Transcription factor clusters enhance gene expression in vivo without modulating bursting dynamics.

Dorsal clusters in vivo amplify gene expression by increasing polymerase loading without altering transcriptional bursting dynamics in Drosophila embryos.

• Why it matters: Understanding how transcription factor condensates regulate gene expression in living organisms is crucial, as current models are based mainly on in vitro studies and lack in vivo validation.
• What they did: Using advanced microscopy, the study examined Dorsal, a NF-κB homolog, in live Drosophila embryos, revealing that Dorsal forms clusters that associate with target genes and enhance transcription by boosting polymerase loading.
• The result: Disruption of cluster-gene association leads to developmental defects, and the findings challenge existing ideas by showing clusters do not initiate or sustain bursts but instead augment transcription during bursts.