Checkpoint for DNA integrity at the first mitosis after oocyte activation.
Activation of oocytes, arrested at the meiosis II (MII) in mammals, initiates meiotic release, mitotic divisions, and development. Unlike most somatic cell types, MII arrested female germ cells lack an efficient DNA integrity checkpoint control. Here we present evidence showing a unique checkpoint for DNA integrity at first mitosis after oocyte activation. Mouse oocytes carrying intact DNA cleaved normally after meiotic release, whereas 50% of oocytes harboring damaged DNA manifested cytofragmentation, a morphological hallmark of apoptosis. If not activated, DNA-damaged MII oocytes did not show apoptotic fragmentation. Further, activated, enucleated oocytes or enucleated fertilized oocytes also underwent cytofragmentation, implicating cytoplasmic coordination of the fragmentation process, independent of the nucleus. Depolymerization of either actin filaments or microtubules induced no cytofragmentation, but inhibited fragmentation upon oocyte activation. During the process of fragmentation, microtubule networks formed, then microtubule asters congregated at discrete locations, around which fragmented cellular bodies formed. Mitotic spindles, however, were not formed inactivated oocytes with damaged or absent DNA; in contrast, normal mitotic spindles were formed in activated oocytes with intact DNA. These results demonstrate that damaged DNA or absence of DNA leads to cytofragmentation after oocyte activation. Further, we found a mechanism of cytoskeletal involvement in the process of cytofragmentation. In addition, possible implication of the present findings in somatic cell cloning and human clinical embryology is discussed.
Liu
Lin
L
Department of Obstetrics and Gynecology, Brown University, Women & Infants Hospital, Providence, Rhode Island, USA.
Trimarchi
James R
JR
Smith
Peter J S
PJ
Keefe
David L
DL
D000818:Animals; D020013:Calcium Signaling; D002467:Cell Nucleus / Q000378:metabolism; D002875:Chromosomes; D004247:DNA / Q000502:physiology*; D004249:DNA Damage; D053938:DNA Fragmentation; D004317:Doxorubicin / Q000494:pharmacology; D005047:Etoposide / Q000494:pharmacology; D005260:Female; D008540:Meiosis / Q000502:physiology; D051379:Mice; D008870:Microtubules; D008938:Mitosis / Q000502:physiology*; D009865:Oocytes / Q000187:drug effects / Q000502:physiology*
D005047:Etoposide; D004317:Doxorubicin; D004247:DNA