Lighting-up Transcription During Development

Since its first adaptation in fruit fly embryos with the fluorescent tagging of RNA, live imaging of transcription during development revealed the unanticipated importance of the temporal dynamics in the decoding of positional information. At the molecular scale, these approaches revealed the bursty dynamics of transcription of many developmental genes. They allowed the precise dissection of these bursty transcription cycles at single loci in vivo and showed that burst frequency and duration are differentially regulated by distinct developmental clues. Live transcriptional imaging also uncovered enhancer-promoter interactions not only through direct looping but also via shared transcriptional hubs, challenging classical contact-based models. In addition, these RNA-labelling systems provided also new tools to visualize and mechanistically dissect in vivo transcriptional memory, dosage compensation, chromosome pairing and transvection. Finally, these approaches were also more recently adapted to the nematode, the flour beetle, the zebrafish, or the mouse, paving the way for a better understanding of cross-species developmental mechanisms.