title: Cyclins E1 and E2 are required for endoreplication in placental trophoblast giant cells.
abstract: In mammalian cells, cyclin E-CDK2 complexes are activated in the late G1 phase of the cell cycle and are believed to have an essential role in promoting S-phase entry. We have targeted the murine genes CCNE1 and CCNE2, encoding cyclins E1 and E2. Whereas single knockout mice were viable, double knockout embryos died around midgestation. Strikingly, however, these embryos showed no overt defects in cell proliferation. Instead, we observed developmental phenotypes consistent with placental dysfunction. Mutant placentas had an overall normal structure, but the nuclei of trophoblast giant cells, which normally undergo endoreplication and reach elevated ploidies, showed a marked reduction in DNA content. We derived trophoblast stem cells from double knockout E3.5 blastocysts. These cells retained the ability to differentiate into giant cells in vitro, but were unable to undergo multiple rounds of DNA synthesis, demonstrating that the lack of endoreplication was a cell-autonomous defect. Thus, during embryonic development, the needs for E-type cyclins can be overcome in mitotic cycles but not in endoreplicating cells.
authors.affiliation: DNAX Research Institute, 901 California Avenue, Palo Alto, CA 94304, USA.
authors.forename: Tiziana
authors.initials: T
authors.lastname: Parisi
authors.forename: Andreas R
authors.initials: AR
authors.lastname: Beck
authors.forename: Nathalie
authors.initials: N
authors.lastname: Rougier
authors.forename: Tom
authors.initials: T
authors.lastname: McNeil
authors.forename: Linda
authors.initials: L
authors.lastname: Lucian
authors.forename: Zena
authors.initials: Z
authors.lastname: Werb
authors.forename: Bruno
authors.initials: B
authors.lastname: Amati
mesh_terms: D000818:Animals; D001483:Base Sequence; D002453:Cell Cycle / Q000502:physiology*; D002455:Cell Division; D019927:Cyclin E / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D016213:Cyclins / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D017931:DNA Primers; D018076:DNA, Complementary; D005260:Female; D015726:Giant Cells / Q000166:cytology*; D051379:Mice; D018345:Mice, Knockout; D008938:Mitosis; D010920:Placenta / Q000166:cytology*; D016133:Polymerase Chain Reaction; D011247:Pregnancy; D014327:Trophoblasts / Q000166:cytology*
chemical_list: C503689:Ccne2 protein, mouse; D019927:Cyclin E; D016213:Cyclins; D017931:DNA Primers; D018076:DNA, Complementary