The roles of Fzy/Cdc20 and Fzr/Cdh1 in regulating the destruction of cyclin B in space and time.
In Drosophila cells cyclin B is normally degraded in two phases: (a) destruction of the spindle-associated cyclin B initiates at centrosomes and spreads to the spindle equator; and (b) any remaining cytoplasmic cyclin B is degraded slightly later in mitosis. We show that the APC/C regulators Fizzy (Fzy)/Cdc20 and Fzy-related (Fzr)/Cdh1 bind to microtubules in vitro and associate with spindles in vivo. Fzy/Cdc20 is concentrated at kinetochores and centrosomes early in mitosis, whereas Fzr/Cdh1 is concentrated at centrosomes throughout the cell cycle. In syncytial embryos, only Fzy/Cdc20 is present, and only the spindle-associated cyclin B is degraded at the end of mitosis. A destruction box-mutated form of cyclin B (cyclin B triple-point mutant [CBTPM]-GFP) that cannot be targeted for destruction by Fzy/Cdc20, is no longer degraded on spindles in syncytial embryos. However, CBTPM-GFP can be targeted for destruction by Fzr/Cdh1. In cellularized embryos, which normally express Fzr/Cdh1, CBTPM-GFP is degraded throughout the cell but with slowed kinetics. These findings suggest that Fzy/Cdc20 is responsible for catalyzing the first phase of cyclin B destruction that occurs on the mitotic spindle, whereas Fzr/Cdh1 is responsible for catalyzing the second phase of cyclin B destruction that occurs throughout the cell. These observations have important implications for the mechanisms of the spindle checkpoint.
Raff
Jordan W
JW
Department of Genetics, Wellcome/Cancer Research UK Institute, Cambridge CB2 1QR, UK. j.raff@welc.cam.ac.uk
Jeffers
Kim
K
Huang
Jun-Yong
JY
D000818:Animals; D064200:Cdh1 Proteins; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D018385:Centrosome / Q000502:physiology; D019926:Cyclin B / Q000378:metabolism*; D004330:Drosophila; D029721:Drosophila Proteins; D005656:Fungal Proteins / Q000378:metabolism*; D049452:Green Fluorescent Proteins; D007700:Kinetics; D018386:Kinetochores / Q000502:physiology; D008164:Luminescent Proteins; D008870:Microtubules / Q000378:metabolism; D008954:Models, Biological; D017354:Point Mutation; D011506:Proteins / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D008941:Spindle Apparatus / Q000502:physiology
C577583:CDH1 protein, S cerevisiae; D064200:Cdh1 Proteins; D018797:Cell Cycle Proteins; C503698:CycB protein, Drosophila; D019926:Cyclin B; D029721:Drosophila Proteins; D005656:Fungal Proteins; D008164:Luminescent Proteins; D011506:Proteins; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D049452:Green Fluorescent Proteins