Measurement of Transcriptional Dynamics in Early Drosophila Development

Abstract

Transcription of messenger RNA from DNA is a fundamentally stochastic process involving noisy interactions on the scale of single molecules. Most systems can be understood in terms of a two-state model of transcription in which a gene transitions between states of activity and inactivity, giving rise to "bursts" of transcriptional activity that increase output variability. We investigate transcriptional activation dynamics in the highly precise context of Drosophila embryogenesis using two-color smFISH measure transcriptional activation states and infer distributions of RNA polymerases along the gene. We find that transcriptional activation states of hb are compatible with the two-state model of transcriptional bursting, and we measure effective rate constants for these dynamics. Additionally, we find that the transcriptional activation states of sister chromatids of a single allele are uncorrelated, suggesting that stochasticity of gene expression is maintained on the level of single chromatids. We suggest a straightforward control that would provide independent verification of the approach undertaken in this work, and discuss possibilities for future experiments.