This study was supported by the Jane and Aatos Erkko Foundation.

This protocol involves the use of animals and all the procedures were approved by Ethical Committees on the Use and Care of Animals and the Animal Facility at the University of Helsinki.
1. Preparation of the organ culture dish
<ol>
	<li>Perform all procedures in a laminar flow hood. Clean work surfaces with 70% ethanol and use autoclaved glass instruments and solutions. Sterilize scissors and other metal equipment in a glass-bead sterilizer.</li>
	<li>Prepare filters normally stored in 70% ...

<ol>
	<li>Balic, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biology+explaining+tooth+repair+and+regeneration:+A+mini-review.">Biology explaining tooth repair and regeneration: A mini-review.</a> Gerontology. 64 (4), 382-388 (2018).</li><li>Harada, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Localization+of+putative+stem+cells+in+dental+epithelium+and+their+association+with+Notch+and+FGF+signaling.">Localization of putative stem cells in dental epithelium and their association with Notch and FGF signaling.</a> The Journal of Cell Biology. 147 (1), 105-120 (1999).</li><li>Smith, C. E., Warshawsky, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cellular+renewal+in+the+enamel+organ+and+the+odontoblast+layer+of+the+rat+incisor+as+followed+by+radioautography+using+3H-thymidine.">Cellular renewal in the enamel organ and the odontoblast layer of the rat incisor as followed by radioautography using 3H-thymidine.</a> The Anatomical Record. 183 (4), 523-561 (1975).</li><li>Balic, A., Thesleff, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tissue+interactions+regulating+tooth+development+and+renewal.">Tissue interactions regulating tooth development and renewal.</a> Current Topics in Developmental Biology. 115, 157-186 (2015).</li><li>Scadden, D. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+stem-cell+niche+as+an+entity+of+action.">The stem-cell niche as an entity of action.</a> Nature. 441 (7097), 1075-1079 (2006).</li><li>Juuri, E., 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=Sox2+marks+epithelial+competence+to+generate+teeth+in+mammals+and+reptiles.">Sox2 marks epithelial competence to generate teeth in mammals and reptiles.</a> Development. 140 (7), 1424-1432 (2013).</li><li>Juuri, E., 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=Sox2++stem+cells+contribute+to+all+epithelial+lineages+of+the+tooth+via+Sfrp5++progenitors.">Sox2+ stem cells contribute to all epithelial lineages of the tooth via Sfrp5+ progenitors.</a> Developmental Cell. 23 (2), 317-328 (2012).</li><li>Feng, J., Mantesso, A., De Bari, C., Nishiyama, A., Sharpe, P. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dual+origin+of+mesenchymal+stem+cells+contributing+to+organ+growth+and+repair.">Dual origin of mesenchymal stem cells contributing to organ growth and repair.</a> Proceedings of the National Academy of Sciences of the United States of America. 108 (16), 6503-6508 (2011).</li><li>Kaukua, 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=Glial+origin+of+mesenchymal+stem+cells+in+a+tooth+model+system.">Glial origin of mesenchymal stem cells in a tooth model system.</a> Nature. 513 (7519), 551-554 (2014).</li><li>Zhao, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Secretion+of+shh+by+a+neurovascular+bundle+niche+supports+mesenchymal+stem+cell+homeostasis+in+the+adult+mouse+incisor.">Secretion of shh by a neurovascular bundle niche supports mesenchymal stem cell homeostasis in the adult mouse incisor.</a> Cell Stem Cell. 14 (2), 160-173 (2014).</li><li>Vidovic, I., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=alphaSMA-expressing+perivascular+cells+represent+dental+pulp+progenitors+in+vivo.">alphaSMA-expressing perivascular cells represent dental pulp progenitors in vivo.</a> Journal of Dental Research. 96 (3), 323-330 (2017).</li><li>Trowell, O. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+modified+technique+for+organ+culture+in+vitro.">A modified technique for organ culture in vitro.</a> Experimental Cell Research. 6 (1), 246-248 (1954).</li><li>Saxen, L., Vainio, T., Toivonen, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+polyoma+virus+on+mouse+kidney+rudiment+in+vitro.">Effect of polyoma virus on mouse kidney rudiment in vitro.</a> Journal of the National Cancer Institute. 29, 597-631 (1962).</li><li>Thesleff, I., Sahlberg, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Organ+culture+in+the+analysis+of+tissue+interactions.">Organ culture in the analysis of tissue interactions.</a> Methods in Molecular Biology. 461, 23-30 (2008).</li><li>Jarvinen, E., Shimomura-Kuroki, J., Balic, A., Jussila, M., Thesleff, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mesenchymal+Wnt/beta-catenin+signaling+limits+tooth+number.">Mesenchymal Wnt/beta-catenin signaling limits tooth number.</a> Development. 145 (4), (2018).</li><li>Ahtiainen, L., Uski, I., Thesleff, I., Mikkola, M. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Early+epithelial+signaling+center+governs+tooth+budding+morphogenesis.">Early epithelial signaling center governs tooth budding morphogenesis.</a> The Journal of Cell Biology. 214 (6), 753-767 (2016).</li><li>Narhi, K., Thesleff, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Explant+culture+of+embryonic+craniofacial+tissues:+analyzing+effects+of+signaling+molecules+on+gene+expression.">Explant culture of embryonic craniofacial tissues: analyzing effects of signaling molecules on gene expression.</a> Methods in Molecular Biology. 666, 253-267 (2010).</li><li>Yang, Z., Balic, A., Michon, F., Juuri, E., Thesleff, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mesenchymal+Wnt/beta-Catenin+signaling+controls+epithelial+stem+cell+homeostasis+in+teeth+by+inhibiting+the+antiapoptotic+effect+of+Fgf10.">Mesenchymal Wnt/beta-Catenin signaling controls epithelial stem cell homeostasis in teeth by inhibiting the antiapoptotic effect of Fgf10.</a> Stem Cells. 33 (5), 1670-1681 (2015).</li><li>Binder, 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=Functionally+distinctive+Ptch+receptors+establish+multimodal+hedgehog+signaling+in+the+tooth+epithelial+stem+cell+niche.">Functionally distinctive Ptch receptors establish multimodal hedgehog signaling in the tooth epithelial stem cell niche.</a> Stem Cells. 37 (9), 1238-1248 (2019).</li><li>Harada, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Localization+of+putative+stem+cells+in+dental+epithelium+and+their+association+with+Notch+and+FGF+signaling.">Localization of putative stem cells in dental epithelium and their association with Notch and FGF signaling.</a> The Journal of Cell Biology. 147 (1), 105-120 (1999).</li><li>Seidel, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hedgehog+signaling+regulates+the+generation+of+ameloblast+progenitors+in+the+continuously+growing+mouse+incisor.">Hedgehog signaling regulates the generation of ameloblast progenitors in the continuously growing mouse incisor.</a> Development. 137 (22), 3753-3761 (2010).</li><li>Hadjantonakis, A. K., Nagy, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=FACS+for+the+isolation+of+individual+cells+from+transgenic+mice+harboring+a+fluorescent+protein+reporter.">FACS for the isolation of individual cells from transgenic mice harboring a fluorescent protein reporter.</a> Genesis. 27 (3), 95-98 (2000).</li><li>Yu, Y. A., Szalay, A. A., Wang, G., Oberg, K. <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+molecular+and+cellular+events+with+green+fluorescent+proteins+in+developing+embryos:+a+review.">Visualization of molecular and cellular events with green fluorescent proteins in developing embryos: a review.</a> Luminescence. 18 (1), 1-18 (2003).</li><li>D'Amour, K. A., Gage, F. 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In vitro organ culture has been used extensively to study inductive potential and epithelial-mesenchymal interactions that govern organ growth and morphogenesis. The Thesleff laboratory has demonstrated how to adapt the Sax&#233;n modification of the Trowell-type organ culture and use it to study tooth development14. The reproducible conditions and advancements in fluorescent reporters have made this a useful method for monitoring tooth morphogenesis and the distinct cell populations with...

Mouse incisors grow continuously due to life-long preservation of the stem cells (SC) that support the unceasing production of tooth components. These include epithelial SCs, which generate enamel-producing ameloblasts, and mesenchymal stem cells (MSCs), which generate dentin-producing odontoblasts, among other cells1. The epithelial SCs in the continuously growing incisors were initially identified as label-retaining cells2,3 and have since been shown to express a number of well-known stemness genes, including Sox24. These cells share common features with epithelial SCs in other organs and reside within the SC niche called the cervical loop located on the labial side of the incisor. The niche is a dynamic entity composed of cells and extracellular matrix that control SC activity5. Lineage-tracing studies have demonstrated that Sox2+ epithelial SCs can regenerate the whole epithelial compartment of the tooth and that they are crucial for successional tooth formation6,7. MSCs with dentin reparative or regenerative potential are largely recruited from outside the organ through blood vessels and nerves8,9,10,11, therefore, providing a suitable model to study recruitment, migration, and housing of the MSC population.
To study SCs in vivo is not always feasible, since many of the genetic and/or pharmacological manipulations can affect organ homeostasis and/or have lethal consequences. Therefore, organ culture provides an excellent tool to study regulation of SCs and their niches in vitro. The organ culture system that utilizes a metal grid was initially developed by Trowell12 to study organ development and has been further modified by Saxen13&#160;to study inductive signals in kidney development. Since then, this in vitro method of culturing the whole or part of the organ has been successfully applied in different fields. In the field of tooth development, this method has been widely used to study the epithelial-mesenchymal interactions that govern tooth development14&#160;and successional tooth formation15. The work of the Thesleff laboratory has demonstrated the utility of this system for temporal analysis of tooth growth and morphogenesis, for analysis of the effect of various molecules and growth factors on tooth growth, and for time-lapse live imaging of tooth development16,17. More recently, this method has been utilized to study regulation of incisor SCs and their niche18,19, which is described in detail here.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>1-mL plastic syringes</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Disposable 20/26 gauge hypodermic needles</td>
			<td>Terumo</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>DMEM</td>
			<td>Gibco</td>
			<td>61965-026</td>
			<td></td>
		</tr>
		<tr>
			<td>Dulbecco&#39;s Phosphate-Buffered Saline</td>
			<td>Gibco</td>
			<td>14287</td>
			<td></td>
		</tr>
		<tr>
			<td>Extra Fine Bonn Scissors</td>
			<td>F.S.T.</td>
			<td>14084-08</td>
			<td></td>
		</tr>
		<tr>
			<td>F-12</td>
			<td>Gibco</td>
			<td>31765-027</td>
			<td></td>
		</tr>
		<tr>
			<td>FBS South American (CE)</td>
			<td>LifeTechn.</td>
			<td>10270106</td>
			<td>divide in aliquotes, store at -20&#176;C</td>
		</tr>
		<tr>
			<td>Glass bead sterilizer, Steri 250 Seconds-Sterilizer</td>
			<td>Simon Keller Ltd</td>
			<td>4AJ-6285884</td>
			<td></td>
		</tr>
		<tr>
			<td>GlutaMAX-1 (200 mM L-alanyl-L-glutamine dipeptide)</td>
			<td>Gibco</td>
			<td>35050-038</td>
			<td></td>
		</tr>
		<tr>
			<td>Isopore Polycarb.Filters, 0,1 um 25-mm diameter</td>
			<td>MerckMillipore</td>
			<td>VCTP02500</td>
			<td>Store in 70% ethanol at room temperature.</td>
		</tr>
		<tr>
			<td>L-Ascobic Acid</td>
			<td>Sigma</td>
			<td>A4544-25g</td>
			<td>diluted 100 mg/ml in MilliQ, filter strerilized and divided in 20&#956;l aliquotes, store at dark, -20&#176;C</td>
		</tr>
		<tr>
			<td>Low melting agarose</td>
			<td>TopVision</td>
			<td>R0801</td>
			<td></td>
		</tr>
		<tr>
			<td>Metal grids</td>
			<td></td>
			<td></td>
			<td>Commercially available, or self-made from stainless-steel mesh (corrosion resistant, size of mesh 0.7 mm). Cut approximately 30 mm diameter disk and bend the edges to give 3 mm height. Use nails to make holes.</td>
		</tr>
		<tr>
			<td>Micro forceps</td>
			<td>Medicon</td>
			<td>07.60.03</td>
			<td></td>
		</tr>
		<tr>
			<td>Paraformaldehyde</td>
			<td>Sigma-Aldrich</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Penicillin-Streptomycin (10,000U/ml) sol.</td>
			<td>Gibco</td>
			<td>15140-148</td>
			<td></td>
		</tr>
		<tr>
			<td>Petri dishes, Soda-Lime glass</td>
			<td>DWK Life Sciences</td>
			<td>9170442</td>
			<td></td>
		</tr>
		<tr>
			<td>Petridish 35 mm, with vent</td>
			<td>Duran</td>
			<td>237554008</td>
			<td></td>
		</tr>
		<tr>
			<td>Petridish 90 mm, no vent classic</td>
			<td>Thermo Fisher</td>
			<td>101RT/C</td>
			<td></td>
		</tr>
		<tr>
			<td>Small scissors</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

use of trowell-type organ culture to study regulation of dental stem cells

Organ development, function, and regeneration depend on stem cells, which reside within discrete anatomical spaces called stem cell niches. The continuously growing mouse incisor provides an excellent model to study tissue-specific stem cells. The epithelial tissue-specific stem cells of the incisor are located at the proximal end of the tooth in a niche called the cervical loop. They provide a continuous influx of cells to counterbalance the constant abrasion of the self-sharpening tip of the tooth. Presented here is a detailed protocol for the isolation and culture of the proximal end of the mouse incisor that houses stem cells and their niche. This is a modified Trowell-type organ culture protocol that enables in vitro culture of tissue pieces (explants), as well as the thick tissue slices at the liquid/air interface on a filter supported by a metal grid. The organ culture protocol described here enables tissue manipulations not feasible in vivo, and when combined with the use of a fluorescent reporter(s), it provides a platform for the identification and tracking of discrete cell populations in live tissues over time, including stem cells. Various regulatory molecules and pharmacological compounds can be tested in this system for their effect on stem cells and their niches. This ultimately provides a valuable tool to study stem cell regulation and maintenance.

The epithelial SCs reside in a niche called the cervical loop, which is located at the proximal end of the incisor (Figure 3A). Cervical loops are morphologically distinct structures composed of inner and outer enamel epithelium that encase the stellate reticulum, a core of loosely arranged epithelial cells (Figure 3B,C). There are two cervical loops in each incisor (Figure 3A), but only the labial cervical loop con...

Watch this Scientific Journal Video about Use of Trowell-Type Organ Culture to Study Regulation of Dental Stem Cells at JoVE.com

Use of Trowell-Type Organ Culture to Study Regulation of Dental Stem Cells

The Trowell-type organ culture method has been used to unravel complex signaling networks that govern tooth development and, more recently, for studying regulation involved in stem cells of the continuously growing mouse incisor. Fluorescent-reporter animal models and live-imaging methods facilitate in-depth analyses of dental stem cells and their specific niche microenvironment.

Organ development, function, and regeneration depend on stem cells, which reside within discrete anatomical spaces called stem cell niches. The ...

The Trowell-type organ culture is used to culture tissue explants. Here, we show how to use this method to study the stem cells in continuously-growing teeth. With this technique, we can study the stem cells and their behavior in the niche and screen the effect of various molecules on the survival and maintenance of stem cells.This method can be applied to study the stem cells of other organs as well, such as skin or mammary gland. Begin by placing 30-millimeter metal grids with one to two-millimeter diameter holes in a 35-millimeter Petri dish. Fill the place with media until the media reaches the grid surface.Then, incubate the plate at 37 degrees Celsius until the tissue is isolated and ready to culture. After decapitating the mouse, remove the skin to expose the mandible and cut through the masseter muscles to separate the mandible from the maxilla and the rest of the head. Once the mandible is isolated, remove the tongue and maximum soft tissue.Split the mandible at the midline by cutting through the symphysis. Place the mandible in the Petri dish containing PBS on the ice. Use a disposable 20 by 26 gauge hypodermic needle to dissect the incisor.Then, clean the soft tissue and muscle tissue from the bone surface for better visualization. For mandibles obtained from animals younger than 10 days, use disposable 20 by 26 gauge hypodermic needles to open each half of the mandible longitudinally to expose the incisor tooth. Gently detach the incisor from the surrounding bone.Cut the proximal end that contains the cervical loop and remove the mineralized enamel and dentin matrix. Keep the collected proximal ends in Dulbecco's PBS on ice until ready to culture. For mice older than 10 days, open each half of the mandible longitudinally to expose the incisor tooth.Use tweezers to grip the mandible and break the bone to expose the tooth. Cut the proximal end that contains the cervical loop. Keep the collected proximal ends in Dulbecco's PBS on ice until ready to culture.Carefully place the rectangle filters on top of the grid in a pre-warmed culture dish and properly orient the tissue pieces. Incubate the plate at 37 degrees Celsius, 5%carbon dioxide, and 90 to 95%humidity. Carefully change the medium on alternate days, avoiding the formation of air bubbles.Monitor the tissue growth and capture images daily. Remove the culture medium from the dish and carefully add ice-cold methanol to the tissue. Then, incubate it for five minutes.Transfer a filter carrying the tissue explant to the sampling tube filled with fixing solution. Fix the explant in 4%paraformaldehyde prepared in PBS for maximum overnight at four degrees Celsius. The epithelial stem cells reside in a niche called the cervical loop, located at the proximal end of the incisor.The cervical loop comprises an inner and outer enamel epithelium that encases the stellate reticulum, a core of loosely-arranged epithelial cells. Each incisor has one labial and one lingual cervical loop but only the labial cervical loop contains the stem cells. The proximal end of an incisor, isolated from two-day postnatal Sox2-GFP mice, were captured, enabling the identification and visualization of the Sox2-expressing incisor epithelial stem cells.In cervical loops isolated from the Sox2-GFP and Fucci red transgenic mice, GFP-positive stem cells and Fucci-red-positive non-proliferative cells were identified. The Sox2-GFP expression was used as a reporter to analyze the effect of Wnt/beta-catenin signaling activator BIO, which negatively affected Sox2-expressing stem cells as well as the GFP expression. This technique can be optimized for live imaging of the stem cell behavior.Pressed or cultured explants can also be processed enzymatically to single-cell suspensions for further analysis.

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JoVE Journal

Developmental Biology

1.9K visualizações.  University of Helsinki. A cultura de órgãos do tipo Trowell é usada para cultivar explantes de tecidos. Aqui, mostramos como usar esse método para estudar as células-tronco em dentes de crescimento contínuo. Com esta técnica, podemos estudar as células-tronco e seu comportamento no nicho e rastrear o efeito de várias moléculas na sobrevivência e manutenção das células-tronco.Este método pode ser aplicado para estudar as células-tronco de outros órgãos também, como a pele ou a glândula mam?...