We thank T. Fritsch, A. Wolf-Asseburg, I. Linde and S.-M. Tokarski for excellent animal care and technical support. We are grateful to all members of the K&#246;ster lab for intense and helpful discussions. We gratefully acknowledge funding by the Deutsche Forschungsgemeinschaft (KO 1949/5-1) and the Federal State of Lower Saxony, Nieders&#228;chsisches Vorab (VWZN2889).

<ol>
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The authors have nothing to disclose.

Here, we present two different protocols to culture primary cells from either 2 dpf zebrafish embryos or adult zebrafish brain.
The preparation of primary cell cultures from 2 dpf zebrafish is relatively easy to perform for anyone with experience in basic cell culture techniques. However, to obtain good and reproducible results, a sufficient number of embryos as starting material is crucial (100 is the minimum). During the raising of the embryos, all possible sources of contamination must be avoided to keep the amount of germs and parasites as low as possible. Most critical is the incubation of the embryos in ethanol &#8212; this step needs to be long enough to ensure thorough sterilization, but not too long either since ethanol is an organic solvent that damages cells and tissue.
Timing is also essential during the enzymatic dissociation of brain tissue or 2 dpf zebrafish embryos. The incubation time shall not be exceeded and enzyme-containing medium shall be removed quickly once complete dissociation to single cell stage is accomplished. Nevertheless, Type 2 collagenase does not damage the cell membrane and it is not as strongly inhibited by FBS, as trypsin33. Thanks to these properties, we were able to perform the dissociation in the presence of FBS as an essential supplement supporting cell viability and reducing cell damage, resulting in higher yield and viability of delicate cell types.
As shown by our representative results, distinct cell types can be either identified by morphology or by the expression of cell type-specific transgenes encoding for fluorescent reporters. The latter is very convenient when performing live cell imaging of specific cell populations19. However, we highly recommend to verify the expression pattern of the respective enhancer in 2 dpf embryos by fluorescence microscopy to ensure consistent results.
To allow for the visualization of subcellular structures in embryonic zebrafish primary cells, we established an electroporation protocol to transfect plasmid DNA encoding for a selection of fluorescent organelle markers. The rate of cells transfected by this method is relatively low but reliable and provides sufficient cell numbers for live cell imaging19. For a successful transfection, a critical step is the correct determination of the number of cells in suspension. In average, 106 cells can be obtained from about 90 2 dpf embryos, but accurate cell counting prior electroporation is mandatory19. However, compared to common mammalian cell lines such as Cos-7 or HeLa, primary cells from 2 dpf zebrafish embryos are very diverse in size, but quite small in average (especially neurons), which can make counting in a Neubauer chamber relatively difficult. The same is true for subsequent imaging applications. To satisfactorily visualize subcellular structures in those small zebrafish cells, an advanced fluorescence microscope with high resolution is required, preferably a confocal laser scanning microscope.
The preparation of primary cells from adult zebrafish brain is more advanced since it requires training in dissecting the animal and extracting the brain tissue14. In addition, sterile conditions need to be maintained already outside the sterile workbench to not contaminate the extracted brain. However, the subsequent steps regarding dissociation and plating are comparable to the first protocol and may be also applied to other tissues of adult fish such as muscle or liver.
For both protocols, the main limitation is the restricted viability of difficult to cultivate cell types in culture, like neurons. After 3 dap using standard conditions, the density of embryonic zebrafish primary cells is strongly reduced thus limiting the time span for imaging experiments19. Mostly fiboblast-like cells survive in the absence of specifically tailored expedients.
To improve the survival rate of the culture in its complexity of cell types, we successfully tested Leibovitz&#39;s L-15 medium. Further we supplemented it with the neuron-promoting additive B-27 for neuronal specific culture. Neuronal cells have been observed to differentiate in cell culture and to survive for several days, when derived from whole embryos (Figure 2F-I) as well as from adult brain (Figure 4E). In addition, the plating of primary cells at high densities (e.g., 0.25 x 106 cells per 100 mm2) improves cell viability in contrast to low densities (G. Russo, preliminary results).
Beside the use of specific culture media and supplements, we reported how the use of different substrates has a direct impact on the variety of cell types which constitute the final culture and can be used as selective parameter to promote the growth of a subset of cell types. Tissue culture-treated plastic compared to poly-L-lysine coating seems to strongly facilitate fibroblast-like cell adhesion and proliferation (Figure 1E, F). At the same time, the numerous cell types that depend on support cells and specific adhesion molecules (like neurons) do not properly adhere, grow, or differentiate on treated plastic, but prefer specific adhesive support. We therefore recommend, when it is not intended to obtain a fibroblast- or epithelial-like culture33, to use poly-L-lysine or other cell-specific substrates for coating cell culture dishes.
We consider our protocol a starting point for the use of primary cell culture as a complement to zebrafish in vivo studies, which can be further developed and adapted to the cultivation of specific cell types and used for many diversified applications.

The zebrafish (Danio rerio, D. rerio) is a popular model vertebrate for numerous fields of basic and biomedical research1. Zebrafish embryos develop rapidly ex utero, are transparent, and fit under a microscope, thus providing excellent prerequisites for studying vertebrate development in a living organism. Due to the genetic tractability of zebrafish2, many stable transgenic reporter lines with cell type-specific expression of various fluorescent markers have been established allowing for the observation of specific cell populations. The zebrafish community offers a broad variety of so-called Gal4-driver lines which carry a transgene expressing the synthetic Kal4TA4 (or the KalTA3-equivalent GalFF) gene with the Gal4-DNA-binding domain of yeast fused to viral transcriptional activation domains under the control of cell type-specific enhancers. These driver lines are crossed to effector lines which carry transgenes consisting of a defined upstream activating sequence (UAS) fused to a reporter gene. The Kal4TA4 protein binds to the UAS element, thus activating the cell type-selective expression of the reporter gene3,4. This approach allows for highly diverse combinatorial studies of almost all available enhancer and reporter elements in double-transgenic animals.
However, in-depth live imaging with focus on individual cells or their subcellular contents is limited in a whole and constantly changing embryo. To address specific cell biological questions with highest resolution, the use of cell cultures is often preferable. Some cell lines of zebrafish exist, but they are considered as heavily selected5,6,7 and their propagation is often time-consuming. Furthermore, all the available cell lines are fibroblast derived, limiting experiments using cell culture to one type of cells. Therefore, we established both an efficient and easy-to-use protocol to prepare primary cells directly from zebrafish embryos and adult zebrafish brain, together with approaches to increase the longevity of the culture and to broaden the diversity of cultivated cell types. In addition, we present a procedure to transfect embryonic primary cells with expression constructs for fluorescent organelle markers. Thus, cellular morphologies and subcellular structures can be analyzed with high spatial and temporal resolution in distinct cell types which retain their key features.

<table>
	<tbody>
		<tr>
			<td>Fish lines</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>AB (wild-type)</td>
			<td></td>
			<td></td>
			<td>established by Streisinger and colleagues, available from the Zebrafish International Resource Center (ZIRC)</td>
		</tr>
		<tr>
			<td>Tg(ptf1a:eGFP)jh1</td>
			<td></td>
			<td></td>
			<td>stable transgenic line in which the enhancer of the zebrafish gene ptf1a drives expression of the fluorescent protein EGFP (Parsons et al., 2007)</td>
		</tr>
		<tr>
			<td>Tg(XITubb:DsRed)zf148</td>
			<td></td>
			<td></td>
			<td>stable transgenic line in which the Xenopus neural-specific beta tubulin promoter drives expression of the fluorescent protein DsRed&#160; (Peri and N&#252;sslein-Volhard, 2008)</td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Equipment</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>centrifuge</td>
			<td>Eppendorf</td>
			<td></td>
			<td>model 5804 R</td>
		</tr>
		<tr>
			<td>ChemiDoc MP imaging system</td>
			<td>BioRad</td>
			<td></td>
			<td>model XRS+, used to acquire black-and-white images of Petri dishes containing 1 da embryos</td>
		</tr>
		<tr>
			<td>confocal laser scanning microscope</td>
			<td>Leica microsystems</td>
			<td></td>
			<td>model SP8, equipped with 28 &#176;C temperature box and a 63 x objective</td>
		</tr>
		<tr>
			<td>epifluorescent microscope</td>
			<td>Leica microsystems</td>
			<td></td>
			<td>model DM5500B, equipped with 28 &#176;C temperature box and a 40 x objective</td>
		</tr>
		<tr>
			<td>Gene Pulser Xcell with capacitance extender</td>
			<td>BioRad</td>
			<td>1652661</td>
			<td>electroporation device</td>
		</tr>
		<tr>
			<td>Horizontal shaker</td>
			<td>GFL</td>
			<td></td>
			<td>model 3011</td>
		</tr>
		<tr>
			<td>incubator for cell culture (28 &#176;C)</td>
			<td>Memmert</td>
			<td></td>
			<td>model incubator I</td>
		</tr>
		<tr>
			<td>incubator for embryos (28 &#176;C)</td>
			<td>Heraeus</td>
			<td></td>
			<td>type B6120</td>
		</tr>
		<tr>
			<td>light microscope</td>
			<td>Zeiss</td>
			<td></td>
			<td>model TELAVAL 31</td>
		</tr>
		<tr>
			<td>micro pipettes</td>
			<td>Gilson</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>sterile work bench</td>
			<td>Bio Base</td>
			<td></td>
			<td>with laminar flow and UV light</td>
		</tr>
		<tr>
			<td>tweezers</td>
			<td>Dumont</td>
			<td></td>
			<td>Style 5, Inox</td>
		</tr>
		<tr>
			<td>vertical tube rotator</td>
			<td>Labinco B.V.</td>
			<td></td>
			<td>model LD-79</td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Software</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Image Lab Software</td>
			<td>BioRad</td>
			<td></td>
			<td>for the ChemiDoc MP imaging system from BioRad</td>
		</tr>
		<tr>
			<td>ImageJ</td>
			<td>National Institutes of Health</td>
			<td></td>
			<td>used for counting 1 dpf embryos by applying the Count particles-tool to the respective black-and-white images; Rasband, W.S., ImageJ, U. S. National Institutes of Health, Bethesda, Maryland, USA, https://imagej.nih.gov/ij/. (1997-2016).</td>
		</tr>
		<tr>
			<td>LAS X</td>
			<td>Leica Microsystems</td>
			<td></td>
			<td>for both confocal and epifluorescent microscopes from Leica Microsystems</td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Plasmids</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>pCS-DCX-tdTomato</td>
			<td>K&#246;ster Lab</td>
			<td># 1599</td>
			<td>based on the backbone pCS2+ (Rupp et al., 1994)</td>
		</tr>
		<tr>
			<td>pCS-eGFP</td>
			<td>K&#246;ster Lab</td>
			<td># 7</td>
			<td>based on the backbone pCS2+ (Rupp et al., 1994)</td>
		</tr>
		<tr>
			<td>pCS-H2B-mseCFP</td>
			<td>K&#246;ster Lab</td>
			<td># 2379</td>
			<td>based on the backbone pCS2+ (Rupp et al., 1994)</td>
		</tr>
		<tr>
			<td>pCS-mClover</td>
			<td>K&#246;ster Lab</td>
			<td># 3865</td>
			<td>based on the backbone pCS2+ (Rupp et al., 1994)</td>
		</tr>
		<tr>
			<td>pCS-MitoTag-YFP</td>
			<td>K&#246;ster Lab</td>
			<td># 2199</td>
			<td>based on the backbone pCS2+ (Rupp et al., 1994)</td>
		</tr>
		<tr>
			<td>pCS-ss-RFP-KDEL</td>
			<td>K&#246;ster Lab</td>
			<td># 4330</td>
			<td>based on the backbone pCS2+ (Rupp et al., 1994)</td>
		</tr>
		<tr>
			<td>pCS-VAMP1-mCitrine</td>
			<td>K&#246;ster Lab</td>
			<td># 2291</td>
			<td>based on the backbone pCS2+ (Rupp et al., 1994)</td>
		</tr>
		<tr>
			<td>pSK-UAS:mCherry</td>
			<td>K&#246;ster Lab</td>
			<td># 1062</td>
			<td>based on the pBluescript-backbone of Stratagene</td>
		</tr>
		<tr>
			<td>Plasmid numbers refer to the database entries of the K&#246;ster lab. Plasmids are available upon request.</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Plastic and glass ware</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>BD Falcon Cell Strainer (40 &#181;m)</td>
			<td>FALCON</td>
			<td>REF 352340</td>
			<td>distributed by BD Bioscience, used as &#8220;landing net&#8221; to dip deyolked embryos into ethanol and to transfer them quickly to fresh cell culture medium</td>
		</tr>
		<tr>
			<td>1.5 mL reaction tubes</td>
			<td>Sarstedt</td>
			<td>72690550</td>
			<td></td>
		</tr>
		<tr>
			<td>24-well plate</td>
			<td>Sarstedt</td>
			<td>83.3922</td>
			<td></td>
		</tr>
		<tr>
			<td>50 mL falconic tube</td>
			<td>Sarstedt</td>
			<td>62.547.004</td>
			<td></td>
		</tr>
		<tr>
			<td>96-well plate</td>
			<td>Sarstedt</td>
			<td>83.3924.005</td>
			<td></td>
		</tr>
		<tr>
			<td>EasyStrainer (40 &#181;m)</td>
			<td>Greiner Bio-One</td>
			<td>542 040</td>
			<td>with venting slots; used to filter cells after collagenase-mediated dissociation</td>
		</tr>
		<tr>
			<td>electroporation cuvette (0.4 cm)</td>
			<td>Kisker</td>
			<td>4905022</td>
			<td></td>
		</tr>
		<tr>
			<td>glass coverslips</td>
			<td>Heinz Herenz Medizinalbedarf GmbH</td>
			<td>1051201</td>
			<td></td>
		</tr>
		<tr>
			<td>Microscope slides</td>
			<td>Thermo Fisher Scientific (Menzel Gl&#228;ser)</td>
			<td>631-0845</td>
			<td></td>
		</tr>
		<tr>
			<td>Neubauer chamber</td>
			<td>Henneberg-Sander GmbH</td>
			<td>9020-01</td>
			<td></td>
		</tr>
		<tr>
			<td>Pasteur pipettes (plastic; 3 mL)</td>
			<td>A. Hartenstein</td>
			<td>PP05</td>
			<td></td>
		</tr>
		<tr>
			<td>Petri dishes (plastic; diameter 10 cm)</td>
			<td>Sarstedt</td>
			<td>821473</td>
			<td>for zebrafish embryos</td>
		</tr>
		<tr>
			<td>pipette tips</td>
			<td>Sarstedt</td>
			<td>Blue (1000 &#181;l): 70762; Yellow (200 &#181;l): 70760002; White (10 &#181;L): 701116</td>
			<td></td>
		</tr>
		<tr>
			<td>sterile cell culture dishes (plastic; diameter 3 cm)</td>
			<td>TPP Techno Plastic Products AG</td>
			<td>93040</td>
			<td></td>
		</tr>
		<tr>
			<td>sterile cell culture dishes (plastic; diameter 6 cm)</td>
			<td>Sarstedt</td>
			<td>72690550</td>
			<td></td>
		</tr>
		<tr>
			<td>sterile Petri dishes (plastic; diameter 10 cm)</td>
			<td>Sarstedt</td>
			<td>83.3902</td>
			<td>for brain dissection</td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Chemicals and Reagents</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>sodium chloride</td>
			<td>Roth</td>
			<td>0601.1</td>
			<td></td>
		</tr>
		<tr>
			<td>4 % paraformaldehyde in 1 x PBS</td>
			<td>Sigma-Aldrich</td>
			<td>16005</td>
			<td></td>
		</tr>
		<tr>
			<td>4&#39;,6-diamidino-2-phenylindole (DAPI)</td>
			<td>Thermo Fisher Scientific</td>
			<td>D1306</td>
			<td></td>
		</tr>
		<tr>
			<td>calcium nitrate tetrahydrate</td>
			<td>Sigma-Aldrich</td>
			<td>C1396</td>
			<td></td>
		</tr>
		<tr>
			<td>ethanol p.a. 100%</td>
			<td>Sigma-Aldrich</td>
			<td>46139</td>
			<td></td>
		</tr>
		<tr>
			<td>goat &#945;-mouse IgG (Fc specific) FITC conjugated</td>
			<td>Thermo Fisher Scientific</td>
			<td>31547</td>
			<td></td>
		</tr>
		<tr>
			<td>HEPES</td>
			<td>Roth</td>
			<td>9105.4</td>
			<td></td>
		</tr>
		<tr>
			<td>high vacuum grease</td>
			<td>DOW CORNING</td>
			<td>3826-50</td>
			<td>silicon grease used for self-made glass bottom dishes</td>
		</tr>
		<tr>
			<td>magnesium sulfate heptahydrate</td>
			<td>Merck</td>
			<td>105886</td>
			<td></td>
		</tr>
		<tr>
			<td>methylene blue</td>
			<td>Serva</td>
			<td>29198.01</td>
			<td></td>
		</tr>
		<tr>
			<td>Monoclonal Anti-Tubulin, Acetylated antibody</td>
			<td>Sigma-Aldrich</td>
			<td>T6793</td>
			<td></td>
		</tr>
		<tr>
			<td>Aqua-Poly/Mount (mounting medium)</td>
			<td>Polyscience</td>
			<td>18606</td>
			<td></td>
		</tr>
		<tr>
			<td>poly-L-lysine</td>
			<td>Biochrom</td>
			<td>L 7240</td>
			<td></td>
		</tr>
		<tr>
			<td>potasssion chloride</td>
			<td>Merck</td>
			<td>104938</td>
			<td></td>
		</tr>
		<tr>
			<td>Skim milk</td>
			<td>Roth</td>
			<td>68514-61-4</td>
			<td></td>
		</tr>
		<tr>
			<td>Texas Red-X Phalloidin</td>
			<td>Thermo Fisher Scientific</td>
			<td>T7471</td>
			<td></td>
		</tr>
		<tr>
			<td>Tricaine</td>
			<td>Sigma-Aldrich</td>
			<td>E10521</td>
			<td>Synonym: Ethyl 3-aminobenzoate methanesulfonate</td>
		</tr>
		<tr>
			<td>Triton X-100</td>
			<td>BioRad</td>
			<td>1610407</td>
			<td></td>
		</tr>
		<tr>
			<td>Trypan Blue</td>
			<td>Gibco by Life Technologies</td>
			<td>15250061</td>
			<td></td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Enzymes</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>collagenase (Type 2)</td>
			<td>Thermo Fisher Scientific</td>
			<td>17101015</td>
			<td>dissolve powder in cell culture medium (8 mg/mL) and sterile-filter the solution, store aliquots at -20 &#176;C</td>
		</tr>
		<tr>
			<td>pronase (from Streptomyces griseus)</td>
			<td>Roche</td>
			<td>11459643001</td>
			<td>distributed by Sigma-Aldrich, dissolve in 30% Danieau (10 mg/mL) and store aliquots at -20 &#176;C</td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Medium and solutions for cell culture</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>1 x PBS (Dulbecco&#39;s Phosphate Buffered Saline)</td>
			<td>Gibco by Life Technologies</td>
			<td>14190-169</td>
			<td>distributed by Thermo Fisher Scientific</td>
		</tr>
		<tr>
			<td>CO2-independent medium</td>
			<td>Gibco by Life Technologies</td>
			<td>18045054</td>
			<td>distributed by Thermo Fisher Scientific</td>
		</tr>
		<tr>
			<td>filtrated bovine serum (FBS)</td>
			<td>PAN-Biotech</td>
			<td></td>
			<td>individual batch</td>
		</tr>
		<tr>
			<td>glutamine 100 x</td>
			<td>Gibco by Life Technologies</td>
			<td>25030081</td>
			<td>distributed by Thermo Fisher Scientific</td>
		</tr>
		<tr>
			<td>Leibovitz&#39;s L-15 medium</td>
			<td>Gibco by Life Technologies</td>
			<td>11415049</td>
			<td>distributed by Thermo Fisher Scientific</td>
		</tr>
		<tr>
			<td>PenStrep (10,000 units/mL)</td>
			<td>Gibco by Life Technologies</td>
			<td>15140148</td>
			<td>distributed by Thermo Fisher Scientific</td>
		</tr>
	</tbody>
</table>

culture and transfection of zebrafish primary cells

Zebrafish embryos are transparent and develop rapidly outside the mother, thus allowing for excellent in vivo imaging of dynamic biological processes in an intact and developing vertebrate. However, the detailed imaging of the morphologies of distinct cell types and subcellular structures is limited in whole mounts. Therefore, we established an efficient and easy-to-use protocol to culture live primary cells from zebrafish embryos and adult tissue.
In brief, 2 dpf zebrafish embryos are dechorionated, deyolked, sterilized, and dissociated to single cells with collagenase. After a filtration step, primary cells are plated onto glass bottom dishes and cultivated for several days. Fresh cultures, as much as long term differenciated ones, can be used for high resolution confocal imaging studies. The culture contains different cell types, with striated myocytes and neurons being prominent on poly-L-lysine coating. To specifically label subcellular structures by fluorescent marker proteins, we also established an electroporation protocol which allows the transfection of plasmid DNA into different cell types, including neurons. Thus, in the presence of operator defined stimuli, complex cell behavior, and intracellular dynamics of primary zebrafish cells can be assessed with high spatial and temporal resolution. In addition, by using adult zebrafish brain, we demonstrate that the described dissociation technique, as well as the basic culturing conditions, also work for adult zebrafish tissue.

Figure 1G shows a transmitted light image of a typical culture derived from wild type embryos with striated myocytes and clusters of neuron-like cells being most abundant. To identify certain cell types more easily, a transgenic line with cell type-specific expression of a fluorescent protein can be used (Figure 1H).
Transfection of a pCS2+-based plasmid11 encoding the enhanced green fluorescent protein (eGFP)15 into primary cells of wild type embryos results in a strong fluorescent signal at 1 dap (Figure 2A). By transfecting pCS2+-based plasmids encoding fluorescent organelle markers such as endoplasmic reticulum-targeted red fluorescent protein (ss-RFP-KDEL)16 or mitochondria-targeted yellow fluorescent protein (MitoTag-YFP)17,18, subcellular structures can be visualized in great detail (Figure 2B, C). Co-transfection of up to three plasmids allows for the simultaneous analysis of the subcellular localization of several fluorescent fusion proteins in the same cell19 such as MitoTag-YFP together with the microtubule marker human Doublecortin (DCX)20 fused to the red fluorescent protein tdTomato21 and the nuclear marker histone H2B fused to a cyan fluorescent protein (H2B-mseCFP)22,23 (Figure 2D). Subcellular structures can also be imaged with high temporal and spatial resolution, as for example the movement of vesicles positive for the membrane marker vesicle-associated membrane protein 1 (VAMP1) fused to the fluorescent protein mCitrine24,25 (Figure 3). Morphological changes over time can be easily observed by labeling the whole cell by the expression of a bright fluorescent protein such as mClover26 (Figure 2G, I). However, successful transfection of a plasmid based on the pBluescriptSK-backbone encoding the red fluorescent protein mCherry27 fused to an UAS element into primary cells derived from double-transgenic embryos carrying both a Gal4 driver construct and an UAS effector construct demonstrates that the electroporation protocol is also suitable for combinatorial genetics (Figure 2E). Furthermore, fixed primary cells can be easily stained by using immunofluorescence and organelle-specific fluorescent dyes (Figure 2F, H).
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/57872/57872fig3.jpg" /> 
Figure 3: Time lapse imaging of subcellular structures. Wild type cell (1 dap) transfected with pCS-VAMP1-mCitrine. Selected frames of a time lapse recording (1 frame was taken every 1.68 s) are shown. Arrow heads and tracks in according colors highlight the subcellular dynamics of three distinct VAMP1-positive vesicles. Scale bar = 10 &#181;m. The time lapse was recorded using a confocal laser scanning microscope. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57872/57872fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
The dissociation technique and the basic culture conditions can also be applied to the tissue of adult zebrafish. Here, we tested adult brain tissue from wild type zebrafish. Figure 4A-D shows the progressive development of a initially debris-coated culture to a complex neuronal-like network. By using adult brain from a transgenic fish carrying the transgene Tg(XITubb:DsRed)zf14828, fully differentiated DsRed-expressing neurons can be examined in close detail (Figure 4E).
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/57872/57872fig4.jpg" /> 
Figure 4: Primary cell culture of adult zebrafish brain. Bright field images of primary cells derived from adult zebrafish brain at (A) 1 dap, (B) 3 dap, (C) 5 dap and (D) 8 dap. From 1 to 3 dap, dead cells and tissue debris disappear while single or clustered neuronal cells become more and more apparent. At 3 dap, neuronal cells begin to form the first short neurites. From 5 dap onward, it is possible to observe the formation of a&#160;network with hundreds of well elongated neurites. Scale bars = 50 &#181;m. Cells were cultured in a poly-L-lysine-coated 96-well plate. (E) Cultured cells at 7 dap from the adult brain of a transgenic fish expressing the transgene Tg(XITubb:DsRed)zf148. DsRed is expressed in differentiated neurons28. Scale bar = 100 &#181;m. Cells were cultured in a poly-L-lysine-coated 24-well plate. All images were acquired by an epifluorescent microscope. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57872/57872fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Culture and Transfection of Zebrafish Primary Cells at JoVE.com

Culture and Transfection of Zebrafish Primary Cells

We present an efficient and easy-to-use protocol for preparing primary cell cultures of zebrafish embryos for transfection and live cell imaging as well as a protocol to prepare primary cells from adult zebrafish brain.

Zebrafish embryos are transparent and develop rapidly outside the mother, thus allowing for excellent in vivo imaging of dynamic biological processes in ...

culture-and-transfection-of-zebrafish-primary-cells

Nanyang Technological University

Research

JoVE Journal

Developmental Biology

12.3K Views.  Braunschweig University of Technology. We present an efficient and easy-to-use protocol for preparing primary cell cultures of zebrafish embryos for transfection and live cell imaging as well as a protocol to prepare primary cells from adult zebrafish brain.

Video: Culture and Transfection of Zebrafish Primary Cells

Isolation and Culture of Adult Zebrafish Brain-derived Neurospheres

The zebrafish is a highly relevant model organism for understanding the cellular and molecular mechanisms involved in neurogenesis and brain regeneration in vertebrates. However, an in-depth analysis of the molecular mechanisms underlying zebrafish adult neurogenesis has been limited due to the lack of a reliable protocol for isolating and culturing neural adult stem/progenitor cells. Here we provide a reproducible method to examine adult neurogenesis using a neurosphere assay derived from zebrafish whole brain or from the telencephalon, tectum and cerebellum regions of the adult zebrafish brain. The protocol involves, first the microdissection of zebrafish adult brain, then single cell dissociation and isolation of self-renewing multipotent neural stem/progenitor cells. The entire procedure takes eight days. Additionally, we describe how to manipulate gene expression in zebrafish neurospheres, which will be particularly useful to test the role of specific signaling pathways during adult neural stem/progenitor cell proliferation and differentiation in zebrafish.

Here we provide a reproducible method to examine adult neurogenesis using a neurosphere assay derived from the whole brain or from either the telencephalic, tectal or cerebellar regions of the adult zebrafish brain. Additionally, we describe the procedure to manipulate gene expression in zebrafish neurospheres.

The zebrafish is a highly relevant model organism for understanding the cellular and molecular mechanisms involved in neurogenesis and brain regeneration ...

Primary Endodermal Epithelial Cell Culture from the Yolk Sac Membrane of Japanese Quail Embryos

We established an endodermal epithelial cell culture model (EEC) for studying the function of certain enzymes and proteins in mediating nutrient utilization by avian embryos during development. Fertilized Japanese quail eggs were incubated at 37 &#176;C for 5 days and then yolk sac membranes (YSM) were collected to establish the EEC culture system. We isolated the embryonic endoderm layer from YSM, and sliced the membrane into 2 - 3 mm pieces and partially digested with collagenase before seeding in 24-well culture plates. The EECs proliferate out of the tissue and are ready for cell culture studies. We found that the EECs had typical characteristics of YSM in vivo, for example, accumulation of lipid droplets, expression of sterol O-acyltransferase and lipoprotein lipase. The partial digestion treatment significantly increased the successful rate of EEC culture. Utilizing the EECs, we demonstrated that the expression of SOAT1 was regulated by the cAMP dependent protein kinase A related pathway. This primary Japanese quail EEC culture system is a useful tool to study embryonic lipid transportation and to clarify the role of genes involved in mediating nutrient utilization in YSM during avian embryonic development.

To study the mechanism of lipid utilization in yolk sac membranes during the late stages of avian embryonic development, we established a primary Japanese quail embryonic endodermal epithelial cell culture system.

We established an endodermal epithelial cell culture model (EEC) for studying the function of certain enzymes and proteins in mediating nutrient ...

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.

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 ...

Large-Scale Production of Cardiomyocytes from Human Pluripotent Stem Cells Using a Highly Reproducible Small Molecule-Based Differentiation Protocol

Maximizing the benefit of human pluripotent stem cells (hPSCs) for research, disease modeling, pharmaceutical and clinical applications requires robust methods for the large-scale production of functional cell types, including cardiomyocytes. Here we demonstrate that the temporal manipulation of WNT, TGF-&#946;, and SHH signaling pathways leads to highly efficient cardiomyocyte differentiation of single-cell passaged hPSC lines in both static suspension and stirred suspension bioreactor systems. Employing this strategy resulted in ~ 100% beating spheroids, consistently containing &#62; 80% cardiac troponin T-positive cells after 15 days of culture, validated in multiple hPSC lines. We also report on a variation of this protocol for use with cell lines not currently adapted to single-cell passaging, the success of which has been verified in 42 hPSC lines. Cardiomyocytes generated using these protocols express lineage-specific markers and show expected electrophysiological functionalities. Our protocol presents a simple, efficient and robust platform for the large-scale production of human cardiomyocytes.

Here, we present a robust, fast and scalable cardiomyocyte differentiation protocol for human pluripotent stem cells (hPSCs). Cardiomyocytes derived using this large-scale method can provide sufficient cell numbers for their effective use in human cardiovascular disease modeling, high-throughput drug screening, and potentially clinical applications.

Maximizing the benefit of human pluripotent stem cells (hPSCs) for research, disease modeling, pharmaceutical and clinical applications requires robust ...

Preparation and Culture of Myogenic Precursor Cells/Primary Myoblasts from Skeletal Muscle of Adult and Aged Humans

Skeletal muscle homeostasis depends on muscle growth (hypertrophy), atrophy and regeneration. During ageing and in several diseases, muscle wasting occurs. Loss of muscle mass and function is associated with muscle fiber type atrophy, fiber type switching, defective muscle regeneration associated with dysfunction of satellite cells, muscle stem cells, and other pathophysiological processes. These changes are associated with changes in intracellular as well as local and systemic niches. In addition to most commonly used rodent models of muscle ageing, there is a need to study muscle homeostasis and wasting using human models, which due to ethical implications, consist predominantly of in vitro cultures. Despite the wide use of human Myogenic Progenitor Cells (MPCs) and primary myoblasts in myogenesis, there is limited data on using human primary myoblast and myotube cultures to study molecular mechanisms regulating different aspects of age-associated muscle wasting, aiding in the validation of mechanisms of ageing proposed in rodent muscle. The use of human MPCs, primary myoblasts and myotubes isolated from adult and aged people, provides a physiologically relevant model of molecular mechanisms of processes associated with muscle growth, atrophy and regeneration. Here we describe in detail a robust, inexpensive, reproducible and efficient protocol for the isolation and maintenance of human MPCs&#160;and their progeny&#160;&#8212; myoblasts and myotubes from human muscle samples using enzymatic digestion. Furthermore, we have determined the passage number at which primary myoblasts from adult and aged people undergo senescence in an in vitro culture. Finally, we show the ability to transfect these myoblasts and the ability to characterize their proliferative and differentiation capacity and propose their suitability for performing functional studies of molecular mechanisms of myogenesis and muscle wasting in vitro.

This protocol describes a robust, reproducible and simple method of isolation and culture of myoblast progenitor cells from the skeletal muscle of adult and aged people. The muscles used here include foot and leg muscles. This approach enables the isolation of an enriched population of primary myoblasts for functional studies.

Skeletal muscle homeostasis depends on muscle growth (hypertrophy), atrophy and regeneration. During ageing and in several diseases, muscle wasting ...

Horizontal Whole Mount: A Novel Processing and Imaging Protocol for Thick, Three-dimensional Tissue Cross-sections of Skin

Processing a tissue of interest to generate a microscopic image that supports a scientific argument can be challenging. The acquisition of high-quality microscopic images is not entirely dependent upon the quality of the microscope, but also upon the methods of tissue processing, which often involve multiple critical actions or steps. Furthermore, mesenchymal cell types in the skin and other tissues represent a new challenge for tissue preparation and imaging. Here, we present a complete process, from tissue harvest to microscopy. Our technique, called &#34;horizontal whole mount,&#34; is one that novices can quickly become proficient in and that allows for antigen preservation and detection in 60-300 &#181;m-thick sections cut with a cryostat. Sections of this thickness provide enhanced visualization of tissue microarchitecture in a three-dimensional environment. In addition, the protocol preserves mesenchymal cells in a manner that enhances image quality when compared to standard cryostat or paraffin sections, thereby increasing the efficacy and reliability of immunostaining. We believe that this protocol will benefit all laboratories that visualize skin, and possibly other tissues and organs.

This work presents a novel processing and imaging protocol for thick, three-dimensional tissue cross-section analysis that enables the full exploitation of confocal imaging modalities. This protocol preserves antigenicity and represents a robust system to analyze skin histology and potentially other tissue types.

Processing a tissue of interest to generate a microscopic image that supports a scientific argument can be challenging. The acquisition of high-quality ...

Single-cell Photoconversion in Living Intact Zebrafish

Animal and plant tissue is composed of distinct populations of cells. These cells interact over time to build and maintain the tissue and can cause disease when disrupted. Scientists have developed clever techniques to investigate characteristics and natural dynamics of these cells within intact tissue by expressing fluorescent proteins in subsets of cells. However, at times, experiments require more selected visualization of cells within the tissue, sometimes at the single-cell or population-of-cells manner. To achieve this and visualize single cells within a population of cells, scientists have utilized single-cell photoconversion of fluorescent proteins. To demonstrate this technique, we show here how to direct UV light to an Eos-expressing cell of interest in an intact, living zebrafish. We then image those photoconverted Eos+ cells 24 h later to determine how they changed in the tissue. We describe two techniques: single cell photoconversion and photoconversions of populations of cell. These techniques can be used to visualize cell-cell interactions, cell-fate and differentiation, and cell migrations, making it a technique that is applicable in numerous biological questions.

Here, we present a protocol to show how cell photoconversion is achieved through UV exposure to specific areas expressing the fluorescent protein, Eos, in living animals.

Animal and plant tissue is composed of distinct populations of cells. These cells interact over time to build and maintain the tissue and can cause ...

The Isolation and Culture of Primary Epicardial Cells Derived from Human Adult and Fetal Heart Specimens

The epicardium, an epithelial cell layer covering the myocardium, has an essential role during cardiac development, as well as in the repair response of the heart after ischemic injury. When activated, epicardial cells undergo a process known as epithelial to mesenchymal transition (EMT) to provide cells to the regenerating myocardium. Furthermore, the epicardium contributes via secretion of essential paracrine factors. To fully appreciate the regenerative potential of the epicardium, a human cell model is required. Here we outline a novel cell culture model to derive primary epicardial derived cells (EPDCs) from human adult and fetal cardiac tissue. To isolate EPDCs, the epicardium is dissected from the outside of the heart specimen and processed into a single cell suspension. Next, EPDCs are plated and cultured in EPDC medium containing the ALK 5-kinase inhibitor SB431542 to maintain their epithelial phenotype. EMT is induced by stimulation with TGF&#946;. This method enables, for the first time, the study of the process of human epicardial EMT in a controlled setting, and facilitates gaining more insight in the secretome of EPDCs that may aid heart regeneration. Furthermore, this uniform approach allows for direct comparison of human adult and fetal epicardial behavior.

The epicardium plays a crucial role in the development and repair of the heart by providing cells and growth factors to the myocardial wall. Here, we describe a method to culture human primary epicardial cells that enables the study and comparison of their developmental and adult characteristics.

The epicardium, an epithelial cell layer covering the myocardium, has an essential role during cardiac development, as well as in the repair response of ...

Computational Analysis of the Caenorhabditis elegans Germline to Study the Distribution of Nuclei, Proteins, and the Cytoskeleton

The Caenorhabditis elegans (C. elegans) germline is used to study several biologically important processes including stem cell development, apoptosis, and chromosome dynamics. While the germline is an excellent model, the analysis is often two dimensional due to the time and labor required for three-dimensional analysis. Major readouts in such studies are the number/position of nuclei and protein distribution within the germline. Here, we present a method to perform automated analysis of the germline using confocal microscopy and computational approaches to determine the number and position of nuclei in each region of the germline. Our method also analyzes germline protein distribution that enables the three-dimensional examination of protein expression in different genetic backgrounds. Further, our study shows variations in cytoskeletal architecture in distinct regions of the germline that may accommodate specific spatial developmental requirements. Finally, our method enables automated counting of the sperm in the spermatheca of each germline. Taken together, our method enables rapid and reproducible phenotypic analysis of the C. elegans germline.

Computational Analysis of the Caenorhabditis elegans Germline to Study the Distribution of Nuclei, Proteins, and the Cytoskeleton

We present an automated method for three-dimensional reconstruction of the Caenorhabditis elegans germline. Our method determines the number and position of each nucleus within the germline and analyses germline protein distribution and cytoskeletal structure.

The Caenorhabditis elegans (C. elegans) germline is used to study several biologically important processes including stem cell development, apoptosis, and ...

Induction and Validation of Cellular Senescence in Primary Human Cells

Cellular senescence is a state of permanent cell cycle arrest activated in response to different damaging stimuli. Activation of cellular senescence is a hallmark of various pathophysiological conditions including tumor suppression, tissue remodeling and aging. The inducers of cellular senescence in vivo are still poorly characterized. However, a number of stimuli can be used to promote cellular senescence ex vivo. Among them, most common senescence-inducers are replicative exhaustion, ionizing and non-ionizing radiation, genotoxic drugs, oxidative stress, and demethylating and acetylating agents. Here, we will provide detailed instructions on how to use these stimuli to induce fibroblasts into senescence. This protocol can easily be adapted for different types of primary cells and cell lines, including cancer cells. We also describe different methods for the validation of senescence induction. In particular, we focus on measuring the activity of the lysosomal enzyme Senescence-Associated &#946;-galactosidase (SA-&#946;-gal), the rate of DNA synthesis using 5-ethynyl-2&#39;-deoxyuridine (EdU) incorporation assay, the levels of expression of the cell cycle inhibitors p16 and p21, and the expression and secretion of members of the Senescence-Associated Secretory Phenotype (SASP). Finally, we provide example results and discuss further applications of these protocols.

Here, we discuss a series of protocols for induction and validation of cellular senescence in cultured cells. We focus on different senescence-inducing stimuli and describe the quantification of common senescence-associated markers. We provide technical details using fibroblasts as a model, but the protocols can be adapted to various cellular models.

Cellular senescence is a state of permanent cell cycle arrest activated in response to different damaging stimuli. Activation of cellular senescence is a ...