title: Cell cycle duration at the time of maternal zygotic transition for in vitro produced bovine embryos: effect of oxygen tension and transcription inhibition.
abstract: Early embryonic cleavages are mostly regulated by maternal components then control of development progressively depends on newly synthesized zygotic products. The timing of the first cleavages is a way to assess embryo quality. The goal of this study was to evaluate the duration of the fourth cell cycle, at the time of maternal-to-zygotic transition (MZT) in in vitro-produced bovine embryos by means of cinematographic analysis. We found that 75% of the embryos displayed a long fourth cycle (43.5 +/- 5.4 h) whereas the remaining embryos had a very short fourth cell cycle (8.9 +/- 2.9 h). Both groups did not differ in cleavage rhythm up to the eight-cell stage and timing of cavitation and blastocyst expansion was identical. However, embryos with a short fourth cell cycle had a better blastocyst rate than embryos with a long cycle (59% versus 38%, P < 0.01). Total cell number, inner cell mass (ICM):total cell ratio, and hatching rate were identical for blastocysts produced from embryos with either a long or a short fourth cell cycle. In a second experiment, we showed that increasing the oxygen tension, from 5% to 20%, decreased the percentage of embryos with a short fourth cell cycle, from 25% to 11% (P < 0.01), indicating that suboptimal culture conditions can influence the length of this cycle. Finally, we investigated whether fourth cell cycle duration could be influenced by transcription inhibition. With alpha-amanitin added at 18 h postinsemination (HPI), cleavage was reduced (66% versus 79%) and, at 70 HPI, the 9- to 16-cell rate increased (50% versus 25%) concomitantly with a 5- to 8-cell rate decrease (16% versus 47%). A similar pattern was observed when the drug was added at 6 HPI or 42 HPI but not at 0 HPI. Cinematographic analysis revealed that alpha-amanitin increased the first cell cycle duration whereas the second and third cell cycles were not affected. With the drug, one third of the embryos could develop up to the 9- to 16-cell stage and they all had a short fourth cell cycle (11.2 +/- 3.7 h) with a good synchrony of cleavage between blastomeres. These results suggest that duration of the fourth cell cycle of bovine embryo, during the MZT, is under a zygotic transcriptional control that can be affected by oxidative conditions.
authors.affiliation: Unité Vétérinaire, Institut des Sciences de la Vie, Université Catholique de Louvain, Louvain-la-Neuve B-1348, Belgium. Lequarre@vete.ucl.ac.be
authors.forename: A S
authors.initials: AS
authors.lastname: Lequarre
authors.forename: J
authors.initials: J
authors.lastname: Marchandise
authors.forename: B
authors.initials: B
authors.lastname: Moreau
authors.forename: A
authors.initials: A
authors.lastname: Massip
authors.forename: I
authors.initials: I
authors.lastname: Donnay
mesh_terms: D000546:Amanitins / Q000494:pharmacology; D000818:Animals; D002417:Cattle; D002452:Cell Count; D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology*; D002467:Cell Nucleus / Q000502:physiology; D004622:Embryo, Mammalian / Q000502:physiology*; D005314:Embryonic and Fetal Development / Q000502:physiology; D005260:Female; D005307:Fertilization in Vitro; D018496:Hyperoxia / Q000503:physiopathology; D066298:In Vitro Techniques; D018715:Microscopy, Video; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D010100:Oxygen / Q000502:physiology*; D011247:Pregnancy; D012319:RNA Polymerase II / Q000037:antagonists & inhibitors; D017382:Reactive Oxygen Species / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D015053:Zygote / Q000187:drug effects / Q000502:physiology*
chemical_list: D000546:Amanitins; D019384:Nucleic Acid Synthesis Inhibitors; D017382:Reactive Oxygen Species; D012319:RNA Polymerase II; D010100:Oxygen