title: Generation of micronuclei during interphase by coupling between cytoplasmic membrane blebbing and nuclear budding.
abstract: Micronucleation, mediated by interphase nuclear budding, has been repeatedly suggested, but the process is still enigmatic. In the present study, we confirmed the previous observation that there are lamin B1-negative micronuclei in addition to the positive ones. A large cytoplasmic bleb was found to frequently entrap lamin B1-negative micronuclei, which were connected to the nucleus by a thin chromatin stalk. At the bottom of the stalk, the nuclear lamin B1 structure appeared broken. Chromatin extrusion through lamina breaks has been referred to as herniation or a blister of the nucleus, and has been observed after the expression of viral proteins. A cell line in which extrachromosomal double minutes and lamin B1 protein were simultaneously visualized in different colors in live cells was established. By using these cells, time-lapse microscopy revealed that cytoplasmic membrane blebbing occurred simultaneously with the extrusion of nuclear content, which generated lamin B1-negative micronuclei during interphase. Furthermore, activation of cytoplasmic membrane blebbing by the addition of fresh serum or camptothecin induced nuclear budding within 1 to 10 minutes, which suggested that blebbing might be the cause of the budding. After the induction of blebbing, the frequency of lamin-negative micronuclei increased. The budding was most frequent during S phase and more efficiently entrapped small extrachromosomal chromatin than the large chromosome arm. Based on these results, we suggest a novel mechanism in which cytoplasmic membrane dynamics pulls the chromatin out of the nucleus through the lamina break. Evidence for such a mechanism was obtained in certain cancer cell lines including human COLO 320 and HeLa. The mechanism could significantly perturb the genome and influence cancer cell phenotypes.
authors.affiliation: Graduate School of Biosphere Science, Hiroshima University, Higashi-hiroshima, Hiroshima, Japan.
authors.forename: Koh-ichi
authors.initials: K
authors.lastname: Utani
authors.forename: Atsushi
authors.initials: A
authors.lastname: Okamoto
authors.forename: Noriaki
authors.initials: N
authors.lastname: Shimizu
mesh_terms: D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism* / Q000648:ultrastructure; D002843:Chromatin / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism*; D006801:Humans; D007399:Interphase; D034921:Lamin Type B / Q000378:metabolism; D016196:S Phase
chemical_list: D002843:Chromatin; D034921:Lamin Type B
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