UCSF

During mitosis, nuclear envelope (NE) disassembles to proceed nuclear division and reassembles to encapsulate the newly generated diploid chromosome set into the daughter nucleus. A failure of this compartmentalization gives rise to micronuclei, leading to DNA damage and chromothripsis which can be a cause of disease. While the secure compartmentalization of the complete chromosome set into the single cell organelle unit is a fundamental biological paradigm, the exact mechanism behind this principle remains largely unknown. Using high-temporal microscopy, we discovered that nuclear filament protein Lamin B1 localizes and spreads from the telomere region of condensed chromosomes. The absence of immediate chromosome de-condensation regulated by barrier-to-autointegration factor (BAF) results in mis-shaped nuclei in daughter cells, while delocalization of Lamin B1 from telomere region results in massive micro-nuclei formation. Our findings reveal a new paradigm of full mitotic chromosome encapsulation that relies on both attraction of nuclear filament protein to telomere region and exclusion due to chromosome de-condensation during telophase.