The author thanks Doug for his constant encouragement and unwavering support, as well as the members of the Melton lab for their helpful feedback and comments on the manuscript. The author would also like to thank the Harvard Office of Animal Resources (OAR) for their dedicated animal care.

All animal experiments were performed in accordance with IACUC (Protocol #: 11-32) and AAALAC guidelines at Harvard University.
1. Preparing solutions and setup for anesthesia and recovery
<ol>
	<li>Prepare fresh 0.1% tricaine solution for anesthesia and 0.5% sulfamerazine sodium salt solution for recovery. Make the solutions using water suitable for axolotl husbandry37 according to approved IACUC protocols at the relevant research institution (modified Holtfreter&#8217;s solution, for instance). Make sure that the solutions are well-mixed and that enough volume is prepared in order to submerge the entire axolotl.
	<ol>
		<li>To prepare 0.1% tricaine solution, mix 1 g of tricaine and 1 g of sodium bicarbonate with 1 L of water. The solution can be scaled up according to this recipe.</li>
		<li>To prepare 0.5% sulfamerazine sodium salt solution, mix 5 g of sulfamerazine sodium salt with 1 L of water. The solution can be scaled up according to this recipe. Sulfamerazine solution is an anti-biotic that will prevent bacterial infection during surgical recovery.</li>
	</ol>
	</li>
	<li>Sanitize the surgical area by spraying it down with Clidox-S or 70% ethanol. Sterilize surgical tools (forceps, dissecting scissors, spring scissors) by autoclaving. If performing multiple surgeries, make sure to sterilize the surgical tools with a hot bead sterilizer between animals.</li>
	<li>To set up the recovery area, place a 15 cm Petri dish or any container that will fit the axolotl on top of a bucket filled with wet ice. Fill the Petri dish with a low level of 0.5% sulfamerazine sodium salt solution, enough such that the axolotl would not be fully submerged. The recovery on ice post-surgery will slow the animal&#8217;s movement while it awakens from anesthesia, allowing the sutured area to heal relatively undisturbed. 
	NOTE: This setup can be customized by researchers depending on what materials they have available.</li>
</ol>
2. Performing the full skin flap surgical procedure
<ol>
	<li>Anesthetize the axolotl by submersing it in a container of 0.1% tricaine solution. This will take approximately 15-20 minutes. Ensure that the axolotl is indeed fully anesthetized by performing a tail pinch. If there is no response from the axolotl, proceed with the surgery. 
	NOTE: Use older, larger axolotls for this surgery (at least 15 cm in size). Make sure that the axolotl remains well hydrated throughout the surgery by wetting the skin periodically with axolotl system water using a plastic pipette. Make sure to aseptically prepare the surgical site by irrigating the area with sterile PBS prior to surgery. The animal should also be placed on a sterile surgical drape for the procedure.</li>
	<li>Perform a limb amputation at the distal end of the zeugopodial skeletal elements using the dissecting scissors (Figure 1.1).</li>
	<li>Using the spring scissors, make a small incision (approximately 2 mm) on the ventral portion of the skin (Figure 1.2).</li>
	<li>Using the forceps, carefully peel back the skin to approximately the midline of the zeugopodial skeletal elements, exposing the underlying limb tissues (muscle, bone, etc.) (Figure 1.3). Make sure not to damage the skin. See note after step 2.8.</li>
	<li>Amputate the exposed underlying limb tissues at the midline of the zeugopod using surgical scissors (Figure 1.4).</li>
	<li>Push back the muscle tissue with the surgical scissors and trim the exposed bone. 
	NOTE: This is necessary to ensure improved healing and also to increase the success of the surgery as protruding bone can be jagged against the sutured flap and disrupt the integrity of an intact skin flap later on.</li>
	<li>Using the forceps, carefully pull the extra full thickness skin over the amputation plane to cover the exposed underlying tissues and suture in place by connecting with the ventral full thickness skin (Figure 1.5).</li>
	<li>Suture the remaining right and left sides of the skin flap into the underlying ventral portions of intact skin. This can be done by either suturing the sides of the flap in a &#8220;criss-cross&#8221; manner (recommended) (Figure 1.6-1.9), or simply suturing straight into the ventral skin. Use the forceps and curved spring scissors for suturing. Make sure no exposed underlying tissues can be seen and that sutures are tied tight (knotted at least three times). 
	NOTE: It is critical that the intact skin is not damaged in steps 2.4, 2.7-2.8. We have found that damage to the full thickness skin has been correlated with unsuccessful surgeries, as the areas of damage may still form a small wound epidermis. If possible, try to use a duller pair of forceps when handing the full thickness skin flap.</li>
	<li>Perform an amputation on the contralateral limb (optional internal animal control) by amputating it at mid-zeugopod level with surgical scissors. Push back the muscle tissue with surgical scissors and trim the exposed bone. 
	NOTE: An internal contralateral limb control can be done to better assess the success of the surgery during step 4 in the same animal. However, amputation of the same limb in a separate animal can also be used to serve as a control.</li>
</ol>
3. Post-operative recovery and care
<ol>
	<li>Once the surgery is complete, place a Kimwipe or sterile paper towel at the bottom of the container or Petri dish to wet it. Place the animal into the container on wet ice and gently wrap the exposed ends of the Kimwipe or paper towel around the top of the animal to keep it well-hydrated with sulfamerazine solution. Leave on wet ice for 30 minutes to 1 hour to ensure minimal movement during recovery from anesthesia.</li>
	<li>Place the animal into a static housing container with 0.5% sulfamerazine solution. Axolotls must remain in this solution for the first 24 hours in order to prevent infection.</li>
	<li>Place the axolotl into normal system water and monitor health daily. Ensure that no sutures fall out each day as this can result in a small wound epidermis forming which will confound results. 
	NOTE: Make sure that the housing container has ample room for the axolotl to move around and minimize the chances that the sutured limb on the axolotl can come into contact with the sides of the container. This will help to ensure that the sutures stay in place, especially during the first week post-surgery.</li>
</ol>
4. Assessing success of the surgery under a stereo microscope
NOTE: We recommend checking animals under a stereo microscope at least once a week to assess the integrity of the full skin flap and success of the surgery.
<ol>
	<li>Anesthetize the axolotl in 0.1% tricaine as in Step 2.1. Make sure there is ample room in the container for the axolotl to move around.</li>
	<li>If inspecting during the first two weeks post-surgery, inspect the sutured limb using a stereomicroscope to make sure no sutures have popped out and that a clear thin wound epidermis is not visible anywhere. If inspecting on the third week post-surgery or later, make sure a blastema has not formed and compare with how the normal control amputated limb (either from the same animal or a different animal) has progressed during regeneration (i.e., whether a blastema has formed).</li>
	<li>When done, return the axolotl to normal system water and husbandry conditions.</li>
</ol>

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The authors have nothing to disclose.

This article describes a protocol for performing full skin flap surgeries in axolotl limbs to inhibit wound epidermis formation. While this surgery is relatively simple and technically reproducible compared to other methods of inhibiting wound epidermis formation, there are several critical steps that can impact the success of the surgery. First, when pulling the intact full skin flap over the exposed underlying tissues, it is paramount that the full thickness skin not be damaged in any way. Damage to the skin flap can still lead to the formation of a small wound epidermis, which can result in a small blastema-like outgrowth. Second, ensure sutures do not fall out during post-operative care as this can also lead to the formation of a small wound epidermis. To this point, minimizing the potential contact between the sutured limb and any surfaces is important, especially during the first week post-surgery. Several ways to prevent this entail housing and anesthetizing the axolotl in a large enough container such that the axolotl has plenty of room to move around post-surgery.
This surgery also has several limitations. Perhaps the most notable is that the success of surgeries can only be assessed in two ways: using the dissecting scope during the first two weeks of surgery to search for an absence of a wound epidermis and/or checking whether a blastema forms within 3 weeks. While these methods are effective, they are relatively low throughput. The development of future transgenic reporter axolotls for wound epidermis-specific markers may aid in quicker screening for successful versus unsuccessful surgeries. Furthermore, this surgery is more difficult to perform on younger animals as the intact skin is more fragile. Using sub-adult or adult axolotls is thus recommended.
While this surgery was originally developed in N. viridiscens19, it has been easily adapted for axolotls25,39 and can likely be applied to other salamander species as well. In sum, applying this technique to future limb regenerative studies will empower researchers to both develop more tools to address wound epidermis biology and identify the underlying mechanisms driving its function in initiating blastema formation.

Since Lazzaro Spallanzani reported it in 17681, salamander limb regeneration has been one of the most well-studied natural regenerative phenomenon that has enamored biologists for centuries. Successful limb regeneration hinges on the formation, outgrowth, and subsequent patterning of an undifferentiated cellular structure known as the blastema. Researchers have made significant strides in understanding the cellular composition of the blastema as well as which supportive tissues and cell types are necessary for its formation2,3,4,5,6,7,8,9,10,11,12,13. Yet, the coordinated signaling mechanisms between different tissues and cell types that lead to the initiation of blastema formation remain poorly understood.
A key requirement for successful blastema formation and regeneration is the wound epidermis, a transient and specialized epithelium that covers the amputation plane within 12 hours post-amputation10. Following amputation, epithelial cells from the intact skin proximal to the injury rapidly migrate over the amputation plane to form a thin wound epithelium14. As the blastema forms in the following weeks, the early wound epidermis develops into a thicker epithelial signaling structure called the apical epithelial cap (AEC)15. While normal full thickness skin contains both an epithelial and dermal layer separated by a basal lamina, the wound epidermis/AEC consists only of an epithelial layer and lacks a basal lamina16,17. The absence of the basal lamina and dermis allows for direct contact between the wound epithelial cells and the underlying tissues, which facilitates bi-directional signaling between the two compartments that is critical for both blastema formation and maintenance17,18.
Classical experimental studies devised various innovative surgical methods to probe wound epidermis/AEC function and necessity via inhibiting its formation. These methods included suturing19 or grafting full thickness skin20,21 over the amputation plane, immediately suturing the amputated limb into the body cavity22, and continuous daily removal or irradiation of the early wound epidermis and AEC23,24. Altogether, these experiments not only established the importance of the wound epidermis/AEC, but also further determined its roles in early tissue histolysis as well as maintaining progenitor cell proliferation and blastemal outgrowth13 throughout regeneration.
However, these previous studies were largely limited to histological staining as well as tritiated thymidine pulses to track cell proliferation. In fact, revisiting these classical experiments with modern sequencing technologies and functional techniques in salamanders has only recently been done and has led to the discovery of additional roles for the wound epidermis in modulating inflammation and ECM degradation/deposition during early stages of regeneration25. With the release of various salamander genome and transcriptome sequences26,27,28,29,30,31,32,33,34, as well as the burgeoning number of functional methods available in salamander species11,35,36,37,38, researchers are now well-positioned to begin to unravel the molecular mechanisms driving wound epidermis formation, function, and AEC development.
Unfortunately, several of these classical methods used to inhibit wound epidermis formation are technically challenging, presenting difficulties for reproducibility between biological replicates in the same experiment. For instance, maintaining skin grafts can be challenging as grafts may eventually fall off the host limb and removal of the wound epidermis/AEC daily is difficult without damaging the underlying tissues. Furthermore, suturing the amputated limb into the body cavity is challenging and also requires additional injury at the site of insertion. On the other hand, suturing full thickness skin immediately over the amputation plane is relatively simple, technically reproducible, and introduces minimal tissue damage. This full skin flap (FSF) surgical method was previously developed by Anthony Mescher in 1976 in adult newts (Notophthalmus viridiscens). He demonstrated that the FSF surgery inhibited wound epidermis formation and function by prohibiting both epithelial cell migration over the amputation plane and direct contact between epithelial cells and the underlying tissues.
Here, this surgical procedure is shown step-by-step using the axolotl limb. Coupled with modern day molecular and sequencing technologies, this technique may prove to be very helpful for researchers to deepen our understanding of wound epidermis/AEC formation and function during limb regeneration.

<table>
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		<tr>
			<td>Curved spring scissors</td>
			<td>Fine Scientific Tools</td>
			<td>15009-08</td>
			<td></td>
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		<tr>
			<td>Ethyl 3-aminobenzoate methanesulfonate (Tricaine)</td>
			<td>Sigma-Aldrich</td>
			<td>886-86-2</td>
			<td></td>
		</tr>
		<tr>
			<td>Forceps</td>
			<td>Fine Scientific Tools</td>
			<td>11252-40</td>
			<td>Need two pairs</td>
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			<td>Nylon monofilament sutures (9-0)</td>
			<td>Roboz</td>
			<td>SUT-1000-21</td>
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		<tr>
			<td>Sodium bicarbonate</td>
			<td>Sigma-Aldrich</td>
			<td>S5761</td>
			<td></td>
		</tr>
		<tr>
			<td>Stereo microscope</td>
			<td>Leica</td>
			<td>MZ6</td>
			<td></td>
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		<tr>
			<td>Sulfamerazine sodium salt</td>
			<td>Sigma-Aldrich</td>
			<td>127-58-2</td>
			<td></td>
		</tr>
		<tr>
			<td>Surgical scissors</td>
			<td>Fine Scientific Tools</td>
			<td>14002-14</td>
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inhibition of wound epidermis formation via full skin flap surgery during axolotl limb regeneration

Classical experiments in salamander regenerative biology over the last century have long established that the wound epidermis is a crucial signaling structure that forms rapidly post-amputation and is required for limb regeneration. However, methods to study its precise function at the molecular level over the last decades have been limited due to a paucity of precise functional techniques and genomic information available in salamander model systems. Excitingly, the recent plethora of sequencing technologies coupled with the release of various salamander genomes and the advent of functional genetic testing methods, including CRISPR, makes it possible to re-visit these foundational experiments at unprecedented molecular resolution. Here, I describe how to perform the classically developed full skin flap (FSF) surgery in adult axolotls in order to inhibit wound epidermis formation immediately following amputation. The wound epidermis normally forms via distal migration of epithelial cells in the skin proximal to the amputation plane to seal off the wound from the outside environment. The surgery entails immediately suturing full thickness skin (which includes both epidermal and dermal layers) over the amputation plane to hinder epithelial cell migration and contact with the underlying damaged mesenchymal tissues. Successful surgeries result in the inhibition of blastema formation and limb regeneration. By combining this surgery method with contemporary downstream molecular and functional analyses, researchers can begin to uncover the molecular underpinnings of wound epidermis function and biology during limb regeneration.

This surgical protocol will allow for the complete inhibition of wound epidermis formation (Figure 1) and ultimately, limb regeneration. A successful surgery results in no blastema formation in approximately 2-3 weeks depending on the size of the animal, while control regenerating limbs should form a blastema normally.
Researchers should inspect the sutured limb by naked eye every 2-3 days to make sure that the sutures have not popped out and that a blastema is not forming. If one or more of the sutures pop out, a wound epidermis can still form resulting in either a small or large blastema and an unsuccessful surgery (Figure 2). Additionally, researchers should inspect the sutured limb at least once every week under a stereomicroscope to make sure that a thin wound epidermis is not evident anywhere on the amputation surface. For comparison, researchers should also examine the control regenerating limb which should have a wound epidermis over the amputation plane and form a blastema over 2-3 weeks. The wound epidermis will appear thin and clear, while the normal skin will appear more opaque and pale pink (almost white), light yellow, or dark green in leucistic, albino, or wildtype axolotls, respectively.
If researchers wish to collect tissue prior to the blastema formation stages at 2-3 weeks, they should inspect the sutured limbs prior to sample collection to make sure the sutures remained in place and that a small wound epidermis did not form. Additionally, sectioning sagitally through the sutured limb tissue and performing histological analyses at any time point can also verify the presence of the dermis from the full skin flap encircling the entire amputation plane and the absence of a wound epidermis (Figure 3).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/61522/61522fig01.jpg" /> 
Figure 1: Schematic of the steps of the full skin flap surgery. 
The steps of the protocol are numbered and diagrammed here. The dotted lines denote the planes of amputation at steps 1 and 3 of the protocol. <a href="https://www.jove.com/files/ftp_upload/61522/61522fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/61522/61522fig02.jpg" /> 
Figure 2: Examples of successful and unsuccessful full skin flap surgeries. 
Representative brightfield image of a limb that has undergone a successful surgery (left), an unsuccessful surgery (right), and a control regenerating limb (no surgery) at 25 days post-amputation (dpa). The successful surgery has a flat amputation plane where the full skin flap was sutured over, whereas the unsuccessful surgery has a small blastema developing. Arrowheads denote the amputation plane and white dotted lines are there to aid visualization of the absence of a blastema in the successful surgery and presence of blastemas in the unsuccessful surgery and control regenerating limbs. <a href="https://www.jove.com/files/ftp_upload/61522/61522fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/61522/61522fig03.jpg" /> 
Figure 3: Histological staining of normal regenerating and FSF sutured limbs. 
(A-B&#8217;) Representative brightfield images of picro-mallory stained sections from regenerating (A-A&#8217;) and sutured axolotl limbs (B-B&#8217;) at 7 dpa. Insets in A and B are shown in A&#8217; and B&#8217;, respectively. The collagen-heavy dermal layer lines and covers the entire amputation plane in sutured limbs. Amputation plane is denoted by arrowheads in A-B. Scale bars represent 500 &#181;m. This figure was adapted from Tsai et al.25. <a href="https://www.jove.com/files/ftp_upload/61522/61522fig03large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Inhibition of Wound Epidermis Formation via Full Skin Flap Surgery During Axolotl Limb Regeneration at JoVE.com

Inhibition of Wound Epidermis Formation via Full Skin Flap Surgery During Axolotl Limb Regeneration

This article describes how to perform a surgical method to inhibit wound epidermis formation during axolotl limb regeneration by immediately suturing full thickness skin over the amputation plane. This method allows researchers to investigate the functional roles of the wound epidermis during the early stages of limb regeneration.

Classical experiments in salamander regenerative biology over the last century have long established that the wound epidermis is a crucial signaling ...

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3.0K Views.  Harvard University. This article describes how to perform a surgical method to inhibit wound epidermis formation during axolotl limb regeneration by immediately suturing full thickness skin over the amputation plane. This method allows researchers to investigate the functional roles of the wound epidermis during the early stages of limb regeneration.

Video: Inhibition of Wound Epidermis Formation via Full Skin Flap Surgery During Axolotl Limb Regeneration

Immunohistochemistry on Paraffin Sections of Mouse Epidermis Using Fluorescent Antibodies

In the epidermis, immunohistochemistry is an efficient means of localizing specific proteins to their relative expression compartment; namely the basal, suprabasal, and stratum corneum layers. The precise localization within the epidermis of a particular protein lends clues toward its functional role within the epidermis. In this chapter, we describe a reliable method for immunolocalization within the epidermis modified for both frozen and paraffin sections that we use very routinely in our laboratory. Paraffin sections generally provide much better morphology, hence, superior results and photographs; however, not all antibodies will work with the harsh fixation and treatment involved in their processing. Therefore, the protocol for frozen sectioning is also included. Within paraffin sectioning, two fixation protocols are described (Bouin's and paraformaldehyde); the choice of fixative will be directly related to the antibody specifications and may require another fixing method.

We describe a reliable method for immunolocalization within the epidermis modified for both frozen and paraffin sections that we use very routinely in our laboratory.

In the epidermis, immunohistochemistry is an efficient means of localizing specific proteins to their relative expression compartment; namely the basal, ...

Rapid Genetic Analysis of Epithelial-Mesenchymal Signaling During Hair Regeneration

Hair follicle morphogenesis, a complex process requiring interaction between epithelia-derived keratinocytes and the underlying mesenchyme, is an attractive model system to study organ development and tissue-specific signaling. Although hair follicle development is genetically tractable, fast and reproducible analysis of factors essential for this process remains a challenge. Here we describe a procedure to generate targeted overexpression or shRNA-mediated knockdown of factors using lentivirus in a tissue-specific manner. Using a modified version of a hair regeneration model 5, 6, 11, we can achieve robust gain- or loss-of-function analysis in primary mouse keratinocytes or dermal cells to facilitate study of epithelial-mesenchymal signaling pathways that lead to hair follicle morphogenesis. We describe how to isolate fresh primary mouse keratinocytes and dermal cells, which contain dermal papilla cells and their precursors, deliver lentivirus containing either shRNA or cDNA to one of the cell populations, and combine the cells to generate fully formed hair follicles on the backs of nude mice. This approach allows analysis of tissue-specific factors required to generate hair follicles within three weeks and provides a fast and convenient companion to existing genetic models.

Tissue-specific analysis of a hair follicle regeneration model using lentivirus to mediate gain- or loss-of-function.

Hair follicle morphogenesis, a complex process requiring interaction between epithelia-derived keratinocytes and the underlying mesenchyme, is an ...

Long-term, High-resolution Confocal Time Lapse Imaging of Arabidopsis Cotyledon Epidermis during Germination

Imaging in vivo dynamics of cellular behavior throughout a developmental sequence can be a powerful technique for understanding the mechanics of tissue patterning. During animal development, key cell proliferation and patterning events occur very quickly. For instance, in Caenorhabditis elegans all cell divisions required for the larval body plan are completed within six hours after fertilization, with seven mitotic cycles1; the sixteen or more mitoses of Drosophila embryogenesis occur in less than 24 hr2. In contrast, cell divisions during plant development are slow, typically on the order of a day 3,4,5 . This imposes a unique challenge and a need for long-term live imaging for documenting dynamic behaviors of cell division and differentiation events during plant organogenesis. Arabidopsis epidermis is an excellent model system for investigating signaling, cell fate, and development in plants. In the cotyledon, this tissue consists of air- and water-resistant pavement cells interspersed with evenly distributed stomata, valves that open and close to control gas exchange and water loss. Proper spacing of these stomata is critical to their function, and their development follows a sequence of asymmetric division and cell differentiation steps to produce the organized epidermis (Fig. 1).
This protocol allows observation of cells and proteins in the epidermis over several days of development. This time frame enables precise documentation of stem-cell divisions and differentiation of epidermal cells, including stomata and epidermal pavement cells. Fluorescent proteins can be fused to proteins of interest to assess their dynamics during cell division and differentiation processes. This technique allows us to understand the localization of a novel protein, POLAR6, during the proliferation stage of stomatal-lineage cells in the Arabidopsis cotyledon epidermis, where it is expressed in cells preceding asymmetric division events and moves to a characteristic area of the cell cortex shortly before division occurs. Images can be registered and streamlined video easily produced using public domain software to visualize dynamic protein localization and cell types as they change over time.

Long-term, High-resolution Confocal Time Lapse Imaging of Arabidopsis Cotyledon Epidermis during Germination

We describe a protocol using chamber slides and media to immobilize plant cotyledons for confocal imaging of the epidermis over several days of development, documenting stomatal differentiation. Fluorophore-tagged proteins can be tracked dynamically by expression and subcellular localization, increasing understanding of their possible roles during cell division and cell-type differentiation.

Imaging in vivo dynamics of cellular behavior throughout a developmental sequence can be a powerful technique for understanding the mechanics of tissue ...

Visualizing Cytoplasmic Flow During Single-cell Wound Healing in Stentor coeruleus

Although wound-healing is often addressed at the level of whole tissues, in many cases individual cells are able to heal wounds within themselves, repairing broken cell membrane before the cellular contents leak out. The giant unicellular organism Stentor coeruleus, in which cells can be more than one millimeter in size, have been a classical model organism for studying wound healing in single cells. Stentor cells can be cut in half without loss of viability, and can even be cut and grafted together. But this high tolerance to cutting raises the question of why the cytoplasm does not simply flow out from the size of the cut. Here we present a method for cutting Stentor cells while simultaneously imaging the movement of cytoplasm in the vicinity of the cut at high spatial and temporal resolution. The key to our method is to use a &#34;double decker&#34; microscope configuration in which the surgery is performed under a dissecting microscope focused on a chamber that is simultaneously viewed from below at high resolution using an inverted microscope with a high NA lens. This setup allows a high level of control over the surgical procedure while still permitting high resolution tracking of cytoplasm.

Visualizing Cytoplasmic Flow During Single-cell Wound Healing in Stentor coeruleus

The giant ciliate Stentor coeruleus is a classical system for studying regeneration and wound healing in single cells.&#160;By imaging Stentor cells simultaneously at low and high magnification it is possible to measure cytoplasmic flows before, during, and after wounding.

Although wound-healing is often addressed at the level of whole tissues, in many cases individual cells are able to heal wounds within themselves, ...

Methods for Skin Wounding and Assays for Wound Responses in C. elegans

The C. elegans epidermis and cuticle form a simple yet sophisticated skin layer that can repair localized damage resulting from wounding. Studies of wound responses and repair in this model have illuminated our understanding of the cytoskeletal and genomic responses to tissue damage. The two most commonly used methods to wound the C. elegans adult skin are pricks with microinjection needles, and local laser irradiation. Needle wounding locally disrupts the cuticle, epidermis, and associated extracellular matrix, and may also damage internal tissues. Laser irradiation results in more localized damage. Wounding triggers a succession of readily assayed responses including elevated epidermal Ca2+ (seconds-minutes), formation and closure of an actin-containing ring at the wound site (1-2 hr), elevated transcription of antimicrobial peptide genes (2-24 hr), and scar formation. Essentially all wild type adult animals survive wounding, whereas mutants defective in wound repair or other responses show decreased survival. Detailed protocols for needle and laser wounding, and assays for quantitation and visualization of wound responses and repair processes (Ca dynamics, actin dynamics, antimicrobial peptide induction, and survival) are presented.

Methods for Skin Wounding and Assays for Wound Responses in C. elegans

The adult C. elegans skin is a tractable model for studies of epithelial wound responses, including wound closure, scar formation, and innate immunity.

The C. elegans epidermis and cuticle form a simple yet sophisticated skin layer that can repair localized damage resulting from wounding. Studies of wound ...

Quantifying Leukocyte Egress via Lymphatic Vessels from Murine Skin and Tumors

Leukocyte egress from peripheral tissues to draining lymph nodes is not only critical for immune surveillance and initiation but also contributes to the resolution of peripheral tissue responses. While a variety of methods are used to quantify leukocyte egress from non-lymphoid, peripheral tissues, the cellular and molecular mechanisms that govern context-dependent egress remain poorly understood. Here, we describe the use of in situ photoconversion for quantitative analysis of leukocyte egress from murine skin and tumors. Photoconversion allows for the direct labeling of leukocytes resident within cutaneous tissue. Though skin exposure to violet light induces local inflammatory responses characterized by leukocyte infiltrates and vascular leakiness, in a head-to-head comparison with transdermal application of fluorescent tracers, photoconversion specifically labeled migratory dendritic cell populations and simultaneously enabled the quantification of myeloid and lymphoid egress from cutaneous microenvironments and tumors. The mechanisms of leukocyte egress remain a missing component in our understanding of intratumoral leukocyte complexity, and thus the application of the tools described herein will provide unique insight into the dynamics of tumor immune microenvironments both at steady state and in response to therapy.

Here, we demonstrate the methods for in vivo quantification of leukocyte egress from na&#239;ve, inflamed, and malignant murine skin. We perform a head-to-head comparison of two models: transdermal FITC application and in situ photoconversion. Furthermore, we demonstrate the utility of photoconversion for tracking leukocyte egress from cutaneous tumors.

Leukocyte egress from peripheral tissues to draining lymph nodes is not only critical for immune surveillance and initiation but also contributes to the ...

Y-27632 Enriches the Yield of Human Melanocytes from Adult Skin Tissues

The isolation and culture of primary melanocytes from skin tissues is very important for biological research and has been widely used for clinical applications. Isolating primary melanocytes from skin tissues by the conventional method usually takes about 3 to 4 weeks to passage sufficiently. More importantly, the tissues used are usually newborn foreskins and it is still a challenge to efficiently isolate primary melanocytes from adult tissues. We recently developed a new isolation method for melanocytes that adds Y-27632, a Rho kinase inhibitor, to the initial culture medium for 48 h. Compared with the conventional protocol, this new method dramatically increases the yield of melanocytes and shortens the time required to isolate melanocytes from foreskin tissues. We now describe this new method in more detail using adult epidermis to efficiently culture primary melanocytes. Importantly, we show that melanocytes obtained from adult tissues prepared by this new method can function normally. This new protocol will significantly benefit studies of pigmentation defects and melanomas using primary melanocytes prepared from easily accessed adult skin tissues.

This paper reports that the addition of Y-27632 to TIVA medium can significantly increase the yield of melanocytes from adult skin tissues.

The isolation and culture of primary melanocytes from skin tissues is very important for biological research and has been widely used for clinical ...

A Murine Model of a Burn Wound Reconstructed with an Allogeneic Skin Graft

Trivial superficial wounds heal without complications by primary intention. Deep wounds, such as full thickness burns, heal by secondary intention and require surgical debridement and skin grafting. Successful integration of the donor graft into a recipient wound bed depends on timely recruitment of immune cells, robust angiogenic response and new extracellular matrix formation. The development of novel therapeutic agents, which target some key processes involved in wound healing, are hindered by the lack of reliable preclinical models with optimized objective assessment of wound closure. Here, we describe an inexpensive and reproducible model of experimental full thickness burn wound reconstructed with an allogeneic skin graft. The wound is induced on the dorsum surface of anaesthetized inbred wild type mice from the BALB/C and SKH1-Hrhr backgrounds. The burn is produced using a brass template measuring 10 mm in diameter, which is preheated to 80 &#176;C and delivered at a constant pressure for 20 s. Burn eschar is excised 24 hours after the injury and replaced with a full thickness graft harvested from the tail of a genetically similar donor mouse. No specialized equipment is required for the procedure and surgical techniques are straightforward to follow. The method may be effortlessly implemented and reproduced in most research settings. Certain limitations are associated with the model. Due to technical difficulties, the harvest of thinner split thickness skin grafts is not possible. The surgical method we describe here allows for the reconstruction of burn wounds using full thickness skin grafts. It may be used to carry out preclinical therapeutic testing.

The aim of this study was to develop a murine model of burn wound healing. A thermal burn was induced on the dorsal skin of mice using a preheated brass template. Burned tissue was debrided and overlaid with a skin graft harvested from the tail of a genetically similar donor mouse.

Trivial superficial wounds heal without complications by primary intention. Deep wounds, such as full thickness burns, heal by secondary intention and ...

Analysis of Motility Patterns of Stentor During and After Oral Apparatus Regeneration Using Cell Tracking

Stentor coeruleus is a well-known model organism for the study of unicellular regeneration. Transcriptomic analysis of individual cells revealed hundreds of genes&#8212;many not associated with the oral apparatus (OA)&#8212;that are differentially regulated in phases throughout the regeneration process. It was hypothesized that this systemic reorganization and mobilization of cellular resources towards growth of a new OA will lead to observable changes in movement and behavior corresponding in time to the phases of differential gene expression. However, the morphological complexity of S. coeruleus necessitated the development of an assay to capture the statistics and timescale. A custom script was used to track cells in short videos, and statistics were compiled over a large population (N ~100). Upon loss of the OA, S. coeruleus initially loses the ability for directed motion; then starting at ~4 h, it exhibits a significant drop in speed until ~8 h. This assay provides a useful tool for the screening of motility phenotypes and can be adapted for the investigation of other organisms.

Analysis of Motility Patterns of Stentor During and After Oral Apparatus Regeneration Using Cell Tracking

We present a protocol for the characterization of motility and behavior of a population of hundred micron- to millimeter-sized cells using brightfield microscopy and cell tracking. This assay reveals that Stentor coeruleus transitions through four behaviorally distinct phases when regenerating a lost oral apparatus.

Stentor coeruleus is a well-known model organism for the study of unicellular regeneration. Transcriptomic analysis of individual cells revealed hundreds ...

Artificial Cartilage Implants for Bone Regeneration via Endochondral Ossification

Integrated Bone Formation Through In Vivo Endochondral Ossification Using Mesenchymal Stem Cells

Conventional bone regeneration therapy using mesenchymal stem cells (MSCs) is difficult to apply to bone defects larger than the critical size because it does not have a mechanism to induce angiogenesis. Implanting artificial cartilage tissue fabricated from MSCs induces angiogenesis and bone formation in vivo via endochondral ossification (ECO). Therefore, this ECO-mediated approach may be a promising bone regeneration therapy in the future. An important aspect of the clinical application of this ECO-mediated approach is establishing a protocol for preparing enough cartilage to be implanted to repair the bone defect. It is especially not practical to design a single mass of grafted cartilage of a size that conforms to the shape of the actual bone defect. Therefore, the cartilage to be transplanted must have the property of forming bone integrally when multiple pieces are implanted. Hydrogels may be an attractive tool for scaling up tissue-engineered grafts for endochondral ossification to meet clinical requirements. Although many naturally derived hydrogels support MSC cartilage formation in vitro and ECO in vivo, the optimal scaffold material to meet the needs of clinical applications has yet to be determined. Hyaluronic acid (HA) is a crucial component of the cartilage extracellular matrix and is a biodegradable and biocompatible polysaccharide. Here, we show that HA hydrogels have excellent properties to support in vitro differentiation of MSC-based cartilage tissue and promote endochondral bone formation in vivo.

Author Spotlight: Enhancing Bone Regeneration with Vascularized Artificial Cartilage Integration 

Bone therapy via endochondral ossification by implanting artificial cartilage tissue produced from mesenchymal stem cells has the potential to circumvent the drawbacks of conventional therapies. Hyaluronic acid hydrogels are effective in scaling up uniformly differentiated cartilage grafts as well as creating integrated bone with vascularization between fused grafts in vivo.

Conventional bone regeneration therapy using mesenchymal stem cells (MSCs) is difficult to apply to bone defects larger than the critical size because it ...