The spindle checkpoint kinase bub1 and cyclin e/cdk2 both contribute to the establishment of meiotic metaphase arrest by cytostatic factor.
In vertebrate unfertilized eggs, metaphase arrest in Meiosis II is mediated by an activity known as cytostatic factor (CSF). CSF arrest is dependent upon Mos-dependent activation of the MAPK/Rsk pathway, and Rsk activates the spindle checkpoint kinase Bub1, leading to inhibition of the anaphase-promoting complex (APC), an E3 ubiquitin ligase required for the metaphase/anaphase transition. However, it is not known whether Bub1 is required for the establishment of CSF arrest or whether other pathways also contribute. Here, we show that immunodepletion of Bub1 from egg extracts blocks the ability of Mos to establish CSF arrest, and arrest can be restored by the addition of wild-type, but not kinase-dead, Bub1. The appearance of CSF arrest at Meiosis II may result from coexpression of cyclin E/Cdk2 with the MAPK/Bub1 pathway. Cyclin E/Cdk2 was able to cause metaphase arrest in egg extracts even in the absence of Mos and could also inhibit cyclin B degradation in oocytes when expressed at anaphase of Meiosis I. Once it has been established, metaphase arrest can be maintained in the absence of MAPK, Bub1, or cyclin E/Cdk2 activity. Both pathways are independent of each other, but each appears to block activation of the APC, which is required for cyclin B degradation and the metaphase/anaphase transition.
Howard Hughes Medical Institute and Department of Pharmacology, University of Colorado School of Medicine, Denver 80262, USA.
Brian J
BJ
Tunquist
Markus S
MS
Schwab
Lin G
LG
Chen
James L
JL
Maller
D000818:Animals; D042846:CDC2-CDC28 Kinases; D002460:Cell Line; D019927:Cyclin E / Q000502:physiology*; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases / Q000235:genetics / Q000502:physiology*; D008540:Meiosis / Q000502:physiology*; D009154:Mutation; D011494:Protein Kinases / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000502:physiology*; D017231:Proto-Oncogene Proteins c-mos / Q000502:physiology*; D014981:Xenopus; D029867:Xenopus Proteins
D019927:Cyclin E; D029867:Xenopus Proteins; D011494:Protein Kinases; C090464:Bub1 spindle checkpoint protein; D017346:Protein Serine-Threonine Kinases; D017231:Proto-Oncogene Proteins c-mos; D042846:CDC2-CDC28 Kinases; C495891:Cdk2 protein, Xenopus; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases