title: Geminin deficiency causes a Chk1-dependent G2 arrest in Xenopus.
abstract: Geminin is an unstable inhibitor of DNA replication that gets destroyed at the metaphase/anaphase transition. The biological function of geminin has been difficult to determine because it is not homologous to a characterized protein and has pleiotropic effects when overexpressed. Geminin is thought to prevent a second round of initiation during S or G2 phase. In some assays, geminin induces uncommitted embryonic cells to differentiate as neurons. In this study, geminin was eliminated from developing Xenopus embryos by using antisense techniques. Geminin-deficient embryos show a novel and unusual phenotype: they complete the early cleavage divisions normally but arrest in G2 phase immediately after the midblastula transition. The arrest requires Chk1, the effector kinase of the DNA replication/DNA damage checkpoint pathway. The results indicate that geminin has an essential function and that loss of this function prevents entry into mitosis by a Chk1-dependent mechanism. Geminin may be required to maintain the structural integrity of the genome or it may directly down-regulate Chk1 activity. The data also show that during the embryonic cell cycles, rereplication is almost entirely prevented by geminin-independent mechanisms.
authors.affiliation: Division of Signal Transduction, Department of Medicine, Beth Israel Deaconess Medical Center, Boston, Massachusetts 02215, USA. t_mcgarry@northwestern.edu
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: McGarry
mesh_terms: D000818:Animals; D016203:CDC2 Protein Kinase / Q000235:genetics / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D000071877:Checkpoint Kinase 1; D004261:DNA Replication / Q000502:physiology; D004625:Embryo, Nonmammalian / Q000033:anatomy & histology / Q000502:physiology*; D016195:G2 Phase / Q000502:physiology*; D064248:Geminin; D016376:Oligonucleotides, Antisense / Q000235:genetics / Q000378:metabolism; D010641:Phenotype; D011494:Protein Kinases / Q000378:metabolism*; D012313:RNA / Q000235:genetics / Q000378:metabolism; D029867:Xenopus Proteins; D014982:Xenopus laevis / Q000502:physiology*; D020687:cdc25 Phosphatases / Q000235:genetics / Q000378:metabolism
chemical_list: D018797:Cell Cycle Proteins; C577998:GMNN protein, Xenopus; D064248:Geminin; D016376:Oligonucleotides, Antisense; D029867:Xenopus Proteins; D012313:RNA; D011494:Protein Kinases; D000071877:Checkpoint Kinase 1; C000605875:Chek1 protein, Xenopus; D016203:CDC2 Protein Kinase; D020687:cdc25 Phosphatases