Geneticists are constantly discovering new ways that genes are expressed, silenced, and altered in other ways. A new study from Princeton University shows how a phenomenon called “transcriptional bursting” impacts gene expression and how the state of the enhancer changes the strength and frequency of each burst.
A new live-imaging technique involving tagging RNA molecules with fluorescent tags so they glow under certain conditions was used to study transcriptional bursting in fly embryos. The researchers looked at the embryos at a specific stage: two hours after the “onset of embryonic life” where they had approximately one hour of quick and continuous DNA transcription to look for and record any bursts of gene activity.
They saw a miraculous pattern of bursting – RNA polymerase, the enzyme responsible for turning DNA into messenger RNA for translation, transcribed a new strand of RNA every 10 to 15 seconds for four to five minutes for every burst that occurred. There was a period of relaxation between bursts, but only for a few minutes until the bursting started all over again.
The researchers also experimented with location of enhancer DNA in relation to the promoter and the effect it might have on the frequency of transcriptional bursting. When the enhancer was placed upstream of the promoter, the researchers saw fluctuations in transcription but no so-called bursts of activity. However, when the enhancer was placed downstream of the promoter, the periodic bursts of transcription returned. Ultimately, the researchers realized that the closer the enhancer is placed to the promoter, the more frequent bursting occurs. The same effect stems from the strength of the enhancer/promoter relationship.
In a surprising conclusion to the study, the researchers discovered that a single enhancer could simultaneously cause transcriptional bursting in two separate promoters existing at different parts of the genome, a finding that somewhat redefines what geneticists previously believed about the interaction between promoters and enhancers. “This means that traditional models for enhancer-promoter looping interactions are just not quite correct,” said Princeton’s Michael Levine, PhD.
While there is no definitive proof that transcriptional bursting occurs in every single gene in the genome, the study scientists saw bursting in every gene that they observed throughout the study, all of which were considered to be critical to embryonic development. “If we see bursting here, the odds are we are going to see it everywhere,” Levine concluded.
This study was recently published in the journal Cell.
Source: Princeton University