MAP kinase dependent cyclinE/cdk2 activity promotes DNA replication in early sea urchin embryos.
Sea urchins provide an excellent model for studying cell cycle control mechanisms governing DNA replication in vivo. Fertilization and cell cycle progression are tightly coordinated by Ca(2+) signals, but the mechanisms underlying the onset of DNA replication after fertilization remain less clear. In this study we demonstrate that calcium-dependent activation of ERK1 promotes accumulation of cyclinE/cdk2 into the male and female pronucleus and entry into first S-phase. We show that cdk2 activity rises quickly after fertilization to a maximum at 4 min, corresponding in timing to the early ERK1 activity peak. Abolishing MAP kinase activity after fertilization with MEK inhibitor, U0126, substantially reduces the early peak of cdk2 activity and prevents cyclinE and cdk2 accumulation in both sperm pronucleus and zygote nucleus in vivo. Both p27(kip1) and roscovitine, cdk2 inhibitors, prevented DNA replication suggesting cdk2 involvement in this process in sea urchin. Inhibition of cdk2 activity using p27(kip1) had no effect on the phosphorylation of MBP by ERK, but completely abolished phosphorylation of retinoblastoma protein, a cdk2 substrate, indicating that cdk2 activity is downstream of ERK1 activation. This pattern of regulation of DNA synthesis conforms to the pattern observed in mammalian somatic cells.
Kisielewska
J
J
The Institute for Cell and Molecular Biosciences, Medical School, Faculty of Medical Sciences, Newcastle University, Framlington Place, NE2 4HH, Newcastle upon Tyne, UK.
Philipova
R
R
Huang
J-Y
JY
Whitaker
M
M
D000818:Animals; D019927:Cyclin E / Q000502:physiology*; D051357:Cyclin-Dependent Kinase 2 / Q000502:physiology*; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000502:physiology; D004261:DNA Replication; D004625:Embryo, Nonmammalian / Q000201:enzymology; D005260:Female; D047331:Lytechinus / Q000196:embryology*; D020935:MAP Kinase Signaling System; D008297:Male; D051379:Mice; D008845:Microinjections; D018809:Proliferating Cell Nuclear Antigen / Q000502:physiology; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000502:physiology; D016160:Retinoblastoma Protein / Q000502:physiology; D016196:S Phase
D019927:Cyclin E; D018809:Proliferating Cell Nuclear Antigen; D011993:Recombinant Fusion Proteins; D016160:Retinoblastoma Protein; D050760:Cyclin-Dependent Kinase Inhibitor p27; D051357:Cyclin-Dependent Kinase 2