When many cells divide, the nuclear envelope poses a problem: the spindle microtubules can't access the chromosomes. Two recent papers in Cell describe how the spindle solves this problem by literally pulling open the nucleus at the beginning of mitosis.
Aitchison, J. D., & Rout, M. P. (2002). A tense time for the nuclear envelope. Cell. Cell Press. https://doi.org/10.1016/S0092-8674(02)00638-4