DNA-replication checkpoint control at the Drosophila midblastula transition

Embryogenesis is typically initiated by a series of rapid mitotic divisions that are under maternal genetic control. The switch to zygotic control of embryogenesis at the midblastula transition is accompanied by significant increases in cell-cycle length and gene transcription, and changes in embryo morphology. Here we show that mutations in the grapes (grp) checkpoint 1 kinase homologue in Drosophila block the morphological and biochemical changes that accompany the midblastula transition, lead to a continuation of the maternal cell-cycle programme, and disrupt DNA-replication checkpoint control of cell-cycle progression. The timing of the midblastula transition is controlled by the ratio of nuclei to cytoplasm (the nucleocytoplasmic ratio), suggesting that this developmental transition is triggered by titration of a maternal factor by the increasing mass of nuclear material that accumulates during the rapid embryonic mitoses. Our observations support a model for cell-cycle control at the midblastula transition in which titration of a maternal component of the DNA-replication machinery slows DNA synthesis and induces a checkpoint-dependent delay in cell-cycle progression. This delay may allow both completion of S phase and transcription of genes that initiate the switch to zygotic control of embryogenesis.

[1]  J. Gergen,et al.  Regulation of runt transcription by Drosophila segmentation genes , 1993, Mechanisms of Development.

[2]  R. Shenkar,et al.  Hypersensitivity of Drosophila mei-41 mutants to hydroxyurea is associated with reduced mitotic chromosome stability. , 1986, Mutation research.

[3]  Stephen J. Elledge,et al.  Cell Cycle Checkpoints: Preventing an Identity Crisis , 1996, Science.

[4]  P. O’Farrell,et al.  Drosophila Wee1 kinase rescues fission yeast from mitotic catastrophe and phosphorylates Drosophila Cdc2 in vitro. , 1995, Molecular biology of the cell.

[5]  W. J. Sullivan,et al.  Mutations affecting the cytoskeletal organization of syncytial Drosophila embryos. , 1993, Development.

[6]  M. Bate,et al.  The development of Drosophila melanogaster , 1993 .

[7]  C. Kimmel,et al.  The zebrafish midblastula transition. , 1993, Development.

[8]  R. Bernards,et al.  rad-Dependent Response of the chk1-Encoded Protein Kinase at the DNA Damage Checkpoint , 1996, Science.

[9]  L. Goldstein,et al.  Anastral meiotic spindle morphogenesis: role of the non-claret disjunctional kinesin-like protein , 1996, The Journal of cell biology.

[10]  Claudio D. Stern,et al.  Developmental biology (3rd edn) , 1992 .

[11]  B. Alberts,et al.  Studies of nuclear and cytoplasmic behaviour during the five mitotic cycles that precede gastrulation in Drosophila embryogenesis. , 1983, Journal of cell science.

[12]  B. Edgar,et al.  Zygotic degradation of two maternal Cdc25 mRNAs terminates Drosophila's early cell cycle program. , 1996, Genes & development.

[13]  G. Schubiger,et al.  Activation of transcription in Drosophila embryos is a gradual process mediated by the nucleocytoplasmic ratio. , 1996, Genes & development.

[14]  A. Spradling,et al.  Insertional mutagenesis of the Drosophila genome with single P elements. , 1988, Science.

[15]  B. Edgar,et al.  Cell cycle control by the nucleo-cytoplasmic ratio in early Drosophila development , 1986, Cell.

[16]  D. Bouvier,et al.  p56chk1 protein kinase is required for the DNA replication checkpoint at 37°C in fission yeast , 1997 .

[17]  G. Schubiger,et al.  Temporal regulation of gene expression in the blastoderm Drosophila embryo. , 1991, Genes & development.

[18]  W. Sullivan,et al.  The Drosophila grapes gene is related to checkpoint gene chk1/rad27 and is required for late syncytial division fidelity , 1997, Current Biology.

[19]  J. Raff,et al.  Nuclear and cytoplasmic mitotic cycles continue in Drosophila embryos in which DNA synthesis is inhibited with aphidicolin , 1988, The Journal of cell biology.

[20]  W. Sullivan,et al.  The Drosophila maternal-effect mutation grapes causes a metaphase arrest at nuclear cycle 13. , 1994, Development.

[21]  M. Kirschner,et al.  A major developmental transition in early xenopus embryos: I. characterization and timing of cellular changes at the midblastula stage , 1982, Cell.

[22]  M. Dasso,et al.  Completion of DNA replication is monitored by a feedback system that controls the initiation of mitosis in vitro: Studies in Xenopus , 1990, Cell.

[23]  H. Jäckle,et al.  Mitotic delay dependent survival identifies components of cell cycle control in the Drosophila blastoderm. , 1995, Development.

[24]  L. Goldstein,et al.  Drosophila Melanogaster: Practical Uses in Cell and Molecular Biology , 1994 .

[25]  B. Alberts,et al.  Behaviour of microtubules and actin filaments in living Drosophila embryos. , 1988, Development.

[26]  Y. Masui,et al.  Regulation of the appearance of division asynchrony and microtubule-dependent chromosome cycles in Xenopus laevis embryos. , 1995, Developmental biology.

[27]  P. O’Farrell,et al.  Distinct molecular mechanism regulate cell cycle timing at successive stages of Drosophila embryogenesis. , 1994, Genes & development.

[28]  P. O’Farrell,et al.  Progression of the cell cycle through mitosis leads to abortion of nascent transcripts , 1991, Cell.