Dynamic Regulation of Eve Stripe 2 Expression Reveals Transcriptional Bursts in Living Drosophila Embryos

Jacques P. Bothma, Hernan G. Garcia, Emilia Esposito, Gavin Schlissel, Thomas Gregor, Michael S. Levine. PNAS 111 (29): 10598–10603 (2014).

We present the use of recently developed live imaging methods to examine the dynamic regulation of even-skipped (eve) stripe 2 expression in the precellular Drosophila embryo.  Nascent transcripts were visualized via MS2 RNA stem loops. The eve stripe 2 transgene exhibits a highly dynamic pattern of de novo transcription, beginning with a broad domain of expression during nuclear cycle (nc) 12, and progressive refinement during nc13 and nc14. The mature stripe 2 pattern is surprisingly transient, constituting just ~15 min of the ~90 min period of expression. Nonetheless, this dynamic transcription profile faithfully predicts the limits of the mature stripe visualized by conventional in situ detection methods. Analysis of individual transcription foci reveals intermittent surges of de novo transcription, with duration cycles of 4–10 min.  We discuss a multi-state model of transcription regulation and speculate on its role in the dynamic repression of the eve stripe 2 expression pattern during development.

Significance: There is considerable information about the spatial regulation of gene expression during pattern formation in animal development. Significantly less is known about temporal control, in part due to our inability to analyze gene activity in real time. Using a recently developed approach for the visualization of gene expression in living Drosophila embryos we examined the well-known eve stripe 2 expression pattern. Surprisingly, we observe that this classic pattern is quite transient and generated by discontinuous surges of transcriptional activity in individual cells. These results challenge a purely static framework for dissecting developmental programs and emphasize the importance of the dynamic features of pattern formation.


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