ABSTRACT
Anaphase, mitotic exit, and cytokinesis proceed in rapid succession, and while mitotic exit is a requirement for cytokinesis in yeast, it may not be a direct requirement for furrow initiation in animal cells. In this report, we physically manipulated the proximity of the mitotic apparatus (MA) to the cell cortex in combination with microinjection of effectors of the spindle checkpoint and CDK1 activity to determine how the initiation of cytokinesis is coupled to the onset of anaphase and mitotic exit. Whereas precocious contact between the MA and the cell surface advanced the onset of cytokinesis into early anaphase A, furrowing could not be advanced prior to the metaphase-anaphase transition. Additionally, while cells arrested in anaphase could be induced to initiate cleavage furrows, cells arrested in metaphase could not. Finally, activation of the mitotic checkpoint in one spindle of a binucleate cell failed to arrest cytokinesis induced by the control spindle but did inhibit the formation of furrows between the arrested MA and the control, nonarrested MA. Our experiments suggest that the competence of the mitotic apparatus to initiate cytokinesis is not dependent on cyclin degradation but does require anaphase-promoting complex (APC) activity and, thus, inactivation of the mitotic checkpoint.
Subject(s)
Carrier Proteins , Embryo, Nonmammalian/cytology , Sea Urchins/cytology , Sea Urchins/embryology , Ubiquitin-Protein Ligase Complexes , Anaphase/drug effects , Anaphase-Promoting Complex-Cyclosome , Animals , Blastomeres/cytology , Blastomeres/drug effects , Calcium-Binding Proteins/administration & dosage , Calcium-Binding Proteins/pharmacology , Cell Cycle Proteins , Cell Division/drug effects , Cyclin B/administration & dosage , Cyclin B/chemistry , Cyclin B/pharmacology , Embryo, Nonmammalian/drug effects , Fungal Proteins/administration & dosage , Fungal Proteins/pharmacology , Ligases/metabolism , Metaphase/drug effects , Mitosis/drug effects , Nuclear Proteins , Sea Urchins/drug effects , Spindle Apparatus/metabolism , Time FactorsABSTRACT
We have examined the expression of glycogen synthase kinase-3beta in oocytes and early embryos of Xenopus and found that the protein is developmentally regulated. In resting oocytes, GSK-3beta is active and it is inactivated on maturation in response to progesterone. GSK-3beta inactivation is necessary and rate limiting for the cell cycle response to this hormone and the subsequent accumulation of beta-catenin. Overexpression of a dominant negative form of the kinase accelerates maturation, as does inactivation by expression of Xenopus Dishevelled or microinjection of an inactivating antibody. Cell cycle inhibition by GSK-3beta is not mediated by the level of beta-catenin or by a direct effect on either the MAP kinase pathway or translation of mos and cyclin B1. These data indicate a novel role for GSK-3beta in Xenopus development: in addition to controlling specification of the dorsoventral axis in embryos, it mediates cell cycle arrest in oocytes.
