Several localized mRNAs have been previously studied, but just how many transcripts are localized in the cell, and in what patterns, is unknown. Lécuyer et al. approached this problem by optimizing fluorescence in situ hybridization (FISH) in a global analysis of developmentally expressed mRNAs. They found that 71% of the mRNAs in early fly embryos showed specific patterns of subcellular localization.
In several cases, they found new examples of mRNAs that colocalized with their protein products. Less energy is probably required to transport a few copies of an mRNA than to move around many more copies of the protein. And the proteins will be created where they are needed and possibly prevented from straying where they are not wanted.
“We need to revise the textbook image of proteins being made in a centralized location near the nucleus, then trafficking to their ultimate locations,” says Krause. “Our work shows that the mRNAs are an intelligent actor, not just a dumb vehicle for creating proteins.” With their new database, the group can now further investigate how and why mRNAs are localized.