The authors would like to acknowledge Patxi Jaso for the production of the video, PEDECIBA and Agencia Nacional de Investigaci&#243;n e Innovaci&#243;n (ANII) for partial funding.

1. Purificación del colorante <ol><li> Preparar una solución acuosa al 4% de verde de metilo disolviendo 0,4 g de polvo de manchas en 10 ml de agua destilada. Mezclar bien hasta que esté completamente disolviéndolo. </li><li> Bajo un humo del capó, se mezcla con al menos 2 partes de cloroformo. Es importante comprobar de antemano si los tubos son resistentes cloroformo. </li><li> Mezclar bien y centrifugar durante 1 min a 2000 xg para acelerar la separación de fases. </li><li> Después de la centrifugación, se obtienen una fase superior acuosa con verde de metilo y una fase orgánica inferior con cloroformo y la habitual cristal violeta contaminante. </li><li> Recuperar la fase superior y repita este paso hasta fase inferior aparece completamente carente de cristal violeta. </li><li> Al final, la fase superior se recuperó y se diluyó en agua hasta una concentración final de 2% de verde de metilo. Esta solución madre es estable en la mesa de trabajo durante meses y no necesita ser protegido de la luz. </li></ol><ol><li> Fijar los embriones durante la noche en 4% de formaldehído (de paraformaldehído) en tampón fosfato salino (PBS). NOTA: Esto puede tardar desde un par de horas para la noche, dependiendo del grosor de los embriones. En el ejemplo, hemos arreglado 48 horas después de la fecundación (HPF) embriones de pez cebra durante la noche. </li><li> Lavar los embriones tres veces en PBS-T (1% Triton X-100 en PBS) durante 5 min. La elevada concentración de detergente permeabiliza la cutícula. </li><li> Preparar una solución 1: 10.000 de verde de metilo (de 2% solución madre) en PBS-T: 5,000-1. La presencia de detergente durante la incubación es útil para muestras gruesas, tales como embriones de pez cebra y larvas. </li><li> Incubar los embriones en la solución durante al menos 6 horas a 4 ° C, con agitación suave. Una vez más, el espesor del embrión es el parámetro de calibración para la longitud de la incubación. </li><li> Lave los embriones 3 times con PBS durante 30 min para eliminar el exceso de detergente. Metil fluorescencia verde sólo es evidente cuando se une al ADN, por lo tanto, el fondo de la molécula no unida es insignificante. </li><li> Montar en una diapositiva excavado o una cámara casera con solución de montaje (75% de glicerol, 0,1 M Tris · HCl pH 8). NOTA: Si la tinción nuclear se va a realizar después de immunolabeling, verde de metilo se puede incorporar a la solución de montaje en la concentración de trabajo, sin necesidad de lavar a la basura. </li><li> Tienda refrigerada o iniciar imágenes inmediatamente. Realizar de imágenes con un confocal de barrido láser (u otro fluorescencia) microscopio con excitación a 633 nm y filtros de emisión establecidos para registrarse en 650-750 nm teniendo en cuenta que el metil emisión verde alcanza su máximo a 677 nm. NOTA: Proporcionamos los datos medidos del perfil de emisión verde de metilo, para ser cargados en el software de adquisición, como material complementario. </li></ol> 3. Fluorescente Nuclear StESP ACIO Plenario polluelo embriones utilizando metil verde <ol><li> Incubar huevos de gallina fertilizados a la etapa de su interés. Fijar los embriones durante la noche en formaldehído al 4% (de paraformaldehído) en PBS a 4 ° C. Lave embriones 3 veces en PBS-T durante 2 horas. </li><li> Preparar una solución 1: 10.000 de verde de metilo (de 2% solución madre) en PBS-T: 5,000-1. Incubar los embriones en la solución de tinción durante la noche a 4 ° C. Lave los embriones 3 veces en PBS, 1 hora cada uno. Monte en la cámara con 75% de glicerol, 0,1 M Tris, pH 8. </li></ol> 4. Imaging marcados con fluorescencia Núcleos de embriones-enteros montada <ol><li> Preparar una cámara de imágenes pegando varias capas de cinta aislante sobre un portaobjetos de microscopio y cuidadosamente cortar un agujero en él con un bisturí para colocar los embriones en su interior. Esto evitará que los embriones de aplastamiento durante la exploración. </li><li> Transferir cuidadosamente los embriones a la cámara de imagen y llenar la cámara a la cima con 75% de glicerol, Tris-HCl 0,1 M, pH = 8 a unla formación de burbujas vacío. </li><li> Cubrir con un # 0 cubreobjetos evitando o eliminando medio desbordante. Selle con esmalte de uñas. </li><li> Adquirir imágenes de la muestra en un microscopio de fluorescencia equipado con un filtro de excitación 633 o línea de láser. NOTA: Los filtros de emisión deben cubrir el máximo 677 emisión de verde de metilo. </li></ol>

<ol>
	<li>Klonisch, T., Wark, L., Hombach-Klonisch, S., Mai, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nuclear+imaging+in+three+dimensions:+a+unique+tool+in+cancer+research.">Nuclear imaging in three dimensions: a unique tool in cancer research.</a> Annals of anatomy. 192 (5), 292-301 (2010).</li><li>Kapuscinski, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=DAPI:+a+DNA-specific+fluorescent+probe.">DAPI: a DNA-specific fluorescent probe.</a> Biotechnic. 70 (5), 220-233 (1995).</li><li>Latt, S. A., Stetten, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spectral+studies+on+33258+Hoechst+and+related+bisbenzimidazole+dyes+useful+for+fluorescent+detection+of+deoxyribonucleic+acid+synthesis.">Spectral studies on 33258 Hoechst and related bisbenzimidazole dyes useful for fluorescent detection of deoxyribonucleic acid synthesis.</a> The journal of histochemistry and cytochemistry. 24 (1), 24-33 (1976).</li><li>Van Hooijdonk, C. A., Glade, C. P., Van Erp, P. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=TO-PRO-3+iodide:+a+novel+HeNe+laser-excitable+DNA+stain+as+an+alternative+for+propidium+iodide+in+multiparameter+flow+cytometry.">TO-PRO-3 iodide: a novel HeNe laser-excitable DNA stain as an alternative for propidium iodide in multiparameter flow cytometry.</a> Cytometry. 17 (2), 185-189 (1994).</li><li>Beumer, T. L., Veenstra, G. J., Hage, W. J., Destr&#233;e, O. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Whole-mount+immunohistochemistry+on+Xenopus+embryos+using+far-red+fluorescent+dyes.">Whole-mount immunohistochemistry on Xenopus embryos using far-red fluorescent dyes.</a> Trends in genetics. 11 (1), 9 (1995).</li><li>Prieto, D., Aparicio, G., Morande, P. E., Zolessi, F. 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+fast,+low+cost,+and+highly+efficient+fluorescent+DNA+labeling+method+using+methyl+green.">A fast, low cost, and highly efficient fluorescent DNA labeling method using methyl green.</a> Histochemistry and cell biology. 142 (3), 335-345 (2014).</li><li>Kim, S. K., Nord&#233;n, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Methyl+green.+A+DNA+major-groove+binding+drug.">Methyl green. A DNA major-groove binding drug.</a> FEBS letters. 315 (1), 61-64 (1993).</li><li>Nord&#233;n, B., Tjerneld, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Binding+of+methyl+green+to+deoxyribonucleic+acid+analyzed+by+linear+dichroism.">Binding of methyl green to deoxyribonucleic acid analyzed by linear dichroism.</a> Chemical Physics Letters. 50 (3), 508-512 (1977).</li><li>Lyon, H., Jakobsen, P., Andersen, a. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Standardized+methyl+green-pyronin+Y+procedures+using+pure+dyes.">Standardized methyl green-pyronin Y procedures using pure dyes.</a> The Histochemical journal. 18 (2-3), 90-94 (1986).</li><li>Amat, F., Keller, P. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Towards+comprehensive+cell+lineage+reconstructions+in+complex+organisms+using+light-sheet+microscopy.">Towards comprehensive cell lineage reconstructions in complex organisms using light-sheet microscopy.</a> Development, growth &amp; differentiation. 55 (4), 563-578 (2013).</li><li>Chung, K., Deisseroth, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=CLARITY+for+mapping+the+nervous+system.">CLARITY for mapping the nervous system.</a> Nature methods. 10 (6), 508-5013 (2013).</li><li>Lenz, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fluorescence+measurement+in+thick+tissue+layers+by+linear+or+nonlinear+long-wavelength+excitation.">Fluorescence measurement in thick tissue layers by linear or nonlinear long-wavelength excitation.</a> Applied. 38 (16), 3662-3669 (1999).</li></ol>

The authors have nothing to disclose.

The progressive development of microscopy techniques in the last decades, with a particular focus in variations of fluorescent microscopy, have led to the possibility of exploring the dynamics and structure of intact tissue samples, including whole embryos10,11. One major limitation has been, however, the availability of good quality fluorophores that can be used to directly and quickly stain subcellular structures. 
The most frequently used fluorescent DNA stains, such as DAPI or H...

Fluorescent staining of DNA is broadly and routinely used both in biological research and in clinical diagnosis, either for the detailed study of nuclear and chromosomal structure, for counterstaining tissues and cells, or for studying cell cycle parameters1. Although several DNA stains are available, the most widely used have been those excited by UV light and emitting in blue, which fit in the usual three-filter systems used in most conventional epifluorescence microscopes when combined with green and orange-red-emitting fluorophores, such as fluorescent proteins or small molecules attached to antibodies. Among these blue-emitting DNA stains, the most common are DAPI and Hoechst minor groove-binding agents2,3. Nonetheless, the incorporation of a wide variety of laser emission lines and spectral detection in laser scanning microscopes, has allowed researchers to choose for the use of far-red-emitting nuclear stains such as propidium iodide (PI) or TO-PRO 34. An advantage of these stains is that they overcome the problem of autofluorescence found in many cells and tissues, particularly in embryos5, but many of them have different problems such as having wide emission profiles or being very sensitive to photobleaching6.
The Swiss researcher Friedrich Miescher discovered DNA in 1869, extracting it from the nuclei of white blood cells found in pus. He called it nuclein, and showed a few years later that it formed precipitates with the relatively new stain methyl green. Methyl green is composed by three aniline rings, with different degrees of methylation, and has two positive charges that allow it to strongly bind to the major groove of DNA7,8. DNA staining by methyl green was very early shown to be specific, leading to the development by Unna and Pappenheim of a combined stain with pyronin, which specifically labels RNA. Methyl green-pyronin has since then been extensively used in routine histological technique9.
Until recently, very little was known about the fluorescent properties of methyl green. Our previous work, however, has uncovered some of methyl green spectral advantages6 such as its excitation at 633 nm, a convenient Stokes shift, its emission on the near-infrared portion of the electromagnetic spectrum, higher photostability than commercially available DNA stains with similar spectral properties and at a very low cost. This is why we decided to test it for being used as a very high affinity and specific fluorescent label for DNA on embryonic tissues and in whole embryos. Furthermore, until now methyl green nuclear staining was performed at low pH, making it difficult to combine with antibody staining. The goal of the method detailed here is to have a protocol for fluorescent nuclear DNA staining which overcomes the aforementioned inconvenience by performing the staining procedure at physiological pH, thus making it a suitable counterstain for immunolabeling on sections and whole tissues.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>Glycerol</td>
			<td>Sigma-Aldrich</td>
			<td>G5516</td>
			<td></td>
		</tr>
		<tr>
			<td>Methyl green</td>
			<td>Dr. G. Gr&#252;bler</td>
			<td></td>
			<td>Also tested Sigma-Aldrich 323829, which is crystal violet-free</td>
		</tr>
		<tr>
			<td>Paraformaldehyde</td>
			<td>Sigma-Aldrich</td>
			<td>158127</td>
			<td></td>
		</tr>
		<tr>
			<td>Laser scanning confocal microscopy Leica TCS-SP5</td>
			<td>Leica Microsystems</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Phalloidin&#8211;Tetramethylrhodamine B isothiocyanate</td>
			<td>Sigma-Aldrich</td>
			<td> 
			P1951&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>chloroform</td>
			<td>Sigma-Aldrich</td>
			<td>372978</td>
			<td></td>
		</tr>
		<tr>
			<td>Centrifuge 5810 R</td>
			<td>eppendorf</td>
			<td>5811 000.010&#160;&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>microscope slides</td>
			<td>Deltalab</td>
			<td>D100004</td>
			<td></td>
		</tr>
		<tr>
			<td>cover slips</td>
			<td>Esco optics</td>
			<td>R525025</td>
			<td></td>
		</tr>
	</tbody>
</table>

application of the dna-specific stain methyl green in the fluorescent labeling of embryos

Methyl green has long been known as a histological stain with a specific affinity for DNA, although its fluorescent properties have remained unexplored until recently. In this article, we illustrate the method for preparing a methyl green aqueous stock solution, that when diluted can be used as a very convenient fluorescent nuclear label for fixed cells and tissues. Easy procedures to label whole zebrafish and chick embryos are detailed, and examples of images obtained shown. Methyl green is maximally excited by red light, at 633 nm, and emits with a relatively sharp spectrum that peaks at 677 nm. It is very inexpensive, non-toxic, highly stable in solution and very resistant to photobleaching when bound to DNA. Its red emission allows for unaltered high resolution scanning confocal imaging of nuclei in thick specimens. Finally, this methyl green staining protocol is compatible with other cell staining procedures, such as antibody labeling, or actin filaments labeling with fluorophore-conjugated phalloidin.

Tinción nuclear de muestras gruesas. El protocolo aquí descrito permite el logro de la tinción homogénea de estructuras profundas en embriones enteros. Lentes en desarrollo forman núcleos 48 HPF embriones de pez cebra son homogéneamente etiquetados (Figura 1). Tinción de ADN verde de metilo permite la discriminación de diferencias morfológicas del ciclo celular dependientes tales como la identificación de figuras mitóticas o núcleos apoptóticos (Figura 2...

Watch this Scientific Journal Video about Application of the DNA-Specific Stain Methyl Green in the Fluorescent Labeling of Embryos at JoVE.com

Application of the DNA-Specific Stain Methyl Green in the Fluorescent Labeling of Embryos

A method for fluorescent staining of fixed biological material with the specific DNA label methyl green is described. Methyl green is used in a diluted aqueous solution and is very resistant to photobleaching. Its far-red emission allows for deep specimen imaging, making it particularly adequate for whole embryos.

Aplicación del ADN específico de la mancha verde de metilo en el etiquetado fluorescente de embriones

Methyl green has long been known as a histological stain with a specific affinity for DNA, although its fluorescent properties have remained unexplored ...

application-dna-specific-stain-methyl-green-fluorescent-labeling

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Developmental Biology

14.0K vistas.  Institut Pasteur de Montevideo. A method for fluorescent staining of fixed biological material with the specific DNA label methyl green is described. Methyl green is used in a diluted aqueous solution and is very resistant to photobleaching. Its far-red emission allows for deep specimen imaging, making it particularly adequate for whole embryos.