestinal pseudo-obstruction.</a> Biomolecules. 12 (12), 1849 (2022).</li><li>Kimmel, C. B., Ballard, W. W., Kimmel, S. R., Ullmann, B., Schilling, T. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stages+of+embryonic+development+of+the+zebrafish.">Stages of embryonic development of the zebrafish.</a> Dev Dyn. 203 (3), 253-310 (1995).</li><li>Lieschke, G. J., Currie, P. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Animal+models+of+human+disease:+zebrafish+swim+into+view.">Animal models of human disease: zebrafish swim into view.</a> Nature Reviews. 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N., Pack, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Unique+and+conserved+aspects+of+gut+development+in+zebrafish.">Unique and conserved aspects of gut development in zebrafish.</a> Developmental Biology. 255 (1), 12-29 (2003).</li><li>Harrison, C., Wabbersen, T., Shepherd, I. T. <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+visualization+of+the+development+of+the+enteric+nervous+system+using+a+Tg(-8.3bphox2b:Kaede)+transgenic+zebrafish.">In vivo visualization of the development of the enteric nervous system using a Tg(-8.3bphox2b:Kaede) transgenic zebrafish.</a> Genesis. 52 (12), 985-990 (2014).</li><li>Kuil, L. E., Chauhan, R. K., Cheng, W. W., Hofstra, R. M. W., Alves, M. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Zebrafish:+a+model+organism+for+studying+enteric+nervous+system+development+and+disease.">Zebrafish: a model organism for studying enteric nervous system development and disease.</a> Frontiers in Cell and Developmental Biology. 8, 629073 (2020).</li><li>Stuart, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comprehensive+Integration+of+Single-Cell+Data.">Comprehensive Integration of Single-Cell Data.</a> Cell. 177 (7), 1888-1902 (2019).</li><li>Kuil, L. 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The authors have no conflicts of interest to disclose.

Here, we present a method for isolation and dissociation of the gut of 5 dpf zebrafish larvae using FACS. With this method, different intestinal cell types were successfully collected and analyzed by scRNA-seq, using the 10x Genomics Chromium platform. We selected the tg(phox2bb:GFP) zebrafish line, as we wanted an indication that viable ENS cells would be also isolated (Figure 2D). However, it is important to note that this method can be readily extended to other zebrafish lines of...

The gastrointestinal (GI) tract is a complex system that plays a vital role in overall health and well-being. It is responsible for the digestion and absorption of nutrients, as well as the elimination of waste products1,2. The GI tract is composed of multiple cell types, including epithelial cells, smooth muscle cells, immune cells, and the enteric nervous system (ENS), which communicate closely together to regulate and maintain proper intestinal function3,4,5. Defects in the development of the GI tract can have far-reaching effects on various aspects such as nutrient absorption, microbiota composition, the gut-brain axis, and the ENS, leading to several enteric neuromuscular disorders, such as Hirschsprung disease and Chronic intestinal pseudo-obstruction6,7. These disorders are characterized by severe gut dysmotility caused by alterations in various key cells, such as the interstitial cells of Cajal, smooth muscle cells, and the ENS6,8,9. However, the molecular mechanisms underlying GI development and dysfunction are still poorly understood.
The zebrafish is a valuable model organism for studying GI development and dysfunction due to its rapid embryonic development, transparency during embryonic and larval stages, and genetic tractability10,11,12,13,14. Numerous transgenic zebrafish lines expressing fluorescent proteins are available. An example of such a line is the tg(phox2bb:GFP) zebrafish, commonly used to study the ENS, as all phox2bb+ cells, including enteric neurons, are labeled15,16. Here, using the tg(phox2bb:GFP) zebrafish line, we present a method for intestinal isolation of 5 days post fertilization (dpf) larvae for single-cell RNA sequencing (scRNA-seq) analysis (Figure 1).

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>10x Trypsin (0.5%)-EDTA (0.2%)</td>
			<td>Sigma</td>
			<td>59418C</td>
			<td></td>
		</tr>
		<tr>
			<td>5 mL round bottom tube with cell-strainer cap</td>
			<td>Falcon</td>
			<td>352235</td>
			<td></td>
		</tr>
		<tr>
			<td>Agarose</td>
			<td>Sigma-Aldrich</td>
			<td>A9539</td>
			<td></td>
		</tr>
		<tr>
			<td>BD Falcon Round-Bottom Tube 5 mL (FACS tubes) snap cap</td>
			<td>BD Biosciences</td>
			<td>352054</td>
			<td></td>
		</tr>
		<tr>
			<td>Cell Ranger v3.0.2</td>
			<td>10X Genomics</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>DAPI</td>
			<td>Sigma-Aldrich</td>
			<td>Cat#D-9542</td>
			<td></td>
		</tr>
		<tr>
			<td>Dissection microscope</td>
			<td>Olympus SZX16</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>FACSAria III sorter machine</td>
			<td>BD Biosciences</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>HBSS with CaCl2 and MgCl2</td>
			<td>Gibco</td>
			<td>14025050</td>
			<td></td>
		</tr>
		<tr>
			<td>Insect pins</td>
			<td>Fine Science Tools</td>
			<td>26000-25</td>
			<td></td>
		</tr>
		<tr>
			<td>L-Cysteine</td>
			<td>Sigma</td>
			<td>C7352</td>
			<td></td>
		</tr>
		<tr>
			<td>MS-222, Tricaine</td>
			<td>Supelco</td>
			<td>A5040-250G</td>
			<td></td>
		</tr>
		<tr>
			<td>Papain</td>
			<td>Sigma</td>
			<td>P4762</td>
			<td></td>
		</tr>
		<tr>
			<td>Seurat v3</td>
			<td>Stuart et&#160;al. (2019)</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Trypan blue&#160;</td>
			<td>Sigma&#160;</td>
			<td>Cat#T8154</td>
			<td></td>
		</tr>
	</tbody>
</table>

gut isolation from zebrafish larvae for single-cell rna sequencing

The gastrointestinal (GI) tract performs a range of functions essential for life. Congenital defects affecting its development can lead to enteric neuromuscular disorders, highlighting the importance to understand the molecular mechanisms underlying GI development and dysfunction. In this study, we present a method for gut isolation from zebrafish larvae at 5 days post fertilization to obtain live,&#160;viable cells which can be used for single-cell RNA sequencing (scRNA-seq) analysis. This protocol is based on the manual dissection of the zebrafish intestine, followed by enzymatic dissociation with papain. Subsequently, cells are submitted to fluorescence-activated cell sorting, and viable cells are collected for scRNA-seq. With this method, we were able to successfully identify different intestinal cell types, including epithelial, stromal, blood, muscle, and immune cells, as well as enteric neurons and glia. Therefore, we consider it to be a valuable resource for studying the composition of the GI tract in health and disease, using the zebrafish.

Author Spotlight: Isolating and Analyzing Intestinal Cells of Zebrafish Larvae for Investigating Transcriptomic Aspects of Gastrointestinal Development 

Gut Isolation from Zebrafish Larvae for Single-cell RNA Sequencing

Our research aims to investigate the transcriptomic changes occurring during gastrointestinal development and dysfunction in zebrafish larvae. Here, we provide a new protocol that allows isolation of different cell types within the zebrafish intestine, which has potential applications in understanding gastrointestinal health and disease. In recent years, there has been growing interest in exploring the interaction between the enteric nervous system and other intestinal cell types during development and disease.Understanding these complex dynamics using advanced techniques like single-cell RNA sequencing, holds the potential to reveal critical insights into enteric neuromyopathies, leading to more precise diagnostics and treatments. Using this protocol, we successfully identified various intestinal cell types, including epithelial, stromal, bloods, muscle, immune cells, and even enteric neurons and glia, which have not been captured before at this amount using similar approaches. Thus, we provide a reliable technique to study the gastrointestinal composition during development and dysfunction.

With this protocol, we achieved successful isolation and dissociation of entire intestines from 5 dpf&#160;larvae. Using papain as the dissociation enzyme, we significantly enhanced cell viability, enabling the capture of 46,139 events involving single, viable cells (6.4% of all cells) out of 244 isolated guts (Figure 2A). Wildtype whole larvae were used as a control to ensure that the sorting process was optimized, enabling effective cell identification and sorting. Whole larvae could be us...

Watch this Scientific Journal Video about Isolating and Analyzing Intestinal Cells of Zebrafish Larvae for Investigating Transcriptomic Aspects of Gastrointestinal Development at JoVE.com

Here, we describe a method for gut isolation from zebrafish larvae at 5 days post fertilization, for single-cell RNA sequencing analysis.

The gastrointestinal (GI) tract performs a range of functions essential for life. Congenital defects affecting its development can lead to enteric ...

gut-isolation-from-zebrafish-larvae-for-single-cell-rna-sequencing

Research

JoVE Journal

Developmental Biology

Obtaining Wildtype and Transgenic Zebrafish Larvae and WildType Whole Larvae Dissociation

Begin by obtaining the wildtype and transgenic zebrafish eggs from the respective breeding setup. Take a 15-centimeter Petri dish containing HEPES-buffered E3 medium or E3.And collect the appropriate amount of fertilized eggs from the desired zebrafish breeding setup. Incubate the fertilized eggs in E3 at 28 degrees Celsius with an appropriate light and dark cycle.At one days post fertilization or dpf, remove any unfertilized eggs and let the fertilized ones develop until five dpf. Select the transgenic zebrafish larvae at one dpf. Before proceeding for whole larvae dissociation, anesthetize the five dpf wildtype larvae using 0.016%Tricaine, and transfer 30 anesthetized larvae into a Petri dish containing one milliliter of 10x trypsin-EDTA solution.Then, using a razor blade, chop the larvae into small pieces in the Petri dish. Transfer the chopped larvae into a micro centrifuge tube with two milliliters of 10x trypsin-EDTA solution, and leave the tube on ice for three hours. Pipette the contents up and down with a P1000 pipette every hour to stimulate dissociation.

Isolation and Dissociation of Gut from Zebrafish Larvae for FACS Enrichment of Gut Cells

To begin, prepare a 1.8%agarose plate with HEPES Buffered E3 medium or E3.While working under a dissection microscope, place six to 10 anesthetized larvae in a row on the agarose plate. Put one insect pin on the head of each larvae. Then remove the remaining E3 from the plate using a tissue.Using another insect pin, isolate the intestine from a larvae without disturbing any other organs. Ensure proper removal of yolk. Once isolated, inspect the intestine and remove all non-intestinal material, such as skin, fat, or liver.Use tweezers to collect the intestine and transfer it to PBS containing 10%FCS in a microcentrifuge tube placed on ice. Immediately after the dissection of all intestines, centrifuge the microcentrifuge tube at 13, 800 g for 30 seconds. Remove the supernatant, leaving about 100 microliters in the tube to prevent the intestines from drying out.Add 500 microliters of papain solution to the intestines in the tube. Activate the papain by adding 2.5 microliters of one molar cysteine. Then incubate the tube containing the intestines in a water bath at 37 degrees Celsius for 10 minutes.Pipette the contents up and down halfway after five minutes to stimulate enzymatic tissue digestion. Transfer the dissociated cells into a fluorescence-activated cell sorting, or FACS, tube through a pre-wedded 35-micron cell strainer. Wash the strainer several times by adding 0.5 milliliters of PBS containing 10%FCS to a total wash volume of two milliliters.Centrifuge the collected filtrate at 700 g for five minutes at 4 degrees Celsius, and remove the supernatant. Add one microgram per milliliter DAPI to 300 microliters of PBS containing 10%FCS. Add this mixture to the pellet and resuspend to label the dead cells.Then incubate for five minutes on ice to allow their exclusion during subsequent FACS analysis.

FACS Enrichment of Zebrafish Gut Cell Suspension for scRNAseq

To perform fluorescence-activated cell sorting, or FACS, on the gut cells isolated from zebrafish larvae, use the wild-type whole larvae sample to set the gates of the sorted cell population by recording 3, 000 cells on the flow cytometer. Use a 100-micron nozzle and set Sort Precision to 4-Way Purity. Put the collection tube containing 200 microliters of PBS with 5%fetal calf serum in the fax machine.Load the cell suspension prepared from the isolated guts, and after excluding doublets in dead cells, sort live or DAPI-negative single cells into the collection tube. Keep the collection tube on ice after cell sorting, employing a viability check with trypan blue. Count the number of cells in the suspension with a hemocytometer.The cells are now ready to be processed for single-cell RNA sequencing. Use approximately 20, 000 cells per sample.

995 Views.  Erasmus University Medical Center - Sophia Children's Hospital.  Here, we describe a method for gut isolation from zebrafish larvae at 5 days post fertilization, for single-cell RNA sequencing analysis.

Processing Gut Cells from Zebrafish Larvae for Single-Cell RNA Sequencing

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