Dynamics ofhunchbacktranslation in real time and at single mRNA resolution in theDrosophilaembryo

AbstractThe Hunchback (Hb) transcription factor is critical for anterior-posterior patterning of theDrosophilaembryo. Despite the maternalhbmRNA acting as a paradigm for translational regulation, due to its repression in the posterior of the embryo, little is known about the translatability of zygotically transcribedhbmRNAs. Here we adapt the SunTag system, developed for imaging translation at single mRNA resolution in tissue culture cells, to theDrosophilaembryo to study the translation dynamics of zygotichbmRNAs. Using singlemolecule imaging in fixed and live embryos, we provide evidence for translational repression of zygoticSunTag-hbmRNAs. While the proportion ofSunTag-hbmRNAs translated is initially uniform, translation declines from the anterior over time until it becomes restricted to a posterior band in the expression domain. We discuss how regulatedhbmRNA translation may help establish the sharp Hb expression boundary, which is a model for precision and noise during developmental patterning. Overall, our data show how use of the SunTag method on fixed and live embryos is a powerful combination for elucidating spatiotemporal regulation of mRNA translation inDrosophila.