Super-Resolution Live Cell Imaging of Subcellular Structures

Summary

Presented here is a protocol for super-resolution live-cell imaging in intact tissue. We have standardized the conditions for imaging a highly sensitive adult stem cell population in its native tissue environment. This technique involves balancing temporal and spatial resolution to allow for the direct observation of biological phenomena in live tissue.

Abstract

There has long been a crucial tradeoff between spatial and temporal resolution in imaging. Imaging beyond the diffraction limit of light has traditionally been restricted to be used only on fixed samples or live cells outside of tissue labeled with strong fluorescent signal. Current super-resolution live cell imaging techniques require the use of special fluorescence probes, high illumination, multiple image acquisitions with post-acquisition processing, or often a combination of these processes. These prerequisites significantly limit the biological samples and contexts that this technique can be applied to.

Here we describe a method to perform super-resolution (~140 nm XY-resolution) time-lapse fluorescence live cell imaging in situ. This technique is also compatible with low fluorescent intensity, for example, EGFP or mCherry endogenously tagged at lowly expressed genes. As a proof-of-principle, we have used this method to visualize multiple subcellular structures in the Drosophila testis. During tissue preparation, both the cellular structure and tissue morphology are maintained within the dissected testis. Here, we use this technique to image microtubule dynamics, the interactions between microtubules and the nuclear membrane, as well as the attachment of microtubules to centromeres.

This technique requires special procedures in sample preparation, sample mounting and immobilizing of specimens. Additionally, the specimens must be maintained for several hours after dissection without compromising cellular function and activity. While we have optimized the conditions for live super-resolution imaging specifically in Drosophila male germline stem cells (GSCs) and progenitor germ cells in dissected testis tissue, this technique is broadly applicable to a variety of different cell types. The ability to observe cells under their physiological conditions without sacrificing either spatial or temporal resolution will serve as an invaluable tool to researchers seeking to address crucial questions in cell biology.

Introduction

Visualizing subcellular structures and protein dynamics in live cells with resolution beyond the diffraction limit of light is typically very challenging^1-3. While multiple super-resolution techniques such as Stochastic-Optical-Reconstruction-Microscopy (STORM), Photo-Activated-Localization-Microscopy (PALM) and Stimulated-Emission-Depletion (STED)^4,5,6 microscopy have been developed, complications in specimen preparation as well as the need to maintain viability and activity ex vivo, limit the use of conventional super-resolution microscopy....

Protocol

1. Preparation of live cell imaging cocktail (live cell media)

1. Supplement Schneider’s Drosophila medium with 15% fetal bovine serum (FBS) and 0.6x penicillin/streptomycin. Adjust the pH to approximately 7.0.
2. Just before using the medium, add insulin to a final concentration of 200 µg/mL.
   NOTE: This media is critical for maintaining normal cell division and development of the Drosophila testis during time-lapse imaging^10,14.

2. Preparation of glass bottom cell culture dish

1. Use a poly L-lysine coated glass-bo....

Results

Live cell imaging beyond the diffraction limit in Drosophila tissue, especially for GSCs, provides an opportunity to investigate the dynamics of subcellular events in the context of cell cycle progression. Recently, a study utilizing this protocol has shown that microtubule activities at the mother centrosome versus the daughter centrosome are temporally asymmetric in GSCs¹⁰. The mother centrosome emanates microtubules approximately 4 hours prior to the mitotic entry, whereas the daughter.......

Discussion

Super-resolution microscopy methods provide spatial resolution as high as 10s of nanometers^4,5,6. The STORM and PALM microscopy methods allow resolution up to 20 to 50 nm (XY-resolution), while STED microscopy offers resolution of 20 to 100 nm (XY-resolution). The spatial resolution of SIM microscopy is limited to 100 to 130 nm¹⁵. However, due to its high-photon density and lengthy acquisition time, it is extremely ch.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Adobe Illustrator CS6 (figure making software)	Adobe	N/A
Dialysis membrane	Spectra/Por 1-4 Standard RC Dialysis Membrane	Cat No. 08-67121
FBS	Thermo Fisher Scientific	Cat. no. 26140079	15% (V/V)
Fiji (analysis software)	NIH	N/A	Image fluorescence intensity quantification
Glass bottom cell culture dishes (FluroDish)	World Precision Instrument, Inc.	FD35PDL-100
Imaris (image reconstruction software)	Bitplane	N/A	3D image reconstruction
Imerssion oil	Zeiss	Immersol 518F/30 °C
Insulin	Sigma	Cat. No. 15550	200 µg/ml
Penicillin/streptomycin	Invitrogen	Cat No. - 15140-122	0.6x
Schneider Drosophila media	Invitrogen	Cat No. - 11720-034
Spinning disc confocal microscope	Zeiss	N/A	equipped with an evolve camera (Photometrics), using a 63x Zeiss objective (1.4 NA).
Tissue paper	Kimwipe	N/A	Wet to form humid chamber
LSM 800 confocal microscope with AiryScan super-resolution module	Zeiss	N/A	equipped with highly sensitive GaAsP (Gallium Arsenide Phosphide) detectors using a 63x Zeiss objective (1.4 NA)
ZEN (imaging software)	Zeiss	N/A