The authors thank Alex Schier for kindly sharing the Zebrabow-M transgenic line, Geoffrey Burns for the pDEST vector and Renee Ethier-Daigle for excellent care of the fish facility and lines.
FUNDING:
We are grateful for generous funding support from NIDCR RO3DE024490 and Shriners Hospitals for Children (E.C.L.) and post-doctoral training fellowships from Shriners Hospitals for Children (L.R. and Y.K).

Massachusetts General Hospital Institutional Animal Care and Use Committee (IACUC) approved all procedures under protocol number #2010N000106. This is in compliance with the Association for Assessment and Accreditation of Laboratory Animal Care International (AAALAC) guidelines.
1. Reagents and Materials Preparation
<ol>
	<li>Prepare 1 L of 50X E3 embryo medium (See Table 1) and prepare 1 L of 1X E3 embryo medium (See Table 2).</li>
	<li>Prepare E3 embryo medium with N-Phenylthiourea (PTU) by adding 30 mg of PTU to 1 L of 1X E3. Stir O/N to ensure that the PTU has completely dissolved. Store at RT.</li>
	<li>To prepare pronase solution, dilute 150 &#181;l&#160;of pronase (0.5 mg/ml) with 15 ml&#160;of 1X E3. This amount is sufficient for 1 petri dish. Use immediately.</li>
	<li>Prepare Methylcellulose solution.
	<ol>
		<li>Prepare E3-tricaine solution by mixing 75 ml&#160;of 0.2% tricaine with 25 ml&#160;of 1X E3. Boil 3 g of methylcellulose in the 75 ml&#160;of E3-tricaine solution.</li>
		<li>Make up the final volume to 100 ml&#160;with E3-tricaine solution. The final methylcellulose solution is viscous and opaque with a yellowish tint. Storage: RT protected from the light.</li>
	</ol>
	</li>
	<li>Tamoxifen stock and induction solution
	<ol>
		<li>Prepare 5 mM tamoxifen stock solution by dissolving 4-hydroxytamoxifen in 100% ethanol. Store stock at -80 &#176;C.</li>
		<li>Prepare fresh dilution of tamoxifen at the desire concentration in 1X E3 to obtain the induction solution. CAUTION! Please consult MSDS before use.</li>
	</ol>
	</li>
	<li>Prepare 1 L of 0.2% tricaine as per Table 3.</li>
	<li>Obtain confocal slides. Glue four coverglass (18 x 18) together to form a block then place 2 blocks on a 24 x 60 coverglass 2 cm apart to allow mounting of the embryo in the middle.</li>
</ol>
2. Embryo Preparation
<ol>
	<li>Transgenic lines. 
	NOTE: Zebrabow-M was a generous gift from Alex Schier&#8217;s laboratory.</li>
	<li>sox10: ERT2-Cre 
	NOTE: Generate the targeting vector pDestTol2-sox10:ERT2-Cre using standard molecular cloning methods and commercially obtained recombination cloning technology.
	<ol>
		<li>Combine 5&#8217; entry clone (pENTR5&#8217;-sox10p) containing 7.2Kb of the sox10 promoter, a Gateway middle clone (pME-ERT2-Cre), and a 3&#8217; entry clone (pENTR3&#8217;-polyA) in an LR reaction with lens destination vector pDestTol2-&#945;-crystallin:YFP.</li>
		<li>Purify construct pDestTol2-sox10:ERT2-Cre. Co-inject the purified construct (100 ng/&#181;l) with Tol2 transposase mRNA (50 ng/&#181;l) into WT embryos (F0) at the one cell stage.</li>
		<li>Screen F0 adult founders for germ-line transmission based on strong yellow fluorescence in F1 embryos.</li>
	</ol>
	</li>
	<li>sox10: ERT2-Cre;Zebrabow-M
	<ol>
		<li>Outcross the Zebrabow-M line (2.1.1) with the sox10:ERT2-Cre transgenic line.</li>
		<li>Select embryos exhibiting a strong ubiquitous RFP expression and YFP lens marker and grow them till adults.</li>
	</ol>
	</li>
</ol>
3. Embryo Collection
<ol>
	<li>Set up several pairs of sox10:ERT2-Cre;Zebrabow-M transgenic zebrafish between 5 pm and 6 pm on Day 1.</li>
	<li>The following day, pull the dividers in the morning and collect the eggs around noon.</li>
	<li>Transfer them to petri dishes and add 15 ml&#160;of the pronase solution to dechorionate the embryos.</li>
	<li>Incubate the embryos for 1 to 5 min&#160;until approximately 60% of the embryos have been dechorionated. Stop the reaction by decanting the pronase solution and wash the embryos 3-4 times with fresh E3 medium.</li>
	<li>Incubate the dechorionated embryos in E3 at RT O/N and let them develop to reach the 10 somites stage. Incubate 50-60 embryos per clutch to avoid different developmental growth.</li>
</ol>
4. Treatment
<ol>
	<li>Check the embryos&#8217; developmental stage under a light field microscope to ensure they are at the 10 somites stage.</li>
	<li>Using a fluorescent microscope with a red fluorescent protein (RFP) filter, isolate the bright red embryos.</li>
	<li>Proceed to the induction of the Cre-recombination by adding 10 &#181;M of hydroxytamoxifen solution to the petri dish and incubating the isolated embryos at 28.5 &#176;C for 3 hr.</li>
	<li>Decant the tamoxifen solution and wash the embryos several times with E3. 
	CAUTION! discard the tamoxifen solution in a special biological waste container.</li>
	<li>Incubate the embryos at 28.5 &#176;C O/N.</li>
	<li>When the embryos are approximately the 28-29 somites stage (around 24 hr post fertilization), incubate the embryos at 28.5 &#176;C in E3-PTU solution hereafter. 
	NOTE: PTU is here used to inhibit formation of melanophores in the developing embryos. This treatment is necessary to avoid the signal distortion of fluorescence by auto-fluorescent melanophores.</li>
	<li>Incubate the embryos at 28.5 &#176;C</li>
</ol>
5. Embryo Selection
<ol>
	<li>To visualize the fully developed craniofacial structures, select the embryos at 4 days post fertilization for the intensity of the Red signal and Cre expression marker positivity (yellow in the retina).</li>
	<li>Anesthetize the embryos with E3/0.015% tricaine solution. Anesthesia is confirmed when no active movements or fin activity is observed when gently prodding the embryo.</li>
</ol>
6. Mounting the Embryo in Methycellulose
<ol>
	<li>Transfer the selected embryo for imaging into a petri dish containing a drop of methylcellulose and gently embalm the embryo with methylcellulose.</li>
	<li>On a clean confocal slide, place a drop of fresh methylcellulose and mount your embryo within the drop using a microloader tip. Position embryo dorsally taking caution not to touch the embryo directly.</li>
	<li>Cover the mounted embryo with a 25 x 25 coverslip and adjust the position of the embryo if necessary by manipulating the coverslip.</li>
	<li>The embryo is now ready to image.</li>
</ol>
7. Analysis by Fluorescence Microscopy
<ol>
	<li>Use the 20x dry lens objective (numerical aperture 0.75; pinhole size 2.0 &#181;m) for focusing the embryo.</li>
	<li>Press the L100 button on the microscope and select the channels in the software.</li>
	<li>Select the confocal setup button and click &#8216;auto&#8217; and select the following channels before closing the window: Ch1: CFP, Ch2: GFP, Ch3: RFP or mCherry</li>
	<li>Turn on Ch2 and Ch3 before clicking the &#8216;remove interlock&#8217; button. Click &#8216;play&#8217; to begin scanning.</li>
	<li>Focus on structure of interest, which is best done by starting with &#189; frame/sec and high voltage (HV) 150 and then adjusting the settings accordingly until the desired image quality is achieved. The RFP would be brighter than other colors, therefore adjust the HV. Change the Z position to find both YFP and RFP positive cells.</li>
	<li>Once set with the settings, capture the image of your embryo. Save your picture in the confocal imaging software format and TIFF format for image processing in each split channel.</li>
	<li>Next, for CFP imaging, turn off Ch2 and Ch3 and turn on Ch1. Re-adjust the settings as in step 5 without changing the focus area. 
	NOTE: CFP can be really hard to detect due to background signal in blue channel that can be circumvented by adjusting the pinhole size. A larger pinhole size permits better detection of the fluorescence by reducing signal/background noise ratio. However, a larger pinhole will reduce confocal effect, compromising image quality. Therefore, careful adjustment of the settings is required to achieve the desired image quality and intensity.</li>
	<li>Capture the image and save it in the both format (confocal software and TIFF) for image processing. Images can then be processed using common image processing software to merge layers and improve color settings as described by Pan and colleagues 8.</li>
</ol>

<ol>
	<li>Dougherty, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Distinct+requirements+for+wnt9a+and+irf6+in+extension+and+integration+mechanisms+during+zebrafish+palate+morphogenesis.">Distinct requirements for wnt9a and irf6 in extension and integration mechanisms during zebrafish palate morphogenesis.</a> Development. 140, 76-81 (2013).</li><li>Dougherty, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Embryonic+fate+map+of+first+pharyngeal+arch+structures+in+the+sox10:+kaede+zebrafish+transgenic+model.">Embryonic fate map of first pharyngeal arch structures in the sox10: kaede zebrafish transgenic model.</a> The Journal of craniofacial surgery. 23, 1333-1337 (2012).</li><li>Eberhart, J. K., Swartz, M. E., Crump, J. G., Kimmel, C. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Early+Hedgehog+signaling+from+neural+to+oral+epithelium+organizes+anterior+craniofacial+development.">Early Hedgehog signaling from neural to oral epithelium organizes anterior craniofacial development.</a> Development. 133, 1069-1077 (2006).</li><li>Dixon, M. J., Marazita, M. L., Beaty, T. H., Murray, J. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cleft+lip+and+palate:+understanding+genetic+and+environmental+influences.">Cleft lip and palate: understanding genetic and environmental influences.</a> Nature reviews Genetics. 12, 167-178 (2011).</li><li>Gfrerer, L., Dougherty, M., Liao, E. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Visualization+of+craniofacial+development+in+the+sox10:+kaede+transgenic+zebrafish+line+using+time-lapse+confocal+microscopy.">Visualization of craniofacial development in the sox10: kaede transgenic zebrafish line using time-lapse confocal microscopy.</a> Journal of visualized experiments : JoVE. , e50525 (2013).</li><li>McCollum, C. W., Ducharme, N. A., Bondesson, M., Gustafsson, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Developmental+toxicity+screening+in+zebrafish.+Birth+defects+research.">Developmental toxicity screening in zebrafish. Birth defects research.</a> Part C, Embryo today : reviews. 93, 67-114 (2011).</li><li>Mossey, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dental+education+and+CPD:+are+you+being+served.">Dental education and CPD: are you being served.</a> British dental journal. Suppl, 3-4 (2002).</li><li>Pan, Y. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Zebrabow:+multispectral+cell+labeling+for+cell+tracing+and+lineage+analysis+in+zebrafish.">Zebrabow: multispectral cell labeling for cell tracing and lineage analysis in zebrafish.</a> Development. 140, 2835-2846 (2013).</li><li>Vieira, A. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Journal of dental research. 87, 119-125 (2008).</li><li>Le Pabic, P., Ng, C., Schilling, T. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fat-Dachsous+Signaling+Coordinates+Cartilage+Differentiation+and+Polarity+during+Craniofacial+Development.">Fat-Dachsous Signaling Coordinates Cartilage Differentiation and Polarity during Craniofacial Development.</a> PLoS genetics. 10, e1004726 (2014).</li><li>Ricks, J. E., Ryder, V. M., Bridgewater, L. C., Schaalje, B., Seegmiller, R. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Altered+mandibular+development+precedes+the+time+of+palate+closure+in+mice+homozygous+for+disproportionate+micromelia:+an+oral+clefting+model+supporting+the+Pierre-Robin+sequence.">Altered mandibular development precedes the time of palate closure in mice homozygous for disproportionate micromelia: an oral clefting model supporting the Pierre-Robin sequence.</a> Teratology. 65, 116-120 (2002).</li><li>Javidan, Y., Schilling, T. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+cartilage+and+bone.">Development of cartilage and bone.</a> Methods in cell biology. 76, 415-436 (2004).</li><li>McCarthy, N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pdgfra+protects+against+ethanol-induced+craniofacial+defects+in+a+zebrafish+model+of+FASD.">Pdgfra protects against ethanol-induced craniofacial defects in a zebrafish model of FASD.</a> Development. 140, 3254-3265 (2013).</li></ol>

The authors declare that they have no competing financial interests.

Alcian blue and photoconvertible transgenic lines as described above complements each other to define the intricate process of cartilage and bone development. However, live cellular migration and organization during organogenesis has long been hypothesized and indirectly demonstrated but never visualized. Zebrabow-M transgenic line coupled with a cartilage specific Cre permits simultaneous live observation of all these distinct events involved in bone and cartilage formation. This technique allows the study of lower jaw ...

Craniofacial development requires complex molecular, cellular and tissue interactions to drive cell proliferation, migration and differentiation1,2,3. This tightly regulated and complex process is subject to genetic and environmental perturbations, such that craniofacial deformities are amongst the most common birth malformations1-9. While surgical interventions remain the mainstay of treatment for craniofacial anomalies, understanding the development basis is essential to innovate future therapies. Therefore, studying the morphogenesis and the mechanisms in the convergence and extension and cell integration provides novel insights into the formation of the craniofacial skeleton1.
Cranial neural crest migrate and populate the first pharyngeal arch, then form paired mandibular processes that extend to form the Meckel&#8217;s cartilage, which prefigures the mandible. Morphogenesis of the Meckel&#8217;s cartilage requires chondrocyte organization via directional proliferation, cell polarization and differentiation1,10. However, the intricacy of chondrocyte organization in the growth and extension of the Meckel&#39;s cartilage&#160;remains unclear. Understanding dynamic cell behavior&#160;is critical to understanding congenital malformations affecting mandibular size, such as hypoplastic mandible phenotypes11.
Zebrafish embryos offer many developmental and genetic advantages for detailed study of Meckel&#8217;s cartilage morphogenesis. Their genetic tractability, transparency, ex vivo and rapid development are powerful advantages lending it well for observation of cell movement and organization by live imaging6. Using lineage-tracing tools, such as sox10:kaede transgenic line, we and others have delineated the neural crest origins of the embryonic craniofacial skeleton1,5. Using the sox10:ERT2-Cre with the ubi:Zebrabow-M transgenic line, it is now possible to explore details of cellular movements during craniofacial development. The Zebrabow-M, is a transgenic line engineered with the ubiquitin promoter driving the expression of different fluorophores, each flanked by Lox sites8. The Zebrabow-M default fluorophore is Red, expressing RFP. After induction of Cre expression, the Zebrabow-M construct recombines and cells express a combination of different fluorophores (RFP, CFP and YFP) creating multi-spectral expression in the embryo. All the daughter cells that divide from the labeled cells after the recombination event are then clonally labeled, so that cell populations that derive from different juxtaposed progenitors are clonally labeled. By this cloning cell labeling, cells proliferation and migration with clonal resolution can be followed (Figure 1 and 2).

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>Pronase</td>
			<td>Roche Life Sciences</td>
			<td>10165921001</td>
			<td>Prepare 500 &#956;L stock aliquots at 50mg/mL</td>
		</tr>
		<tr>
			<td>Methylcellulose</td>
			<td>Sigma-Aldrich</td>
			<td>M0262</td>
			<td></td>
		</tr>
		<tr>
			<td>PTU (N-Phenylthiourea)</td>
			<td>Sigma-Aldrich</td>
			<td>P7619</td>
			<td></td>
		</tr>
		<tr>
			<td>Tricaine</td>
			<td>Sigma-Aldrich</td>
			<td>E10521</td>
			<td></td>
		</tr>
		<tr>
			<td>4-HydoxyTamoxifen</td>
			<td>Sigma-Aldrich</td>
			<td>T176</td>
			<td></td>
		</tr>
		<tr>
			<td>24 x 60 coverslips</td>
			<td>Fisher Scientific</td>
			<td>12-548-5P</td>
			<td></td>
		</tr>
		<tr>
			<td>18 x 18 coverslips</td>
			<td>Fisher Scientific</td>
			<td>12-540A</td>
			<td></td>
		</tr>
		<tr>
			<td>25 x 25 coverslips</td>
			<td>Fisher Scientific</td>
			<td>12-540C</td>
			<td></td>
		</tr>
		<tr>
			<td>pENTR5&#39;-TOPO TA Cloning Kit</td>
			<td>Life technologies&#160;</td>
			<td>K591-20</td>
			<td></td>
		</tr>
		<tr>
			<td>pENTR/D-TOPO Cloning Kit&#160;</td>
			<td>Life Technologies</td>
			<td>K2400-20</td>
			<td></td>
		</tr>
		<tr>
			<td>pENTR3&#39;-pA</td>
			<td>Tol2Kit</td>
			<td>302</td>
			<td></td>
		</tr>
		<tr>
			<td>pDEST</td>
			<td></td>
			<td></td>
			<td>Gift from Geoffrey Burns labs</td>
		</tr>
		<tr>
			<td></td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Equipments</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Bright field microscope&#160;</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Fluorescent microscope&#160;</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Confocal microscope</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Image processing software</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

visualization of chondrocyte intercalation and directional proliferation via zebrabow clonal cell analysis in the embryonic meckel&#8217;s cartilage

Development of the vertebrate craniofacial structures requires precise coordination of cell migration, proliferation, adhesion and differentiation. Patterning of the Meckel&#39;s cartilage, a first pharyngeal arch derivative, involves the migration of cranial neural crest (CNC) cells and the progressive partitioning, proliferation and organization of differentiated chondrocytes. Several studies have described CNC migration during lower jaw&#160;morphogenesis, but the details of how the chondrocytes achieve organization in the growth and extension of Meckel&#8217;s cartilage remains unclear. The sox10 restricted and chemically induced Cre recombinase-mediated recombination generates permutations of distinct fluorescent proteins (RFP, YFP and CFP), thereby creating a multi-spectral labeling of progenitor cells and their progeny, reflecting distinct clonal populations. Using confocal time-lapse photography, it is possible to observe the chondrocytes behavior during the development of the zebrafish Meckel&#8217;s cartilage.
Multispectral cell labeling enables scientists to demonstrate extension of the Meckel&#8217;s chondrocytes.&#160;During extension phase of the Meckel&#8217;s cartilage, which prefigures the mandible, chondrocytes intercalate to effect extension as they stack in an organized single-cell layered row. Failure of this organized intercalating process to mediate cell extension provides the cellular mechanistic explanation for hypoplastic mandible that we observe in mandibular malformations.

Traditional cartilage visualization by whole mount Alcian blue stains has been invaluable in observing the developing Meckel&#8217;s cartilage and commonly used to visualize final cellular organization12 (Figure 1A). To further analyze the developing chondrocytes overtime, lineage tracing using sox10:Kaede transgenic lines has enabled us to study cell migration, convergence and extension in live embryos2,12(Figure 1B). However, the organization of chondrocy...

Watch this Scientific Journal Video about Visualization of Chondrocyte Intercalation and Directional Proliferation via Zebrabow Clonal Cell Analysis in the Embryonic Meckelâ€™s Cartilage at JoVE.

Visualization of Chondrocyte Intercalation and Directional Proliferation via Zebrabow Clonal Cell Analysis in the Embryonic Meckel&amp;#8217;s Cartilage

Cell organization of craniofacial bones has long been hypothesized but never directly visualized. Multi-spectral cell labeling and in vivo live imaging allows visualization of dynamic cell behavior in zebrafish lower jaw. Here, we detail the protocol to manipulate Zebrabow transgenic fish and directly observe cell intercalation and morphological changes of chondrocytes in the Meckel&#8217;s cartilage.

Visualization of Chondrocyte Intercalation and Directional Proliferation via Zebrabow Clonal Cell Analysis in the Embryonic Meckel&#8217;s Cartilage

Development of the vertebrate craniofacial structures requires precise coordination of cell migration, proliferation, adhesion and differentiation. ...

visualization-chondrocyte-intercalation-directional-proliferation-via

Research

JoVE Journal

Developmental Biology

9.0K Views.  Harvard Medical School. Cell organization of craniofacial bones has long been hypothesized but never directly visualized. Multi-spectral cell labeling and in vivo live imaging allows visualization of dynamic cell behavior in zebrafish lower jaw. Here, we detail the protocol to manipulate Zebrabow transgenic fish and directly observe cell intercalation and morphological changes of chondrocytes in the Meckel’s cartilage.

Video: Visualization of Chondrocyte Intercalation and Directional Proliferation via Zebrabow Clonal Cell Analysis in the Embryonic Meckel&#8217;s Cartilage

Analysis of Coronary Vessels in Cleared Embryonic Hearts

Whole mount visualization of the embryonic coronary plexus from which the capillary and arterial networks will form is rendered problematic using standard microscopy techniques, due to the scattering of imaging light by the thick heart tissue, as these vessels are localized deep within the walls of the developing heart. As optical clearing of tissues using organic solvents such as BABB (1 part benzyl alcohol to 2 parts benzyl benzoate) has been shown to greatly improve the optical penetration depth that can be achieved, we combined clearance of whole, PECAM1-immunostained hearts, with laser-scanning confocal microscopy, in order to obtain high-resolution images of vessels throughout the entire heart. BABB clearance of embryonic hearts takes place rapidly and also acts to preserve the fluorescent signal for several weeks; in addition, samples can be imaged multiple times without loss of signal. This straightforward method is also applicable to imaging other types of blood vessels in whole embryos.

We present a protocol for the analysis of coronary vessels in whole embryonic murine hearts up to E15.5, using standard immunological staining methods followed by optical clearance and confocal microscopy. This technique enables visualization of blood vessels throughout the entire heart without the need for time-consuming analysis of serial sections.

Whole mount visualization of the embryonic coronary plexus from which the capillary and arterial networks will form is rendered problematic using standard ...

A 5-mC Dot Blot Assay Quantifying the DNA Methylation Level of Chondrocyte Dedifferentiation In Vitro

The dedifferentiation of hyaline chondrocytes into fibroblastic chondrocytes often accompanies monolayer expansion of chondrocytes in vitro. The global DNA methylation level of chondrocytes is considered to be a suitable biomarker for the loss of the chondrocyte phenotype. However, results based on different experimental methods can be inconsistent. Therefore, it is important to establish a precise, simple, and rapid method to quantify global DNA methylation levels during chondrocyte dedifferentiation.
Current genome-wide methylation analysis techniques largely rely on bisulfite genomic sequencing. Due to DNA degradation during bisulfite conversion, these methods typically require a large sample volume. Other methods used to quantify global DNA methylation levels include high-performance liquid chromatography (HPLC). However, HPLC requires complete digestion of genomic DNA. Additionally, the prohibitively high cost of HPLC instruments limits HPLC&#39;s wider application.
In this study, genomic DNA (gDNA) was extracted from human chondrocytes cultured with varying number of passages. The gDNA methylation level was detected using a methylation-specific dot blot assay. In this dot blot approach, a gDNA mixture containing the methylated DNA to be detected was spotted directly onto an N+ membrane as a dot inside a previously drawn circular template pattern. Compared with other gel electrophoresis-based blotting approaches and other complex blotting procedures, the dot blot method saves significant time. In addition, dot blots can detect overall DNA methylation level using a commercially available 5-mC antibody. We found that the DNA methylation level differed between the monolayer subcultures, and therefore could play a key role in chondrocyte dedifferentiation. The 5-mC dot blot is a reliable, simple, and rapid method to detect the general DNA methylation level to evaluate chondrocyte phenotype.

A 5-mC Dot Blot Assay Quantifying the DNA Methylation Level of Chondrocyte Dedifferentiation In Vitro

We present a method to quantify DNA methylation based on the 5-methylcytosine (5-mC) dot blot. We determined the 5-mC levels during chondrocyte dedifferentiation. This simple technique could be used to quickly determine the chondrocyte phenotype in ACI treatment.

The dedifferentiation of hyaline chondrocytes into fibroblastic chondrocytes often accompanies monolayer expansion of chondrocytes in vitro. The global ...

Visualization and Quantitative Analysis of Embryonic Angiogenesis in Xenopus tropicalis

Blood vessels supply oxygen and nutrients throughout the body, and the formation of the vascular network is under tight developmental control. The efficient in vivo visualization of blood vessels and the reliable quantification of their complexity are key to understanding the biology and disease of the vascular network. Here, we provide a detailed method to visualize blood vessels with a commercially available fluorescent dye, human plasma acetylated low density lipoprotein DiI complex (DiI-AcLDL), and to quantify their complexity in Xenopus tropicalis. Blood vessels can be labeled by a simple injection of DiI-AcLDL into the beating heart of an embryo, and blood vessels in the entire embryo can be imaged in live or fixed embryos. Combined with gene perturbation by the targeted microinjection of nucleic acids and/or the bath application of pharmacological reagents, the roles of a gene or of a signaling pathway on vascular development can be investigated within one week without resorting to sophisticated genetically engineered animals. Because of the well-defined venous system of Xenopus and its stereotypic angiogenesis, the sprouting of pre-existing vessels, vessel complexity can be quantified efficiently after perturbation experiments. This relatively simple protocol should serve as an easily accessible tool in diverse fields of cardiovascular research.

Visualization and Quantitative Analysis of Embryonic Angiogenesis in Xenopus tropicalis

This protocol demonstrates a fluorescence-based method to visualize the vasculature and to quantify its complexity in Xenopus tropicalis. Blood vessels can be imaged minutes after the injection of a fluorescent dye into the beating heart of an embryo after genetic and/or pharmacological manipulations to study cardiovascular development in vivo.

Blood vessels supply oxygen and nutrients throughout the body, and the formation of the vascular network is under tight developmental control. The ...

Bioengineering of Humanized Bone Marrow Microenvironments in Mouse and Their Visualization by Live Imaging

Human hematopoietic stem cells (HSCs) reside in the bone marrow (BM) niche, an intricate, multifactorial network of components producing cytokines, growth factors, and extracellular matrix. The ability of HSCs to remain quiescent, self-renew or differentiate, and acquire mutations and become malignant depends upon the complex interactions they establish with different stromal components. To observe the crosstalk between human HSCs and the human BM niche in physiological and pathological conditions, we designed a protocol to ectopically model and image a humanized BM niche in immunodeficient mice. We show that the use of different cellular components allows for the formation of humanized structures and the opportunity to sustain long-term human hematopoietic engraftment. Using two-photon microscopy, we can live-image these structures in situ at the single-cell resolution, providing a powerful new tool for the functional characterization of the human BM microenvironment and its role in regulating normal and malignant hematopoiesis.

A method to create and live-image different humanized bone-marrow niches in mice is presented. Based on the supportive niche created by human mesenchymal cells, the addition of human endothelial cells induces the formation of human vessels, while the addition of rhBMP-2 induces the formation of human-mouse chimeric mature bone tissue.

Human hematopoietic stem cells (HSCs) reside in the bone marrow (BM) niche, an intricate, multifactorial network of components producing cytokines, growth ...

Clonal Analysis of Embryonic Hematopoietic Stem Cell Precursors Using Single Cell Index Sorting Combined with Endothelial Cell Niche Co-culture

The ability to study hematopoietic stem cell (HSC) genesis during embryonic development has been limited by the rarity of HSC precursors in the early embryo and the lack of assays that functionally identify the long-term multilineage engraftment potential of individual putative HSC precursors. Here, we describe methodology that enables the isolation and characterization of functionally validated HSC precursors at the single cell level. First, we utilize index sorting to catalog the precise phenotypic parameter of each individually sorted cell, using a combination of phenotypic markers to enrich for HSC precursors with additional markers for experimental analysis. Second, each index-sorted cell is co-cultured with vascular niche stroma from the aorta-gonad-mesonephros (AGM) region, which supports the maturation of non-engrafting HSC precursors to functional HSC with multilineage, long-term engraftment potential in transplantation assays. This methodology enables correlation of phenotypic properties of clonal hemogenic precursors with their functional engraftment potential or other properties such as transcriptional profile, providing a means for the detailed analysis of HSC precursor development at the single cell level.

Here we present methodology for the clonal analysis of hematopoietic stem cell precursors during murine embryonic development. We combine index sorting of single cells from the embryonic aorta-gonad-mesonephros region with endothelial cell co-culture and transplantation to characterize the phenotypic properties and engraftment potential of single hematopoietic precursors.

The ability to study hematopoietic stem cell (HSC) genesis during embryonic development has been limited by the rarity of HSC precursors in the early ...

Visualization of Tangential Cell Migration in the Developing Chick Optic Tectum

Time-lapse imaging is a powerful method to analyze migrating cell behavior. After fluorescent cell labeling, the movement of the labeled cells in culture can be recorded under video microscopy. For analyzing cell migration in the developing brain, slice culture is commonly used to observe cell migration parallel to the slice section, such as radial cell migration. However, limited information can be obtained from the slice culture method to analyze cell migration perpendicular to the slice section, such as tangential cell migration. Here, we present the protocols for time-lapse imaging to visualize tangential cell migration in the developing chick optic tectum. A combination of cell labeling by electroporation in ovo and a subsequent flat-mount culture on the cell culture insert enables detection of migrating cell movement in the horizontal plane. Moreover, our method facilitates detection of both individual cell behavior and the collective action of a group of cells in the long term. This method can potentially be applied to detect the sequential change of the fluorescent-labeled micro-structure, including the axonal elongation in the neural tissue or cell displacement in the non-neural tissue.

We describe the methods for fluorescent labeling of tangentially migrating cells by electroporation, and for time-lapse imaging of the labeled cell movement in a flat-mount culture in order to visualize migrating cell behavior in the developing chick optic tectum.

Time-lapse imaging is a powerful method to analyze migrating cell behavior. After fluorescent cell labeling, the movement of the labeled cells in culture ...

In Vitro Assays to Evaluate the Migration, Invasion, and Proliferation of Immortalized Human First-trimester Trophoblast Cell Lines

Cell movement is a critical property of trophoblasts during placental development and early pregnancy. The significance of proper trophoblast migration and invasion is demonstrated by pregnancy disorders such as pre-eclampsia and intrauterine growth restriction, which are associated with inadequate trophoblast invasion of the maternal vasculature. Unfortunately, our understanding of the mechanisms by which the placenta develops from migrating trophoblasts is limited. In vitro analysis of cell migration via the scratch assay is a useful tool in identifying factors that regulate trophoblast migratory capacity. However, this assay alone does not define the cellular changes that can result in altered cell migration. This protocol describes three different in vitro assays that are used collectively to evaluate trophoblast cell movement: the scratch assay, the invasion assay, and the proliferation assay. The protocols described here may also be modified for use in other cell lines to quantify cell movement in response to stimuli. These methods allow investigators to identify individual factors that contribute to the cell movement and provide a thorough examination of potential mechanisms underlying apparent changes in cell migration.

Here, we present a highly accessible protocol for evaluating the cell movement in human trophoblast cells using three in vitro assays: the scratch assay, the transwell invasion assay, and the cell proliferation assay.

Cell movement is a critical property of trophoblasts during placental development and early pregnancy. The significance of proper trophoblast migration ...

Microinjection-based System for In Vivo Implantation of Embryonic Cardiomyocytes in the Avian Embryo

Interpreting the relative impact of cell autonomous patterning versus extrinsic microenvironmental influence on cell lineage determination represents a general challenge in developmental biology research. In the embryonic heart, this can be particularly difficult as regional differences in the expression of transcriptional regulators, paracrine/juxtacrine signaling cues, and hemodynamic force are all known to influence cardiomyocyte maturation. A simplified method to alter a developing cardiomyocyte's molecular and biomechanical microenvironment would, therefore, serve as a powerful technique to examine how local conditions influence cell fate and function. To address this, we have optimized a method to physically transplant juvenile cardiomyocytes into ectopic locations in the heart or the surrounding embryonic tissue. This allows us to examine how microenvironmental conditions influence cardiomyocyte fate transitions at single cell resolution within the intact embryo. Here, we describe a protocol in which embryonic myocytes can be isolated from a variety of cardiac sub-domains, dissociated, fluorescently labeled, and microinjected into host embryos with high precision. Cells can then be directly analyzed in situ using a variety of imaging and histological techniques. This protocol is a powerful alternative to traditional grafting experiments that can be prohibitively difficult in a moving tissue such as the heart. The general outline of this method can also be adapted to a variety of donor tissues and host environments, and its ease of use, low cost, and speed make it a potentially useful application for a variety of developmental studies.

In this method, embryonic cardiac tissues are surgically microdissected, dissociated, fluorescently labeled, and implanted into host embryonic tissues. This provides a platform for studying the individual or tissue level developmental organization under ectopic hemodynamic conditions, and/or altered paracrine/juxtacrine environments.

Interpreting the relative impact of cell autonomous patterning versus extrinsic microenvironmental influence on cell lineage determination represents a ...

A Semi-high-throughput Imaging Method and Data Visualization Toolkit to Analyze C. elegans Embryonic Development

C. elegans is the premier system for the systematic analysis of cell fate specification and morphogenetic events during embryonic development. One challenge is that embryogenesis dynamically unfolds over a period of about 13 h; this half day-long timescale has constrained the scope of experiments by limiting the number of embryos that can be imaged. Here, we describe a semi-high-throughput protocol that allows for the simultaneous 3D time-lapse imaging of development in 80&#8211;100 embryos at moderate time resolution, from up to 14 different conditions, in a single overnight run. The protocol is straightforward and can be implemented by any laboratory with access to a microscope with point visiting capacity. The utility of this protocol is demonstrated by using it to image two custom-built strains expressing fluorescent markers optimized to visualize key aspects of germ-layer specification and morphogenesis. To analyze the data, a custom program that crops individual embryos out of a broader field of view in all channels, z-steps, and timepoints and saves the sequences for each embryo into a separate tiff stack was built. The program, which includes a user-friendly graphical user interface (GUI), streamlines data processing by isolating, pre-processing, and uniformly orienting individual embryos in preparation for visualization or automated analysis. Also supplied is an ImageJ macro that compiles individual embryo data into a multi-panel file that displays maximum intensity fluorescence projection and brightfield images for each embryo at each time point. The protocols and tools described herein were validated by using them to characterize embryonic development following knock-down of 40 previously described developmental genes; this analysis visualized previously annotated developmental phenotypes and revealed new ones. In summary, this work details a semi-high-throughput imaging method coupled with a cropping program and ImageJ visualization tool that, when combined with strains expressing informative fluorescent markers, greatly accelerates experiments to analyze embryonic development.

A Semi-high-throughput Imaging Method and Data Visualization Toolkit to Analyze C. elegans Embryonic Development

This work describes a semi-high-throughput protocol that allows simultaneous 3D time-lapse imaging of embryogenesis in 80&#8211;100 C. elegans embryos in a single overnight run. Additionally, image processing and visualization tools are included to streamline data analysis. The combination of these methods with custom reporter strains enables detailed monitoring of embryogenesis.

C. elegans is the premier system for the systematic analysis of cell fate specification and morphogenetic events during embryonic development. One ...

Laser Capture Microdissection of Mouse Embryonic Cartilage and Bone for Gene Expression Analysis

Laser capture microdissection (LCM) is a powerful tool to isolate specific cell types or regions of interest from heterogeneous tissues. The cellular and molecular complexity of skeletal elements increases with development. Tissue heterogeneity, such as at the interface of cartilaginous and osseous elements with each other or with surrounding tissues, is one obstacle to the study of developing cartilage and bone. Our protocol provides a rapid method of tissue processing and isolation of cartilage and bone that yields high quality RNA for gene expression analysis. Fresh frozen tissues of mouse embryos are sectioned and brief cresyl violet staining is used to visualize cartilage and bone with colors distinct from surrounding tissues. Slides are then rapidly dehydrated, and cartilage and bone are isolated subsequently by LCM. The minimization of exposure to aqueous solutions during this process maintains RNA integrity. Mouse Meckel&rsquo;s cartilage and mandibular bone at E16.5 were successfully collected and gene expression analysis showed differential expression of marker genes for osteoblasts, osteocytes, osteoclasts, and chondrocytes. High quality RNA was also isolated from a range of tissues and embryonic ages. This protocol details sample preparation for LCM including cryoembedding, sectioning, staining and dehydrating fresh frozen tissues, and precise isolation of cartilage and bone by LCM resulting in high quality RNA for transcriptomic analysis.

This protocol describes laser capture microdissection for the isolation of cartilage and bone from fresh frozen sections of the mouse embryo. Cartilage and bone can be rapidly visualized by cresyl violet staining and collected precisely to yield high quality RNA for transcriptomic analysis.

Laser capture microdissection (LCM) is a powerful tool to isolate specific cell types or regions of interest from heterogeneous tissues. The cellular and ...