title: The effects of DNA double-strand breaks on mouse oocyte meiotic maturation.
abstract: Both endogenous and exogenous factors can induce DNA double-strand breaks (DSBs) in oocytes, which is a potential risk for human-assisted reproductive technology as well as animal nuclear transfer. Here we used bleomycin (BLM) and laser micro-beam dissection (LMD) to induce DNA DSBs in germinal vesicle (GV) stage oocytes and compared the germinal vesicle breakdown (GVBD) rates and first polar body extrusion (PBE) rates between DNA DSB oocytes and untreated oocytes. Employing live cell imaging and immunofluorescence labeling, we observed the dynamics of DNA fragments during oocyte maturation. We also determined the cyclin B1 expression pattern in oocytes to analyze spindle assembly checkpoint (SAC) activity in DNA DSB oocytes. We used parthenogenetic activation to determine if the DNA DSB oocytes could be activated. As a result, we found that the BLM- or LMD-induced DSB oocytes showed lower GVBD rates and took a longer time to undergo GVBD compared with untreated oocytes. PBE was also delayed in DSB oocytes, but once GVBD had occurred, PBE was not affected, even in oocytes with severe DSBs. Compared with control oocytes, the DSB oocytes showed higher SAC activity, as indicated by less Ccnb1-GFP degradation during metaphase I to anaphase I transition. Parthenogenetic activation could activate the metaphase to interphase transition in the DNA DSB mature oocytes, but many oocytes contained multiple pronuclei or numerous micronuclei. These data suggest that DNA damage inhibits or delays the G2/M transition, but once GVBD occurs, DNA-damaged oocytes can complete chromosome separation and polar body extrusion even under a higher SAC activity, causing the formation of numerous micronuclei in early embryos.
authors.affiliation: State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing, China.
authors.forename: Jun-Yu
authors.initials: JY
authors.lastname: Ma
authors.forename: Ying-Chun
authors.initials: YC
authors.lastname: Ou Yang
authors.forename: Zhong-Wei
authors.initials: ZW
authors.lastname: Wang
authors.forename: Zhen-Bo
authors.initials: ZB
authors.lastname: Wang
authors.forename: Zong-Zhe
authors.initials: ZZ
authors.lastname: Jiang
authors.forename: Shi-Ming
authors.initials: SM
authors.lastname: Luo
authors.forename: Yi
authors.initials: Y
authors.lastname: Hou
authors.forename: Zhong-Hua
authors.initials: ZH
authors.lastname: Liu
authors.forename: Heide
authors.initials: H
authors.lastname: Schatten
authors.forename: Qing-Yuan
authors.initials: QY
authors.lastname: Sun
mesh_terms: D000818:Animals; D001761:Bleomycin / Q000494:pharmacology; D020090:Chromosome Segregation / Q000187:drug effects / Q000502:physiology; D053903:DNA Breaks, Double-Stranded / Q000187:drug effects*; D005455:Fluorescent Antibody Technique; D061346:Laser Capture Microdissection; D008540:Meiosis / Q000502:physiology*; D051379:Mice; D008845:Microinjections; D009865:Oocytes / Q000502:physiology*; D010312:Parthenogenesis / Q000502:physiology; D059705:Polar Bodies / Q000187:drug effects / Q000502:physiology; D013997:Time Factors; D059008:Time-Lapse Imaging
chemical_list: D001761:Bleomycin
keywords: Ccnb1; double-strand breaks; meiosis; oocyte; polar body extrusion; spindle assembly checkpoint