We would like to thank Anne-Laure Duchemin, Denise Duchemin, Nathalie Faggianelli and Basile Gurchenkov for helping to design and make the mold described in this protocol. This work was supported by FRM (DEQ20140329553), the ANR (ANR-15-CE13-0015-01, ANR-12-ISV2-0001-01), the EMBO Young Investigator Program, the European Community, ERC CoG N&#176;682938 Evalve and by the grant ANR-10-LABX-0030-INRT, a French State fund managed by the Agence Nationale de la Recherche under the frame program Investissements d'Avenir labeled ANR-10-IDEX-0002-02.

1. Preparing molds and mounting agarose
<ol>
	<li>Create a mold with the dimensions shown in Figure 1 using either a 3D printer or traditional mechanical workshop tools.</li>
	<li>Pipette about 1.5 mL of melted 1 % agarose into a 35-mm plastic mounting dish. Place the plastic mold in the liquid agarose, taking care to avoid trapping air between the mold and the agarose. Place the dish at 4 &#176;C, wait till the agarose hardens (this takes about 5 min), then remove the plastic mold.</li>
	...

<ol>
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J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Patterning+and+development+of+the+atrioventricular+canal+in+zebrafish.">Patterning and development of the atrioventricular canal in zebrafish.</a> J Cardiovasc Transl Res. 4, 720-726 (2011).</li><li>Boselli, F., Freund, J. B., Vermot, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Blood+flow+mechanics+in+cardiovascular+development.">Blood flow mechanics in cardiovascular development.</a> Cell Mol Life Sci. 72 (13), 2545-2559 (2015).</li><li>Steed, E., Boselli, F., Vermot, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hemodynamics+driven+cardiac+valve+morphogenesis.">Hemodynamics driven cardiac valve morphogenesis.</a> Biochim Biophys Acta. , (2015).</li><li>Boselli, F., Vermot, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Live+imaging+and+modeling+for+shear+stress+quantification+in+the+embryonic+zebrafish+heart.">Live imaging and modeling for shear stress quantification in the embryonic zebrafish heart.</a> Methods. , (2015).</li><li>Steed, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=klf2a+couples+mechanotransduction+and+zebrafish+valve+morphogenesis+through+fibronectin+synthesis.">klf2a couples mechanotransduction and zebrafish valve morphogenesis through fibronectin synthesis.</a> Nat Commun. 7, 11646 (2016).</li><li>Herwig, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Distinct+cellular+mechanisms+of+blood+vessel+fusion+in+the+zebrafish+embryo.">Distinct cellular mechanisms of blood vessel fusion in the zebrafish embryo.</a> Curr Biol. 21 (22), 1942-1948 (2011).</li><li>Boselli, F., Steed, E., Freund, J., Vermot, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Anisotropic+shear+stress+patterns+predict+the+orientation+of+convergent+tissue+movements+in+the+embryonic+heart.">Anisotropic shear stress patterns predict the orientation of convergent tissue movements in the embryonic heart.</a> Development. , (2017).</li><li>Lombardo, V. A., Sporbert, A., Abdelilah-Seyfried, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cell+Tracking+Using+Photoconvertible+Proteins+During+Zebrafish+Development.">Cell Tracking Using Photoconvertible Proteins During Zebrafish Development.</a> J. Vis. Exp. (67), (2012).</li><li>JoVE Science Education Database. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Biology II: Mouse, Zebrafish, and Chick. Zebrafish Breeding and Embryo Handling. , (2017).</li><li>Watanabe, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Inhibitory+effect+of+2,3-butanedione+monoxime+(BDM)+on+Na(+)/Ca(2+)+exchange+current+in+guinea-pig+cardiac+ventricular+myocytes.">Inhibitory effect of 2,3-butanedione monoxime (BDM) on Na(+)/Ca(2+) exchange current in guinea-pig cardiac ventricular myocytes.</a> Br J Pharmacol. 132 (6), 1317-1325 (2001).</li><li>Jou, C. J., Spitzer, K. W., Tristani-Firouzi, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Blebbistatin+effectively+uncouples+the+excitation-contraction+process+in+zebrafish+embryonic+heart.">Blebbistatin effectively uncouples the excitation-contraction process in zebrafish embryonic heart.</a> Cell Physiol Biochem. 25 (4-5), 419-424 (2010).</li><li>Pestel, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Real-time+3D+visualization+of+cellular+rearrangements+during+cardiac+valve+formation.">Real-time 3D visualization of cellular rearrangements during cardiac valve formation.</a> Development. 143 (12), 2217-2227 (2016).</li><li>Swinburne, I. A., Mosaliganti, K. R., Green, A. A., Megason, S. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Improved+Long-Term+Imaging+of+Embryos+with+Genetically+Encoded+alpha-Bungarotoxin.">Improved Long-Term Imaging of Embryos with Genetically Encoded alpha-Bungarotoxin.</a> PLoS One. 10 (8), e0134005 (2015).</li><li>Kaufmann, A., Mickoleit, M., Weber, M., Huisken, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multilayer+mounting+enables+long-term+imaging+of+zebrafish+development+in+a+light+sheet+microscope.">Multilayer mounting enables long-term imaging of zebrafish development in a light sheet microscope.</a> Development. 139 (17), 3242-3247 (2012).</li><li>Marchant, J. S., Stutzmann, G. E., Leissring, M. A., LaFerla, F. M., Parker, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multiphoton-evoked+color+change+of+DsRed+as+an+optical+highlighter+for+cellular+and+subcellular+labeling.">Multiphoton-evoked color change of DsRed as an optical highlighter for cellular and subcellular labeling.</a> Nat Biotechnol. 19 (7), 645-649 (2001).</li><li>Dempsey, W. P. <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+single-cell+labeling+by+confined+primed+conversion.">In vivo single-cell labeling by confined primed conversion.</a> Nat Methods. 12 (7), 645-648 (2015).</li><li>Mohr, M. A., Pantazis, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single+neuron+morphology+in+vivo+with+confined+primed+conversion.">Single neuron morphology in vivo with confined primed conversion.</a> Methods Cell Biol. 133, 125-138 (2016).</li><li>Mohr, M. A., Argast, P., Pantazis, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Labeling+cellular+structures+in+vivo+using+confined+primed+conversion+of+photoconvertible+fluorescent+proteins.">Labeling cellular structures in vivo using confined primed conversion of photoconvertible fluorescent proteins.</a> Nat Protoc. 11 (12), 2419-2431 (2016).</li><li>Mohr, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rational+Engineering+of+Photoconvertible+Fluorescent+Proteins+for+Dual-Color+Fluorescence+Nanoscopy+Enabled+by+a+Triplet-State+Mechanism+of+Primed+Conversion.">Rational Engineering of Photoconvertible Fluorescent Proteins for Dual-Color Fluorescence Nanoscopy Enabled by a Triplet-State Mechanism of Primed Conversion.</a> Angew Chem Int Ed Engl. 56 (38), 11628-11633 (2017).</li><li>Dempsey, W. P., Fraser, S. E., Pantazis, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=PhOTO+zebrafish:+a+transgenic+resource+for+in+vivo+lineage+tracing+during+development+and+regeneration.">PhOTO zebrafish: a transgenic resource for in vivo lineage tracing during development and regeneration.</a> PLoS One. 7 (3), e32888 (2012).</li><li>Dempsey, W. P., Qin, H., Pantazis, P. <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+cell+tracking+using+PhOTO+zebrafish.">In vivo cell tracking using PhOTO zebrafish.</a> Methods Mol Biol. 1148, 217-228 (2014).</li></ol>

No conflict of interest declared.

Timing of photoconversion: Although Kaede remains brightly expressed in EdCs even at 96 hpf, it should be noted that as the embryo grows, laser light diffuses more before it reaches the AVC, making confined photoconversion of Kaede more difficult. At embryonic stages later than 55 hpf, the ballooning of the ventricle and the atrium also means that the violet laser beam used for photoconversion cannot reach AVC cells without first passing through either the atrium or ventricle. This means that beyond 55 hpf, in o...

The zebrafish is currently one of the most important vertebrate models to study cellular and developmental processes in vivo. This is largely due to the zebrafish's optical transparency and amenability to genetics, which makes it a powerful model for applying optical techniques involving genetically encoded photoresponsive protein technologies1. Specific to the study of heart development, zebrafish receive sufficient oxygen via diffusion such that even mutants without heartbeat can survive through the first week of development, permitting analyses on the effects of developmental genes and perturbed blood flow on heart morphogenesis not possible in most vertebrates2.
The zebrafish heart tube is formed by 24 hours post fertilization (hpf). Shortly after its formation, the heart tube starts actively beating. By 36 hpf, a clear constriction separates the atrium from the ventricle. This region of constriction is called the atrioventricular canal (AVC), and cells in this region change from a squamous morphology to a cuboidal morphology3. Zebrafish atrioventricular valve morphogenesis starts around 48 h post fertilization. By 5 days post fertilization, two valve leaflets extend into the AVC and prevent the back flow of blood from the ventricle to the atrium during the cardiac cycle4. Tracking cells during AVC and valve formation is challenging as the rapid beating of the heart makes it difficult to follow cells via traditional time-lapse microscopy5,6. This protocol, adapted from Steed et al., 20167, describes a method that uses the Tg(fli1a:gal4FFubs, UAS:kaede)8 zebrafish transgenic line, in which the photoconvertible protein Kaede is expressed in endothelial cells, including the endocardium. The drug 2,3-butanedione-2-monoxime (BDM) is used to temporarily stop the heart beating, allowing accurate photoconversion of EdCs between 36 and 55 hpf, and high-resolution imaging of photoconverted EdCs at specific developmental time points. It has previously been shown that EdCs photoconverted using this method can remain distinguishable from their unconverted neighbors for five days or more after the time of photoconversion7. This protocol also details a method used for image analysis of photoconverted EdCs in embryos younger than 48 hpf, which has successfully been used to follow tissue movements during AVC development (Boselli et al., in press)9. We hope that readers would find this protocol useful for studying AVC and valve development in normal embryos, and in mutants, morphants, or drug-treated embryos. For a more general protocol relating to cell tracking using photoconvertible proteins during zebrafish development, please view the article by Lombardo et al., 201210.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Materials</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Necessary equipment for raising fish and collecting eggs (see the Zebrafish Book22 for details).</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Stereomicroscope</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Upright confocal microscope (Equipped with lasers operating at 488 nm, 561 nm, and 405 nm, a tunable multiphoton laser, and a Leica HCX IRAPO L, 25 &#215;, N.A. 0.95 objective)</td>
			<td>Leica</td>
			<td>Leica SP8</td>
			<td></td>
		</tr>
		<tr>
			<td>Heat block</td>
			<td>ThermoScientific</td>
			<td>88870001</td>
			<td></td>
		</tr>
		<tr>
			<td>35 mm x 10 mm tissue culture dish</td>
			<td>Falcon</td>
			<td>353001</td>
			<td></td>
		</tr>
		<tr>
			<td>6 well plate</td>
			<td>Falcon</td>
			<td>353046</td>
			<td></td>
		</tr>
		<tr>
			<td>Petri dish</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Forceps</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Glass pipette</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Mold</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Reagents</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>8 mg/mL Tricaine stock solution&#160;</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>1 M BDM stock solution</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>UltraPure low melting point agarose</td>
			<td>Invitrogen</td>
			<td>16520-050</td>
			<td></td>
		</tr>
		<tr>
			<td>Agarose</td>
			<td>Lonza</td>
			<td>50004</td>
			<td></td>
		</tr>
		<tr>
			<td>PTU (1-phenyl-2-thiourea)</td>
			<td>Sigma Aldrich</td>
			<td>P7629</td>
			<td></td>
		</tr>
		<tr>
			<td>Embryo medium: 30x stock solution</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Software</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Matlab equipped with the Image Analysis, Curve Fitting, Bio-Formats Toolboxes</td>
			<td>MathWorks</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>8 mg/mL Tricaine stock solution</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>200 mg of tricaine powder (Ethyl 3-aminobenzoate methanesulfonic acid)</td>
			<td>Sigma-Aldrich</td>
			<td>E10521</td>
			<td></td>
		</tr>
		<tr>
			<td>25 mL Danieau</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Adjust to pH 7, aliquot and store at -20 &#176;C&#160;</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>1 M BDM stock solution</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>1 g BDM</td>
			<td>Sigma-Aldrich</td>
			<td>112135</td>
			<td></td>
		</tr>
		<tr>
			<td>10 mL ddH2O</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Aliquot and store at -20 &#176;C</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Embryo medium: 30x stock solution</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>50.7 g NaCl</td>
			<td>Sigma-Aldrich</td>
			<td>7647-14-5</td>
			<td></td>
		</tr>
		<tr>
			<td>0.78 g KCl</td>
			<td>Sigma-Aldrich</td>
			<td>7447-40-7</td>
			<td></td>
		</tr>
		<tr>
			<td>1.47 g Magnesium sulfate</td>
			<td>Sigma-Aldrich</td>
			<td>&#160;7487-88-9</td>
			<td></td>
		</tr>
		<tr>
			<td>2.1 g Calcium nitrite tetrahydrate</td>
			<td>Sigma-Aldrich</td>
			<td>13477-34-4</td>
			<td></td>
		</tr>
		<tr>
			<td>19.52 g HEPES (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid)</td>
			<td>Sigma-Aldrich</td>
			<td>7365-45-9</td>
			<td></td>
		</tr>
		<tr>
			<td>Adjust to pH 7.2 and store at room temperature</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Mold</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>PlasCLEAR resin</td>
			<td>Asiga</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Plus 39&#160;Freeform Pico 3D printer</td>
			<td>Asiga</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

following endocardial tissue movements via cell photoconversion in the zebrafish embryo

During embryogenesis, cells undergo dynamic changes in cell behavior, and deciphering the cellular logic behind these changes is a fundamental goal in the field of developmental biology. The discovery and development of photoconvertible proteins have greatly aided our understanding of these dynamic changes by providing a method to optically highlight cells and tissues. However, while photoconversion, time-lapse microscopy, and subsequent image analysis have proven to be very successful in uncovering cellular dynamics in organs such as the brain or the eye, this approach is generally not used in the developing heart due to challenges posed by the rapid movement of the heart during the cardiac cycle. This protocol consists of two parts. The first part describes a method for photoconverting and subsequently tracking endocardial cells (EdCs) during zebrafish atrioventricular canal (AVC) and atrioventricular heart valve development. The method involves temporally stopping the heart with a drug in order for accurate photoconversion to take place. Hearts are allowed to resume beating upon removal of the drug and embryonic development continues normally until the heart is stopped again for high-resolution imaging of photoconverted EdCs at a later developmental time point. The second part of the protocol describes an image analysis method to quantify the length of a photoconverted or non-photoconverted region in the AVC in young embryos by mapping the fluorescent signal from the three-dimensional structure onto a two-dimensional map. Together, the two parts of the protocol allows one to examine the origin and behavior of cells that make up the zebrafish AVC and atrioventricular heart valve, and can potentially be applied for studying mutants, morphants, or embryos that have been treated with reagents that disrupt AVC and/or valve development.

An example of an embryo photoconverted at 48 hpf and imaged again at 80 hpf is shown in Figure 2, Movies 1 and 2. Exposing Kaede to 405 nm light irreversibly converts from the protein from its fluorescent green form to fluorescent red form, enabling the behavior of cells labeled with either the green or their red form to be followed with respect to their differentially colored neighbors during valve formation. It can be seen ...

Watch this Scientific Journal Video about Following Endocardial Tissue Movements via Cell Photoconversion in the Zebrafish Embryo at JoVE.com

Following Endocardial Tissue Movements via Cell Photoconversion in the Zebrafish Embryo

This protocol describes a method for the photoconversion of Kaede fluorescent protein in endocardial cells of the living zebrafish embryo that enables the tracking of endocardial cells during atrioventricular canal and atrioventricular heart valve development.

During embryogenesis, cells undergo dynamic changes in cell behavior, and deciphering the cellular logic behind these changes is a fundamental goal in the ...

The overall goal of this procedure is to follow endocardial cells during atrioventricular canal and heart valve formation. This method can help to address key question in the field of cardiac development, such as to understand how endocardial cells behave in different types of mutants. Tracking cells during AVC and valve formation is challenging because of the rapid beat of the heart.It makes it difficult to follow cells via traditional time-lapse microscopy. The main advantage of this technique is that it bypasses some of these difficulties. Demonstrating the procedure will be Renee, a postdoc in my lab.After creating a mold according to the text protocol, pipette about 1.5 milliliters of melted 1%agarose into a 35-millimeter plastic mounting dish. Then, position the plastic mold in the liquid agarose, taking care to avoid trapping air between the mold and the agarose. Place the dish at four degrees Celsius until the agarose hardens.Then, remove the plastic mold from the agarose. Next, add two milliliters of previously prepared mounting medium to the mounting dish, and allow 15 to 30 minutes for the solution to diffuse into the agarose. In the meantime, melt a one-milliliter aliquot of 0.7%low melting point, or LMP, agarose by placing the tube in a 70-degree Celsius heat block for about five minutes.Pipette the LMP agarose up and down to cool it slightly. Then, add 25 microliters of eight milligram per milliliter tricaine and 40 microliters of one molar BDM solutions to the tube. Mix by pipetting up and down.Then, transfer the tube to a 38-degree Celsius heat block to keep the LMP agarose in its liquid state. Transfer the embryos to a separate dish containing two milliliters of mounting medium. Then, when the hearts have stopped beating, transfer the embryos to the mounting dish and use forceps to arrange them in the wells so that they lie at a 25-degree angle, tails pointing toward the deeper part of the well, with the yolk facing up.When the embryos are roughly in place, remove the medium, and embed them in approximately 200 microliters of 0.7%LMP agarose containing tricaine and BDM. Then, readjust the embryo positions, tilting them to the left or right as necessary. Press down on the walls of the indented square to allow excess agarose to overflow to the side areas of the mounting dish.Wait approximately five minutes for the LMP agarose to set, then add mounting medium to the dish. The embryos are now ready to be photoconverted. To carry out photoconversion, on an upright confocal microscope equipped with a 405, 488, and 561-nanometer laser sources, use transmitted white light and an objective lens to locate the embryo's heart.Using the 561-nanometer laser, check for red Kaede fluorescence. Then, use the 488-nanometer laser to visualize the endocardium. Next, on the microscope acquisition software, enter FRAP mode.Then, select approximately 1%laser power for both the 488 and the 561-nanometer lasers. While focusing on the plane of interest, select a region of interest, or ROI. Then, using the 405-nanometer diode laser at 25%laser power, photoconvert the cells, scanning over the ROI three times.Should insufficient Kaede be photoconverted in the ROI, scan the 405-nanometer laser over the area three times again. Return to the TCS SP8 mode on the software, and using the 561 and 488-nanometer lasers sequentially, in Bidirectional mode, acquire a Z-stack. After photoconversion, use a glass pipette to press down slightly just above the head of the embryo to break the LMP agarose.Then, gently suck up the embryo. To wash away the BDM containing medium, eject the embryo from the glass pipette into an 85-millimeter Petri dish containing embryo medium with PTU. Transfer the embryo to a well in a six-well plate containing embryo medium with PTU.During this step, make sure to keep note of which embryo goes into which well, as this is essential to correlate the position of photoconverted cells at later developmental stages. Now that the embryos have been removed from the BDM containing medium, their hearts should start beating again in about five minutes. Return embryos to the dark at 28.5 degrees Celsius to allow them to continue to develop normally.At the desired stage, stop the heart and re-embed the embryos, as demonstrated earlier in this video, with the important difference that the embryos must be treated with BDM in separate, marked dishes to keep track of them. For embryos up to 62 hpf, acquire Z-stacks of the endocardium using 561 and 488 nanometers for red and green fluorescent signals, respectively. For embryos older than 62 hpf, use a multiphoton laser set to 940 nanometers to image green Kaede instead of the 488-nanometer laser.For embryos younger than 48 hpf, it is possible to project the three-dimensional AVC onto a two-dimensional image for analysis. First, threshold the image. Then, erase points that lie outside of the heart.To perform manual segmentation, orient the image on the left to match the image on the right. Segment the side of the heart in which the orange vector passes through, and add points in the direction of the blue vector. Next, interpolate the cross-sections, and project the color intensity onto the surface.Finally, adjust the orientation of the AVC, and project it onto a 2D surface. An example of an embryonic heart just after photoconversion at 48 hpf is shown here. Cytoplasmic Kaede in several cells of the superior side of the AVC has been converted from green to red.In the same embryo at 80 hpf, it's evident that the photoconverted cells have proliferated and have migrated to the inner side of the superior atrioventricular valve. An example of a 36 hpf embryo where the EdCs in the atrium and ventricle have been photoconverted is shown here. The AVC is then projected into two dimensions for easier visualization and analysis and allows one to quantify the distance between the two photoconverted regions.While attempting this procedure, it's important to keep the time the heart is stopped to a minimum to avoid affecting normal development. With practice, photoconversion can be completed within about 30 minutes provided that everything is prepared in advance. After watching this video, you should have a good understanding of how to track endocardial cells after photoconversion in live zebrafish embryo and analyze your data sets.

following-endocardial-tissue-movements-via-cell-photoconversion

Research

JoVE Journal

Developmental Biology

6.4K vues.  Institut de Génétique et de Biologie Moléculaire et Cellulaire. The overall goal of this procedure is to follow endocardial cells during atrioventricular canal and heart valve formation. This method can help to address key question in the field of cardiac development, such as to understand how endocardial cells behave in different types of mutants. Tracking cells during AVC and valve formation is challenging because of the rapid beat of the heart.It makes it difficult to follow cells via traditional time-lapse microscopy. The main advantage of this...