Visualizing the Live Drosophila Glial-neuromuscular Junction with Fluorescent Dyes

Summary

We described structural features of the Glia-neuromuscular synapses in a novel Inside-out tissue preparation of live fly larvae using fluorescent dyes with confocal microscopy. We labeled live neuron terminals with fluorescent primary antibodies to HRP, and also visualized the perisynaptic space with fluorescent Dextrans.

Abstract

Our project identified GFP labeled glial structures at the developing larval fly neuromuscular synapse. To look at development of live glial-nerve-muscle synapses, we developed a larval tissue preparation that had features of live intact larvae, but also had good optical properties. This new preparation also allowed for access of perfusates to the synapse. We used fly larvae, immersed them in artificial hemolymph, and relaxed their normal rhythmic body contractions by chilling them. Next we dissected off the posterior segments of each animal and with a blunt insect pin pushed the mouth parts backward through the body cavity. This everted the larval body wall, like turning a sock inside-out. We completed the dissection with ultra-fine dissection scissors and thus exposed the visceral side of the body wall muscles. The glial structures at the NMJ expressed membrane targeted GFP under the control of glial specific promoters. The post-synaptic membrane, the SSR (Subsynaptic Reticula) in muscle expressed synaptically targeted dsRed. We needed to acutely label the motor neuron terminals, the third part of the synapse. To do this we applied primary antibodies to HRP, conjugated to a far-red emitting flurophore. To test for dye diffusion properties into the perisynaptic space between the motor neuron terminals and the SSR, we applied a solution of large Dextran molecules conjugated to far-red emitting flurophore and collected images.

Protocol

Part 1: Tissue Preparation

1. Our goal is a tissue preparation of fly larvae where the nervous system is intact, but the interior surface of the body wall muscle is exposed to an artificial hemolymph, and can be positioned close to a microscope cover slip for good optics. In other words, an inside out larval preparation.
   
   Since conventional tissue preparations involve cutting, pinning and stretching the body wall muscle, and sometimes removing part of the nervous system, we needed a different approach.
   
   We wanted the animals inside-out because we wanted to get a good look at structural features and structural changes over time in t....

Discussion

This procedure permits long- term imaging of live labeled proteins and cell processes. The in situ tissue prep we described has an intact and functioning CNS, PNS and reflex circuits. This tissue prep has advantages over standard larval fly muscle protocols, where the larval body wall muscle is stretched (when it is pinned out). Stretching can distort synaptic morphology and trigger reflex based contractions. Our inside out prep was mechanically stable, and had exceptionally good optics that facilitated high r.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
HL-6: Artifical Drosophila hemolymph, with 5 mM L-glutamate added, and 2 mM Calcium.	Reagent	N/A	NA	5 mM L-glutamate blocked muscle contractions. We used Molecular grade L-Glutamate (Sigma).2 mM Calcium is close to physiological Calcium levels in natural larval hemolymph.References: Macleod et al 2002 and Macleod 2004
Dextran, Alex Fluor 680; 10,000 MW, anionic, fixable	Reagent	Molecular Probes, Life Technologies	D34680	Use a small volume perfusion chamber to keep the total volume of dye low
Anti-HRP-CY5 conjugate (goat)	Reagent	Jackson ImmunoResearch	123-175-021	Dilute 2.0 mg into 1 ml ddH2O; aliquot into 4 microliter aliquots. Freeze at –20C. Dilute one aliquot into 100 microliters of HL-6
Alexa 647 antibody labeling kit	Reagent	Molecular Probes, Life Technologies	A10475	We prepared a total of 80 micro liters of conjugated primary antibody, and stored as 2 microliter aliquots. We diluted each aliquot into 100 microliter of HL-6 for labeling.
Custom Formulated Objective Oil, refractive index 1.3379	Reagent	Cargill Labs	Custom Formulated
Ultra Fine Forceps	Tool	Fine Science Tools	11252-23 or 11295-20
Spring scissors	Tool	Fine Science Tools	91500-09
Ultra fine clipper scissors	Tool	Fine Science Tools	15200-00
Perfusion Chamber RC 20 Series	Tool	Warner Instruments	64-02222
Spinning Disc confocal	Microscope	Quorum Technologies	Quorum Wave FX	Mounted on a Leica DMI6000 Inverted Microscope