Imaging Cell Shape Change in Living Drosophila Embryos
Summary
Early development of the fruit fly, Drosophila melanogaster, is characterized by a number of cell shape changes that are well suited for imaging approaches. This article will describe basic tools and methods required for live confocal imaging of Drosophila embryos, and will focus on a cell shape change called cellularization.
Abstract
The developing Drosophila melanogaster embryo undergoes a number of cell shape changes that are highly amenable to live confocal imaging. Cell shape changes in the fly are analogous to those in higher organisms, and they drive tissue morphogenesis. So, in many cases, their study has direct implications for understanding human disease (Table 1)1-5. On the sub-cellular scale, these cell shape changes are the product of activities ranging from gene expression to signal transduction, cell polarity, cytoskeletal remodeling and membrane trafficking. Thus, the Drosophila embryo provides not only the context to evaluate cell shape changes as they relate to tissue morphogenesis, but also offers a completely physiological environment to study the sub-cellular activities that shape cells.
The protocol described here is designed to image a specific cell shape change called cellularization. Cellularization is a process of dramatic plasma membrane growth, and it ultimately converts the syncytial embryo into the cellular blastoderm. That is, at interphase of mitotic cycle 14, the plasma membrane simultaneously invaginates around each of ~6000 cortically anchored nuclei to generate a sheet of primary epithelial cells. Counter to previous suggestions, cellularization is not driven by Myosin-2 contractility6, but is instead fueled largely by exocytosis of membrane from internal stores7. Thus, cellularization is an excellent system for studying membrane trafficking during cell shape changes that require plasma membrane invagination or expansion, such as cytokinesis or transverse-tubule (T-tubule) morphogenesis in muscle.
Note that this protocol is easily applied to the imaging of other cell shape changes in the fly embryo, and only requires slight adaptations such as changing the stage of embryo collection, or using “embryo glue” to mount the embryo in a specific orientation (Table 1)8-19. In all cases, the workflow is basically the same (Figure 1). Standard methods for cloning and Drosophila transgenesis are used to prepare stable fly stocks that express a protein of interest, fused to Green Fluorescent Protein (GFP) or its variants, and these flies provide a renewable source of embryos. Alternatively, fluorescent proteins/probes are directly introduced into fly embryos via straightforward micro-injection techniques9-10. Then, depending on the developmental event and cell shape change to be imaged, embryos are collected and staged by morphology on a dissecting microscope, and finally positioned and mounted for time-lapse imaging on a confocal microscope.
Protocol
Discussion
The protocol described herein will permit the live, confocal imaging of a number of cell shape changes in the developing fly embryo. GFP stocks for imaging can be prepared by an individual lab (Table 2), but many such stocks are also publicly available from centers such as Bloomington Drosophila Stock Center at Indiana University (http://flystocks.bio.indiana.edu) and FlyTrap Stock Center at Yale University (http://flytrap.med….
Disclosures
The authors have nothing to disclose.
Acknowledgements
We gratefully acknowledge Eric Wieschaus, who provided the foundation on which this protocol was developed. Our work is supported by a Verna & Marrs McLean Department of Biochemistry and Molecular Biology Start-up Award, Baylor College of Medicine.
Materials
| Material Name | Type | Company | Catalogue Number | Comment |
|---|---|---|---|---|
| Slides | Fisherbrand/Fisher Scientific | 12-550-343 | ||
| Cover slips 25×25 | Fisher Scientific (Corning #2865-25) | 1 2-524C | ||
| Squirt bottles (H2O) | Fisher Scientific | 02-897-11 | ||
| 50 ml Falcon tubes | Fisher Scientific (BD# 352070) | 14-432-22 | ||
| Bulbs for small pipets, 1 mL | Fisherbrand/Fisher Scientific | 03-448-21 | ||
| Scintillation vials with caps | VWR (Wheaton #986546) | 66021-533 | ||
| Tri-Corn Beakers, 100 mL | Electron Microscopy Sciences | 60970 | ||
| BD Falcon Petri dish 60x15mm | Fisher Scientific (BD# 351007) | 08757 100B | ||
| BD Falcon Cell strainer | Fisher Scientific (BD#352350) | 08-771-2 | ||
| Yellow pipet tips | Ranin | L200 | ||
| Stainless steel mesh, 304, 12×24 | Small Parts | CX-0150-F-01 | ||
| Glass 5¾ inch Pasteur Pipets | Fisherbrand/Fisher Scientific | 13-678-20B | ||
| P4 Filter paper | Fisherbrand/Fisher Scientific | 09-803-6F | ||
| Rubber bands | Office Max | A620645 | ||
| Scotch double-sided tape, ½ inch | Office Max | A8137DM-2 | ||
| Robert Simmons Expression paint brushes E85 round #2 | Jerry’s Artarama | 56460 | ||
| Dumont #5 Forceps High Precision Inox | Electron Microscopy Services | 72701-DZ | ||
| Razor blades | VWR (BD #214010) | 55411-050 | ||
| Halocarbon Oil 27 | Sigma-Aldrich | H 8773 | ||
| Heptane | Fisher Chemical/Fisher Scientific | H360-1 | ||
| BD Bacto Agar | VWR (BD# 214010) | 90000-760 | ||
| Sucrose | Sigma-Aldrich | S7903 | ||
| p-Hydroxybenzoic acid | Sigma-Aldrich | H5501 | ||
| Red Star Active Dry Yeast | LeSaffre | 15700 | ||
| Paper towels, C-fold | Kleenex | |||
| Heavy duty aluminum foil | Reynolds Wrap | |||
| Bleach | Austin’s A-1 Commercial | |||
| 100% Apple juice | Ocean Spray or Tree Top |
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