Abstract
BackgroundMorphogen molecules form concentration gradients to provide spatial information to cells in a developing embryo. Precisely how cells decode such information to form patterns with sharp boundaries remains an open question. For example, it remains controversial whether the Drosophila morphogenetic protein Bicoid (Bcd) plays a transient or sustained role in activating its target genes to establish sharp expression boundaries during development.Methodology/Principal FindingsIn this study, we describe a method to simultaneously detect Bcd and the nascent transcripts of its target genes in developing embryos. This method allows us to investigate the relationship between Bcd and the transcriptional status of individual copies of its target genes on distinct scales. We show that, on three scales analyzed concurrently—embryonic, nuclear and local, the actively-transcribing gene copies are associated with high Bcd concentrations. These results underscore the importance of Bcd as a sustained input for transcriptional decisions of individual copies of its target genes during development. We also show that the Bcd-dependent transcriptional decisions have a significantly higher noise than Bcd-dependent gene products, suggesting that, consistent with theoretical studies, time and/or space averaging reduces the noise of Bcd-activated transcriptional output. Finally, our analysis of an X-linked Bcd target gene reveals that Bcd-dependent transcription bursts at twice the frequency in males as in females, providing a mechanism for dosage compensation in early Drosophila embryos.Conclusion/SignificanceOur study represents a first experimental uncovering of the actions of Bcd in controlling the actual transcriptional events while its positional information is decoded during development. It establishes a sustained role of Bcd in transcriptional decisions of individual copies of its target genes to generate sharp expression boundaries. It also provides an experimental evaluation of the effect of time and/or space averaging on Bcd-dependent transcriptional output, and establishes a dosage compensation mechanism in early Drosophila embryos.
Highlights
Regulation of transcription plays a pivotal role in many biological processes including pattern formation during embryonic development [1,2,3,4]
Experimental design We developed a method to simultaneously detect Bcd and the nascent transcripts of its target genes in early Drosophila embryos
We focused on two Bcd target genes, hunchback and orthodentical, for our study
Summary
Regulation of transcription plays a pivotal role in many biological processes including pattern formation during embryonic development [1,2,3,4]. While most experimental studies performed up to date have focused on the input-output relationship between Bcd and its target genes on the embryonic scale through the analysis of mature mRNA or protein [9,10,11,12,13,17,18,19,20,21], there is currently no knowledge about this relationship on time and space scales that are approaching the actual transcriptional events Such information is essential for evaluating the controversial question of whether Bcd plays a transient or sustained role in the transcriptional decisions of its target genes to generate sharp expression boundaries during development. It remains controversial whether the Drosophila morphogenetic protein Bicoid (Bcd) plays a transient or sustained role in activating its target genes to establish sharp expression boundaries during development
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call