Detection of LacZ-Positive Cells in Living Tissue with Single-Cell Resolution

The LacZ gene, which encodes Escherichia coli β‐galactosidase, is widely used as a marker for cells with targeted gene expression or disruption. However, it has been difficult to detect lacZ‐positive cells in living organisms or tissues at single‐cell resolution, limiting the utility of existing lacZ reporters. Herein we present a newly developed fluorogenic β‐galactosidase substrate suitable for labeling live cells in culture, as well as in living tissues. This precisely functionalized fluorescent probe exhibited dramatic activation of fluorescence upon reaction with the enzyme, remained inside cells by anchoring itself to intracellular proteins, and provided single‐cell resolution. Neurons labeled with this probe preserved spontaneous firing, which was enhanced by application of ligands of receptors expressed in the cells, suggesting that this probe would be applicable to investigate functions of targeted cells in living tissues and organisms. To detect lacZ‐positive cells in living organisms or tissues at single‐cell resolution, a fluorogenic β‐galactosidase substrate, SPiDER‐βGal‐1, was synthesized. The substrate exhibited a dramatic increase in fluorescence upon reaction with the enzyme, remained inside cells by anchoring itself to intracellular proteins, and provided single‐cell resolution.