Bluo-Gal  (Synonyms: 5-Bromo-3-indolyl β-D-galactopyranoside; ブルオ-Gal)

5-Bromo-3-indolyl β-D-galactopyranoside (Bluo-Gal) is a chromogenic substrate for β-galactosidase. 5-Bromo-3-indolyl β-D-galactopyranoside is hydrolyzed by the enzyme to generate a 5-bromoindole intermediate, which is further oxidized to form an insoluble blue precipitate. 5-Bromo-3-indolyl β-D-galactopyranoside can specifically recognize bacterial β-galactosidases (such as the product of the Escherichia coli lacZ gene) and reacts at pH 7.4, making it suitable for light and electron microscopic observations. 5-Bromo-3-indolyl β-D-galactopyranoside can be used in histochemical detection of reporter gene expression in transgenic organisms, such as the localization analysis of β-galactosidase activity in mouse embryos or muscle tissues^[1][2].

Guide (Following is our recommended protocol. This protocol only provides a guideline, and should be modified according to your specific needs).
1. Tissue samples: skeletal muscle tissue (e.g. tibialis anterior muscle) from transgenic mice, and control group: tissue from the same part of non-transgenic mice.
2. Fixative:
- Optimal formulation: 2.5% glutaraldehyde + 1% paraformaldehyde, dissolved in 0.1 M phosphate buffered saline (PBS, pH 7.4).
- Other formulations tested: including different concentrations of glutaraldehyde and paraformaldehyde mixtures, or single aldehyde fixatives.
3. Chromogenic substrate solution:
- 1 mg/mL Bluo-Gal (dissolved in dimethyl sulfoxide (DMSO), 40 mg/mL stock solution, stored at -20°C in the dark).
- 10 mM potassium ferrocyanide (K₃[Fe(CN)₆])
- 10 mM potassium ferrocyanide (K₄[Fe(CN)₆])
- 2 mM MgCl₂
- 0.1 M PBS (pH 7.4)
4. Post-fixative solution: 1% osmium acid (OsO₄), dissolved in 0.2 M colloidine buffer, pH 7.4.
5. Dehydration reagent: gradient ethanol (25%, 50%, 75%, 95%, 100%), propylene oxide.
6. Embedding reagent: Epoxy resin.
Experimental steps
1. Tissue fixation
Sample collection: Rapidly sample the mouse tibialis anterior muscle and cut it into small pieces of about 1-2 mm³.
Fixation conditions:
- Immerse tissue blocks in a mixture of 2.5% glutaraldehyde + 1% paraformaldehyde and fix at 4°C for 3 hours (optimal time, avoid too long fixation resulting in decreased enzyme activity).
- The control group (non-transgenic mice) was treated simultaneously to exclude the interference of endogenous β-galactosidase.
2. Rinsing
- After fixation, rinse the tissue with 0.1 M PBS (pH 7.4) for 1 hour to remove residual fixative.
3. Bluo-Gal color incubation
- Substrate preparation: Dilute Bluo-Gal stock solution (40 mg/mL DMSO) to 1 mg/mL before use, add potassium ferrocyanide, potassium ferrocyanide and MgCl2, and mix well (avoid light to prevent substrate decomposition).
- Incubation conditions:
- Immerse tissue in substrate solution and incubate at 30-32°C for 3-4 hours (optimal color development time, overnight incubation does not affect staining intensity, but no need to extend).
- Control group (without substrate) is incubated simultaneously to verify the absence of endogenous activity.
4. Post-fixation (for electron microscopy observation)
- After color development, the tissue is post-fixed with 1% osmium acid solution at 4°C for 1 hour to enhance structural contrast.
5. Dehydration and embedding
- Gradient dehydration: The tissue is dehydrated in 25%, 50%, 75%, and 95% ethanol for 10-20 minutes each, and 100% ethanol twice (20 minutes each time).
- Transparent treatment: Soak in propylene oxide twice, 10-20 minutes each time (avoid dissolving the reaction product due to too long time).
- Embedding: embedding with epoxy resin, polymerizing at 60°C for 24 hours.
6. Sectioning and observation
- Semi-thin sections (light microscopy): cutting 0.5-1 μm sections, differential interference contrast (DIC) microscopy observation, β-galactosidase positive areas appear as blue needle crystals.
- Ultra-thin sections (electron microscopy): cutting 80 nm sections, uranium-lead double staining, transmission electron microscopy observation of subcellular localization of enzyme activity products.
Key parameters and optimization
1. Fixative selection: 2.5% glutaraldehyde + 1% paraformaldehyde mixture balances enzyme activity preservation and tissue morphology, which is better than a single aldehyde fixative (Table 1).
2. Incubation time: 3 hours of fixation + 3-4 hours of color development can obtain a strong blue precipitate, avoiding excessive fixation (6-12 hours) that leads to a significant decrease in enzyme activity.
3. Control experiment: Non-transgenic mouse tissues were incubated without substrate to confirm that there was no background staining.
4. Substrate characteristics: The 5-bromoindigo precipitate generated by Bluo-Gal is a birefringent needle-shaped crystal, which is easier to identify under a low-power microscope than X-Gal and is resistant to elution by organic solvents.
Precautions
- Light-proof operation: Bluo-Gal mother solution and working solution must be stored and used in the dark to prevent photodegradation.
- Temperature control: Both fixation and incubation steps must be performed at low temperature (4°C) or mild temperature (30-32°C) to avoid loss of enzyme activity.
- Dehydration time: The propylene oxide treatment time should not be too long (≤20 minutes) to reduce the dissolution of the reaction product.

MedChemExpress (MCE) has not independently confirmed the accuracy of these methods. They are for reference only.

374.18

C₁₄H₁₆BrNO₆

97753-82-7

Solid

White to off-white

BrC1=CC=C2C(C(O[C@@H]([C@@H]([C@H]3O)O)O[C@@H]([C@@H]3O)CO)=CN2)=C1

Room temperature in continental US; may vary elsewhere.

4°C, protect from light

*In solvent : -80°C, 6 months; -20°C, 1 month (protect from light)

* Please refer to the solubility information to select the appropriate solvent. Once prepared, please aliquot and store the solution to prevent product inactivation from repeated freeze-thaw cycles.
Storage method and period of stock solution: -80°C, 6 months; -20°C, 1 month (protect from light). When stored at -80°C, please use it within 6 months. When stored at -20°C, please use it within 1 month.

• [1]. Gioglio L, et al. An improved method for beta-galactosidase activity detection on muscle tissue. A light and electron microscopic study. Ann Anat. 2002;184(2):153-157.  [Content Brief]

  [2]. Blanco MJ, et al. Tracing Gene Expression Through Detection of β-galactosidase Activity in Whole Mouse Embryos. J Vis Exp. 2018 Jun 26;(136):57785.  [Content Brief]