Lampe, M. | Search bioRxiv

bioRxiv2018

Bleaching-independent, whole-cell, 3D and multi-color STED imaging with exchangeable fluorophores

We demonstrate bleaching-independent STED microscopy using fluorogenic labels that reversibly bind to their target structure. A constant exchange of labels guarantees the removal of photobleached fluorophores and their replacement by intact fluorophores, thereby circumventing bleaching-related limitations of STED super-resolution imaging in fixed and living cells. Foremost, we achieve a constant labeling density and demonstrate a fluorescence signal for long and theoretically unlimited acquisition times. Using this concept, we demonstrate whole-cell, 3D, multi-color and live cell STED microscopy with up to 100 min acquisition time.

biophysics↗

bioRxiv2018

A quantitative map of human Condensins provides new insights into mitotic chromosome architecture

The two Condensin complexes in human cells are essential for mitotic chromosome structure. We used homozygous genome editing to fluorescently tag Condensin I and II subunits and mapped their absolute abundance, spacing and dynamic localization during mitosis by fluorescence correlation spectroscopy-calibrated live cell imaging and super-resolution microscopy. While [~]35,000 Condensin II complexes are stably bound to chromosomes throughout mitosis, [~]195,000 Condensin I complexes dynamically bind in two steps, in prometaphase and early anaphase. The two Condensins rarely co-localize at the chromatid axis, where Condensin II is centrally confined but Condensin I reaches [~]50% of the chromatid diameter from its center. Based on our comprehensive quantitative data, we propose a three-step hierarchical loop model of mitotic chromosome compaction: Condensin II initially fixes loops of a maximum size of [~]450 kb at the chromatid axis whose size is then reduced by Condensin I binding to [~]90 kb in prometaphase and [~]70 kb in anaphase, achieving maximum chromosome compaction upon sister chromatid segregation.

cell biology↗