부산대학교 도서관

The chromatin fiber folds into loops, but the mechanisms controlling loop extrusion are still poorly understood. Using super-resolution microscopy, we visualize that loops in intact nuclei are formed by a scaffold of cohesin complexes from which the DNA protrudes. RNA polymerase II decorates the top of the loops and is physically segregated from cohesin. Augmented looping upon increased loading of cohesin on chromosomes causes disruption of Lamin at the nuclear rim and chromatin blending, a homogeneous distribution of chromatin within the nucleus. Altering supercoiling via either transcription or topoisomerase inhibition counteracts chromatin blending, increases chromatin condensation, disrupts loop formation, and leads to altered cohesin distribution and mobility on chromatin. Overall, negative supercoiling generated by transcription is an important regulator of loop formation in vivo. [Display omitted] • Super-resolution imaging reveals the structural organization of chromatin loops • Increased looping results into chromatin blending • Transcription regulates cohesin distribution and mobility on chromatin • Transcription-mediated supercoiling controls loop formation The mechanisms underlying chromatin loop formation by cohesin-mediated extrusion are still partially unknown. Using super-resolution imaging, Neguembor et al. visualize how loops are organized at the nanoscale level in intact nuclei and show that transcriptionally generated supercoiling regulates loop formation in vivo. [ABSTRACT FROM AUTHOR]