We thank Dr. Jingrong Peng for sharing the Tg (fabp10a: DsRed) transgenic line; Dr. Zilong Wen for sharing the Tg (mpeg1: GFP) transgenic lines; Dr. Koichi Kawakami for providing the pTol2 vector. This work was supported by the National Natural Science Foundation of China (31771594), Guangdong Science and Technology Plan projects (2019A030317001) and the Fundamental Research Funds for the Central Universities (D2191450).

NOTE: All the samples were treated by phenylthiourea(PTU) egg water to inhibit pigment.
1. Generation of Tg (fabp10a:il34) Transgenic Constructs and Fish Injection
<ol>
	<li>Clone the 2.8 kb fabp10a promoter8 and the IL-34 coding regions (ENSDART00000126460.3) of zebrafish into the pTol2 vector to generate the fabp10a-il34 construct. Inject the constructs into one-cell stage Tg (mpeg1: GFP) and WT fish embryos together with the transposase mRNA. Raise the fabp10a-il34 injected WT embryos to adult9 and identify the transgenic founder by in situ hybridization. 
	NOTE: The injection of the Tol2 construct directly into another transgenic could be problematic if the other transgenic line is made with the same transposon system. A general practice would be to make an independent transgenic line and subsequently cross the new line with another reporter line. This ensures that there will be no effects of the new transgenesis on a previously inserted transgene.</li>
</ol>
2. Fluorescent Whole Mount In Situ Hybridization (WISH) Combine with Immunostaining
<ol>
	<li>Sample fixation
	<ol>
		<li>Collect embryos of transient injection or stable IL-34 transgenic line which crossed with Tg (mpeg1: GFP) at desired stages. 
		NOTE: For this case, the embryos were collected at 4 d post fertilization (dpf). (If needed) remove the chorion by syringe.</li>
		<li>Fix the embryos with 4% paraformaldehyde (PFA) overnight at 4 &#176;C or 2 h at room temperature (RT) (about 25 &#176;C).</li>
		<li>Wash the embryos with phosphate buffered saline plus Tween 20 (PBST) 3x 5 min.</li>
		<li>Dehydrate the embryos separately with 50% methanol in PBST (50% Methanol/PBST) and 100% methanol, 1x 5 min each. Then, change to fresh 100% methanol and store at -20 &#176;C (at least 2 h). 
		NOTE: The protocol can be paused here.</li>
	</ol>
	</li>
	<li>Probe hybridization (Day I)
	<ol>
		<li>Rehydrate the embryos in the previous steps with 50% methanol in PBST (50% Methanol/PBST), then wash with PBST 3x 5 min.</li>
		<li>Digest the embryos with proteinase K in PBST at RT (final concentration: 10 &#181;g/mL; 1:2000 in PBST). 
		NOTE: Digestion time depends on the embryos stage: Less than 36 h post fertilization (hpf), no need; 36 hpf-2 dpf embryo, 3-5 min; 2-3 dpf embryo, 10 min; 3-4 dpf embryo, 15 min; 4-5 dpf embryo, 15-20 min; 5-6 dpf embryo, 20-27 min; &#62;6 dpf embryo, 25-30 min at RT (about 25 &#176;C).</li>
		<li>Discard the digestion solution and perform fixation again with 4% PFA, for 20 min at RT.</li>
		<li>Wash the embryos with PBST 2x 10 min.</li>
		<li>Discard the PBST, perform pre-hybridization with heated hybridization buffer (HB buffer) at 65 &#176;C for 5 min, recycle the HB buffer into the original tube.</li>
		<li>Perform pre-hybridization with new heated HB buffer at 65 &#176;C at least 1 h.</li>
		<li>Pre-heat the probe9 (for this case was an il34 probe, 1 ng/mL) at 65 &#176;C at least 10 min. Then recycle the HB buffer into the original tube. Perform hybridization with the pre-heated probe at 65 &#176;C overnight.</li>
	</ol>
	</li>
	<li>Antibody treatment (Day II)
	<ol>
		<li>Pre-heat the 50% formamide/2x saline sodium citrate plus Tween 20 (SSCT), 2x SSCT, 0.2x SSCT at 65 &#176;C.</li>
		<li>Recycle the probe into the original tube and store the probe at -20 &#176;C.</li>
		<li>Wash the embryos separately with 50% formamide/2x SSCT; 2x SSCT; 0.2x SSCT, 3x 20 min or 2x 30 min each at 65 &#176;C.</li>
		<li>Wash the embryos with PBST 3x 5 min.</li>
		<li>Block the samples with 600 &#181;L of blocking buffer (5% filtered fetal bovine serum (FBS) in PBST) for 1 h at RT.</li>
		<li>Add 400 &#181;L of Anti-digoxigenin-HRP antibody solution (1:1,000-1:2,000 in blocking buffer) and incubate the embryos at 4 &#176;C overnight. If signals are weak, use 1:500 dilution of antibody.</li>
	</ol>
	</li>
	<li>Coloring and primary antibody incubating (Day III)
	<ol>
		<li>Remove the antibody; wash the embryos with PBST, 6x 20 min at RT.</li>
		<li>Rinse the sample with 30 &#181;L of 1x Plus Amplification Diluent for 5 min at RT.</li>
		<li>Discard the diluent by pipetting out; dilute Fluorophore Tyramide Stock Solution (Cyanine 3 Plus Amplification Reagent (Cy3) or Cyanine 5 Plus Amplification Reagent (Cy5), for this case Cy3 was used) 1:50 in 1x Plus Amplification Diluent to make the Fluorophore Tyramide Working Solution. Prepare 50-100 &#181;L of working solution for each sample.</li>
		<li>Incubate the sample in the Fluorophore Tyramide Working Solution for 5-15 min in dark at RT. If signals are weak, extend the incubation time to 30 min.</li>
		<li>Stop the reaction by changing the working solution with PBST and examine the signals.</li>
		<li>Wash the embryos with PBST 3x 10 min at RT.</li>
		<li>Incubate the sample with primary antibody at 4 &#176;C overnight. For this case, use the Goat-Anti-GFP antibody as the primary antibody.</li>
	</ol>
	</li>
	<li>Secondary antibody staining (Day IV)
	<ol>
		<li>Wash the embryos with PBST for 4x 30 min.</li>
		<li>Incubate the embryos with secondary antibody at 4 &#176;C overnight. For this case, use Alexa 488-Anti-Goat antibody as the secondary antibody.</li>
	</ol>
	</li>
	<li>Take pictures (Day V)
	<ol>
		<li>Wash the embryos with PBST 3x 10 min at RT.</li>
		<li>Store the embryos in 70% glycerol in dark at 4 &#176;C overnight or -20 &#176;C for longer.</li>
	</ol>
	</li>
</ol>
3. Live Imaging
<ol>
	<li>Sample selecting 
	NOTE: Use the live image to directly observe whether macrophages of Tg (fabp10a: il34; fabp10a: DsRed; mpeg1: GFP) fish would migrate into the liver under IL-34 induction during 3-3.5 dpf. Here the Tg (fabp10a-DsRed) transgenic line is used to label the liver region and make it visible, to facilitate the localization of the liver and to determine whether macrophages migrate into the liver. Before imaging, use a fluorescence microscope to select the DsRed and GFP double positive embryos.</li>
	<li>Fish mounting
	<ol>
		<li>Use a metal bath to heat 1 mL of 1% low melting agarose to above 90 &#176;C to completely melt it.</li>
		<li>After the low melting agarose is cooled to body temperature, add 50 &#181;L of 0.2% tricaine, and uniformly mix tricaine with the agarose.</li>
		<li>Move the anesthetized embryos to a small dish mounted with a cover slide on the bottom, remove the surrounding water, slowly drop the low melting agarose on the embryos, carefully set the position of the fish before the agarose is solidified, keep the liver area close to the cover slide on the bottom of the dish.</li>
		<li>After the low melting agarose is solidified, carefully cover it with another layer of agarose to reinforce it.</li>
		<li>Place the dish on the confocal microscope carrier table, cover the fish with the E2 solution10 with tricaine and start imaging.</li>
	</ol>
	</li>
	<li>Software operation of the confocal microscope
	<ol>
		<li>Open the ZEN black 2.3 software, install the living cell workbench onto the microscope carrier table.</li>
		<li>Click Locate | Incubation | Temperature to set the temperature to 29 &#176;C.</li>
		<li>Place the dish in the center of the living cell workbench, cover the fish with the E2 solution10 with tricaine.</li>
		<li>Click the Acquisition menu, select the required scan mode and lasers in the Smart Setup menu, then select Z-Stack and Position.</li>
		<li>Click the Experiment Designer menu, select Enable Multi Block Experiment, in the first block, to find the sample under the low magnification, then switch to the high magnification, let the observed area in the center of the visual field.</li>
		<li>Set the position and Z-Stack information, select the appropriate laser intensity, scanning layers and imaging speed.</li>
		<li>Create a new block and repeat the above steps. After setting up all blocks, set the appropriate number of loops and start recording (Figure 1).</li>
	</ol>
	</li>
</ol>

<ol>
	<li>Howe, K., 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=The+zebrafish+reference+genome+sequence+and+its+relationship+to+the+human+genome.">The zebrafish reference genome sequence and its relationship to the human genome.</a> Nature. 496 (7446), 498-503 (2013).</li><li>Wang, Y., 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=IL-34+is+a+tissue-restricted+ligand+of+CSF1R+required+for+the+development+of+Langerhans+cells+and+microglia.">IL-34 is a tissue-restricted ligand of CSF1R required for the development of Langerhans cells and microglia.</a> Nature Immunology. 13 (8), 753-760 (2012).</li><li>Lin, H., 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=Discovery+of+a+cytokine+and+its+receptor+by+functional+screening+of+the+extracellular+proteome.">Discovery of a cytokine and its receptor by functional screening of the extracellular proteome.</a> Science. 320 (5877), 807-811 (2008).</li><li>Wei, S., 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=Functional+overlap+but+differential+expression+of+CSF-1+and+IL-34+in+their+CSF-1+receptor-mediated+regulation+of+myeloid+cells.">Functional overlap but differential expression of CSF-1 and IL-34 in their CSF-1 receptor-mediated regulation of myeloid cells.</a> Journal of leukocyte biology. 88 (3), 495-505 (2010).</li><li>Etienne, D., Foucher, S. B. L. P., Norbert Ifrah, P. G. Y. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=IL-34+Induces+the+Differentiation+of+Human+Monocytes+into+Immunosuppressive+Macrophages.+Antagonistic+Effects+of+GM-CSF+and+IFNc.">IL-34 Induces the Differentiation of Human Monocytes into Immunosuppressive Macrophages. Antagonistic Effects of GM-CSF and IFNc.</a> PLoS One. 8 (2), e56045 (2013).</li><li>Segaliny, A. I., 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=Syndecan-1+regulates+the+biological+activities+of+interleukin-34.">Syndecan-1 regulates the biological activities of interleukin-34.</a> Biochimica et Biophysica Acta. 1853 (5), 1010-1021 (2015).</li><li>Zhou, S. L., 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=miR-28-5p-IL-34-macrophage+feedback+loop+modulates+hepatocellular+carcinoma+metastasis.">miR-28-5p-IL-34-macrophage feedback loop modulates hepatocellular carcinoma metastasis.</a> Hepatology. 63 (5), 1560-1575 (2016).</li><li>Gordon, J. I., 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=Tissue+specific+expression+and+developmental+regulation+of+two+genes+coding+for+rat+fatty+acid+binding+proteins.">Tissue specific expression and developmental regulation of two genes coding for rat fatty acid binding proteins.</a> Journal of Biological Chemistry. 260 (4), 1995-1998 (1985).</li><li>Westerfield, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> The Zebrafish Book: A Guide for the Laboratory Use of Zebrafish (Danio rerio). , (2000).</li><li>N&#252;sslein-Volhard, C., Dahm, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Zebrafish: a practical approach. , (2002).</li><li>Jiang, Y., Chen, J., Yen, K., Xu, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ectopically+Expressed+IL-34+Can+Efficiently+Induce+Macrophage+Migration+to+the+Liver+in+Zebrafish.">Ectopically Expressed IL-34 Can Efficiently Induce Macrophage Migration to the Liver in Zebrafish.</a> Zebrafish. 16 (2), 165-170 (2019).</li></ol>

The authors have nothing to disclose.

The protocol described here allows us to investigate the function of a chemokine on the behavior of macrophagein vivo and the procedure requires some technical expertise. In summary, there are several critical steps to avoid complications in the protocol: 1) select a suitable transgenic line which shows specific and strong transgenic signal to label the cell of interest; 2) select an appropriate tissue which is accessible for imaging and transgenic gene overexpression; 3) make a sensitive and specific RNA probe; 4) selec...

Zebrafish is a small tropical hard-bones freshwater fish originated in India. Regarding the gene conservation, zebrafish have a similarity of 87% to the human1. It can provide us insights on related subjects of human by studying the gene regulation, protein function and cell behavior such as migration, proliferation et.al in zebrafish. Zebrafish embryo can be used to observe the development of early embryos at different stages after inhibiting pigment. Meanwhile, it takes only three months for zebrafish to develop into sexual maturity, then the zebrafish can produce hundreds of eggs every 4 days. Mini-size, simple breeding, strong reproductive capacity, these advantages make zebrafish culture very space-saving, conducive to large-scale culture. The traditional mammalian model mouse has a higher maintenance costs than zebrafish, therefore limiting the scale of mouse raising. In the aspect of early embryo development, mouse embryo is difficult to observe in live condition due to the characteristics of mouse embryo development in the mother womb. On the contrary, zebrafish embryos develop externally and are transparent, therefore they are easy to observe under a microscope. Furthermore, zebrafish is very easy to construct a variety of transgenic lines for related gene function research. Currently, various zebrafish transgenic lines are available to label different types of cells. It is very convenient now to construct transgenic lines to overexpress chemokines in specific locations and study the chemokines function on cell behavior in zebrafish.
Here, we provided a workflow to use zebrafish transgenic line to investigate the function of IL-34 on macrophage behavior in vivo2,3,4,5,6,7. Firstly, we constructed a liver-specific overexpression plasmid of the gene il34 and injected the plasmid into one-cell stage Tg (mpeg1: GFP) fish embryos which specifically labeled the macrophages by fluorescent protein GFP. Then, we used whole mount fluorescent in situ hybridization and immunostaining to detect the pattern of the il34 expression and the number or location of macrophages. The injected WT embryos were raised to generate a stable transgenic line. In these steps, we established and validated the cytokine-producing line and visually assessed the effects that can be seen on macrophage distribution. Finally, to investigate macrophage behavior in response to the cytokine, we used confocal live imaging to directly observe the macrophage migration to confirm the function of il34 on the macrophage migration in vivo.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Antibody</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Alexa 488-Anti-Goat antibody</td>
			<td>Invitrogen</td>
			<td>A11055</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti-Digoxigenin-HRP&#160;</td>
			<td>perkinelmer</td>
			<td>NEF832001EA</td>
			<td></td>
		</tr>
		<tr>
			<td>Goat-Anti-GFP antibody</td>
			<td>Abcam</td>
			<td>ab6658</td>
			<td></td>
		</tr>
		<tr>
			<td>Reagent</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>CaCl2&#183; 2H2O</td>
			<td>Sigma</td>
			<td>21097</td>
			<td></td>
		</tr>
		<tr>
			<td>Cyanine 3 Plus Amplification Reagent</td>
			<td>perkinelmer</td>
			<td>NEL745001KT</td>
			<td></td>
		</tr>
		<tr>
			<td>E2 solution</td>
			<td></td>
			<td></td>
			<td>15 mM&#160; NaCl +0.5 mM KCl +1.0 mM MgSO4+150 &#181;M&#160; KH2PO4 + 50 &#181;M&#160; Na2HPO4 +1.0 mM CaCl2 + 0.7 mM NaHCO3&#160;</td>
		</tr>
		<tr>
			<td>Fetal Bovine Serum(FBS)</td>
			<td>Life</td>
			<td>10099-133</td>
			<td></td>
		</tr>
		<tr>
			<td>formamide</td>
			<td>Diamond</td>
			<td>A100314</td>
			<td></td>
		</tr>
		<tr>
			<td>glycerol&#160;</td>
			<td>Sigma</td>
			<td>V900860</td>
			<td></td>
		</tr>
		<tr>
			<td>heparin sodium</td>
			<td>Sigma</td>
			<td>H3149</td>
			<td></td>
		</tr>
		<tr>
			<td>hybridization buffer(HB)</td>
			<td></td>
			<td></td>
			<td>50% formamide+ 5&#215;SSC+9 mM sodium citrate+50 &#956;g/ml heparin sodium+ 500 &#956;g/ml tRNA+ 0.1% Tween20</td>
		</tr>
		<tr>
			<td>KCl</td>
			<td>Sigma</td>
			<td>P5405</td>
			<td></td>
		</tr>
		<tr>
			<td>KH2PO4</td>
			<td>Sigma</td>
			<td>P5655</td>
			<td></td>
		</tr>
		<tr>
			<td>low melting agarose</td>
			<td>Sigma</td>
			<td>A9414</td>
			<td></td>
		</tr>
		<tr>
			<td>methanol</td>
			<td>GHTECH</td>
			<td>1.17112.023</td>
			<td></td>
		</tr>
		<tr>
			<td>methylene blue&#160;</td>
			<td>Sigma</td>
			<td>M9140</td>
			<td></td>
		</tr>
		<tr>
			<td>MgSO4</td>
			<td>Sigma</td>
			<td>M2643</td>
			<td></td>
		</tr>
		<tr>
			<td>Na2HPO4</td>
			<td>Sigma</td>
			<td>S5136</td>
			<td></td>
		</tr>
		<tr>
			<td>NaCl</td>
			<td>Sigma</td>
			<td>S5886</td>
			<td></td>
		</tr>
		<tr>
			<td>NaHCO3&#160;</td>
			<td>Sigma</td>
			<td>S5761</td>
			<td></td>
		</tr>
		<tr>
			<td>paraformaldehyde(PFA)</td>
			<td>Sigma</td>
			<td>158127</td>
			<td>Suspend 16 g of PFA in 400 ml of 1x PBS, heat at 60 &#176;C&#160; to dissolve about 30 min. This solution can be prepared in advance and stored at -4 &#176;C. Caution. Manipulate with mask.</td>
		</tr>
		<tr>
			<td>10&#215;PBS</td>
			<td></td>
			<td></td>
			<td>14.2 g Na2HPO4+80 g NaCl+2 g KCl+ 2.4 g KH2PO4 in 1L ddH2O</td>
		</tr>
		<tr>
			<td>phenylthiourea(PTU)</td>
			<td>Sigma</td>
			<td>P7629</td>
			<td></td>
		</tr>
		<tr>
			<td>1&#215;Plus Amplification Diluent</td>
			<td>perkinelmer</td>
			<td>NEL745001KT</td>
			<td></td>
		</tr>
		<tr>
			<td>Proteinase K&#160;</td>
			<td>Fermentas</td>
			<td>E00492</td>
			<td></td>
		</tr>
		<tr>
			<td>20&#215;Saline sodium citrate(SSC)</td>
			<td></td>
			<td></td>
			<td>175.3 g NaCl+ 88.2 g sodium citrate in 1 L ddH2O, PH 7.0</td>
		</tr>
		<tr>
			<td>sodium citrate</td>
			<td>Sigma</td>
			<td>A5040</td>
			<td></td>
		</tr>
		<tr>
			<td>tricaine</td>
			<td>Sigma</td>
			<td>E10521</td>
			<td></td>
		</tr>
		<tr>
			<td>tRNA&#160;</td>
			<td>Sigma</td>
			<td>R6625</td>
			<td></td>
		</tr>
		<tr>
			<td>Tween20</td>
			<td>Sigma</td>
			<td>P2287</td>
			<td></td>
		</tr>
		<tr>
			<td>Plasmid</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>pBLK-fabp10a-il34-sv40</td>
			<td></td>
			<td></td>
			<td>For Tg (fab10a:il34) transgenic line generation</td>
		</tr>
		<tr>
			<td>pBSK-il34</td>
			<td></td>
			<td></td>
			<td>For il34 probe preparation</td>
		</tr>
		<tr>
			<td>Fish</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Tg (mpeg1: GFP)</td>
			<td></td>
			<td></td>
			<td>Label macrophages with GFP</td>
		</tr>
		<tr>
			<td>Tg (fabp10a: DsRed)</td>
			<td></td>
			<td></td>
			<td>Label liver cells with DsRed</td>
		</tr>
		<tr>
			<td>Tg (fab10a:il34)</td>
			<td></td>
			<td></td>
			<td>Over-expression IL-34 in liver cells</td>
		</tr>
	</tbody>
</table>

an ectopic chemokine expression model for testing macrophage recruitment in vivo

Zebrafish are widely used in basic and biomedical research. Many zebrafish transgenic lines are currently available to label various types of cells. Owing to the transparent embryonic body of zebrafish, it is convenient for us to study the effect of one chemokine on the behavior of a certain type of cells in vivo. Here we provided a workflow to investigate the function of a chemokine on macrophage migration in vivo. We constructed a tissue-specific overexpression plasmid to overexpress IL-34 and injected the plasmid into one-cell stage transgenic fish embryos whose macrophages were specifically labeled by a fluorescent protein. We then used whole mount fluorescent in situ hybridization and immunostaining to detect the pattern of the chemokine expression and the number or location of macrophages. The injected WT embryos were raised to generate a stable transgenic line. Finally, we used confocal live imaging to directly observe macrophage behavior in the stable transgenic fish to study the function of IL-34 on macrophages in vivo.

The steps involved in the protocol of zebrafish are illustrated in Figure 2. First, we generated the pBLK-fabp10a-il34-sv40 construct in which il34 was driven by the fabp10a promoter (Figure 2). The construct was microinjected into one-cell stage Tg (mpeg1: GFP) zebrafish embryos which can label macrophages with GFP and WT embryos which were raised to adults to generate transgenic stable line (...

Watch this Scientific Journal Video about An Ectopic Chemokine Expression Model for Testing Macrophage Recruitment In Vivo at JoVE.com

An Ectopic Chemokine Expression Model for Testing Macrophage Recruitment In Vivo

To test the effect of a chemokine on macrophage recruitment in vivo, the whole mount in situ hybridization was used to detect the ectopic expression of the chemokine, and immunostaining was used to label macrophages. Live imaging was used for real-time observation of macrophage migration.

Zebrafish are widely used in basic and biomedical research. Many zebrafish transgenic lines are currently available to label various types of cells. Owing ...

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5.2K Views.  Southern Medical University. To test the effect of a chemokine on macrophage recruitment in vivo, the whole mount in situ hybridization was used to detect the ectopic expression of the chemokine, and immunostaining was used to label macrophages. Live imaging was used for real-time observation of macrophage migration.

Video: An Ectopic Chemokine Expression Model for Testing Macrophage Recruitment In Vivo

Live Imaging of Innate Immune and Preneoplastic Cell Interactions Using an Inducible Gal4/UAS Expression System in Larval Zebrafish Skin

Here we describe a method to conditionally induce epithelial cell transformation by the use of the 4-Hydroxytamoxifen (4-OHT) inducible KalTA4-ERT2/UAS expression system1 in zebrafish larvae, and the subsequent live imaging of innate immune cell interaction with HRASG12V expressing skin cells. The KalTA4-ERT2/UAS system is both inducible and reversible which allows us to induce cell transformation with precise temporal/spatial resolution in vivo. This provides us with a unique opportunity to live image how individual preneoplastic cells interact with host tissues as soon as they emerge, then follow their progression as well as regression. Recent studies in zebrafish larvae have shown a trophic function of innate immunity in the earliest stages of tumorigenesis2,3. Our inducible system would allow us to live image the onset of cellular transformation and the subsequent host response, which may lead to important insights on the underlying mechanisms for the regulation of oncogenic trophic inflammatory responses. We also discuss how one might adapt our protocol to achieve temporal and spatial control of ectopic gene expression in any tissue of interest.

Studying the earliest events of preneoplastic cell progression and innate immune cell interaction is pivotal to understand and treat cancer. Here we describe a method to conditionally induce epithelial cell transformations and the subsequent live imaging of innate immune cell interaction with HRASG12V expressing skin cells in zebrafish larvae.

Here we describe a method to conditionally induce epithelial cell transformation by the use of the 4-Hydroxytamoxifen (4-OHT) inducible KalTA4-ERT2/UAS ...

An Optogenetic Approach for Assessing Formation of Neuronal Connections in a Co-culture System

Here we describe a protocol to generate a co-culture consisting of 2 different neuronal populations. Induced pluripotent stem cells (iPSCs) are reprogrammed from human fibroblasts using episomal vectors. Colonies of iPSCs can be observed 30 days after initiation of fibroblast reprogramming. Pluripotent colonies are manually picked and grown in neural induction medium to permit differentiation into neural progenitor cells (NPCs). iPSCs rapidly convert into neuroepithelial cells within 1 week and retain the capability to self-renew when maintained at a high culture density. Primary mouse NPCs are differentiated into astrocytes by exposure to a serum-containing medium for 7 days and form a monolayer upon which embryonic day 18 (E18) rat cortical neurons (transfected with channelrhodopsin-2 (ChR2)) are added. Human NPCs tagged with the fluorescent protein, tandem dimer Tomato (tdTomato), are then seeded onto the astrocyte/cortical neuron culture the following day and allowed to differentiate for 28 to 35 days. We demonstrate that this system forms synaptic connections between iPSC-derived neurons and cortical neurons, evident from an increase in the frequency of synaptic currents upon photostimulation of the cortical neurons. This co-culture system provides a novel platform for evaluating the ability of iPSC-derived neurons to create synaptic connections with other neuronal populations.

A protocol to generate a co-culture system consisting of neurons derived from induced pluripotent stem cells (iPSCs), primary cortical neurons and astrocytes is described. This co-culture system allows detection of the formation of synaptic contacts and circuits between new, iPSC-derived neurons and pre-existing cortical neurons expressing channelrhodopsin-2.

Here we describe a protocol to generate a co-culture consisting of 2 different neuronal populations. Induced pluripotent stem cells (iPSCs) are ...

Development of an Ethanol-induced Fibrotic Liver Model in Zebrafish to Study Progenitor Cell-mediated Hepatocyte Regeneration

Sustained liver fibrosis with continuation of extracellular matrix (ECM) protein build-up results in the loss of cellular competency of the liver, leading to cirrhosis with hepatocellular dysfunction. Among multiple hepatic insults, alcohol abuse can lead to significant health problems including liver failure and hepatocellular carcinoma. Nonetheless, the identity of endogenous cellular sources that regenerate hepatocytes in response to alcohol has not been properly investigated. Moreover, few studies have effectively modeled hepatocyte regeneration upon alcohol-induced injury. We recently reported on establishing an ethanol (EtOH)-induced fibrotic liver model in zebrafish in which hepatic progenitor cells (HPCs) gave rise to hepatocytes upon near-complete hepatocyte loss in the presence of fibrogenic stimulus. Furthermore, through chemical screens using this model, we identified multiple small molecules that enhance hepatocyte regeneration. Here we describe in detail the procedures to develop an EtOH-induced fibrotic liver model and to perform chemical screens using this model in zebrafish. This protocol will be a critical tool to delineate the molecular and cellular mechanisms of how hepatocyte regenerates in the fibrotic liver. Furthermore, these methods will facilitate potential discovery of novel therapeutic strategies for chronic liver disease in vivo.

Sustained fibrosis with deposition of excessive extracellular matrix proteins leads to cirrhosis. Alcohol abuse is one of the main causes of severe liver disease. We established an ethanol-induced zebrafish fibrotic liver model to study the mechanisms and strategies of promoting hepatocyte regeneration upon alcohol-induced injury.

Sustained liver fibrosis with continuation of extracellular matrix (ECM) protein build-up results in the loss of cellular competency of the liver, leading ...

Drug Treatment and In Vivo Imaging of Osteoblast-Osteoclast Interactions in a Medaka Fish Osteoporosis Model

Bone-forming osteoblasts interact with bone-resorbing osteoclasts to coordinate the turnover of bone matrix and to control skeletal homeostasis. Medaka and zebrafish larvae are widely used to analyze the behavior of bone cells during bone formation, degeneration, and repair. Their optical clarity allows the visualization of fluorescently labeled bone cells and fluorescent dyes bound to the mineralized skeletal matrix. Our lab has generated transgenic medaka fish that express the osteoclast-inducing factor Receptor Activator of Nuclear-factor &#954;B Ligand (RANKL) under the control of a heat&#160;shock-inducible promoter. Ectopic expression of RANKL results in the excess formation of activated osteoclasts, which can be visualized in reporter lines with nlGFP expression under the control of the cathepsin K (ctsk) promoter. RANKL induction and ectopic osteoclast formation leads to severe osteoporosis-like phenotypes. Compound transgenic medaka lines that express ctsk:nlGFP in osteoclasts, as well as mCherry under the control of the osterix (osx) promoter in premature osteoblasts, can be used to study the interaction of both cell types. This facilitates the in vivo observation of cellular behavior under conditions of bone degeneration and repair. Here, we describe the use of this system to test a drug commonly used in human osteoporosis therapy and describe a protocol for live imaging. The medaka model complements studies in cell culture and mice, and offers a novel system for the in vivo analysis of drug action in the skeletal system.

Drug Treatment and In Vivo Imaging of Osteoblast-Osteoclast Interactions in a Medaka Fish Osteoporosis Model

Small laboratory fish have become popular models for bone research on the mechanisms underlying human bone disorders and for the screening of bone-modulating drugs. In this report, we describe a protocol to assess the effect of alendronate on bone cells in medaka larvae with osteoporotic lesions.

Bone-forming osteoblasts interact with bone-resorbing osteoclasts to coordinate the turnover of bone matrix and to control skeletal homeostasis. Medaka ...

An Ex Vivo Method for Time-Lapse Imaging of Cultured Rat Mesenteric Microvascular Networks

Angiogenesis, defined as the growth of new blood vessels from pre-existing vessels, involves endothelial cells, pericytes, smooth muscle cells, immune cells, and the coordination with lymphatic vessels and nerves. The multi-cell, multi-system interactions necessitate the investigation of angiogenesis in a physiologically relevant environment. Thus, while the use of in vitro cell-culture models have provided mechanistic insights, a common critique is that they do not recapitulate the complexity associated with a microvascular network. The objective of this protocol is to demonstrate the ability to make time-lapse comparisons of intact microvascular networks before and after angiogenesis stimulation in cultured rat mesentery tissues. Cultured tissues contain microvascular networks that maintain their hierarchy. Immunohistochemical labeling confirms the presence of endothelial cells, smooth muscle cells, pericytes, blood vessels and lymphatic vessels. In addition, labeling tissues with BSI-lectin enables time-lapse comparison of local network regions before and after serum or growth factor stimulation characterized by increased capillary sprouting and vessel density. In comparison to common cell culture models, this method provides a tool for endothelial cell lineage studies and tissue specific angiogenic drug evaluation in physiologically relevant microvascular networks.

An Ex Vivo Method for Time-Lapse Imaging of Cultured Rat Mesenteric Microvascular Networks

Angiogenesis involves multi-cell, multi-system interactions that need to be investigated in a physiologically relevant environment. The objective of this study is to demonstrate the ability of the rat mesentery culture model to make time-lapse comparisons of intact microvascular networks during angiogenesis.

Angiogenesis, defined as the growth of new blood vessels from pre-existing vessels, involves endothelial cells, pericytes, smooth muscle cells, immune ...

In Vivo Imaging of Transgenic Gene Expression in Individual Retinal Progenitors in Chimeric Zebrafish Embryos to Study Cell Nonautonomous Influences

The genetic and technical strengths have made the zebrafish vertebrate a key model organism in which the consequences of gene manipulations can be traced in vivo throughout the rapid developmental period. Multiple processes can be studied including cell proliferation, gene expression, cell migration and morphogenesis. Importantly, the generation of chimeras through transplantations can be easily performed, allowing mosaic labeling and tracking of individual cells under the influence of the host environment. For example, by combining functional gene manipulations of the host embryo (e.g., through morpholino microinjection) and live imaging, the effects of extrinsic, cell nonautonomous signals (provided by the genetically modified environment) on individual transplanted donor cells can be assessed. Here we demonstrate how this approach is used to compare the onset of fluorescent transgene expression as a proxy for the timing of cell fate determination in different genetic host environments.
In this article, we provide the protocol for microinjecting zebrafish embryos to mark donor cells and to cause gene knockdown in host embryos, a description of the transplantation technique used to generate chimeric embryos, and the protocol for preparing and running in vivo time-lapse confocal imaging of multiple embryos. In particular, performing multiposition imaging is crucial when comparing timing of events such as the onset of gene expression. This requires data collection from multiple control and experimental embryos processed simultaneously. Such an approach can easily be extended for studies of extrinsic influences in any organ or tissue of choice accessible to live imaging, provided that transplantations can be targeted easily according to established embryonic fate maps.

In Vivo Imaging of Transgenic Gene Expression in Individual Retinal Progenitors in Chimeric Zebrafish Embryos to Study Cell Nonautonomous Influences

Live tracking of individual WT retinal progenitors in distinct genetic backgrounds allows for the assessment of the contribution of cell non-autonomous signaling during neurogenesis. Here, a combination of gene knockdown, chimera generation via embryo transplantation and in vivo time-lapse confocal imaging was utilized for this purpose.

The genetic and technical strengths have made the zebrafish vertebrate a key model organism in which the consequences of gene manipulations can be traced ...

Establishment of Larval Zebrafish as an Animal Model to Investigate Trypanosoma cruzi Motility In Vivo

Chagas disease is a parasitic infection caused by Trypanosoma cruzi, whose motility is not only important for localization, but also for cellular binding and invasion. Current animal models for the study of T. cruzi allow limited observation of parasites in vivo, representing a challenge for understanding parasite behavior during the initial stages of infection in humans. This protozoan has a flagellar stage in both vector and mammalian hosts, but there are no studies describing its motility in vivo.The objective of this project was to establish a live vertebrate zebrafish model to evaluate T. cruzi motility in the vascular system. Transparent zebrafish larvae were injected with fluorescently labeled trypomastigotes and observed using light sheet fluorescence microscopy (LSFM), a noninvasive method to visualize live organisms with high optical resolution. The parasites could be visualized for extended periods of time due to this technique&#39;s relatively low risk of photodamage compared to confocal or epifluorescence microscopy. T. cruzi parasites were observed traveling in the circulatory system of live zebrafish in different-sized blood vessels and the yolk. They could also be seen attached to the yolk sac wall and to the atrioventricular valve despite the strong forces associated with heart contractions. LSFM of T. cruzi-inoculated zebrafish larvae is a valuable method that can be used to visualize circulating parasites and evaluate their tropism, migration patterns, and motility in the dynamic environment of the cardiovascular system of a live animal.

Establishment of Larval Zebrafish as an Animal Model to Investigate Trypanosoma cruzi Motility In Vivo

In this protocol, fluorescently labeled T. cruzi&#160;were injected into transparent zebrafish larvae, and parasite motility was observed in vivo using light sheet fluorescence microscopy.

Chagas disease is a parasitic infection caused by Trypanosoma cruzi, whose motility is not only important for localization, but also for cellular binding ...

Application of RNAi and Heat-shock-induced Transcription Factor Expression to Reprogram Germ Cells to Neurons in C. elegans

Studying the cell biological processes during converting the identities of specific cell types provides important insights into mechanism that maintain and protect cellular identities. The conversion of germ cells into specific neurons in the nematode Caenorhabditis elegans (C. elegans) is a powerful tool for performing genetic screens in order to dissect regulatory pathways that safeguard established cell identities. Reprogramming of germ cells to a specific type of neurons termed ASE requires transgenic animals that allow broad over-expression of the Zn-finger transcription factor (TF) CHE-1. Endogenous CHE-1 is expressed exclusively in two head neurons and is required to specify the glutamatergic ASE neurons fate, which can easily be visualized by the gcy-5prom::gfp reporter. A trans gene containing the heat-shock promoter-driven che-1 gene expression construct allows broad mis-expression of CHE-1 in the entire animal upon heat-shock treatment. The combination of RNAi against the chromatin-regulating factor LIN-53 and heat-shock-induced che-1 over-expression leads to reprogramming of germ cell into ASE neuron-like cells. We describe here the specific RNAi procedure and appropriate conditions for heat-shock treatment of transgenic animals in order to successfully induce germ cell to neuron conversion.

Application of RNAi and Heat-shock-induced Transcription Factor Expression to Reprogram Germ Cells to Neurons in C. elegans

This protocol describes how to study cellular processes during cell fate conversion in Caenorhabditis elegans in vivo. Using transgenic animals, allowing heat-shock promoter-driven overexpression of the neuron fate-inducing transcription factor CHE-1 and RNAi-mediated depletion of the chromatin-regulating factor LIN-53 germ cell to neuron reprogramming can be observed in vivo.

Studying the cell biological processes during converting the identities of specific cell types provides important insights into mechanism that maintain ...

Culturing of Retinal Pigment Epithelial Cells on an Ex Vivo Model of Aged Human Bruch's Membrane

Aside from vitamins and antioxidants recommended by the Age-Related Eye Disease Study, there is no effective therapy for &#34;dry,&#34;&#160;or atrophic age-related macular degeneration (AMD) which represents 90% of the cases. Therapies are needed to slow or retard the development of geographic atrophy (GA), and understanding Bruch&#39;s membrane pathology is part of this process. Alterations in human Bruch&#39;s membrane precede the progression of AMD by contributing to the damage of retinal pigment epithelial (RPE) cells. Given the lack of sufficient animal models to study AMD, ex vivo models of aged human Bruch&#39;s membrane serve as a useful tool to study the behavior of RPE cells from immortalized and primary cell lines as well as RPE lines derived from induced pluripotent stem cells (iPSCs). Here, we present a detailed method that allows one to determine the effects of RPE cell behavior seeded on harvested human Bruch&#39;s membrane explants from human donors, including attachment, apoptosis and proliferation, ability to phagocytize photoreceptor outer segments, establishment of polarity, and gene expression. This assay provides an ex vivo model of aged Bruch&#39;s membrane to assess the functional characteristics of RPE cells when seeded on aged/compromised extracellular matrix.

Culturing of Retinal Pigment Epithelial Cells on an Ex Vivo Model of Aged Human Bruch&#039;s Membrane

The goal of this protocol is to demonstrate the culturing of retinal pigment epithelial (RPE) cells on aged and/or diseased human Bruch&#39;s membrane. This method is suitable to study RPE cell behavior on a compromised extracellular matrix.

Aside from vitamins and antioxidants recommended by the Age-Related Eye Disease Study, there is no effective therapy for &#34;dry,&#34;&#160;or atrophic ...

An In Vitro Model of a Parallel-Plate Perfusion System to Study Bacterial Adherence to Graft Tissues

Various valved conduits and stent-mounted valves are used for right ventricular outflow tract (RVOT) valve replacement in patients with congenital heart disease. When using prosthetic materials however, these grafts are susceptible to bacterial infections and various host responses.
Identification of bacterial and host factors that play a vital role in endovascular adherence of microorganisms is of importance to better understand the pathophysiology of the onset of infections such as infective endocarditis (IE) and to develop preventive strategies. Therefore, the development of competent models to investigate bacterial adhesion under physiological shear conditions is necessary. Here, we describe the use of a newly designed in vitro perfusion chamber based on parallel plates that allows the study of bacterial adherence to different components of graft tissues such as exposed extracellular matrix, endothelial cells and inert areas. This method combined with colony-forming unit (CFU) counting is adequate to evaluate the propensity of graft materials towards bacterial adhesion under flow. Further on, the flow chamber system might be used to investigate the role of blood components in bacterial adhesion under shear conditions. We demonstrated that the source of tissue, their surface morphology and bacterial species specificity are not the major determining factors in bacterial adherence to graft tissues by using our in-house designed in vitro perfusion model.

An In Vitro Model of a Parallel-Plate Perfusion System to Study Bacterial Adherence to Graft Tissues

We describe an in-house designed in vitro flow chamber model, which allows the investigation of bacterial adherence to graft tissues.

Various valved conduits and stent-mounted valves are used for right ventricular outflow tract (RVOT) valve replacement in patients with congenital heart ...