title: Cyclin E in centrosome duplication and reduplication in sea urchin zygotes.
abstract: When protein synthesis is completely blocked from before fertilization, the sea urchin zygote arrests in first S phase and the paternal centrosome reduplicates multiple times. However, when protein synthesis is blocked starting in prophase of first mitosis, the zygote divides and the blastomeres arrest in a G1-like state. The centrosome inherited from this mitosis duplicates only once in each blastomere for reasons that are not understood. The late G1 rise in cyclin E/cdk2 kinase activity initiates centrosome duplication in mammalian cells and its activity is needed for centrosome duplication in Xenopus egg extracts. Since the half-time for cyclin E turnover is normally approximately 1 h in sea urchin zygotes, the different behaviors of centrosomes during G1 and S phase arrests could be due to differential losses of cyclin E and its associated kinase activities at these two arrest points. To better understand the mechanisms that limit centrosome duplication, we characterize the levels of cyclin E and its associated kinase activity at the S phase and G1 arrest points. We first demonstrate that cyclin E/cdk2 kinase activity is required for centrosome duplication and reduplication in sea urchin zygotes. Next we find that cyclin E levels and cyclin E/cdk2 kinase activities are both constitutively and equivalently elevated during both the S phase and G1 arrests. This indicates that centrosome duplication during the G1 arrest is limited by a block to reduplication under conditions permissive for duplication. The cytoplasmic conditions of S phase, however, abrogate this block to reduplication.
authors.affiliation: Program in Molecular Biology and Biotechnology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA. schnackenbergbradley@uams.edu
authors.forename: Bradley J
authors.initials: BJ
authors.lastname: Schnackenberg
authors.forename: William F
authors.initials: WF
authors.lastname: Marzluff
authors.forename: Greenfield
authors.initials: G
authors.lastname: Sluder
mesh_terms: D000818:Animals; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D018385:Centrosome / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D019927:Cyclin E / Q000378:metabolism*; D051357:Cyclin-Dependent Kinase 2 / Q000378:metabolism; D016193:G1 Phase / Q000187:drug effects; D011687:Purines / Q000494:pharmacology; D000077546:Roscovitine; D016196:S Phase / Q000187:drug effects; D012617:Sea Urchins / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D015053:Zygote / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*
chemical_list: D019927:Cyclin E; D011687:Purines; D000077546:Roscovitine; D051357:Cyclin-Dependent Kinase 2