Interactions between the genome and the nuclear lamina are multivalent and cooperative (Hi-C)
Mammalian genomes contain hundreds of lamina-associated domains (LADs), which are large, often megabase-sized heterochromatin domains that are anchored to the nuclear lamina (NL). Even though LADs play a key role in the spatial organization of the genome and potently repress gene activity, it is not yet understood how their interactions with the NL are encoded in their DNA. Here, we investigated the principles that govern LAD-NL interactions by taking a "LAD scrambling" approach. This approach relies on 1) local "hopping" of a Sleeping Beauty transposon to randomly insert loxP sites within and around a LAD of choice; and 2) Cre-mediated recombination between the loxP sites. This approach is highly efficient, enabling us to establish a large collection of clonal cell lines with deletions and inversions up to ~2Mb in size, spanning LAD and their flanking inter-LAD sequences. Mapping of NL interactions in these clones revealed that a single LAD contacts the NL through multiple regions. These regions act cooperatively and redundantly; however, some have more affinity for the NL and can boost NL contacts of neighbouring sequences. We also observed a crosstalk between two neighbouring LADs, when close enough to each other. Finally, changes in the heterochromatin mark H3K9me3 only partially mirrored changes in NL contacts. They also correlated more with gene expression changes than NL contacts did. These principles of LAD - NL interactions provide insight into the overall architecture of the genome and the impact on gene regulation. Overall design: Hi-C experiment were performed on parental (non-edited) and Cre-recombined clones.