Every one of our cells stores its genome within the nucleus – the quintessential subcellular structure that distinguishes eukaryotic cells from bacteria. When animal cells divide, they disassemble their nucleus, releasing individual chromosomes for proper segregation to daughter cells. At the end of cell division, the daughter cells reassemble a single nucleus around a complete set of chromosomes. The formation of a single nucleus is critical for the maintenance of genomic integrity. Individual chromosomes packaged into separate, small nuclei are prone to massive DNA damage, leading to mutations as well as chromosome rearrangement and loss. Cancer cells often contain small, multiple nuclei, which may drive genome disruption as well as disease progression. Nonetheless, how cells package their genome into just one nucleus has been a mystery.