The nuclear lamina maintains global spatial organization of chromatin in Drosophila

The nuclear lamina (NL) is a meshwork of lamins and lamin-associated proteins lining the nuclear envelope (NE). Chromatin adjoining the NL in lamina-associated domains (LADs) is densely packed and contains predominantly silent genes. However, how the NL impacts on global chromatin architecture is poorly understood. Here, we show that NL disruption in Drosophila S2 cells leads to bulk chromatin compactization and repositioning from the NE. This increases the chromatin density in the topologically-associating domains (TADs) harboring active genes, and enhances inter-TAD interactions resulting in the intermingling of active and inactive compartments. Importantly, upon NL disruption, a fraction of TADs strongly overlapping with LADs becomes less compact, whilst resident genes are derepressed. Two-color FISH confirms that a a TAD is more decompacted following its release from the NL. Finally, polymer simulations show that chromatin binding to the NL can per se compact attached TADs. Collectively, our findings demonstrate a dual function of the NL in shaping the 3D genome. Attachment of TADs to the NL makes them more condensed but decreases the overall chromatin density in the nucleus by stretching interphase chromosomes. Hi-C analysis of chromatin spatial structure in cultured Drosophila cell line S2 upon lamin Dm0 knock-down.