|Title||The snail repressor inhibits release, not elongation, of paused Pol II in the Drosophila embryo.|
|Publication Type||Journal Article|
|Year of Publication||2011|
|Authors||Bothma, JP, Magliocco, J, Levine, M|
|Date Published||2011 Sep 27|
|Keywords||Animals, Body Patterning, DNA Polymerase II, Drosophila, Embryonic Development, Gene Expression Regulation, Developmental, Repressor Proteins, Time Factors, Transcription Factors, Transcription, Genetic|
The development of the precellular Drosophila embryo is characterized by exceptionally rapid transitions in gene activity, with broadly distributed maternal regulatory gradients giving way to precise on/off patterns of gene expression within a one-hour window, between two and three hours after fertilization . Transcriptional repression plays a pivotal role in this process, delineating sharp expression patterns (e.g., pair-rule stripes) within broad domains of gene activation. As many as 20 different sequence-specific repressors have been implicated in this process, yet the mechanisms by which they silence gene expression have remained elusive . Here we report the development of a method for the quantitative visualization of transcriptional repression. We focus on the Snail repressor, which establishes the boundary between the presumptive mesoderm and neurogenic ectoderm . We find that elongating Pol II complexes complete transcription after the onset of Snail repression. As a result, moderately sized genes (e.g., the 22 kb sog locus) are fully silenced only after tens of minutes of repression. We propose that this "repression lag" imposes a severe constraint on the regulatory dynamics of embryonic patterning and further suggest that posttranscriptional regulators, like microRNAs, are required to inhibit unwanted transcripts produced during protracted periods of gene silencing.
|Alternate Journal||Curr. Biol.|