This protocol provides a guide for live confocal imaging of microtubule dynamics using fluorescent microtubule markers in Drosophila larval sensory neurons.
Method Article
* These authors contributed equally
This protocol provides a guide for live confocal imaging of microtubule dynamics using fluorescent microtubule markers in Drosophila larval sensory neurons.
Drosophila larval class IV sensory neurons are located just beneath the cuticle and are characterized by highly branched dendritic arbors that expand isotropically in two dimensions as the larvae develop. The growth of these arbors is driven by stochastic processes involving growth, shrinkage, and pausing of the dendritic terminal tips. To test the hypothesis that tip dynamics are driven by microtubule dynamics, protocols have been developed for imaging fluorescently labeled microtubules within dendrites. The method enables visualization of microtubule dynamics in fine terminal dendrites of class IV sensory neurons using confocal microscopy. It is designed to preserve dendritic arbor morphology during imaging while allowing microtubules to be visualized together with a membrane marker. This manuscript describes the procedures used to prepare Drosophila larvae for live imaging and to visualize fluorescently labeled microtubules in dendrites. The protocol, therefore, provides an approach to examining microtubule behavior in fine terminal dendrites while remaining compatible with membrane co-labeling.
Neurons are highly polarized cells whose cytoskeletons define their architecture. Microtubules, one component of the neuronal cytoskeleton, provide structural support and serve as tracks for long-distance cargo transport1,2. The microtubule cytoskeleton is crucial for dendrite development3. Dendrites grow stochastically through a process of branching, elongation, and contraction4. Drosophila larval dendritic arborization (da) neurons are a powerful in vivo model system for studying dendritic morphogenesis. These sensory neurons are grouped into four classes (I–IV) based on increasing dendritic complexity3,5. Class IV da neurons have complex, highly branched dendrites and function as multimodal nociceptors6,7,8. The dendrites of these neurons form stereotyped receptive fields along the abdominal segments and lie just beneath the transparent cuticle9,10. This anatomy, together with the genetic tractability of Drosophila, makes class IV da neurons a suitable system for visualizing dendrite development in vivo with high spatial and temporal resolution. As the dendrites grow during development, their tips stochastically transition between states of growth, shrinkage, and pause11. Tip growth and shrinkage share many kinetic similarities with microtubule growth and shrinkage12. Therefore, visualizing microtubule dynamics in these cells is of considerable interest.
A common approach for visualizing microtubule dynamics in living cells, including those in Drosophila larvae, is to image fluorescently labeled end-binding proteins such as EB1 and EB313,14,15,16,17,18. However, interpretation of EB-GFP signals can be ambiguous. For example, a distally moving EB-GFP punctum, moving away from the cell body, could represent an outward-growing microtubule plus end or an inward-growing plus end of a microtubule sliding in the distal direction. Although EB-GFP predominantly labels the plus ends of growing microtubules, it can also label growing minus ends19, leading to additional ambiguity. Direct visualization of microtubules can reduce these ambiguities.
An alternative approach to EB-GFP is direct labeling of microtubules using GFP-tubulin20,21. However, fluorescent tubulin robustly labels proximal dendrites22, it fails to label distal dendrites23. Another difficulty with fluorescent tubulin is that the high concentration of soluble tubulin makes individual microtubules difficult to distinguish in narrow processes such as terminal dendrites. Therefore, imaging microtubule dynamics in intact neurons under normal physiological conditions remains challenging.
The Drosophila microtubule-associated protein (MAP) Jupiter, a structural homolog of mammalian Tau, MAP2, and MAP4, has been used to label microtubules in Drosophila tissues, including the ovary and embryos24. In class IV dendrites, mCherry-Jupiter and sfGFP-Jupiter have been used to quantify microtubules in proximal branches22,25,26. This protocol describes a live-imaging method that enables high-resolution, time-lapse observation of neuronal microtubule behavior in distal dendrites of Drosophila class IV neurons using fly lines expressing the fluorescently labeled tubulin-binding domain of Jupiter.
This study used Drosophila melanogaster, an invertebrate model for which institutional animal ethics approval was not required. The tools used for the protocol are listed in the Table of Materials.
1. Generation of experimental fly lines
2. Egg laying on grape-agar plates, egg collection, and larval staging
3. Cleaning the larvae
4. Anesthetization
5. Mounting
6. Microscopy and image acquisition
7. Image processing and analysis

Figure 1: Components of the anesthetization setup. (A) A small cardboard box covering a 35 mm cell-culture dish containing an evaporation anesthetic wand secured with duct tape (black dashed circle). The lid of the cell-culture dish was used to hold clean, dry larvae before and during anesthesia (black arrowhead). (B) Inside view of the box. (C) A microscope slide with a square Vaseline enclosure prepared using a henna dispenser to contain the larval sample during imaging. A small gap (white arrowhead) facilitates air removal during coverslip placement. Please click here to view a larger version of this figure.
Following the protocol described above, microtubules were successfully visualized in class IV dendritic arborization (da) neurons using mNG-Jupiter in combination with the membrane marker CD4tdTomato (Figure 2A–C). The membrane marker delineated the overall morphology of the dendritic arbor, whereas mNG-Jupiter labeled the microtubule-containing regions within the dendrites. At the distal ends of terminal dendrites, mNG-Jupiter fluorescence was weak or absent near the dendritic tips, whereas CD4tdTomato fluorescence remained strong in the corresponding terminals (Figure 2D–F).
The dendritic arbors showed no obvious morphological differences compared with larvae imaged with the membrane marker alone in earlier studies11. To quantitatively assess whether mNG-Jupiter expression caused morphological abnormalities, the number of dendritic tips was counted in mNG-Jupiter-expressing arbors and control arbors at 72 h AEL. In eight cells from eight mNG-Jupiter larvae, the number of tips in one quarter of the arbor was 153 ± 25 (mean ± SD), compared with 144 ± 27 (mean ± SD) in control larvae (Figure 2G). No significant difference was detected using Welch’s t-test (see Figure 2 legend). Therefore, mNG-Jupiter expression did not detectably alter the number of dendritic branches.
Time-lapse imaging demonstrated the dynamic behavior of the mNG-Jupiter signal within terminal dendrites. In the representative sequence shown in Figure 3A, the position of the bright mNG-Jupiter-labeled microtubule end changed over time. Successive line scans of the mNG-Jupiter signal were arranged over time to visualize changes in microtubule position and length. The resulting kymograph in Figure 3B shows alternating phases of extension and retraction of the fluorescent signal, consistent with the observed growth and shrinkage of the labeled microtubule in terminal dendrites (Videos 1 and 2). In thicker dendrites closer to the soma, the greater number of microtubules prevented visualization of the dynamics of individual microtubules.
Together, the representative images and time-lapse recordings show that the protocol enables visualization of both dendritic morphology and dynamic changes in microtubule-associated fluorescence in intact Drosophila larval sensory neurons. The membrane marker provides a reference for dendritic structure, whereas mNG-Jupiter allows microtubule behavior within the dendrite to be followed over time (Figures 2 and 3).

Figure 2: Dendrites in class IV neurons. The dendritic arbor of a class IV dendritic arborization (da) neuron imaged by spinning-disk confocal microscopy at 72 h after egg laying (AEL). Microtubules are visualized using the GAL4/UAS binary expression system. The class IV cell-specific driver ppk-GAL4 (pickpocket) facilitates expression of mNG-tagged Jupiter (UAS-mNG-Jupiter). Dendritic membranes are marked by direct ppk promoter-mediated expression of tdTomato fused to the CD4 membrane marker (ppk-CD4tdTomato). (A) Membrane marker, CD4tdTomato. (B) Microtubule marker, mNG-Jupiter. (C) Merged image. (D–F) Enlarged views of the regions outlined by white dashed boxes in A–C, respectively, illustrate the distribution of the microtubule and membrane markers. White arrowheads indicate the distribution of mNG-Jupiter in terminal dendrites. (G) Quantification of dendritic tip number in control and mNG-Jupiter-expressing neurons at 72 h AEL. Each dot represents the number of tips counted within one quarter of a single neuron from a distinct larva. A total of eight neurons from eight independent larvae were analyzed per group. Error bars represent mean ± SD. Groups were compared using a two-sided unpaired Welch’s t-test; ns, not significant (P > 0.05). Please click here to view a larger version of this figure.

Figure 3: Microtubule dynamics in a terminal dendrite. (A) Three images of a terminal dendrite expressing CD4tdTomato (upper) and mNG-Jupiter (lower) at the indicated time points. Arrowheads indicate the microtubule end. A dim mNG signal is visible beyond the bright microtubule signal. (B) Kymograph showing microtubule growth and shrinkage. Arrowheads indicate growth phases, and arrows indicate shrinkage phases. Successive 3-pixel-wide line scans of the mNG signal are arranged one below another, with time increasing in the downward direction. Please click here to view a larger version of this figure.
Video 1: Time-lapse imaging of mNG-Jupiter in class IV dendritic arborization neurons. Time-lapse sequence showing mNG-Jupiter fluorescence in Drosophila larval class IV dendrites. The sequence illustrates changes in microtubule-associated fluorescence over time within the dendritic arbor. Images were acquired using the live-imaging conditions described in the Protocol. Scale bar, 20 µm. Please click here to download this file.
Video 2: Time-lapse imaging of the CD4tdTomato membrane marker in class IV dendritic arborization neurons. Time-lapse sequence showing CD4tdTomato fluorescence in the corresponding Drosophila larval class IV dendritic arbor. The membrane marker provides a reference for dendritic morphology during the imaging period. Images were acquired using the live-imaging conditions described in the Protocol. Scale bar, 20 µm. Please click here to download this file.
This protocol demonstrates the use of transgenic Jupiter fly lines for live imaging of microtubule dynamics in Drosophila sensory neurons using confocal microscopy. The method enables visualization of microtubule-associated fluorescence in intact larvae while preserving dendritic morphology, as assessed using a membrane marker11,29. A similar approach has also been used to image actin dynamics using GFP-actin and LifeAct-GFP in class IV neurons22,30,31,32. In principle, the same general approach may also be applied to imaging other microtubule-binding proteins in class IV cells and in other classes of dendritic arborization neurons (classes I, II, and III). In particular, combining fluorescent microtubule labeling with EB labeling may reduce ambiguity in interpreting microtubule growth. For example, the absence of an EB comet could indicate either the absence of microtubules or the presence of microtubules that are not actively growing; direct visualization of microtubules can help distinguish these possibilities. Thus, co-labeling mNG-Jupiter with fluorescent EB1 may enable interpretation of microtubule growth dynamics within the local context of microtubule organization, abundance, and inferred orientation.
Several steps are critical for obtaining suitable live-imaging data. The protocol uses the volatile anesthetic isoflurane for a defined, short immobilization regimen. The isoflurane dose must be carefully controlled during immobilization because insufficient anesthesia permits larval movement, whereas excessive anesthesia may lead to neuronal degradation. Air bubbles should also be avoided during mounting because they can interfere with image quality and contribute to sample drift. In addition, excessive pressure from the coverslip should be avoided because it may cause dendritic blebbing and subsequent neuronal damage. These steps are important for maintaining sample stability and dendritic morphology throughout imaging.
An important limitation of this protocol is that the immobilization and visualization method, involving the combination of anesthetic exposure and physical constraint by the coverslip, may influence microtubule dynamics. To determine whether microtubules are perturbed under these conditions, alternative immobilization methods can be used separately or in combination with this protocol. Such approaches include imaging embryos and using temperature-sensitive mutants, such as Shibirets 33, followed by comparison of kinetic parameters such as growth rates and catastrophe frequency.
With this limitation, the current protocol allows larvae to be imaged for approximately 30 minutes after mounting without dendritic blebbing, deterioration of morphology, or loss of detectable microtubule and tip dynamics. The method enables acquisition of high-resolution, time-lapse data from intact larvae and visualization of dynamic microtubule behavior in terminal dendrites.
The authors have no conflicts of interest to disclose.
The authors thank all members of the Howard laboratory, especially former laboratory member Dr. Maijia Liao, for initiating the microtubule-labeling project, and Dr. Sonal Shree for developing the protocol for visualizing dendritic dynamics in Drosophila within the Howard laboratory. Research reported in this publication was supported by the National Institutes of Health under Award Number R35 GM161634 (National Institute of General Medical Sciences) and Award Number R01 NS118884 (National Institute of Neurological Disorders and Stroke) to J.H. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. This work was also supported by NSF Grant PHY-2210464 and PEW Charitable Trusts Award 38044 to J.H.
| Name | Company | Catalog Number | Comments |
|---|---|---|---|
| Acetic acid (glacial, ACS reagent, ≥99.7%) | Sigma-Aldrich | 695092 | Used to prepare grape-agar medium; 5 mL per approximately 0.5 L preparation |
| Agar (bactoagar) | Becton Dickinson | 214010 | Used to prepare grape-agar medium; 15 g per approximately 0.5 L preparation |
| Anesthetic wand | Carolina Biological Supply Co. | 173010 | Used to hold isoflurane within the evaporation reservoir during larval anesthetization |
| Beaker, 1 L, microwave-safe | Corning Inc. | 1000-1L | Used to prepare approximately 0.5 L of grape-agar medium |
| Beaker, 100 mL | Corning Inc. | 1000-100 | Used to prepare yeast paste |
| Bio-Formats importer | Open Microscopy Environment Project | Not applicable | FIJI plugin used to import .ND2 time-lapse files |
| Camera (sCMOS, Zyla 4.2 Plus) | Andor Technology | ZYLA-4.2P-USB3 | 6.5 µm sensor; used for image acquisition |
| Cardboard box (5 × 5 × 3 in) | Uline | S-4579 | Used to cover the anesthetization setup and reduce air movement over the cell-culture dish |
| Cell-culture dish | Corning Incorporated | 430165 | 35 × 10 mm; used for larval handling and as the isoflurane evaporation reservoir |
| Coverslip | Globe Scientific Inc. | 1404-15 | 22 × 22 mm, No. 1.5; placed over the mounted larva |
| Darwin chamber | Darwin Chambers | IN030-AA-LT-DA-MP | Used for maintaining fly crosses, egg laying, and larval staging at 25 °C |
| Distilled water, laboratory reagent grade | Research Products International (RPI) | Not applicable | Used for grape-agar preparation, yeast-paste preparation, and washing larvae |
| Duct tape | Uline | S-6519 | Used to secure the anesthetic wand inside the cell-culture dish |
| Egg-laying cage/embryo collection cage | Genesee Scientific | 59-100 | Small size; fits a 60 × 15 mm Petri dish; used for controlled egg collection |
| Ethanol (anhydrous, 200 proof) | Decon Labs Inc. | V1001G | Used to prepare grape-agar medium; 10 mL per approximately 0.5 L preparation |
| FIJI (Fiji Is Just ImageJ) | NIH | Version 2.16.0/1.54p | Used for image import, stabilization, maximum-intensity projection, ROI analysis, kymograph generation, and intensity-profile extraction |
| Fly lines: (1) w; ppk-Gal4; ppk-cd4-tdTom; (2) w; w+, UASt-mNeonGreen-Jupiter-RD/CyO | Bloomington Drosophila Stock Center(1); Howard Lab (2) | BDSC# 32078, BDSC# 35845 | Used to express CD4tdTomato and mNG-Jupiter in class IV dendritic arborization neurons |
| Grape juice, 100% Concord grape | Welch's | Not applicable | Used to prepare grape-agar medium; 126 mL per approximately 0.5 L preparation |
| Halocarbon oil 700 | Sigma-Aldrich | H8898 | Used to mount larvae for live imaging |
| Henna dispenser | ZEYER | ZEYER-1005 | Used to form the Vaseline enclosure on the microscope slide |
| Image Stabilizer | Developed by Kang Li | Not applicable | FIJI plugin used with affine transformation settings to correct sample drift |
| Isoflurane | Santa Cruz Biotechnology, Inc. | sc-470926 | Used to immobilize larvae before mounting and imaging |
| Laboratory tissue (Kimwipes) | Kimberly-Clark Professional | 34120 | Used to remove excess water from washed larvae before anesthetization |
| Maintenance bottle | Lab Express Inc. | 7001-PBT | Square-bottom polypropylene bottle, 6 oz; contains Fly Food B (Bloomington Recipe) and is used to maintain fly stocks and crosses |
| Microwave | Panasonic | NN-SN686S | Used to dissolve agar during preparation of grape-agar medium |
| Microscope, inverted | Nikon Instruments Inc. | 736228 | Ti Eclipse inverted microscope equipped with a perfect-focus system for live imaging |
| Microscope slide | Fisherbrand | 12550143 | Superfrost slide; used to mount larvae for imaging |
| Multi Kymograph | Developed by Jens Rietdorf, Arne Seitz, and Johannes Schindelin | Not applicable | FIJI plugin used to generate kymographs of microtubule dynamics |
| Nikon Elements software | Nikon Instruments Inc. | Version 5.21.03 | Used for acquisition of time-lapse microscopy images and generation of .ND2 files |
| Objective, water immersion | Nikon Instruments Inc. | MRD77400 | 40×, 1.25 NA; used for live imaging |
| Paintbrush | Dynasty | 2157r | Sizes 0 and 3/0; used to transfer larvae and seal the Vaseline enclosure |
| Petri dish | Falcon | 351007 | 60 × 15 mm; used for grape-agar plates |
| Spatula | VWR | 82027-532 | 22.9 cm (9 in); used to mix yeast and water during yeast-paste preparation |
| Spinning-disk confocal unit | Yokogawa CSU-W1 | SBW001 | 50 µm pinhole; used for live confocal imaging |
| Sucrose | Sigma-Aldrich | 57-50-1 | Used in grape-agar medium and as a 5% solution for washing larvae |
| Vaseline | Unilever | Not applicable | Used to form the enclosure between the microscope slide and coverslip |
| Yeast (Red Star Active Dry Yeast) | Lesaffre Corporation | Not applicable | Used to prepare yeast paste and support egg laying |
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