Cyclin E and its associated cdk activity do not cycle during early embryogenesis of the sea Urchin.
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.
Sumerel
J L
JL
Program in Molecular Biology and Biotechnology, University of North Carolina, Chapel Hill, North Carolina 27599, USA.
Moore
J C
JC
Schnackenberg
B J
BJ
Nichols
J A
JA
Canman
J C
JC
Wessel
G M
GM
Marzluff
W F
WF
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
D019927:Cyclin E; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases