Immunohistochemical Detection of FLAG-Tagged Endogenous Proteins in Knock-In Mice

With recent advances in immunohistochemical (IHC) techniques, immunohistochemistry now plays a more important role in research, especially in mouse models where characterization of cellular patterns of protein expression has become critical. Even with these recent advances, a paucity of IHC quality antibodies for some proteins still exists. To address this, we have developed a novel IHC assay that utilizes a commercially available goat anti-DDDDK peptide polyclonal antibody on paraffin-embedded tissues from knock-in mice expressing proteins of interest tagged with a 3×FLAG epitope at physiologically relevant levels. Focusing on two 3×FLAG-tagged proteins for which specific antibodies were available, USP48 and RIPK3, we were able to validate our anti-DDDDK assay by comparing the IHC directed against the actual proteins to the anti-DDDDK IHC assay, which recognizes the FLAG epitope. We were also able to detect a third 3×FLAG-tagged protein, BAP1, for which quality reagents were not available. This universal...