The authors would like to thank members of the Translational Genomics Group and Kathryn J Hanson for the feed-back and the improvements on this protocol. This project was carried out with research grant SAF2015-64500-R, which includes European Regional Development Funds, awarded to R.A by the Ministerio de Economia y Competitividad.

1. Fixation and resin embedding
<ol>
	<li>Anesthetize the flies with carbon dioxide (CO2) or via hypothermia using an ice block. Use a dissecting microscope (with low magnification to see the whole fly) and scissors to remove the legs, wings, head and the terminal part of abdomen to facilitate the penetration of the fixative. Careful handling of the carcasses is required at this step to avoid the deformation of the thorax. 
	NOTE: Start with at least 12 flies per genotype to ensure a sufficient number o...

<ol>
	<li>Fernandes, J., Bate, M., Vijayraghavan, K. <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+the+indirect+flight+muscles+of+Drosophila.">Development of the indirect flight muscles of Drosophila.</a> Development. 113, 67-77 (1991).</li><li>Fernandes, J. J., Keshishian, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Patterning+the+dorsal+longitudinal+flight+muscles+(DLM)+of+Drosophila:+insights+from+the+ablation+of+larval+scaffolds.">Patterning the dorsal longitudinal flight muscles (DLM) of Drosophila: insights from the ablation of larval scaffolds.</a> Development. 122, 3755-3763 (1996).</li><li>Hartenstein, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Atlas+of+Drosophila+Development.">Atlas of Drosophila Development.</a> Atlas Drosoph. Dev. , 1-57 (1993).</li><li>Tomlinson, A., Ready, D. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cell+fate+in+the+Drosophila+ommatidium.">Cell fate in the Drosophila ommatidium.</a> Dev. Biol. 123, 264-275 (1987).</li><li>Griffith, W. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Osmium+Tetroxide+And+Its+Applications.">Osmium Tetroxide And Its Applications.</a> Platin Met Rev. 18, 94-96 (1974).</li><li>Bird, T. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Myotonic+Dystrophy+Type+1.">Myotonic Dystrophy Type 1.</a> GeneReviews. 1, 1-23 (1993).</li><li>Bargiela, 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=Increased+autophagy+and+apoptosis+contribute+to+muscle+atrophy+in+a+myotonic+dystrophy+type+1+Drosophila+model.">Increased autophagy and apoptosis contribute to muscle atrophy in a myotonic dystrophy type 1 Drosophila model.</a> Dis Model Mech. 8, 679-690 (2015).</li><li>Llamusi, B., 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=Muscleblind,+BSF+and+TBPH+are+mislocalized+in+the+muscle+sarcomere+of+a+Drosophila+myotonic+dystrophy+model.">Muscleblind, BSF and TBPH are mislocalized in the muscle sarcomere of a Drosophila myotonic dystrophy model.</a> Dis. Model. Mech. 6, 184-196 (2012).</li><li>Garc&#237;a-L&#243;pez, A., Llamus&#237;, B., Orz&#225;ez, M., P&#233;rez-Pay&#225;, E., Artero, R. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vivo+discovery+of+a+peptide+that+prevents+CUG-RNA+hairpin+formation+and+reverses+RNA+toxicity+in+myotonic+dystrophy+models.">In vivo discovery of a peptide that prevents CUG-RNA hairpin formation and reverses RNA toxicity in myotonic dystrophy models.</a> Proc. Natl. Acad. Sci. U.S.A. 108, 11866-11871 (2011).</li><li>van der Plas, M. 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=Drosophila+Dystrophin+is+required+for+integrity+of+the+musculature.">Drosophila Dystrophin is required for integrity of the musculature.</a> Mech. Dev. 124, 617-630 (2007).</li><li>Lloyd, T. E., Taylor, J. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Flightless+flies:+Drosophila+models+of+neuromuscular+disease.">Flightless flies: Drosophila models of neuromuscular disease.</a> Ann New York Acad Sci. , 1184 (2010).</li><li>Babcock, D. T., Ganetzky, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+improved+method+for+accurate+and+rapid+measurement+of+flight+performance+in+Drosophila.">An improved method for accurate and rapid measurement of flight performance in Drosophila.</a> J. Vis. Exp. , e51223 (2014).</li></ol>

It has been demonstrated that Drosophila melanogaster is a useful model to study human neuromuscular diseases7,10,11, including Myotonic Dystrophies, which are characterized by the appearance of muscular atrophy. The protocol presented here is a useful tool for quantifying the muscle degeneration caused by the onset or progression of a particular disease in a fly model. For example, it is also possible to follow and qua...

The thorax of the fruit fly contains two different classes of flight muscles, which are functionally, physiologically and anatomically distinct. These muscles are: the indirect flight muscles (IFM), which are composed of dorso-longitudinal (DLM) and dorso-ventral (DVM) muscles (Figure 1), and the synchronous flight control muscles1,2. These muscles together generate the elevated mechanical power required for flight. The size, distribution and rostro-caudal disposition of the IFMs allow an easy orientation for transversal sectioning3 (Figure 2A). For this reason, we have selected these muscles to study muscle atrophy in Drosophila melanogaster.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/56179/56179fig1.jpg" /> 
Figure 1. Diagram of the thorax of the fruit fly showing the indirect flight muscles (IFMs) arrangement. (Left) represents a lateral view and (Right) represents a cross section of the thorax. The IFMs are composed of the Dorso-longitudinal (DLM) muscles (in red) and the Dorso-ventral (DVM) muscles (in green).
Preservation of tissue structure and the control over dorso-ventral axis orientation of histological sections are critical to ensure proper assessment of muscle cross-sectional area. To preserve muscle structure we used a fixation mixture modified from Tomlinson et al.4 . Moreover, because muscles are internal tissues, the impermeability of Drosophila&#39;s exoskeleton is a problem as fixation mixtures cannot penetrate to the target tissues. To circumvent this problem, we removed the fly head, legs, wings and the last two segments of the abdomen to create holes that allowed the fixation mixture to enter. As part of the fixation protocol we included treatment with osmium tetroxide (OsO4)5, which is extensively used because of its ability to fix fats, including triglycerides. OsO4 preserves most structures extremely well, particularly at the cytological level and at the same time provides contrast to the image. After fixation, Drosophila thoraces were embedded in resin for transversal semi-thin sectioning (1.5 &#181;m). For improved contrast, tissue can be additionally stained with toluidine blue. Images of complete thoraces were taken at 10X and muscle area was quantified by binarizing images (of equal dimensions) and quantifying percentage of pixels corresponding to muscle tissue (black pixels) out of total, with ImageJ software.
Modifications on the tissue preparation and fixation mixtures, as the increase of the concentration of OsO4 and glutaraldehyde solution, introduced in this protocol, allowed unique preservation of muscle tissue. This is because the protocol avoids the degradation and deformation of the tissue, making the posterior analysis of the samples more reliable&#160;even in highly atrophic conditions associated with neuromuscular degenerative diseases such as Myotonic Dystrophy (DM). In its more common form, DM type 1, this rare genetic disorder is brought about by expanded CUG repeats in myotonic dystrophy protein kinase (DMPK) transcripts. Mutant DMPK RNA aggregates form&#160;ribonuclear foci that sequester the Muscleblind-like nuclear RNA-binding proteins (MBNL1-3; Muscleblind (Mbl) in Drosophila)6. We generated a Drosophila model of Myotonic Dystrophy by expressing 250 CTG repeats under the muscular myosin heavy chain promoter (Mhc-Gal4). Model flies were flightless with a typical &#39;up-held wings&#39; phenotype and had serious muscle atrophy in their IFMs (Figure 2B). Previous studies performed in our laboratory have shown that determination of the muscle area of IFMs is a reliable method to quantify the effects of different chemical or genetic modifiers of the muscle atrophy in these model flies7. As an example, overexpression of Mbl isoform C in flies expressing the 250 CTG repeats in the muscle, achieved a rescue of muscle area, as Mbl depletion by sequestration is the triggering factor in DM1 pathogenesis8 (Figure 2C). Muscle area was also rescued after feeding the DM model flies with Abp1, a hexapeptide with proven anti-DM1 activity9 (Figure 2D).
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/56179/56179fig2.jpg" /> 
Figure 2. Quantification of dorsoventral sections of resin-embedded adult thoraces. (A-D) Indirect flight muscles of Drosophila melanogaster with the indicated relevant genotypes. (A) Control flies (yw). (B) Expression of 250 non-coding CTG repeats in muscle (UAS-CTG(250)x) caused a reduction of muscle area in DLMs in comparison to control flies. (C) This muscle atrophy phenotype was rescued by overexpression of Muscleblind (MblC) (UAS-CTG(250)x UAS-MblC) and (D) feeding the model flies with the hexapeptide Abp1 (UAS-CTG(250)x Abp1). In all images the dorsal side is on top. Transgenes were driven to muscle using a Myosin heavy-chain promoter (Mhc)-Gal4. (E) Quantification of percentage of muscle area relative to the control flies&#160;confirmed that the differences were significant. The histogram shows means &#177; S.E.M. **p&#60;0.01 and *p&#60;0.05 (Student&#180;s t-test). Scale bar: 200 &#181;m. <a href="//cloudflare.jove.com/files/ftp_upload/56179/56179fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
The method here reported will be of interest to researchers focusing on muscle development, maintenance and aging, disease pathology and drug testing as it provides reliable information about how muscle tissue responds to both endogenous and external factors.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Image-J software</td>
			<td>National Institutes of Health</td>
			<td></td>
			<td>https://imagej.nih.gov/ij/</td>
		</tr>
		<tr>
			<td>Ultramicrotome</td>
			<td>Leica</td>
			<td>Leica UC6</td>
			<td></td>
		</tr>
		<tr>
			<td>Microscope</td>
			<td>Leica</td>
			<td>Leica MZ6</td>
			<td>Bright field technique.</td>
		</tr>
		<tr>
			<td>Razor blades</td>
			<td>Electron Microscopy Sciences</td>
			<td>71970</td>
			<td>Several alternative providers exist.</td>
		</tr>
		<tr>
			<td>Scissors</td>
			<td>World Precision World</td>
			<td>14003</td>
			<td>Several alternative providers exist.</td>
		</tr>
		<tr>
			<td>Embedding molds</td>
			<td>Electron Microscopy Sciences</td>
			<td>70900</td>
			<td>Several alternative providers exist.</td>
		</tr>
		<tr>
			<td>Glutaraldehyde</td>
			<td>Fluka (Sigma)</td>
			<td>49624</td>
			<td>Toxic.</td>
		</tr>
		<tr>
			<td>OsO4</td>
			<td>Polyscience</td>
			<td>0972A</td>
			<td>Extremely toxic.</td>
		</tr>
		<tr>
			<td>Propylene oxide</td>
			<td>Sigma Aldrich</td>
			<td>82320-250ML</td>
			<td>Extremely toxic.</td>
		</tr>
		<tr>
			<td>resin (Durcupan)</td>
			<td>Sigma Aldrich</td>
			<td>44611-44614</td>
			<td>Carcinogenic when it is unpolymerized.</td>
		</tr>
		<tr>
			<td>Toluidine blue</td>
			<td>Panreac</td>
			<td>251176</td>
			<td>Toxic.</td>
		</tr>
		<tr>
			<td>Mountant Medium (DPX)</td>
			<td>Sigma Aldrich</td>
			<td>44581</td>
			<td>Dangerous.</td>
		</tr>
		<tr>
			<td>Paraformaldehyde</td>
			<td>Sigma Aldrich</td>
			<td>P6148-500G</td>
			<td>Harmful.</td>
		</tr>
		<tr>
			<td>Na2HPO4</td>
			<td>Panreac</td>
			<td>122507</td>
			<td>0.2 M dilution.</td>
		</tr>
		<tr>
			<td>NaH2PO4</td>
			<td>Panreac</td>
			<td>121677</td>
			<td>0.2 M dilution.</td>
		</tr>
		<tr>
			<td>Borax</td>
			<td>Panreac</td>
			<td>3052</td>
			<td>Toxic.</td>
		</tr>
	</tbody>
</table>

optical cross-sectional muscle area determination of drosophila melanogaster adult indirect flight muscles

Muscle mass wasting, known as muscle atrophy, is a common phenotype in Drosophila models of neuromuscular diseases. We have used the indirect flight muscles (IFMs) of flies, specifically the dorso-longitudinal muscles (DLM), as the experimental subject to measure the atrophic phenotype brought about by different genetic causes. In this protocol, we describe how to embed fly thorax muscles for semi thin sectioning, how to obtain a good contrast between muscle and the surrounding tissue, and how to process optical microscope images for semiautomatic acquisition of quantifiable data and analysis. We describe three specific applications of the methodological pipeline. First, we show how the method can be applied to quantify muscle degeneration in a myotonic dystrophy fly model; second, measurement of muscle cross-sectional area can help to identify genes that either promote or prevent muscle atrophy and/or muscle degeneration; third, this protocol can be applied to determine whether a candidate compound is able to significantly modify a given atrophic phenotype induced by a disease-causing mutation or by an environmental trigger.

To quantify whether the overexpression of MblC or the administration of Abp1 had any effect in the atrophic phenotype of the Myotonic Dystrophy fly model we focused on the DLMs, which are part of IFMs (Figure 1). We determined that the model flies, which express 250 non-coding CTG repeats throughout the musculature driven by the Myosin heavy-chain promoter (Mhc)-Gal4, had a 50% reduction of muscle area compared to control flies. In contrast, co-expre...

Watch this Scientific Journal Video about Optical Cross-Sectional Muscle Area Determination of Drosophila Melanogaster Adult Indirect Flight Muscles at JoVE.com

Optical Cross-Sectional Muscle Area Determination of Drosophila Melanogaster Adult Indirect Flight Muscles

We report a method to quantify muscle area, which is an indirect method to determine muscle mass in Drosophila adults. We demonstrate the application of our methodology by analyzing the indirect flight muscles in a Drosophila model of Myotonic Dystrophy disease.

Optical Cross-Sectional Muscle Area Determination of Drosophila Melanogaster Adult Indirect Flight Muscles

Muscle mass wasting, known as muscle atrophy, is a common phenotype in Drosophila models of neuromuscular diseases. We have used the indirect flight ...

The overall goal of this procedure is to quantify the muscle area in the Drosophila adult muscles as a means to indirectly quantify muscle mass and correctly size the generation or muscle atrophy. For this purpose, we focused on dorsal longitudinal muscles because of their size, distribution, and also count on this position, a low and easy orientation for transversal sectioning. One, fixation and resin embedding.The first step of the procedure is to anesthetize the flies with CO2, and, with the help of scissors and forceps, remove the legs, the wings, and the terminal part of the abdomen. Secondly, carefully transfer the carcasses, to avoid the deformation of the thorax, to a one point five milliliter tube on ice, placing a maximum of six individuals per tube containing 200 microliters of solution one. The carcasses cannot remain in this solution for more than 20 minutes.Finally, add 200 microliters of solution two and incubate on ice for 30 minutes. After incubation, remove all of the liquid, add 200 microliters of solution two, and incubate the carcasses on ice for one to two hours. The next step is to remove the solution and dehydrate the samples through a graded ethanol series.Incubate the samples twice in propylene oxide for ten minutes each incubation. Then, replace the propylene oxide with a mixture of 500 microliters resin and 500 microliters propylene oxide and incubate the samples at room temperature overnight. The next day, replace the mixture with 100 percent resin and incubate the samples for four hours.Afterwards, transfer the carcasses to plastic molds containing new resin, making sure you put one carcass in each well of the mold. With a wooden stick, orient the carcasses in the wells and let the resin polymerase overnight in a pasteur oven at 70 degrees Celsius. To discard the resin, bake it at 70 degrees Celsius for 24 hours, because solid, baked resin is not toxic.Two, trimming and sectioning of blocks. With the help of razor blades, trim away the resin and form a trapezoidal shape surrounding the carcass to give the appropriate orientation in the microtome. Check in the microscope that the muscles are perfectly oriented.After this, cut one point five micrometer thick sections with an ultramicrotome, and transfer the sections into water drops over gelatinized slides. Finally, place the slides containing the sections on a heating block at 70 to 80 degrees Celsius until all the water evaporates. Three, staining IFM sections.Cover the sections with toluidine blue for approximately 30 seconds on the heating block. Then, rinse in several changes of water and leave the slides on a warm plate to evaporate the water. Four, mounting IFM sections.Taking the slides, put one or two drops of mountant medium on the sections and put on a long coverslip. Five, acquisition of images and quantification of muscle area. Use ImageJ software to select an area containing only the DLMs.Taking as a control the dimensions of the image of the fly with the biggest muscle area, finerize the images, and delete the areas, or pixels, that do not correspond to the muscles of interest. Quantify the percentage of pixels corresponding to muscle tissue out of total with the command analyze, measurement, and select the option, area fraction. This percentage of area is an estimation of the DLM muscular mass of each fly.Representative results. We determined that the model flies, which express 250 noncoding CTG repeats throughout the musculature, driven by the myosin heavy chain promoter, MhC Gal four, had a 50 percent reduction of muscle area compared to control flies. In contrast, co expression of muscle blind C and expanded CTG repeats with the same driver strongly suppressed such phenotype and cross sectional muscle area was 70 percent of control flies.Administration of the Abp1 hexapeptide in the nutritive media similarly suppressed the atrophic phenotype and model flies that had taken the compound showed approximately 60 percent of normal muscle area, instead of 50 percent, that is typical of DF1 flies.Conclusions. The protocol presented here is a useful tool for quantifying the muscle degeneration caused by the onset or progression of a particular disease in a fly model. Finally, this method is also optimized to detect small muscle area differences, or even to quantify the area of different structures such as nephyocytes.Thank you for watching.

optical-cross-sectional-muscle-area-determination-drosophila

Research

JoVE Journal

Biology

8.8K Views.  University of Valencia. The overall goal of this procedure is to quantify the muscle area in the Drosophila adult muscles as a means to indirectly quantify muscle mass and correctly size the generation or muscle atrophy. For this purpose, we focused on dorsal longitudinal muscles because of their size, distribution, and also count on this position, a low and easy orientation for transversal sectioning. One, fixation and resin embedding.The first step of the procedure is to anesthetize the flies with CO2, and,...