We thank Dr. Ying Xiong for discussions and comments on the manuscript. This work is supported by a grant from the National Science Foundation of China (NSFC) to C. M. (31500839).

1. Dissection of larvae
NOTE: The dissecting solution hemolymph-like saline (HL3.1)18 and the fixing solution 4% paraformaldehyde (PFA)19,20are used at room temperature because the microtubules depolymerize when the temperature is too low.
<ol>
	<li>Pick out a wandering 3rd instar larva with long blunt forceps. Wash it with HL3.1 and place it on the dissection dish under the stereomicroscope. 
	NOTE: Wandering 3rd instar larva is identified by branched anterior spiracle and crawls around the tube at approximately 96 h (25 &#176;C)21.</li>
	<li>Position the larva with the dorsal or ventral side up. Identify the dorsal side by the two long tracheas and the ventral by the abdominal denticle belts.
	<ol>
		<li>Depending on the tissue to observe, opt for dorsal or ventral dissection. This will allow for a more precise and detailed view of the specific area of interest. For NMJ and muscle cell observation, cut open the larval dorsal and ventral regions, respectively.</li>
	</ol>
	</li>
	<li>Pin the mouth hooks and the tail. Adjust the pins to keep the larva in an extended state. Add a drop of HL3.1 to the larva to prevent it from drying. 
	NOTE: Ca2+ -free HL 3.1 can be used to minimize contraction of the muscles during dissection.</li>
	<li>Use the dissecting scissors to make a small transverse cut close to the posterior end, but do not cut off the posterior end. Then cut along the ventral midline towards the anterior end.</li>
	<li>Insert four insect pins on the four corners of the larva. Readjust insect pins such that the larva is maximally stretched in all directions.</li>
	<li>Use the forceps to remove internal organs while not damaging the muscles.</li>
</ol>
2. Fixation
<ol>
	<li>Add 100 &#181;L of PFA (4%) to immerse carcasses for 40 min while the carcasses are still pinned on the dissecting dish. 
	CAUTION: Effective protection measures are taken to avoid direct contact with skin or inhalation, as PFA is a hazard.</li>
	<li>Dismount the pins and transfer the sample to a 2 mL microcentrifuge tube. Rinse off PFA with 1x phosphate buffered saline containing 0.2% Triton X-100 (0.2% PBST) to fill 2 mL microcentrifuge tube for 10 min on the decoloring shaker at 15 rpm. Repeat the wash process 5x.</li>
</ol>
3. Immunocytochemistry
<ol>
	<li>Immerse the carcasses in blocking agent (5% goat serum in 0.2% PBST) and block for 40 min at room temperature.</li>
	<li>Remove the blocking agent and replace it with 200 &#181;L of the primary antibody (e.g., anti-&#945;-tubulin, 1:1000; anti-Futsch, 1:50) diluted with 0.2% PBST at 4 &#176;C overnight. Visualize muscle microtubules by immunostaining with monoclonal anti-&#945;-tubulin. Anti-Futsch can indirectly reflect the microtubule morphology in NMJ.</li>
	<li>After incubation of the primary antibody, wash larvae with 0.2% PBST for 10 min. Repeat 5x.</li>
	<li>Incubate the larvae with 200 &#181;L of secondary antibody (e.g., goat anti-Mouse-488, 1:1000) diluted with 0.2% PBST at room temperature for 1.5 h in the dark.</li>
	<li>Next, add a nuclear dye such as TO-PRO(R) 3 iodide (T3605) at a concentration of 1:1000 into the incubating tube for 30 min when staining the microtubules in the dark20,22.</li>
	<li>Rinse off the secondary antibody and the nuclear dye with 0.2% PBST for 10 min. Repeat 5x in the dark.</li>
</ol>
4. Mounting
<ol>
	<li>Place the larval carcass in 0.2% PBST on a glass slide and adjust it under the stereomicroscope. Make sure the inner surface of the larval carcass is facing up and all larval carcasses are arranged as desired.</li>
	<li>Absorb excess PBST solution with a wipe and gently add a drop of antifade mounting medium.</li>
	<li>Place a coverslip on the slide to cover the dissected larvae slowly and gently to avoid bubbles.</li>
	<li>Apply fingernail polish around the coverslip. Place the slide in the dark space to reduce fluorescent attenuation.</li>
</ol>
5. Image acquisition
<ol>
	<li>To acquire the images, use a laser scanning confocal microscope, select the 60x oil immersion objective (numerical aperture 1.42) or similar, and adjust the laser power and wavelength based on the experiment.</li>
	<li>To identify the NMJ, capture images in muscle 4 in segment A3 (as shown in the location in Figure 1F). Select a 488 nm laser to activate the &#945;-tubulin or Futsch and 543 nm to activate the HRP imaging track. Adjust the parameters to a frame size of 800 pixels x 800 pixels, a digital zoom of 2.0, and an imaging interval of 0.8 &#181;m in NMJs (Figure 2).</li>
	<li>To identify the microtubules in muscle, capture images of muscle 2 in segment A3-A5 (as shown in the location in Figure 1G) as it has fewer tracheal branches. Choose a 488 nm laser for activating &#945;-tubulin and a 635 nm laser for activating the T3605 imaging track. Adjust the parameters to a frame size of 1024 pixels x 1024 pixels, a digital zoom of 3.0, and an imaging interval of 0.4 &#181;m in muscle cells (Figure 3).</li>
</ol>

Viewing Microtubule Networks in &lt;em&gt;Drosophila&lt;/em&gt; Neuromuscular Junctions and Muscle Cells

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S., Bate, M. <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+embryonic+neuromuscular+synapse+of+Drosophila+melanogaster.">Development of the embryonic neuromuscular synapse of Drosophila melanogaster.</a> The Journal of neuroscience: the official journal of the Society for Neuroscience. 13 (1), 144-166 (1993).</li><li>Xiong, Y., 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=HDAC6+mutations+rescue+human+tau-induced+microtubule+defects+in+Drosophila.">HDAC6 mutations rescue human tau-induced microtubule defects in Drosophila.</a> Proceedings of the National Academy of Sciences of the United States of America. 110 (12), 4604-4609 (2013).</li><li>Sullivan, W., Ashburner, M., Hawley, R. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Drosophila Protocols. , (2000).</li><li>Mao, C. X., 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=Microtubule-severing+protein+Katanin+regulates+neuromuscular+junction+development+and+dendritic+elaboration+in+Drosophila.">Microtubule-severing protein Katanin regulates neuromuscular junction development and dendritic elaboration in Drosophila.</a> Development. 141 (5), 1064-1074 (2014).</li><li>Jin, 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=Drosophila+Tubulin-specific+chaperone+E+functions+at+neuromuscular+synapses+and+is+required+for+microtubule+network+formation.">Drosophila Tubulin-specific chaperone E functions at neuromuscular synapses and is required for microtubule network formation.</a> Development. 136 (9), 1571-1581 (2009).</li><li>Sarthi, J., Elefant, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=dTip60+HAT+activity+controls+synaptic+bouton+expansion+at+the+Drosophila+neuromuscular+junction.">dTip60 HAT activity controls synaptic bouton expansion at the Drosophila neuromuscular junction.</a> PloS one. 6 (10), 26202 (2011).</li><li>Weingarten, M. 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The authors have nothing to disclose.

Here a protocol is described for the dissection and immunostaining of Drosophila larval neuromuscular junctions and muscle cells. There are several essential points to consider. Firstly, avoiding injury to the observed muscles is crucial during the dissection process. It may be worth fixing the fillet before removing internal organs to prevent direct contact between the forceps and the muscles. To avoid muscle damage or separation from the larval epidermis, it is important to ensure that the speed of the shaker ...

Microtubules (MTs), as one of the structural components of the cytoskeleton, play an important role in diverse biological processes, including cell division, cell growth and motility, intracellular transport, and the maintenance of cell shape. Microtubule dynamics and function are modulated by interactions with other proteins, such as MAP1, MAP2, Tau, Katanin, and Kinesin1,2,3,4,5.
In neurons, microtubules are essential for the development and maintenance of axons and dendrites. Abnormalities in microtubules lead to dysfunction and even the death of neurons. For instance, in the brain of Alzheimer&#39;s patients, Tau protein hyperphosphorylation reduces the stability of the microtubule network, causing neurological irregularities6. Thus, examining microtubule networks will contribute to a comprehension of neurodevelopment and the pathogenesis of neurological diseases.
The neuromuscular junction (NMJ) is the peripheral synapse formed between a motor neuron axon terminal and a muscle fiber, which is an excellent and powerful model system for studying synaptic structure and functions7. Futsch is a protein in Drosophila that is homologous to the microtubule-binding protein MAP1B found in mammals8. It is expressed only in neurons and plays a role in the development of the NMJ&#39;s synaptic buttons8,9. In wild-type, filamentous bundles that run along the center of NMJ processes are visualized by immunostaining with anti-Futsch. When reaching NMJ&#39;s end, this bundle has the ability to either form a loop consisting of microtubules or to lose its filamentous structure, resulting in a diffuse and punctate appearance10. Microtubule loops are associated with paused growth cones, which suggests the microtubule array is stable11. Therefore, we can indirectly determine the stable microtubule development in NMJ by Futsch staining. The large size of muscle cells in Drosophila larva allows for clear visualization of the microtubule network. The factors affecting the stability of the microtubule network can be found by analyzing the density and shape of microtubules. Simultaneously, the microtubule network status of muscle cells can be cross-verified with the result of NMJ to obtain more comprehensive conclusions.
Many protocols have been employed for investigating the network and dynamics of microtubules. However, these researches have often focused on in vitro studies12,13,14,15,16. Alternatively, some in vivo experiments have employed electron microscopy to detect the cytoskeleton17. According to the specific binding of fluorescently labeled antibodies or chemical dyes to proteins or DNA, the methods presented here allow the detection of microtubule networks in NMJ at the level of individual neurons in vivo, with results corroborated by observations in muscle cells. This protocol is simple, stable, and repeatable when combined with the powerful genetic tools available in Drosophila melanogaster, enabling a diverse range of phenotypic examinations and genetic screenings for the role of microtubule network regulatory proteins in the nervous system in vivo.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Alexa Fluor Plus 405 phalloidin</td>
			<td>invitrogen</td>
			<td>A30104</td>
			<td>dilute 1:200</td>
		</tr>
		<tr>
			<td>Enhanced Antifade Mounting Medium</td>
			<td>Beyotime</td>
			<td>P0128M</td>
			<td></td>
		</tr>
		<tr>
			<td>FV10-ASW confocal microscope</td>
			<td>Olympus</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Goat anti-Mouse antibody, Alexa Fluor 488 conjugated</td>
			<td>Thermo Fisher</td>
			<td>A-11001</td>
			<td>dilute 1:1,000</td>
		</tr>
		<tr>
			<td>Laser confocal microscope LSM 710</td>
			<td>Zeiss</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Micro Scissors</td>
			<td>66vision</td>
			<td>54138B</td>
			<td></td>
		</tr>
		<tr>
			<td>Mouse anti-Futsch antibody</td>
			<td>Developmental Studies Hybridoma Bank&#160;&#160;</td>
			<td>22C10</td>
			<td>dilute 1:50</td>
		</tr>
		<tr>
			<td>Mouse anti-&#945;-tubulin antibody</td>
			<td>Sigma</td>
			<td>T5168</td>
			<td>dilute 1:1,000</td>
		</tr>
		<tr>
			<td>Paraformaldehyde</td>
			<td>Wako</td>
			<td>168-20955</td>
			<td>Final concentration: 4% in PB Buffer</td>
		</tr>
		<tr>
			<td>Stainless Steel Minutien Pins</td>
			<td>Entomoravia</td>
			<td></td>
			<td>0.1mm Diam</td>
		</tr>
		<tr>
			<td>Stereomicroscope SMZ161</td>
			<td>Motic</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>stereoscopic fluorescence microscope BX41</td>
			<td>Olympus</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Texas Red-conjugated goat anti-HRP</td>
			<td>Jackson ImmunoResearch</td>
			<td></td>
			<td>dilute 1:100</td>
		</tr>
		<tr>
			<td>TO-PRO(R) 3 iodide</td>
			<td>Invitrogen</td>
			<td>T3605</td>
			<td>dilute 1:1,000</td>
		</tr>
		<tr>
			<td>Transfer decoloring shaker TS-8</td>
			<td>Kylin-Bell lab instruments</td>
			<td>E0018</td>
			<td></td>
		</tr>
		<tr>
			<td>TritonX-100</td>
			<td>BioFroxx</td>
			<td>1139</td>
			<td></td>
		</tr>
		<tr>
			<td>Tweezers&#160;</td>
			<td>dumont</td>
			<td>500342</td>
			<td></td>
		</tr>
	</tbody>
</table>

using drosophila larval neuromuscular junction and muscle cells to visualize microtubule network

The microtubule network is an essential component of the nervous system. Mutations in many microtubules regulatory proteins are associated with neurodevelopmental disorders and neurological diseases, such as microtubule-associated protein Tau to neurodegenerative diseases, microtubule severing protein Spastin and Katanin 60 cause hereditary spastic paraplegia and neurodevelopmental abnormalities, respectively. Detection of microtubule networks in neurons is advantageous for elucidating the pathogenesis of neurological disorders. However, the small size of neurons and the dense arrangement of axonal microtubule bundles make visualizing the microtubule networks challenging. In this study, we describe a method for dissection of the larval neuromuscular junction and muscle cells, as well as immunostaining of &#945;-tubulin and microtubule-associated protein Futsch to visualize microtubule networks in Drosophila melanogaster. The neuromuscular junction permits us to observe both pre-and post-synaptic microtubules, and the large size of muscle cells in Drosophila larva allows for clear visualization of the microtubule network. Here, by mutating and overexpressing Katanin 60 in Drosophila melanogaster,&#160;and then examining the microtubule networks in the neuromuscular junction and muscle cells, we&#160;accurately reveal the regulatory role of Katanin 60 in neurodevelopment. Therefore, combined with the powerful genetic tools of Drosophila&#160;melanogaster, this protocol greatly facilitates genetic screening and microtubule dynamics analysis for the role of microtubule network regulatory proteins in the nervous system.

Author Spotlight: Understanding Microtubule Network in Drosophila Neuromuscular Junctions 

Using Drosophila Larval Neuromuscular Junction and Muscle Cells to Visualize Microtubule Network

Currently, microtubule dynamics are observed indirectly through microtubule-binding proteins such as EB1. Since alphabeta tubulin heterodimers are abundant in the cytoplasm, fold directly, neighboring tubulin heterodimers are lacking the dynamics of microtubule networks in vivo. Our protocol visualizes microtubules in neuromuscular synapses and muscle cells.When combined with the powerful genetic tools available in Drosophila melanogaster, enabling a diverse range of phenotypic examinations and the genetic screening for the role of microtubule network regulatory proteins in the nervous system in vivo. Our research focuses on the relationship between the cytoskeleton and the neurodevelopment, as well as its implications for neurological diseases. We hope to discover the mechanism of neurodevelopment and the parthenogenesis for neurological diseases by highlighting the effect of cytoskeletal regulatory proteins on neurons.

We demonstrated a step-by-step procedure for visualizing the microtubule network in both neuromuscular junctions (NMJs) and muscle cells. Following dissection according to the schematic diagram (Figure 1A-E), immunostaining is performed, and images are subsequently observed and collected under a laser confocal microscope or a stereoscopic fluorescence microscope (Figure 1F,G).
Both pre-and post-synapt...

Watch this Scientific Journal Video about Understanding Microtubule Network in Drosophila Neuromuscular Junctions at JoVE.com

Here, we present a detailed protocol to visualize the microtubule networks in neuromuscular junctions and muscle cells. Combined with the powerful genetic tools of Drosophila melanogaster, this protocol greatly facilitates genetic screening and microtubule-dynamics analysis for the role of microtubule network regulatory proteins in the nervous system.

The microtubule network is an essential component of the nervous system. Mutations in many microtubules regulatory proteins are associated with ...

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Neuroscience

Drosophila Larval Dissection and Fixation for Microtubule Visualization

Begin by picking out a wandering Drosophila third instar larva using long blunt forceps. Wash the larva with hemolymph-like saline, then dry it with a wipe. Next, position the larva dorsally or ventrally on a dissection dish under the stereo microscope.Depending on the tissue to be observed, opt for dorsal or ventral dissection. Pin the larva's mouth hooks and tail to maintain extended positioning. Next, add a drop of the hemolymph-like saline to prevent the larva from drying.Using dissection scissors, make a small transverse incision close to the posterior end without severing it completely. Proceed to cut along the ventral midline, moving toward the anterior end. Now insert four insect pins each into the corners of the larva.Make necessary adjustments to the insect pins to maximize the stretching of the larva. Use forceps to gently remove the internal organs while avoiding harm to the muscles. To fix the larva, immerse the carcasses in 100 L of 4%paraformaldehyde, while still affixed to the dissecting dish.After this, dismount the pins. Then transfer the sample into a 2 mL microcentrifuge tube filled with 0.2%PBST. Place the tube on a shaker for 10 minutes at 15 RPM.

Immunohistochemistry of Drosophila Larva for Microtubule Visualization

Remove the PBST and immerse the paraformaldehyde-fixed drosophila larval carcasses in a blocking agent for 40 minutes at room temperature. Replace the blocking agent with 200 microliters of the primary antibody diluted with 0.2%PBST. Leave the larvae to incubate at four degrees Celsius overnight.The next day, wash the larvae with 0.2%PBST for 10 minutes. Next, remove the PBST from the tube and add 200 microliters of diluted secondary antibody. Incubate it at ambient temperature for 1.5 hours in the dark.Introduce a nuclear dye such as TO-PRO R 3 iodide into the incubating tube for 30 minutes while staining the microtubules in the dark. Finally, rinse off the secondary antibody and the nuclear dye with 0.2%PBST for 10 minutes.

Mounting and Image Acquisition of Drosophila Larval Microtubules

Begin by placing the antibody labeled drosophila larval carcasses in 0.2%PBST on a glass slide. Adjusted under the stereo microscope, ensuring that the inner surface of the larval carcass is facing up. Absorb the excess PBST solution using a wipe.Then delicately add a drop of Anti-Fade mounting medium. Next place a cover slip on the slide covering the dissected larvae slowly and gently, avoiding bubble formation. Secure the cover slip in place by applying fingernail polish around its edges.Store the slide in a dark location to minimize fluorescent attenuation. For image acquisition, use the laser scanning confocal microscope with the 63x Oil immersion objective. Then adjust the wavelength and laser power to fit the requirements of the experiment best.To identify the neuromuscular junctions and capture images of muscle four in segment A three, select a 488 nanometer laser to activate alpha tubulin or Futsch, and 546 nanometers to activate the HRP imaging track. Modify the parameters to achieve a frame size of 1, 024 by 1, 024 pixels, a digital zoom of 1.0, and an imaging interval of 0.8 micrometers. To visualize microtubules in the muscle, capture images of muscle two in the segments A three to A five as it has fewer tracheal branches.Choose a 488 nanometer laser for activating alpha tubulin and a 633 nanometer laser for activating the T3605 imaging track. Adjust the imaging parameters to a frame size of 1, 024 by 1, 024 pixels, a digital zoom of 2.0, and an imaging interval of 0.4 micrometers. Both pre-and post-synaptic microtubule organizations of the neuromuscular junction were labeled with anti-alpha tubulin.Futsch staining reflected the abundance of stable microtubules in the pre-synaptic neurons. Decreased signal intensity of anti-Futsch was observed when microtubules severing protein Katanin 60 was overexpressed in the presynaptic neurons. The staining intensity of the axon trunk was stronger than that of the branches.Katanin 60 mutations resulted in increased microtubule loops. Overexpression of Katanin 60 caused short microtubule fragments within the terminal buttons. Alpha tubulin staining demonstrated a clear network of microtubules around the nucleus.Muscle cells had a significantly increased perinuclear microtubular intensity and exhibited stronger bundles in the Katanin 60 mutant. Overexpression resulted in fragmentation of the microtubule fibers.

1.4K Views.  Hubei University.  Here, we present a detailed protocol to visualize the microtubule networks in neuromuscular junctions and muscle cells. Combined with the powerful genetic tools of Drosophila melanogaster, this protocol greatly facilitates genetic screening and microtubule-dynamics analysis for the role of microtubule network regulatory proteins in the nervous system.

Viewing Microtubule Networks in Drosophila Neuromuscular Junctions and Muscle Cells

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