Cell Cycle Duration at the Time of Maternal Zygotic Transition for In Vitro Produced Bovine Embryos: Effect of Oxygen Tension and Transcription Inhibition1

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.

Temporal detection of caspase-3 and -7 in bovine in vitro produced embryos of different developmental capacity

“…Fast cleaving bovine embryos have an altered gene expression (Lonergan et al 2000, Ward et al 2001, Gutiérrez-Adán et al 2004, Dode et al 2006 or altered polyadenylation status of several developmentally important gene transcripts (Pocar et al 2001, Brevini-Gandolfi et al 2002 and a higher chance of reaching advanced developmental stages in comparison with late cleaving embryos (Van Soom et al 1992, Dinnyés et al 1999, Lequarré et al 2003, Favetta et al 2004, Gutiérrez-Adán et al 2004. Studies investigating the effect of developmental kinetics on the incidence of apoptosis during preimplantation embryo development in bovine are scarce.…”

“…1). The time points and criteria for the selection of fast or slow developing embryos were determined on the basis of previous studies in similar culture conditions (Dinnyés et al 1999, Yoshioka et al 2000, Lequarré et al 2003 and verified in a preliminary experiment (data not shown).…”

Correlation of the Mitochondrial Activity of Two‐Cell Embryos Produced In Vitro and the Two‐Cell Block In Kunming and B6C3F1 Mice

“…In particular, when the early bovine embryo was cultured in an atmosphere containing 20% oxygen, gene activation was greatly inhibited (Lequarre et al, 2003). Hamster one-cell embryos and mouse two-cell embryos can overcome the two-cell block when cultured under low oxygen tension and with added antioxidants (Noda et al, 1991;Umaoka et al, 1993).…”

“…There have been abundant reports that early embryo blocks are related to increased reactive oxygen species (ROS) levels (Noda et al, 1991;Umaoka et al, 1993;Lequarre et al, 2003). Glutamine and hypotaurine have been shown to improve intracellular oxidative status and in vitro development of porcine preimplantation embryos (Suzuki et al, 2007), and the free radical scavenger, glutathione (GSH), has been employed to ameliorate the two-cell block in mouse embryo culture (Legge and Sellens, 1991).…”

Effect of follicular diameter, time of first cleavage and H3K4 methylation on embryo production rates of Bos indicus cattle

“…A possible explanation for the disparity between the results of in vitro and in vivo embryo production is the source of the oocytes (LEQUARRE et al, 2005). The majority of available ovarian follicles that are punctured during the aspiration process are small follicles; however, during physiological events, the fertilized oocyte comes from a dominant, large follicle (GONÇALVES et al, 2007).…”