title: Cyclin E and its associated cdk activity do not cycle during early embryogenesis of the sea Urchin.
abstract: Female sea urchins store their gametes as haploid eggs. The zygote enters S-phase 1 h after fertilization, initiating a series of cell cycles that lack gap phases. We have cloned cyclin E from the sea urchin Strongylocentrotus purpuratus. Cyclin E is synthesized during oogenesis, is present in the germinal vesicle, and is released into the egg cytoplasm at oocyte maturation. Cyclin E synthesis is activated at fertilization, although there is no increase in cyclin E protein levels due to continuous turnover of the protein. Cyclin E protein levels decline in morula embryos, while cyclin E mRNA levels remain high. After the blastula stage, cyclin E mRNA and protein levels are very low, and cyclin E expression is predominant only in cells that are actively dividing. These include cells in the left coelomic pouch, which forms the adult rudiment in the embryo. The cyclin E present in the egg is complexed with a protein kinase. Activity of the cyclin E/cdk2 changes little during the initial cell cycles. In particular, cyclin E-cdk2 levels remain high during both S-phase and mitosis. Our results suggest that progression through the early embryonic cell cycles in the sea urchin does not require fluctuations in cyclin E kinase activity.
authors.affiliation: Program in Molecular Biology and Biotechnology, University of North Carolina, Chapel Hill, North Carolina 27599, USA.
authors.forename: J L
authors.initials: JL
authors.lastname: Sumerel
authors.forename: J C
authors.initials: JC
authors.lastname: Moore
authors.forename: B J
authors.initials: BJ
authors.lastname: Schnackenberg
authors.forename: J A
authors.initials: JA
authors.lastname: Nichols
authors.forename: J C
authors.initials: JC
authors.lastname: Canman
authors.forename: G M
authors.initials: GM
authors.lastname: Wessel
authors.forename: W F
authors.initials: WF
authors.lastname: Marzluff
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D042846:CDC2-CDC28 Kinases; D002451:Cell Compartmentation; D002455:Cell Division; D019927:Cyclin E / Q000378:metabolism*; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D004625:Embryo, Nonmammalian / Q000166:cytology / Q000378:metabolism; D005260:Female; D005306:Fertilization; D008297:Male; D008969:Molecular Sequence Data; D009866:Oogenesis; D010063:Ovum / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D012617:Sea Urchins / Q000196:embryology*; D017386:Sequence Homology, Amino Acid; D014018:Tissue Distribution
chemical_list: D019927:Cyclin E; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases