The authors thank Dr. Le Trinh and Dr. Tobin for generously providing the &#945;-catenin:citrine fish line and Bill Jackman for allowing us to do the filming in his lab. The authors acknowledge the funding sources National Institutes of Health (Grants 5P20RR016463, 8P20GM103423 and R15AI094406) and USDA (Project # ME0-H-1-00517-13). This manuscript is published as Main Agriculture and Forestry Experiment Station publication number 3371.

NOTE: All zebrafish care protocols and experiments were performed in accordance with NIH guidelines under Institutional Animal Care and Use Committee (IACUC) protocol A2012-11-03.
1. Zebrafish Rearing to 4 Days Post Fertilization
<ol>
	<li>Collect AB zebrafish, or any other transgenic lines, within the first 3 hr post fertilization, as shown in another video34.</li>
	<li>Incubate 120 eggs in a 15 cm Petri dishes containing 150 ml of E3 media (5 mM NaCl; 0.17 mM KCl; 0.33 mM CaCl<s...

The authors have nothing to disclose.

Advances and limitations of the swimbladder microinjection disease model
The model presented here is an extension of the mucosal candidiasis immersion model described in Gratacap et al. (2013); it adds the advantages of a controlled infection time, a highly reproducible infection dose, and therefore improved efficiency. We demonstrate here new methods that permit non-invasive temporal documentation of infection dynamics in great detail as well as higher resolution ex vivo imagin...

Mucosal infections can lead to life threatening bloodstream infections due to the damage of the epithelial barrier, which allows pathogens access to the systemic environment1,2. In addition, mucosal infections can also cause significant immunopathology even when contained externally3-5. The commensal unicellular fungus Candida albicans is present in the majority of the population in the oral cavity and other mucosal sites6-9. Although normally contained by innate and adaptive immune responses, innate immune defects and medical interventions can lead to severe mucosal candidiasis. The assault on the epithelial barrier results in an increased risk of life threatening disseminated disease as well as immunopathology, as in the case of vulvo-vaginal candidiasis, additionally C. albicans colonization has been linked with lung immune homeostasis10,11. Disseminated candidiasis is now the fourth most common bloodstream infection in intensive care units12 and mortality as high as 40% makes it a major concern. Due to the increase in immunomodulatory treatments for patients with autoimmune diseases, cancer or organ transplants, it is imperative to understand the interaction between this pathogen and the mucosal immune compartment.
The majority of cell biological advances regarding C. albicans-cell interactions at the mucosal level come from in vitro13-15 and murine models16-18. Both these approaches have distinct advantages, but the ability to image live cells at high resolution in an intact host has limited the temporal and spatial characterization of the infection. For these studies, there is the need for an in vivo model where the interaction of pathogen, innate immune and epithelial cells can be visualized in an intact vertebrate host.
The zebrafish has emerged as an invaluable tool for the understanding of human disease, mainly due to its transparency and amenability to genetic manipulation. Cell and organ development have been imaged in exquisite detail, which has led to the description of novel immune cell behaviors, such as T cell behavior in the developing thymus19 or the battle between intracellular mycobacteria and phagocytes20-22. Recent work has described intestinal microbe-host interactions in zebrafish and shown that microbial colonization of the intestinal tract affects host intestinal physiology and resistance to other infections23,24. Furthermore, infection through the gut epithelium has been described for several pathogens.
In contrast to the intestinal tract, the swimbladder represents a more isolated and complementary mucosal model. This organ is an extension of the developing gut tube and forms anteriorly to the liver and pancreas25,26. It produces surfactant, mucus and antimicrobial peptides27,28 and anatomically, as well as ontogenetically, this organ is considered a homologue of the mammalian lung29,30. Since the pneumatic duct remains connected to the gut in the zebrafish, this allows for immersion infection to occur naturally. Remarkably, the only known naturally occurring infections of fish with Candida species are C. albicans infections in the swimbladder31. We recently described an experimental immersion infection model where C. albicans infects the swimbladder, and found that this infection recapitulates some of the hallmarks of C. albicans-epithelial interaction in vitro32,33. 
In the method presented here, the original immersion infection model is improved by directly injecting C. albicans into the swimbladder of 4 days post fertilization (dpf) zebrafish. This allows for precise temporal control of infection as well as a highly reproducible inoculum. It permits detailed intravital imaging, coupled with the versatility of the zebrafish model. As an example of what can be done with this method, we present the spatio-temporal dynamics of C. albicans growth along with neutrophil recruitment to the site of infection. Because zebrafish swimbladder tissue is challenging to image intravitally, we also present a rapid swimbladder dissection technique that improves fluorescence signal and microscopic resolution. These methods expand the toolbox for fungal, immunological, and aquaculture research as well as describing a novel infection route that may be translated to model other fungal, bacterial or viral infections of mucosal surfaces.

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			<td height="21" style="height:21px;width:261px;">Name</td>
			<td style="width:259px;">Company</td>
			<td style="width:176px;">Catalog Number</td>
			<td style="width:88px;">Comments</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;"></td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">1.7 mL tubes</td>
			<td>Axygen</td>
			<td>MCT-175-C</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Deep Petri dishes</td>
			<td>Fisher Scientific</td>
			<td>89107-632</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Transfer pipettes</td>
			<td>Fisher Scientific</td>
			<td>13-711-7M</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Yeast Extract</td>
			<td>VWR Scientific</td>
			<td>90000-726</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Peptone</td>
			<td>VWR Scientific</td>
			<td>90000-264</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Dextrose</td>
			<td>Fisher Scientific</td>
			<td>D16-1</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Agar</td>
			<td>VWR Scientific</td>
			<td>90000-760</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Fine tweezers (Dumont Dumoxel #5)</td>
			<td>Fine Science Tools</td>
			<td>11251-30</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Wooden Dowels</td>
			<td>VWR Scientific</td>
			<td>10805-018</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Low Melt Agarose</td>
			<td>VWR Scientific</td>
			<td>12001-722</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Flaming Brown Micropipette Puller</td>
			<td>Sutter Instruments</td>
			<td>P-97</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Borosilicate capillary</td>
			<td>Sutter Instruments</td>
			<td>BF120-69-10</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">MPPI-3 Injection system</td>
			<td>Applied Scientific Instrumentation</td>
			<td>MPPI-3</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Back Pressure Unit</td>
			<td>Applied Scientific Instrumentation</td>
			<td>BPU</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Micropipette Holder kit</td>
			<td>Applied Scientific Instrumentation</td>
			<td>MPIP</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Foot Switch</td>
			<td>Applied Scientific Instrumentation</td>
			<td>FSW</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Micromanipulator</td>
			<td>Applied Scientific Instrumentation</td>
			<td>MM33</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Magnetic Base</td>
			<td>Applied Scientific Instrumentation</td>
			<td>Magnetic Base</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Tricaine methane sulfonate</td>
			<td>Western Chemical Inc.</td>
			<td>MS-222</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Dissecting Scope</td>
			<td>Olympus</td>
			<td colspan="2">SZ61 top SZX-ILLB2-100 base</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Confocal Microscope</td>
			<td>Olympus</td>
			<td colspan="2">IX-81 with FV-1000 laser scanning confocal system</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">20x microscope objective</td>
			<td>Olympus</td>
			<td>UPlanSApo 20x/0.75</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Roller drum</td>
			<td>New Brunswick Scientific</td>
			<td>TC-7</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Microloader pipette tips</td>
			<td>Eppendorf</td>
			<td>930001007</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Glass culture tubes (16 x 150 mm)</td>
			<td>VWR Scientific</td>
			<td>60825-435</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">NaCl</td>
			<td>VWR Scientific</td>
			<td>BDH4534-500GP</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">KCl</td>
			<td>VWR Scientific</td>
			<td>BDH4532-500GP</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">MgSO4</td>
			<td>VWR Scientific</td>
			<td>BDH0246-500GP</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">HEPES (Corning)</td>
			<td>VWR Scientific</td>
			<td>BDH4520-500GP</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Children clay (Play-Doh)</td>
			<td>Hasbro</td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">CaCl2</td>
			<td>Fisher Scientific</td>
			<td>C69-500</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Methylene Blue</td>
			<td>VWR Scientific</td>
			<td>VW6276-0</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">PTU</td>
			<td>Sigma</td>
			<td>P7629-10G</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Petri dishes</td>
			<td>Fisher Scientific</td>
			<td>FB0875712</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Hemocytometer (Hausser scientific)</td>
			<td>VWR Scientific</td>
			<td>15170-172</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Type A immersion oil</td>
			<td>Blue Marble Products</td>
			<td>51935</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Centrifuge</td>
			<td>Eppendorf</td>
			<td>5424</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Vortex Genie</td>
			<td>VWR Scientific</td>
			<td>14216-184</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Agarose (Lonza)</td>
			<td>VWR Scientific</td>
			<td>12001-870</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Na2HPO4</td>
			<td>Fisher Scientific</td>
			<td>S374-500</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">KH2PO4</td>
			<td>Fisher Scientific</td>
			<td>P285-500</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Fishing wire</td>
			<td>Stren</td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">96 well imaging plate (Sensoplate)</td>
			<td>Greiner Bio-One</td>
			<td>655892</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">High vacuum grease (Dow Corning)</td>
			<td>VWR Scientific</td>
			<td>59344-055</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Microslide (25 x 75 mm)</td>
			<td>VWR Scientific</td>
			<td>48300-025</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Cover slips (18 x 18 mm), No 1.5</td>
			<td>VWR Scientific</td>
			<td>48366-045</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">15 cm Petri dish (Olympus plastics)</td>
			<td>Genesee Scientific</td>
			<td>32-106</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Glycerol (EMD chemicals)</td>
			<td>VWR Scientific</td>
			<td>EMGX0185-5</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">24-well culture dish (Olympus plastics)</td>
			<td>Genesee Scientific</td>
			<td>25-107</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Weight boats (8.9 cm)</td>
			<td>VWR Scientific</td>
			<td>89106-766</td>
			<td></td>
		</tr>
	</tbody>
</table>

modeling mucosal candidiasis in larval zebrafish by swimbladder injection

Early defense against mucosal pathogens consists of both an epithelial barrier and innate immune cells. The immunocompetency of both, and their intercommunication, are paramount for the protection against infections. The interactions of epithelial and innate immune cells with a pathogen are best investigated in vivo, where complex behavior unfolds over time and space. However, existing models do not allow for easy spatio-temporal imaging of the battle with pathogens at the mucosal level.
The model developed here creates a mucosal infection by direct injection of the fungal pathogen, Candida albicans, into the swimbladder of juvenile zebrafish. The resulting infection enables high-resolution imaging of epithelial and innate immune cell behavior throughout the development of mucosal disease. The versatility of this method allows for interrogation of the host to probe the detailed sequence of immune events leading to phagocyte recruitment and to examine the roles of particular cell types and molecular pathways in protection. In addition, the behavior of the pathogen as a function of immune attack can be imaged simultaneously by using fluorescent protein-expressing C. albicans. Increased spatial resolution of the host-pathogen interaction is also possible using the described rapid swimbladder dissection technique.
The mucosal infection model described here is straightforward and highly reproducible, making it a valuable tool for the study of mucosal candidiasis. This system may also be broadly translatable to other mucosal pathogens such as mycobacterial, bacterial or viral microbes that normally infect through epithelial surfaces.

Microinjection in the posterior swimbladder
The experimental method presented here describes the injection of a consistent dose of C. albicans yeast cells in the swimbladder of 4 dpf zebrafish. Previous work with the immersion model suggests that the swimbladder immune response to C. albicans is similar to mammalian mucosal candidiasis32. Here we demonstrate a modified infection method that is more straightforward, reproducible and rapid; several hundreds of zebrafish...

Watch this Scientific Journal Video about Modeling Mucosal Candidiasis in Larval Zebrafish by Swimbladder Injection at JoVE.com

Modeling Mucosal Candidiasis in Larval Zebrafish by Swimbladder Injection

In vivo spatio-temporal interactions of pathogen and immune defenses at the mucosal level are not easily imaged in existing vertebrate hosts. The method presented here describes a versatile platform to study mucosal candidiasis in live vertebrates using the swimbladder of the juvenile zebrafish as an infection site.

Early defense against mucosal pathogens consists of both an epithelial barrier and innate immune cells. The immunocompetency of both, and their ...

modeling-mucosal-candidiasis-larval-zebrafish-swimbladder

Research

JoVE Journal

Immunology and Infection

10.1K Views.  University of Maine. In vivo spatio-temporal interactions of pathogen and immune defenses at the mucosal level are not easily imaged in existing vertebrate hosts. The method presented here describes a versatile platform to study mucosal candidiasis in live vertebrates using the swimbladder of the juvenile zebrafish as an infection site.