Breaking the seals: efficient mRNA detection from human archival paraffin-embedded tissue

Area of Science:

• Molecular Biology
• Histology
• Genetics

Background:

• Standard in situ hybridization protocols often fail with over-fixed human tissues, yielding unreliable mRNA expression data.
• Over-fixation inhibits probe penetration and can trap mRNA within ribosomes, complicating analysis.
• Existing methods struggle with tissues stored long-term at room temperature.

Purpose of the Study:

• To develop a robust, nonradioactive in situ hybridization technique for detecting low-level mRNA in diverse human tissues, including those with over-fixation.
• To improve target retrieval and probe detection strategies for enhanced mRNA visualization.
• To validate the method's efficacy across a range of fixation durations and sample storage conditions.

Main Methods:

• Developed a novel nonradioactive in situ hybridization protocol.
• Optimized target retrieval and probe detection steps.
• Tested the method on human adult and embryonic tissues with varying fixation times (4 hours to over 1 week) and long-term storage (17-19 years).

Main Results:

• Achieved reliable mRNA detection in over-fixed and long-term archived human tissues, overcoming limitations of standard protocols.
• The technique successfully visualized low-level mRNA expression, exceeding the sensitivity of purely fluorescent methods.
• Demonstrated high suitability for detecting CDX-2 mRNA in carcinoma specimens and other mRNAs in nonpathological tissues.

Conclusions:

• The new in situ hybridization protocol enables sensitive and reliable mRNA detection in challenging human tissue samples.
• This method enhances the investigation of mRNA expression in both pathological and nonpathological adult and embryonic tissues.
• The standardized probes suggest broad applicability for detecting various other mRNAs.