Microtubule Probes

Microtubules

Microtubules are found in all eukaryotic cells and are major components of their cytoskeleton. They are hollow cylindrical structures of 20-25 nm in diameter and consist of α- and β-tubulin heterodimers organized into linear protofilaments. They are highly dynamic structures that undergo continual assembly and disassembly in a process driven by GTP hydrolysis. They are polar structures with a fast-growing β-subunits (+) end, and a slow-growing α-subunits (-) end.

Microtubules are important in many cellular processes. They participate in vital cell functions such as intracellular transport, signalling, proliferation and maintain the cell structure. They also form the mitotic spindle which pull eukaryotic chromosomes apart during cell division.

Taxol-Based Microtubule Probes

Fluorescent probes present opportunities for the selective imaging of microtubules within the cell cytoplasm. Tocris offers two categories of fluorescent microtubule probes: Flutax and Taxol Janelia Fluor^®, both Taxol (Cat. No. 1097) based molecules.

Taxol (often referred to as Paclitaxel) is a diterpenoid originally isolated from yew tree bark. Taxol binds to the β-tubulin subunit in the microtubule lumen which promotes and stabilizes its polymerization, blocking the microtubule dynamics necessary for mitotic cellular functions and leading to cell death. Given its antimitotic and cytotoxic action, Taxol has been used for many years as an antitumor drug particularly in breast, prostate, lung, and ovarian cancer treatment.

The conjugation of fluorescent dyes to Taxol offers a convenient way to visualize microtubule formation and study factors that influence microtubule assembly. It is important to be aware when using these probes that the pharmacological action of Taxol itself remains after conjugation to a fluorescent dye. The stabilization of tubulin polymerization causes cell cycle arrest at the G2/M phase and cell death.

Flutax Microtubule Probes

Flutax 1 (Cat. No. 2226) and Flutax 2 (Cat. No. 6254) are probes constituting of Taxol conjugated to the fluorescent dyes fluorescein and Oregon Green 488, respectively. The main difference between the two probes is the pH sensitivity of the dye used. In the physiological pH range, fluorescein is considered highly pH sensitive, whereas Oregon Green 488 is essentially pH insensitive. Both Flutax 1 and Flutax 2 are green fluorescent probes, cell permeable, bright, with similar absorption and emission maxima. They bind selectively to microtubules with high affinity (Ka ≈ 10⁷ M^-1, at 37^ºC). Their use is compatible with confocal microscopy and flow cytometry.

Taxol Janelia Fluor^® Microtubule Probes

Taxol Janelia Fluor^® probes consist of a Janelia Fluor^® dye conjugated to Taxol. They offer significant advantages over spectrally similar dyes in terms of their brightness and photostability. Additionally, Janelia Fluor^® dyes are especially well suited to super-resolution microscopy (SRM) techniques.

Tocris provides three Taxol Janelia Fluor^® probes for microtubule staining. These include Taxol Janelia Fluor^® 526 (Cat. No. 7315; green), Taxol Janelia Fluor^® 549 (Cat. No. 6267; yellow) and Taxol Janelia Fluor^® 646 (Cat. No. 6266; red). Both Taxol Janelia Fluor^® 549 and 646 are designed with the same chemical linkage position as the Flutax compounds. In contrast, Taxol Janelia Fluor^® 526 is conjugated at the 3' N position which has been shown to reduce toxicity.

Probe Featured Product: Taxol Janelia Fluor^® 526

Taxol Janelia Fluor^® 526 (Cat. No. 7315) is a fluorogenic green-emitting microtubule probe. This fluorogenic probe is non-fluorescent until bound to microtubules, which allows researchers to carry out no-wash experiments, with bright, low noise signals, perfect for sensitive or low expression experiments. It enables easy multicolor, multi-labeling microscopy experiments. Taxol Janelia Fluor^® 526 is suitable for live-cell imaging in confocal microscopy and super-resolution microscopy techniques including STED (standard 775 nm laser for depletion).

	Emission Color	Green
	λabs	531 nm
	λem	549 nm
	Extinction Coefficient (ε)	118,000 M-1cm-1
	Quantum Yield (φ)	0.87
	Application	Confocal microscopy, STED, super-resolution microscopy

Figure 1: Spectral and photophysical data for Taxol Janelia Fluor^® 526

Application of Taxol Janelia Fluor^® 646 in COS7 Cells

Taxol Janelia Fluor^® 646 (Cat. No. 6266) has been utilized for microtubule staining in COS7 cells and visualized using confocal microscopy.

Figure 2: Application of Taxol Janelia Fluor^® 646, dye on COS7 cells; COS7 cells were labeled with 3 µM Taxol Janelia Fluor^® 646 for one hour at 37°C. Images were taken on a Leica TCS SP8 Confocal Laser Scanning Microscope.

All images kindly provided by Prof. Christian Soeller, University of Exeter; acquired by Evelina Lucinskaite, Anna Meletiou and Alexander Clowsley.

Microtubule Probes Imaging Application

Table 1: Summary of spectral data and imaging application for Taxol derivative microtubule probes

References

Literature for Microtubule Probes

Tocris offers the following scientific literature for Microtubule Probes to showcase our products. We invite you to request* your copy today!

*Please note that Tocris will only send literature to established scientific business / institute addresses.

Fluorescent Dyes and Probes Research Product Guide

This product guide provides a background to the use of Fluorescent Dyes and Probes, as well as a comprehensive list of our:

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• Tissue Clearing Kits and Reagents
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• Fluorescent Probes for Imaging Bacteria
• TSA Vivid^TM Fluorophore Kits
• TSA Reagents for Enhancing IHC, ICC & FISH Signals

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