Research Requires Flexibility: Protease-Free Permeabilization Expands FISH Tissue Applications.-Andrelie Branicky, Shared Laboratory Resources, Lerner Research Institute, Cleveland Clinic, Cleveland, OH

Fluorescence in situ hybridization (FISH) visualizes the presence of a specific DNA or RNA sequence in a tissue sample or cell. This method, particularly the mRNA version, detects gene expression when protein might not be present or IHC is impossible. FISH combined with immunohistochemistry enables spatial transcriptomics, which provides significantly more information about the tissue microenvironment.

Formalin-fixed paraffin-embedded (FFPE) tissues are the standard for tissue preservation in the clinical world. Most commercial mRNA probe and amplification systems are built around the model of FFPE tissue that can withstand harsh protease permeabilization. In the research world, tissues are fixed in different fixatives for varying times; all at the discretion of the investigator instead of an organization like the CLIA.

Given the wide range of tissue preparations, the HCR automated FISH-ISH protease-free program provides the flexibility to combine FISH and fluorescent immunohistochemistry on tissue fixed in a variety of ways such as: 10% NBF, Histochoice (a glyoxal-based fixative), and methanol/acetic acid, with only minor changes to the basic protocol. Additionally, the lack of harsh protease pre-treatment maintains tissue integrity and morphology for staining and imaging.