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dc.contributor.authorWroble, Brian Noelen_US
dc.date.accessioned2014-03-14T20:18:59Z
dc.date.available2014-03-14T20:18:59Z
dc.date.issued2005-11-22en_US
dc.identifier.otheretd-11232005-154240en_US
dc.identifier.urihttp://hdl.handle.net/10919/29723
dc.description.abstractIn somatic cells, when DNA is damaged or incompletely replicated, checkpoint pathways arrest the cell cycle prior to M or S phases by inhibiting cyclin-dependent kinases (Cdks). In Xenopus laevis, embryonic cellular divisions (2-12) consist of rapid cleavage cycles in which gap phases, checkpoint engagement, and apoptosis are absent. Upon the completion of the 12th cellular division, the midblastula transition (MBT) begins and the cell cycle lengthens, acquiring gap phases. In addition, cell cycle checkpoint pathways and an apoptotic program become functional. The studies described here were performed to better understand the roles of two protein kinases, Chk2/Cds1 and Wee1, during checkpoint signaling in the developing embryo. The DNA damage checkpoint is mediated by the Chk2/Cds1 kinase. Conflicting evidence implicates Chk2 as an inhibitor or promoter of apoptosis. To better understand the developmental function of Chk2 and its role in apoptosis, we expressed wild-type (wt) and dominant-negative (DN) Chk2 in Xenopus embryos. Wt-Chk2 created a pre-MBT checkpoint by promoting degradation of Cdc25A and phosphorylation of Cdks. Embryos expressing DN-Chk2 developed normally until gastrulation and then underwent apoptosis. Conversely, low doses of wt-Chk2 blocked radiation-induced apoptosis. These data indicate that Chk2 inhibits apoptosis in the early embryo. Therefore, Chk2 operates as a switch between cell cycle arrest and apoptosis in response to genomic assaults. In Xenopus laevis, Wee1 kinase phosphorylates and inhibits Cdks. To determine the role of Wee1 in cell cycle checkpoint signaling and remodeling at the MBT, exogenous Wee1 was expressed in one-cell stage embryos. Modest overexpression of Wee1 created a pre-MBT cell cycle checkpoint, similar to Chk2, characterized by cell cycle delay and phosphorylation of Cdks. Furthermore, overexpression of Wee1 disrupted remodeling events that normally occur at the MBT, including degradation of Cdc25A, cyclin E, and Wee1. Interestingly, overexpression of Wee1 also resulted in post-MBT apoptosis. Taken together, these data suggest the importance of Wee1 as not only a Cdk inhibitory kinase, but also potentially as a promoter of apoptosis during early development of Xenopus laevis. The studies described here provide evidence that Chk2 and Wee1 have both similar and distinct roles in the developing embryo.en_US
dc.publisherVirginia Techen_US
dc.relation.haspartBrianWrobledissertation.pdfen_US
dc.rightsI hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to Virginia Tech or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report.en_US
dc.subjectXenopus laevisen_US
dc.subjectMBTen_US
dc.subjectChk2en_US
dc.subjectapoptosisen_US
dc.subjectWee1en_US
dc.titleThe Role of Chk2 and Wee1 Protein Kinases during the Early Embryonic Development of Xenopus laevisen_US
dc.typeDissertationen_US
dc.contributor.departmentBiologyen_US
dc.description.degreePh. D.en_US
thesis.degree.namePh. D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen_US
thesis.degree.disciplineBiologyen_US
dc.contributor.committeechairSible, Jill C.en_US
dc.contributor.committeememberRutherford, Charles L.en_US
dc.contributor.committeememberHuckle, William R.en_US
dc.contributor.committeememberWalker, Richard A.en_US
dc.contributor.committeememberMcNabb, F. M. Anneen_US
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-11232005-154240/en_US
dc.date.sdate2005-11-23en_US
dc.date.rdate2006-11-29
dc.date.adate2005-11-29en_US


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