Imaging Real-Time Gene Expression in Mammalian Cells with Single-Transcript Resolution
- 1 Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA
- 2 Gruss-Lipper Biophotonics Center, Albert Einstein College of Medicine, Bronx, NY 10461, USA
- ↵3Corresponding author (rhsinger{at}aecom.yu.edu)
INTRODUCTION
The MS2 system provides optimal sensitivity for single-molecule detection in cells. It requires two genetically encoded moieties: a reporter mRNA that contains MS2 binding site (MBS) stem loops and a fluorescent MS2 coat protein (MCP-xFP) that binds to the stem loops with high affinity, thus tagging the mRNA within the cell. This protocol describes transfection of COS-7 cells with reporter RNA (e.g., pRSV-Z-24 MBS-β-actin) and MCP-xFP (e.g., pPolII-MCP-GFP-NLS) plasmids using calcium phosphate precipitation. The reporter mRNA plasmid must be co-transfected with the MCP-xFP-NLS plasmid for simultaneous expression in a cell. The unbound MCP-xFP-NLS is sequestered in the nucleus, leaving only the MCP-xFP-NLS that is bound to the reporter mRNA in the cytoplasm. This provides a high signal-to-noise ratio (SNR) that permits detection of single mRNA molecules. The Delta T Imaging System is used for image acquisition of fluorescent particles in the cells.
