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Checkpoint pathways inhibit cyclin-dependent kinases (Cdks) to arrest cell cycles when DNA is damaged or unreplicated. Early embryonic cell cycles of Xenopus laevis lack these checkpoints. Completion of 12 divisions marks the midblastula transition (MBT), when the cell cycle lengthens, acquiring gap phases and checkpoints of a somatic cell cycle. Although Xenopus embryos lack checkpoints prior to the MBT, checkpoints are observed in cell-free egg extracts supplemented with sperm nuclei. These checkpoints depend upon the Xenopus Chk1 (XChk1)-signaling pathway. To understand why Xenopus embryos lack checkpoints, xchk1 was cloned, and its expression was examined and manipulated in Xenopus embryos. Although XChk1 mRNA is degraded at the MBT, XChk1 protein persists throughout development, including pre-MBT cell cycles that lack checkpoints. However, when DNA replication is blocked, XChk1 is activated only after stage 7, two cell cycles prior to the MBT. Likewise, DNA damage activates XChk1 only after the MBT. Furthermore, overexpression of XChk1 in Xenopus embryos creates a checkpoint in which cell division arrests, and both Cdc2 and Cdk2 are phosphorylated on tyrosine 15 and inhibited in catalytic activity. These data indicate that XChk1 signaling is intact but blocked upstream of XChk1 until the MBT.
Anderson,
Ionizing radiation induces apoptosis and elevates cyclin A1-Cdk2 activity before but not after the midblastula transition in Xenopus.
1997, Pubmed,
Xenbase
Anderson,
Ionizing radiation induces apoptosis and elevates cyclin A1-Cdk2 activity before but not after the midblastula transition in Xenopus.
1997,
Pubmed
,
Xenbase Clute,
Microtubule dependence of chromosome cycles in Xenopus laevis blastomeres under the influence of a DNA synthesis inhibitor, aphidicolin.
1997,
Pubmed
,
Xenbase Dasso,
Completion of DNA replication is monitored by a feedback system that controls the initiation of mitosis in vitro: studies in Xenopus.
1990,
Pubmed
,
Xenbase Elledge,
Cell cycle checkpoints: preventing an identity crisis.
1996,
Pubmed Ferrell,
Cell cycle tyrosine phosphorylation of p34cdc2 and a microtubule-associated protein kinase homolog in Xenopus oocytes and eggs.
1991,
Pubmed
,
Xenbase Fogarty,
The Drosophila grapes gene is related to checkpoint gene chk1/rad27 and is required for late syncytial division fidelity.
1997,
Pubmed Frederick,
Cell cycle remodeling requires cell-cell interactions in developing Xenopus embryos.
1994,
Pubmed
,
Xenbase Furnari,
Cdc25 mitotic inducer targeted by chk1 DNA damage checkpoint kinase.
1997,
Pubmed Gabrielli,
Cdc25 regulates the phosphorylation and activity of the Xenopus cdk2 protein kinase complex.
1992,
Pubmed
,
Xenbase Hartley,
In vivo regulation of the early embryonic cell cycle in Xenopus.
1996,
Pubmed
,
Xenbase Hartley,
A role for cyclin E/Cdk2 in the timing of the midblastula transition in Xenopus embryos.
1997,
Pubmed
,
Xenbase Hensey,
A developmental timer that regulates apoptosis at the onset of gastrulation.
1997,
Pubmed
,
Xenbase Howe,
A developmental timer regulates degradation of cyclin E1 at the midblastula transition during Xenopus embryogenesis.
1996,
Pubmed
,
Xenbase Jackson,
Early events in DNA replication require cyclin E and are blocked by p21CIP1.
1995,
Pubmed
,
Xenbase Kim,
A maternal form of the phosphatase Cdc25A regulates early embryonic cell cycles in Xenopus laevis.
1999,
Pubmed
,
Xenbase Kimelman,
The events of the midblastula transition in Xenopus are regulated by changes in the cell cycle.
1987,
Pubmed
,
Xenbase Kumagai,
The Xenopus Chk1 protein kinase mediates a caffeine-sensitive pathway of checkpoint control in cell-free extracts.
1998,
Pubmed
,
Xenbase Kumagai,
14-3-3 proteins act as negative regulators of the mitotic inducer Cdc25 in Xenopus egg extracts.
1998,
Pubmed
,
Xenbase Levine,
p53, the cellular gatekeeper for growth and division.
1997,
Pubmed Nakajo,
Involvement of Chk1 kinase in prophase I arrest of Xenopus oocytes.
1999,
Pubmed
,
Xenbase Newport,
A major developmental transition in early Xenopus embryos: I. characterization and timing of cellular changes at the midblastula stage.
1982,
Pubmed
,
Xenbase Newport,
On the coupling between DNA replication and mitosis.
1989,
Pubmed
,
Xenbase Newport,
A major developmental transition in early Xenopus embryos: II. Control of the onset of transcription.
1982,
Pubmed
,
Xenbase Paulovich,
When checkpoints fail.
1997,
Pubmed Peng,
Mitotic and G2 checkpoint control: regulation of 14-3-3 protein binding by phosphorylation of Cdc25C on serine-216.
1997,
Pubmed Rempel,
Maternal Xenopus Cdk2-cyclin E complexes function during meiotic and early embryonic cell cycles that lack a G1 phase.
1995,
Pubmed
,
Xenbase Sanchez,
Conservation of the Chk1 checkpoint pathway in mammals: linkage of DNA damage to Cdk regulation through Cdc25.
1997,
Pubmed Sible,
Zygotic transcription is required to block a maternal program of apoptosis in Xenopus embryos.
1997,
Pubmed
,
Xenbase Sibon,
DNA-replication checkpoint control at the Drosophila midblastula transition.
1997,
Pubmed Stack,
Developmentally regulated activation of apoptosis early in Xenopus gastrulation results in cyclin A degradation during interphase of the cell cycle.
1997,
Pubmed
,
Xenbase Walworth,
Fission yeast chk1 protein kinase links the rad checkpoint pathway to cdc2.
1993,
Pubmed Walworth,
rad-dependent response of the chk1-encoded protein kinase at the DNA damage checkpoint.
1996,
Pubmed Westphal,
Cell-cycle signaling: Atm displays its many talents.
1997,
Pubmed Zeng,
Replication checkpoint requires phosphorylation of the phosphatase Cdc25 by Cds1 or Chk1.
1998,
Pubmed
