This work was supported by the Ellison Medical Foundation grant AG-NS-0843-11, and the NIH Pilot Grant within the NCI Cancer Center Support Grant P30CA030199 to A.S.

The housing, treatment, and sacrifice of mice were performed following the approved IACUC protocol of the Sanford Burnham Prebys Medical Discovery Institute.
1. Reagent preparation
<ol>
	<li>Prepare 100 mL of cell isolation media: F10 medium supplemented with 10% horse serum (HS).</li>
	<li>Prepare 50 mL of collagenase type II solution: dissolve 1 g of collagenase type II powder in 50 mL of cell isolation media (note the units of the enzyme per 1 mL of media, since the number of units change...

<ol>
	<li>Dagogo-Jack, I., Shaw, A. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tumour+heterogeneity+and+resistance+to+cancer+therapies.">Tumour heterogeneity and resistance to cancer therapies.</a> Nature Reviews Clinical Oncology. 15 (2), 81-94 (2018).</li><li>Wicha, M. S., Liu, S., Dontu, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cancer+stem+cells:+an+old+idea--a+paradigm+shift.">Cancer stem cells: an old idea--a paradigm shift.</a> Cancer Research. 66 (4), 1883-1890 (2006).</li><li>Al-Hajj, M., Wicha, M. S., Benito-Hernandez, A., Morrison, S. J., Clarke, M. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Prospective+identification+of+tumorigenic+breast+cancer+cells.">Prospective identification of tumorigenic breast cancer cells.</a> Proceedings National Academy of Science of the United States of America. 100 (7), 3983-3988 (2003).</li><li>Oishi, N., Yamashita, T., Kaneko, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+biology+of+liver+cancer+stem+cells.">Molecular biology of liver cancer stem cells.</a> Liver Cancer. 3 (2), 71-84 (2014).</li><li>Crous, A. M., Abrahamse, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lung+cancer+stem+cells+and+low-intensity+laser+irradiation:+a+potential+future+therapy.">Lung cancer stem cells and low-intensity laser irradiation: a potential future therapy.</a> Stem Cell Research &amp; Therapy. 4 (5), 129 (2013).</li><li>Tomao, F., 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=Investigating+molecular+profiles+of+ovarian+cancer:+an+update+on+cancer+stem+cells.">Investigating molecular profiles of ovarian cancer: an update on cancer stem cells.</a> Journal of Cancer. 5 (5), 301-310 (2014).</li><li>Zhan, H. X., Xu, J. W., Wu, D., Zhang, T. P., Hu, S. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pancreatic+cancer+stem+cells:+new+insight+into+a+stubborn+disease.">Pancreatic cancer stem cells: new insight into a stubborn disease.</a> Cancer Letters. 357 (2), 429-437 (2015).</li><li>Sharpe, B., Beresford, M., Bowen, R., Mitchard, J., Chalmers, A. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Searching+for+prostate+cancer+stem+cells:+markers+and+methods.">Searching for prostate cancer stem cells: markers and methods.</a> Stem Cell Reviews and Reports. 9 (5), 721-730 (2013).</li><li>Lapidot, T., 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=A+cell+initiating+human+acute+myeloid+leukaemia+after+transplantation+into+SCID+mice.">A cell initiating human acute myeloid leukaemia after transplantation into SCID mice.</a> Nature. 367 (6464), 645-648 (1994).</li><li>Lee, C. -. H., Yu, C. -. C., Wang, B. -. Y., Chang, W. -. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tumorsphere+as+an+effective+in+vitro+platform+for+screening+anti-+cancer+stem+cell+drugs.">Tumorsphere as an effective in vitro platform for screening anti- cancer stem cell drugs.</a> Oncotarget. 7 (2), 1215-1226 (2015).</li><li>Sultan, I., Qaddoumi, I., Yaser, S., Rodriguez-Galindo, C., Ferrari, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparing+adult+and+pediatric+rhabdomyosarcoma+in+the+surveillance,+epidemiology+and+end+results+program.">Comparing adult and pediatric rhabdomyosarcoma in the surveillance, epidemiology and end results program.</a> Journal of Clinical Oncology. 27 (20), 3391-3397 (1973).</li><li>Blum, J. 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+and+overlapping+sarcoma+subtypes+initiated+from+muscle+stem+and+progenitor+cells.">Distinct and overlapping sarcoma subtypes initiated from muscle stem and progenitor cells.</a> Cell Reports. 5 (4), 933-940 (2013).</li><li>Rubin, B. P., 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=Evidence+for+an+unanticipated+relationship+between+undifferentiated+pleomorphic+sarcoma+and+embryonal+rhabdomyosarcoma.">Evidence for an unanticipated relationship between undifferentiated pleomorphic sarcoma and embryonal rhabdomyosarcoma.</a> Cancer Cell. 19 (2), 177-191 (2011).</li><li>Keller, C., 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=Alveolar+rhabdomyosarcomas+in+conditional+Pax3:Fkhr+mice:+cooperativity.">Alveolar rhabdomyosarcomas in conditional Pax3:Fkhr mice: cooperativity.</a> of Ink4a/ARF and Trp53 loss of function. Genes &amp; Development. 18 (21), 2614-2626 (2004).</li><li>Tremblay, A. 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=The+Hippo+transducer+YAP1+transforms+activated+satellite+cells+and+is+a+potent+effector+of+embryonal+rhabdomyosarcoma+formation.">The Hippo transducer YAP1 transforms activated satellite cells and is a potent effector of embryonal rhabdomyosarcoma formation.</a> Cancer Cell. 26 (2), 273-287 (2014).</li><li>Hatley, M. 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=A+mouse+model+of+rhabdomyosarcoma+originating+from+the+adipocyte+lineage.">A mouse model of rhabdomyosarcoma originating from the adipocyte lineage.</a> Cancer Cell. 22 (4), 536-546 (2012).</li><li>Drummond, C. J., 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+Pathway+Drives+Fusion-Negative+Rhabdomyosarcoma+Initiated+From+Non-myogenic+Endothelial+Progenitors.">Hedgehog Pathway Drives Fusion-Negative Rhabdomyosarcoma Initiated From Non-myogenic Endothelial Progenitors.</a> Cancer Cell. 33 (1), 108-124 (2018).</li><li>Almazan-Moga, 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=Hedgehog+Pathway+Inhibition+Hampers+Sphere+and+Holoclone+Formation+in+Rhabdomyosarcoma.">Hedgehog Pathway Inhibition Hampers Sphere and Holoclone Formation in Rhabdomyosarcoma.</a> Stem Cells International. , (2017).</li><li>Walter, D., 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=CD133+positive+embryonal+rhabdomyosarcoma+stem-like+cell+population+is+enriched+in+rhabdospheres.">CD133 positive embryonal rhabdomyosarcoma stem-like cell population is enriched in rhabdospheres.</a> PLoS One. 6 (5), (2011).</li><li>Ciccarelli, C., 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=Key+role+of+MEK/ERK+pathway+in+sustaining+tumorigenicity+and+in+vitro+radioresistance+of+embryonal+rhabdomyosarcoma+stem-like+cell+population.">Key role of MEK/ERK pathway in sustaining tumorigenicity and in vitro radioresistance of embryonal rhabdomyosarcoma stem-like cell population.</a> Molecular Cancer. 15, (2016).</li><li>Deel, M. D., 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=The+Transcriptional+Coactivator+TAZ+Is+a+Potent+Mediator+of+Alveolar+Rhabdomyosarcoma+Tumorigenesis.">The Transcriptional Coactivator TAZ Is a Potent Mediator of Alveolar Rhabdomyosarcoma Tumorigenesis.</a> Clinical Cancer Research. 24 (11), 2616-2630 (2018).</li><li>Boscolo Sesillo, F., Fox, D., Sacco, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Muscle+Stem+Cells+Give+Rise+to+Rhabdomyosarcomas+in+a+Severe+Mouse+Model+of+Duchenne+Muscular+Dystrophy.">Muscle Stem Cells Give Rise to Rhabdomyosarcomas in a Severe Mouse Model of Duchenne Muscular Dystrophy.</a> Cell Reports. 26 (3), 689-701 (2019).</li><li>Chamberlain, J. S., Metzger, J., Reyes, M., Townsend, D., Faulkner, 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=Dystrophin-deficient+mdx+mice+display+a+reduced+life+span+and+are+susceptible+to+spontaneous+rhabdomyosarcoma.">Dystrophin-deficient mdx mice display a reduced life span and are susceptible to spontaneous rhabdomyosarcoma.</a> The FASEB Journal. 21 (9), 2195-2204 (2007).</li><li>Kessel, S., 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=High-Throughput+3D+Tumor+Spheroid+Screening+Method+for+Cancer+Drug+Discovery+Using+Celigo+Image+Cytometry.">High-Throughput 3D Tumor Spheroid Screening Method for Cancer Drug Discovery Using Celigo Image Cytometry.</a> SLAS Technology. 22 (4), 454-465 (2017).</li><li>Johnson, S., Chen, H., Lo, P. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vitro+Tumorsphere+Formation+Assays.">In vitro Tumorsphere Formation Assays.</a> Bio-Protocol. 3 (3), (2013).</li><li>Zhu, Z. W., 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=A+novel+three-dimensional+tumorsphere+culture+system+for+the+efficient+and+low-cost+enrichment+of+cancer+stem+cells+with+natural+polymers.">A novel three-dimensional tumorsphere culture system for the efficient and low-cost enrichment of cancer stem cells with natural polymers.</a> Experimental and Therapeutic. 15 (1), 85-92 (2018).</li><li>Takahashi, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Downstream+molecular+pathways+of+FLT3+in+the+pathogenesis+of+acute+myeloid+leukemia:+biology+and+therapeutic+implications.">Downstream molecular pathways of FLT3 in the pathogenesis of acute myeloid leukemia: biology and therapeutic implications.</a> Jornal of Hematology and Oncology. 4, (2011).</li><li>Laouar, Y., Welte, T., Fu, X. Y., Flavell, R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=STAT3+is+required+for+Flt3L-dependent+dendritic+cell+differentiation.">STAT3 is required for Flt3L-dependent dendritic cell differentiation.</a> Immunity. 19 (6), 903-912 (2003).</li><li>Ogawa, M., Bergsagel, D. E., McCulloch, E. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Differential+effects+of+melphalan+on+mouse+myeloma+(adj.+PC-5)+and+hemopoietic+stem+cells.">Differential effects of melphalan on mouse myeloma (adj. PC-5) and hemopoietic stem cells.</a> Cancer Research. 31 (12), 2116-2119 (1971).</li><li>Hamburger, A. W., Salmon, S. 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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=NRP1-positive+lung+cancer+cells+possess+tumor-initiating+properties.">NRP1-positive lung cancer cells possess tumor-initiating properties.</a> Oncology Reports. 39 (1), 349-357 (2018).</li><li>Singh, S. 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=Identification+of+human+brain+tumour+initiating+cells.">Identification of human brain tumour initiating cells.</a> Nature. 432 (7015), 396-401 (2004).</li><li>Kimlin, L. C., Casagrande, G., Virador, V. 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Multiple methods have been employed for isolation and characterization of TPCs from tumor heterogeneous cell populations: tumor clonogenic assays, FACS isolation, and tumorsphere formation assay. The tumor clonogenic assay was first described in 1971, used for stem cell studies, and only subsequently applied to cancer biology29,30. This method is based on the cancer stem cells intrinsic property to expand without constraints in soft gels cultures<sup class='xref'...

Cancer is a heterogeneous disease; furthermore, the same type of tumor can present different genetic mutations in different patients, and within a patient a tumor is composed by multiple populations of cells1. Heterogeneity presents a challenge in the identification of cells responsible for initiating and propagating cancer, but their characterization is essential for the development of efficient treatments. The notion of tumor propagating cells (TPC), a rare population of cells that contribute to tumor development, has been previously extensively reviewed2. Despite the fact that TPCs have been characterized in multiple types of cancer, the identification of markers for their reliable isolation remains a challenge for several tumor types3,4,5,6,7,8,9. Thus, a method that does not rely on molecular markers but rather on TPC functional properties (high self-renewal and the ability to grow in low-attachment conditions), known as the tumorsphere formation assay, can be widely applied for the identification of TPCs from most tumors. Importantly, this assay can also be employed for expansion of TPCs and thus directly applied to cancer drug screening and studies on cancer resistance1,10.
Rhabdomyosarcoma (RMS) is a rare form of soft tissue sarcoma most common in young children11. Althoug RMS can be histologically identified through assessment of expression of myogenic markers, the RMS cell of origin has not been univocally characterized due to the multiple tumor subtypes and high heterogeneity of the tumor developmental stimuli. Indeed, recent studies have generated significant scientific discussion about whether RMS is of myogenic or non-myogenic origins, suggesting that RMS may derive from different cells types depending on the context12,13,14,15,16,17. Numerous studies on RMS cell lines have been performed employing the tumorsphere formation assay for the identification of pathways involved in tumor development and characterization of markers associated with highly self-renewal populations18,19,20,21.
However, despite the tumorsphere formation assay&#39;s potential for identifying RMS cells of origin, a reliable method that can be employed on primary RMS cells has not yet been described. In this context, a recent study from our group employed an optimized tumorsphere formation assay for the identification of the RMS cells of origin in a Duchenne muscular dystrophy (DMD) mouse model22. Multiple pre-tumorigenic cell types, isolated from muscle tissues, are tested for their ability to grow in low-attachment conditions, allowing the identification of muscle stem cells as cells of origin for RMS in dystrophic contexts. Described here is a reproducible and reliable protocol for the tumorsphere formation assay (Figure 1), which has been successfully employed for the identification of extremely rare cell populations that are responsible for mouse RMS development.

<table>
	<tbody>
		<tr>
			<td>Accutase cell dissociation reagent</td>
			<td>Gibco</td>
			<td>A1110501</td>
			<td>Detach adherent cells and dissociate tumorspheres</td>
		</tr>
		<tr>
			<td>Celigo</td>
			<td>Nexcelom</td>
			<td>Celigo</td>
			<td>Microwell plate based image cytometer for adherent and suspension cells</td>
		</tr>
		<tr>
			<td>Collagenase, Type II</td>
			<td>Life Technologies</td>
			<td>17101015</td>
			<td>Tissue digestion enzyme</td>
		</tr>
		<tr>
			<td>Dispase II, protease</td>
			<td>Life Technologies</td>
			<td>17105041</td>
			<td>Tissue digestion enzyme</td>
		</tr>
		<tr>
			<td>DMEM high glucose media</td>
			<td>Gibco</td>
			<td>11965092</td>
			<td>Component of tumor cells media</td>
		</tr>
		<tr>
			<td>DMEM/F12 Media</td>
			<td>Gibco</td>
			<td>11320033</td>
			<td>Component of tumosphere media</td>
		</tr>
		<tr>
			<td>EDTA</td>
			<td>ThermoFisher</td>
			<td>S312500</td>
			<td>Component of FACS buffer</td>
		</tr>
		<tr>
			<td>EGF recombinant mouse protein</td>
			<td>Gibco</td>
			<td>PMG8041</td>
			<td>Component of tumosphere media</td>
		</tr>
		<tr>
			<td>FACSAria II Flow Cytometry</td>
			<td>BD Biosciences</td>
			<td>650033</td>
			<td>Fluorescent activated cell sorter</td>
		</tr>
		<tr>
			<td>Fetal Bovine Serum</td>
			<td>Omega Scientific</td>
			<td>FB-11</td>
			<td>Component of tumor cells media</td>
		</tr>
		<tr>
			<td>Fluriso (Isofluornae) anesthetic agent</td>
			<td>MWI Vet Supply</td>
			<td>502017</td>
			<td>Anesthetic reagent for animals</td>
		</tr>
		<tr>
			<td>FxCycle Violet Stain</td>
			<td>Life Technologies</td>
			<td>F10347</td>
			<td>Discriminate live and dead cells</td>
		</tr>
		<tr>
			<td>Goat Serum</td>
			<td>Life Technologies</td>
			<td>16210072</td>
			<td>Component of FACS buffer</td>
		</tr>
		<tr>
			<td>Ham&#39;s F10 Media</td>
			<td>Life Technologies</td>
			<td>11550043</td>
			<td>Component of FACS buffer</td>
		</tr>
		<tr>
			<td>Horse Serum</td>
			<td>Life Technologies</td>
			<td>16050114</td>
			<td>Component of cell isolation media</td>
		</tr>
		<tr>
			<td>Lipofectamine 3000 transfection reagent</td>
			<td>ThermoFisher</td>
			<td>L3000015</td>
			<td>Transfection Reagent</td>
		</tr>
		<tr>
			<td>Matrigel membrane matrix</td>
			<td>Corning</td>
			<td>CB40234</td>
			<td>Provides support to trasplanted cells</td>
		</tr>
		<tr>
			<td>N-2 Supplemtns (100X)</td>
			<td>Gibco</td>
			<td>17502048</td>
			<td>Component of tumosphere media</td>
		</tr>
		<tr>
			<td>Neomycin-Polymyxin B Sulfates-Bacitracin Zinc Ophthalmic Ointment</td>
			<td>MWI Vet Supply</td>
			<td>701008</td>
			<td>Eyes ointment</td>
		</tr>
		<tr>
			<td>PBS</td>
			<td>Gibco</td>
			<td>10010023</td>
			<td>Component of FACS buffer and used for washing cells</td>
		</tr>
		<tr>
			<td>pEGFP-C1</td>
			<td>Addgene</td>
			<td>6084-1</td>
			<td>GFP plasmid</td>
		</tr>
		<tr>
			<td>Penicillin - Streptomyocin</td>
			<td>Life Technologies</td>
			<td>15140163</td>
			<td>Component of tumosphere and tumor cells media</td>
		</tr>
		<tr>
			<td>Recombinant Human &#946;FGF-basic</td>
			<td>Peprotech</td>
			<td>10018B</td>
			<td>Component of tumosphere media</td>
		</tr>
		<tr>
			<td>Recombinant mouse Flt-3 Ligand Protein</td>
			<td>R&#38;D Systems</td>
			<td>427-FL-005</td>
			<td>Recombinant protein</td>
		</tr>
		<tr>
			<td>Trypan blue</td>
			<td>ThermoFisher</td>
			<td>15250061</td>
			<td>Discriminate live and dead cells</td>
		</tr>
	</tbody>
</table>

tumorsphere derivation and treatment from primary tumor cells isolated from mouse rhabdomyosarcomas

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children. Although significant efforts have enabled the identification of common mutations associated with RMS and allowed discrimination of different RMS subtypes, major challenges still exist for the development of novel treatments to further improve prognosis. Although identified by the expression of myogenic markers, there is still significant controversy over whether RMS has myogenic or non-myogenic origins, as the cell of origin is still poorly understood. In the present study, a reliable method is provided for the tumorsphere assay for mouse RMS. The assay is based on functional properties of tumor cells and allows the identification of rare populations in the tumor with tumorigenic functions. Also described are procedures for testing recombinant proteins, integrating transfection protocols with the tumorsphere assay, and evaluating candidate genes involved in tumor development and growth. Described further is a procedure for allograft transplantation of tumorspheres into recipient mice to validate tumorigenic function in vivo. Overall, the described method allows reliable identification and testing of rare RMS tumorigenic populations that can be applied to RMS arising in different contexts. Finally, the protocol can be utilized as a platform for drug screening and future development of therapeutics.

Tumorspheres detection 
Cell isolation was optimized to obtain the maximum heterogeneity of cell populations present in the tumor tissue. First, since isolated tissues presented morphologically dissimilar areas, to enhance the chances of isolating uniform rare cell populations, sampling was performed from multiple areas of the tumor (Figure 1A, first panel on the left). Second, mechanical dissociation of the harvested samples was perform...

Watch this Scientific Journal Video about Tumorsphere Derivation and Treatment from Primary Tumor Cells Isolated from Mouse Rhabdomyosarcomas at JoVE.com

Tumorsphere Derivation and Treatment from Primary Tumor Cells Isolated from Mouse Rhabdomyosarcomas

This protocol describes a reproducible method for isolation of mouse rhabdomyosarcoma primary cells, tumorsphere formation and treatment, and allograft transplantation starting from tumorspheres cultures.

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children. Although significant efforts have enabled the identification of common ...

Rhabdomyosarcoma is a rare form of soft-tissue sarcomas characterized histologically by tissue morphology and the expression of myogenic markers. However, given the existence of different subtypes of these tumors and the heterogeneity of the stimuli that contributes to its formation, the identification of the cell of origin has been very challenging. Here we describe reproducible and reliable methods for the identification of the cell of origin of rhabdomyosarcomas starting from freshly harvest tumor tissues from mice and this assay is the tumorsphere formation assay.The main advantages of tumorsphere formation assay is that it relies on cellular properties that are known to be present in tumor-originating cells and it can also be used for expansion and enrichment of the specific cell population. Furthermore, its spheroid structure mimic the tumor environment, thus they can be used as drug-screening studies. This method has the potential to be applied to others type of tumors because it does not require prior knowledge of molecular markers but it may require optimization of culture conditions.Tumorsphere may take some time to form, especially if trying to identify a rare cell population within your tumor. Thus, it's not suggested to look at your subculture plate every day, since it might negatively affect the results of your experiments. Start by warming up a 10-centimeter plate with five milliliters of isolation media in an incubator at 37 degrees Celsius.Weigh 500 to 1, 000 milligrams of the tumor tissue and place it in the plate. Bring the plate with the tumor tissue to a sterile culture hood and mince it with a razor blade. For optimal digestion, make sure that the sizes of the minced pieces are uniform.Transfer the minced tissue and cell isolation media to a 15-milliliter centrifuge tube. Wash the plate with another four milliliters of media and add that to the tube. Add 700 units per milliliter of collagenase solution to the tube and incubate it in a shaking water bath at 37 degrees Celsius for 1 1/2 hours.After the incubation, spin down the tissue at 300 times g for five minutes at room temperature. Aspirate the supernatant without disrupting the pellet, then resuspend the pellet in 10 milliliters of second digestion solution and incubate in the shaking water bath for 30 more minutes. After the second digestion, pipette the cell suspension up and down and pass it through a 70-micrometer nylon filter on a 50-milliliter centrifuge tube.Then wash the filter with 10 milliliters of cell isolation media and spin down the tissue at 300 times g for five minutes. Aspirate the supernatant and resuspend the pellet in 20 milliliters of tumor cell media. Transfer the suspension to a 15-centimeter culture plate and place the cells in a 37 degrees Celsius incubator overnight.On the next day, change the media to remove debris and dead cells that may negatively influence cell survival. At this point, assess cell confluency and allow the cells to grow in the incubator until it reaches 90%Monitor the cells every day and change the media every two days. For tumorsphere derivation, use cells at Passage P1 or P2 to avoid cell selection through multiple passages.Wash the cell dish with PBS and then cover them with detachment solution. Place them in the incubator for five to 10 minutes and then confirm detachment by looking at the plate under a brightfield microscope. Once the cells have detached, add tumor cell media to the plate and transfer the cell suspension to a centrifuge tube.Spin the cells down at 300 times g for five minutes, remove supernatant, and resuspend the cells in tumorsphere media. After resuspending the cells, count them using Trypan blue and calculate cell concentration. Plate the proper number of cells in a 96-well low-attachment plate and place the cells in the incubator until the end of the experiment, taking care not to disturb the plate unless replenishing media.After completion of the experiment, identify tumorspheres manually under a brightfield microscope or using Celigo software. The number and size of the tumorspheres can be evaluated as a result of this assay. To prepare tumorspheres for allograft transplantation, pull together all tumorspheres obtained from a specific cell type or treatment.Centrifuge the tumorspheres and carefully remove the supernatant with a one-millimeter pipette followed by a 200-microliter pipette, then wash them with 10 milliliters of sterile PBS. Spin the tumorspheres down again and aspirate the PBS. Add 500 microliters to one milliliter of cell detachment solution on top of the tumorsphere pellet and incubate the cells in a shaking water bath at 37 degrees Celsius.Check progression of digestion every 10 minutes. The entire process make take up to 30 minutes. If digestion of tumorsphere in the shaking water bath is not enough to obtain a single-cell solution, mechanical disruption through pipetting up and down is suggested.Note that after spinning the tumorspheres do not form a stable pellet, so aspirating the supernatant should be done carefully with a one-milliliter pipette and 200-microliter pipettes. Once a single-cell solution is obtained, add a volume of tumor cell media and spin it down at 300 times g for five minutes at 4 degrees Celsius. After this centrifugation, all subsequent steps must be performed on ice.Resuspend the cells in cold tumor cell media and count live cells using Trypan blue exclusion. Determine the proper number of cells for the allograft and dilute it in 50 microliters of cold tumor cell media. Place a pipette tip in cold tumor cell media to cool it and then use it to take 50 microliters of cold ECM solution and add it to the tube with cells, making sure not to remove the ECM tube from ice during this process.Maintain the cells on ice until transplantation and place a capped, 0.5-milliliter insulin syringe with a 29-gauge needle on ice. After confirming that the mouse has been properly anesthetized, shave the right side of the animal, aspirate the cell solution into the cooled syringe, and inject the cells subcutaneously into the shaved area. If the injection is performed correctly, a visible bump will form under the skin.This protocol can be used to reliably form tumorspheres for identification of rare cell populations that are responsible for soft-tissue sarcoma development. A fundamental part of this assay is discrimination between tumorspheres and cell clusters, which exhibit clear morphological differences. To determine the optimal concentration at which a protein of interest triggers an effect on tumor cells, it is necessary to assess the level of expression of the protein's downstream targets.Three of the tested genes showed a dose-dependent response to recombinant protein treatment and one did not. In order to establish an efficient protocol, the effects of transfection on inherent tumor cells were analyzed;two different amounts of reagent were tested and efficiency was assessed with a GFP-reporter plasmid. Lower amounts of reagent resulted in higher transfection efficiency.A two-step protocol had to be implemented to perform transfection on cells in suspension. Transfection was performed on adherent cells and 24 hours later they were detached and plated in suspension;after seven days, controlled tumorspheres were expressing GFP. After tumorspheres are obtained, treated, and transplanted it is possible to compare the effect of this different treatment in tumor growth in vivo.These methods will allow scientists to answer the still-standing questions of the cell of origin of rhabdomyosarcomas while at the same time setting the basis for drug screening.

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Research

JoVE Journal

Genetics

7.0K ビュー.  Sanford Burnham Prebys Medical Discovery Institute. 横紋筋肉腫は、組織形態と筋形成マーカーの発現によって組織学的に特徴づけられる軟部肉腫の稀な形態である。しかし、これらの腫瘍の異なるサブタイプの存在とその形成に寄与する刺激の不均一性を考えると、起源の細胞の同定は非常に困難であった。ここでは、マウスから採取したばかりの腫瘍組織から始まる横紋肉腫の起源の細胞を同定するための再現性と信?...