Mitotic chromosomes are mechanically connected by chromatin-based interchromosome linkers

Chromosomal organization is essential for gene regulation and maintaining genomic stability. While metaphase chromosomes appear distinct, interchromosomal connections, or linkers, have been detected among mitotic chromosomes and could be vital for coordinated chromosome movements and genome stability. Through micropipette-based isolation and manipulation, researchers analyzed these linkers between mammalian mitotic chromosomes.

Upon pulling an isolated chromosome, thin linkers were found to connect them. Staining with CREST revealed their locations to be specifically at centromeres. The linkers exhibited linear elasticity and had a length-doubling force of around 300 pN, which is similar to the force required to double the length of an entire metaphase chromosome.

Further studies using enzymatic treatments indicated that the linkers are broken down by DNase but remain intact when treated with RNase, protease, or microtubule polymerization (spindle fiber) inhibitors. This suggests that the connectivity of linkers is based on DNA.

Immunofluorescence experiments showed that histones and topoisomerase II (topo II) are present on the linkers, with topo II organized into discrete foci spaced approximately 0.4 megabases apart. When mitotic chromosomes are arrested in metaphase using spindle inhibitors, isolated genomes no longer display interchromosome linkers.

Experiments conducted on intact cells further demonstrated that interchromosome linkers containing CENP-B can be observed between mitotic chromosomes, suggesting that these linkers are not an artifact resulting from genome isolation.