Imaging Translation in Early Embryo Development.

The ultimate output of gene expression is to ensure that proteins are synthesized at the right levels, locations, and timings. Recently different imaging-based methods have been developed to visualize the translation of single mRNA molecules. These methods rely on signal amplification with the introduction of an array of a short peptide sequence (a tag such as SunTag), recognized by a genetically encodable single-chain antibody (a detector such as scFv). In this chapter, we discuss such methods to image and quantify translation dynamics in the early Drosophila embryo and provide examples based on a twist-32XSunTag reporter. We outline a step-by-step protocol to light-up translation in living embryos. We also detail a combinatorial strategy in fixed samples (smFISH-IF), allowing to distinguish single mRNA molecules engaged in translation.