title: G2 acquisition by transcription-independent mechanism at the zebrafish midblastula transition.
abstract: Following fertilization of many animal embryos, rapid synchronous cleavage divisions give way to longer, asynchronous cell cycles at the midblastula transition (MBT). The cell cycle changes at the MBT, including the addition of gap phases and checkpoint controls, are accompanied by activation of the zygotic genome and the onset of cell motility. Whereas the biochemical changes accompanying the MBT in the vertebrate embryo have been extensively documented, the cellular events are not well understood. We show that cell cycle remodeling during the zebrafish MBT includes the transcription-independent acquisition of a G2 phase that is essential for preventing entry into mitosis before S-phase completion in cycles 11-13. We provide evidence from high-resolution imaging that inhibition of Cdc25a and Cdk1 activity, but not Cdk2 activity, is essential for cell cycle lengthening and asynchrony between cycles 9 and 12. We demonstrate that lengthening is not required for initiation of zygotic transcription. Our results are consistent with findings from Drosophila and Xenopus that indicate the central importance of G2 addition in checkpoint establishment, and point to similar mechanisms governing the MBT in diverse species.
authors.affiliation: Department of Biochemistry and Cell Biology, Rice University, MS-140, PO Box 1892, Houston, Texas 77251-1892, USA.
authors.forename: Damian E
authors.initials: DE
authors.lastname: Dalle Nogare
authors.forename: Philip T
authors.initials: PT
authors.lastname: Pauerstein
authors.forename: Mary Ellen
authors.initials: ME
authors.lastname: Lane
mesh_terms: D000818:Animals; D036703:Blastula / Q000502:physiology*; D016203:CDC2 Protein Kinase / Q000502:physiology; D002453:Cell Cycle / Q000502:physiology; D051357:Cyclin-Dependent Kinase 2 / Q000502:physiology; D016195:G2 Phase / Q000502:physiology*; D015533:Transcriptional Activation / Q000502:physiology; D015027:Zebrafish / Q000196:embryology*; D029961:Zebrafish Proteins / Q000502:physiology*; D020687:cdc25 Phosphatases / Q000502:physiology
chemical_list: D029961:Zebrafish Proteins; D016203:CDC2 Protein Kinase; D051357:Cyclin-Dependent Kinase 2; D020687:cdc25 Phosphatases