Name: visualize drosophila leg motor neuron axons through the adult cuticle
Uploaded: 2018-10-30T14:30:00
Description: Watch this Scientific Journal Video about Visualize Drosophila Leg Motor Neuron Axons Through the Adult Cuticle at JoVE.com

We thank Robert Renard for preparing fly food medium. This work was supported by an NIH grant NS070644 to R.S.M. and funding from the ALS Association (#256), FRM (#AJE20170537445) and ATIP-Avenir Program to J.E.

1. Leg Dissection and Fixation
<ol>
	<li>Take a glass multi-well plate and fill appropriate number of wells with 70% ethanol. Add 15&#8211;20 CO2-anesthetized flies (of either sex and any age) to each well and by using a brush, gently dab the flies into the ethanol solution until flies are fully submerged. 
	NOTE: This step is to remove the hydrophobicity of the cuticle. Do not wash for more than 1 min, because this increases auto-fluorescence of the cuticle.</li>
	<li>Rinse the flies 3 times with 0.3% ...

<ol>
	<li>Miller, A., Demerec, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+internal+anatomy+and+histology+of+the+imago+of+Drosophila+melanogaster.">The internal anatomy and histology of the imago of Drosophila melanogaster.</a> Biology of Drosophila. , 420-531 (1950).</li><li>Soler, C., Ladddada, L., Jagla, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Coordinated+development+of+muscles+and+tendons+of+the+Drosophila+leg.">Coordinated development of muscles and tendons of the Drosophila leg.</a> Development. 131 (24), 6041-6051 (2004).</li><li>Baek, M., Mann, 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=Lineage+and+Birth+Date+Specify+Motor+Neuron+Targeting+and+Dendritic+Architecture+in+adult+Drosophila.">Lineage and Birth Date Specify Motor Neuron Targeting and Dendritic Architecture in adult Drosophila.</a> Journal of Neuroscience. 29 (21), 6904-6916 (2009).</li><li>Brierley, D. J., Rathore, K., VijayRaghavan, K., Williams, D. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Developmental+origins+and+architecture+of+Drosophila+leg+motoneurons.">Developmental origins and architecture of Drosophila leg motoneurons.</a> Journal of Comparative Neurology. 520 (8), 1629-1649 (2012).</li><li>Enriquez, J., Mann, 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=Specification+of+Individual+Adult+Motor+Neuron+Morphologies+by+Combinatorial+Transcription+Factor+Codes.">Specification of Individual Adult Motor Neuron Morphologies by Combinatorial Transcription Factor Codes.</a> Neuron. 86 (4), 955-970 (2015).</li><li>Mahr, A., Aberle, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+expression+pattern+of+the+Drosophila+vesicular+glutamate+transporter:+a+marker+protein+for+motoneurons+and+glutamatergic+centers+in+the+brain.">The expression pattern of the Drosophila vesicular glutamate transporter: a marker protein for motoneurons and glutamatergic centers in the brain.</a> Gene Expression Patterns. 6 (3), 299-309 (2006).</li><li>Lee, T., Luo, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mosaic+analysis+with+a+repressible+cell+marker+(MARCM)+for+Drosophila+neural+development.">Mosaic analysis with a repressible cell marker (MARCM) for Drosophila neural development.</a> Trends in Neuroscience. 24 (5), 251-254 (2001).</li><li>Enriquez, J., Rio, L. Q., Blazeski, R., Bellemin, S., Godement, P., Mason, C. A., Mann, 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=Differing+Strategies+Despite+Shared+Lineages+of+Motor+Neurons+and+Glia+to+Achieve+Robust+Development+of+an+Adult+Neuropil+in+Drosophila.">Differing Strategies Despite Shared Lineages of Motor Neurons and Glia to Achieve Robust Development of an Adult Neuropil in Drosophila.</a> Neuron. 97 (3), 538-554 (2018).</li><li>Preibisch, S., Saalfeld, S., Tomancak, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Globally+optimal+stitching+of+tiled+3D+microscopic+image+acquisitions.">Globally optimal stitching of tiled 3D microscopic image acquisitions.</a> Bioinformatics. 25 (11), 1463-1465 (2009).</li><li>Brierley, D. J., Blanc, E., Reddy, O. V., Vijayraghavan, K., Williams, D. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dendritic+targeting+in+the+leg+neuropil+of+Drosophila:+the+role+of+midline+signalling+molecules+in+generating+a+myotopic+map.">Dendritic targeting in the leg neuropil of Drosophila: the role of midline signalling molecules in generating a myotopic map.</a> PLoS Biology. 7 (9), e1000199 (2009).</li></ol>

The cuticle of adult Drosophila and of other arthropods, which contains many dark pigments, is a major obstacle for viewing structures inside their body. In addition, it is strongly auto fluorescent which is made worse by fixation. These two features are very problematic for observations of fluorescent dyes or molecules inside the body of animals with an exoskeleton.
The procedure that we have described and that we routinely use in the lab yields clean and detailed images of axon trajectories ...

Like the vertebrate limb, the Drosophila adult leg is organized into segments. Each fly leg contains 14 muscles, each of which comprises multiple muscle fibers1,2. The cell bodies of the adult leg MNs are located in the T1 (prothoracic), T2 (mesothoracic), and T3 (metathoracic) ganglia on each side of the ventral nerve cord (VNC), a structural analogous to the vertebrate spinal cord (Figure 1). There are approximately 50 MNs in each ganglia, which target muscles in four segments of the ipsilateral leg (coxa, trochanter, femur, and tibia) (Figure 1)3. Importantly, each individual adult leg MN has a unique morphological identity that is highly stereotyped between animals3,4. All these unique MNs are derived from 11 stem cells, called neuroblasts (NBs) producing leg MNs during the larval stages3,4. At the end of the larval stages all the immature postmitotic MNs differentiate during metamorphosis to acquire their specific dendritic arbors and axonal terminal targets that define their unique morphology3,4. Previously we tested the hypothesis that a combinatorial code of transcription factors (TFs) specifies the unique morphology of each Drosophila adult leg MN5. As a model, we used lineage B, one of the 11 NB lineages which produces seven out of the MNs and demonstrated that a combinatorial code of TFs expressed in postmitotic adult leg MNs dictates their individual morphologies. By reprograming the TF code of MNs we have been able to switch MN morphologies in a predictable manner. We call these TFs: mTFs (morphological TFs)5.
One of the most challenging parts of the morphological analyses of adult MNs is to visualize the axons through a thick and auto-fluorescent cuticle with high resolution. We usually label axons with a membrane-tagged GFP that is expressed in MNs with a binary expression system, such as DVglut-Gal4/UAS-mCD8::GFP or DVglut-QF/ QUAS mCD8::GFP, where DVglut is a strong driver expressed in motoneurons6. By combining these tools with other clonal techniques such as mosaic analysis with a repressible marker (MARCM)7, cis-MARCM8, or MARCMbow5, we can restrict the GFP expression to subpopulations of MNs making the phenotypic analysis of axons easier. We have generated a protocol in order to keep leg MN axonal morphology intact for imaging and subsequent 3D reconstruction by addressing specific issues intrinsic to the adult Drosophila leg such as (1) fixation of the internal structures of the adult leg without affecting axon morphology, endogenous fluorescent expression, and leg musculature, (2) mounting of the leg to preserve the overall structure under a coverslip and in the appropriate orientation for imaging, and (3) image processing to obtain the cuticle background as well as axonal fluorescent signal. While this protocol has been detailed for the detection of fluorescent expression in MN axons, it can be applied to visualize other components of leg neuromusculature in arthropods.

<table>
	<tbody>
		<tr>
			<td>Ethanol absolute</td>
			<td>Fisher</td>
			<td>E/6550DF/17</td>
			<td>Absolute analytical reagent grade</td>
		</tr>
		<tr>
			<td>nonionic&#160;surfactant&#160;detergent</td>
			<td>Sigma-Aldrich</td>
			<td>T8787</td>
			<td>Triton X-100, for molecular biology</td>
		</tr>
		<tr>
			<td>Fine forceps</td>
			<td>Sigma-Aldrich</td>
			<td>F6521</td>
			<td>Jewelers forceps, Dumont No. 5</td>
		</tr>
		<tr>
			<td>Glass multi-well plate</td>
			<td>Electron Microscopy Sciences</td>
			<td>71563-01</td>
			<td>9 cavity Pyrex, 100x85 mm</td>
		</tr>
		<tr>
			<td>PFA</td>
			<td>Thermofisher</td>
			<td>28908</td>
			<td>Pierc 16% Formaldehyde (w/v), Methanol-free</td>
		</tr>
		<tr>
			<td>Glycerol</td>
			<td>Fisher BioReagents</td>
			<td>BP 229-1</td>
			<td>Glycerol (Molecular Biology)</td>
		</tr>
		<tr>
			<td>Spacers</td>
			<td>Sun Jin Lab Co</td>
			<td>IS006</td>
			<td>iSpacer, four wells, around 12 &#956;L working volume per well, 7 mm diameter, 0.18 mm deep</td>
		</tr>
		<tr>
			<td>Square 22x22 mm coverslips</td>
			<td>Fisher Scientific</td>
			<td>FIS#12-541-B</td>
			<td>No.1.5 -0.16 to 0.19mm thick</td>
		</tr>
		<tr>
			<td>Mounting Medium</td>
			<td>Vector Laboratories</td>
			<td>H-1000</td>
			<td>Vectashield Antifade Mounting Medium</td>
		</tr>
		<tr>
			<td>Confocal microscope</td>
			<td>Carl Zeiss</td>
			<td></td>
			<td>LSM780; objective used LD LCI Plan-Apochromat 
			25x/0,8 Imm Korr DIC M27 (oil/ 
			silicon/glycerol/water 
			immersion) (420852-9871-000)</td>
		</tr>
		<tr>
			<td>imaging software</td>
			<td>Carl Zeiss</td>
			<td></td>
			<td>ZEN 2011</td>
		</tr>
		<tr>
			<td>3D-Image software</td>
			<td>ThermoFisher Scientific</td>
			<td></td>
			<td>Amira 6.4</td>
		</tr>
		<tr>
			<td>ImageJ</td>
			<td>National Institutes of Health</td>
			<td>https://imagej.nih.gov/ij/</td>
			<td>ImageJ/FIJI</td>
		</tr>
	</tbody>
</table>

visualize drosophila leg motor neuron axons through the adult cuticle

The majority of work on the neuronal specification has been carried out in genetically and physiologically tractable models such as C. elegans, Drosophila larvae, and fish, which all engage in undulatory movements (like crawling or swimming) as their primary mode of locomotion. However, a more sophisticated understanding of the individual motor neuron (MN) specification&#8212;at least in terms of informing disease therapies&#8212;demands an equally tractable system that better models the complex appendage-based locomotion schemes of vertebrates. The adult Drosophila locomotor system in charge of walking meets all of these criteria with ease, since in this model it is possible to study the specification of a small number of easily distinguished leg MNs (approximately 50 MNs per leg) both using a vast array of powerful genetic tools, and in the physiological context of an appendage-based locomotion scheme. Here we describe a protocol to visualize the leg muscle innervation in an adult fly.

As shown in Figure 4, this procedure allows excellent imaging of GFP-labeled axons in adult Drosophila legs, together with their terminal arbors. Importantly a clean GFP signal is obtained without any contamination from the fluorescence emitted by the leg cuticle. The signal from the cuticle can then be combined with the GFP signal to identify the positioning of axons in the legs (Figure 4E, Figure 1...

Watch this Scientific Journal Video about Visualize Drosophila Leg Motor Neuron Axons Through the Adult Cuticle at JoVE.com

Visualize Drosophila Leg Motor Neuron Axons Through the Adult Cuticle

Here we describe a protocol to visualize the axonal targeting with a florescent protein in adult legs of Drosophila by fixation, mounting, imaging, and post-imaging steps.

Visualize Drosophila Leg Motor Neuron Axons Through the Adult Cuticle

The majority of work on the neuronal specification has been carried out in genetically and physiologically tractable models such as C. elegans, Drosophila ...

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