A protocol for single-molecule translation imaging in xenopus retinal ganglion cells
Single-molecule translation imaging (SMTI) is a straightforward technique for the direct quantification of local protein synthesis. The protein of interest is fused to a fast-folding and fast-bleaching fluorescent protein, allowing one to monitor the appearance of individual fluorescence events after photobleaching of pre-existing proteins in the cell under investigation. The translation of individual molecules is then indicated by photon bursts of sub-second length that appear over a dark background. The method thus shares attributes with fluorescence recovery after photobleaching (FRAP) microscopy. Resulting datasets are similar to those generated by localization-based super-resolution microscopy techniques and can be used both to generate density maps of local protein production and to quantify the kinetics of local synthesis. The detailed protocol described in this chapter uses a Venus-β-actin fusion construct to visualize and measure the β-actin mRNA translational activity in Xenopus retinal ganglion cell growth cones upon Netrin-1 stimulation, which can be readily adapted for detecting translation events of other mRNAs in various cell types.