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

Dorsal clusters in vivo enhance gene expression by increasing polymerase loading without affecting transcriptional bursting 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 data and remain contested.
• What they did: Using advanced microscopy, the study measured transcription and manipulated Dorsal concentrations in live embryos, revealing that Dorsal forms clusters that associate with target genes and amplify transcription by increasing polymerase loading.
• The result: Disrupting cluster-gene association causes developmental defects, and clusters are shown not to initiate or sustain bursts but to augment polymerase loading during bursts, challenging existing models of transcription regulation.