Over the past decades, there have been great advances in in vitro production (IVP) systems, with improved culture methods and new knowledge regarding embryo physiology, ultrastructure and morphology. Currently, the major obstacle associated with the extensive use of this technology is the great sensitivity of IVP embryos to cryopreservation. According to the literature, the reduced cryotolerance of IVP embryos is frequently associated with their high lipid content. Although is not clear until now how the lipid accumulation occurs, it may be influenced by the use of undefined culture media, supplemented with fetal calf serum (FCS); or as a result of embryo energy metabolism abnormalities that affect mitochondrial function, leading to the decrease in both the embryo quality and survival after cryopreservation. In this context, phenazine ethosulfate (PES), a reducer of NADPH electrons, which favours pentose–phosphate pathways and also inhibits the fatty acids synthesis, has been used to increase IVP embryo cryotolerance (Sudano et al. 2011 Theriogenology 75, 1211–1220). The aim of the present study was to evaluate the phenazine ethosulfate and FCS effect in the ultrastructure of IVP bovine embryos. A 2 × 2 factorial experiment design was used to test 2 FCS concentrations (0 or 10%) and the addition of PES (without or with PES) in the culture media. Slaughterhouse ovaries were used to obtain oocytes which were matured and fertilized in vitro (Day 0). Presumptive zygotes (n = 1440) were divided in 4 culture media: SOFaa without FCS; SOFaa without FCS + 0.3 μM PES (started on Day 4); SOFaa + 10% FCS; SOFaa + 10% FCS + 0.3 μM PES (started on Day 4). Embryo development was evaluated after 7 days under standard culture conditions (at 38.5°C in atmosphere of 5% O2, 5% CO2 and 90% N2). Transmission electron microscopy (TEM) was performed on Day-7 blastocysts from each group (n = 5) through standard protocol. For the statistical analysis, the arcsine transformation was applied to blastocyst percentage data and submitted to the ANOVA, followed by Tukeys' test through PROC GLM (SAS Institute Inc., Cary, NC, USA). In the absence of significant interactions, only main effect means are presented. The blastocyst production was not affected (P = 0.47) by the use of PES (42.7 ± 3.2 vs 39.3 ± 3.2, respectively for control and PES Day 4). The addition of 10% of FCS increased (P < 0.0001) the percentage of blastocysts (48.9 ± 3.2 vs 33.0 ± 3.2, respectively, for 10% and 0% of FCS). The ultrastructure analysis showed similar features in embryos from all studied groups. However, embryos cultured in the absence of FCS presented fewer and smaller lipid droplets. Moreover, embryos cultured without FCS presented more cellular debris in the perivitelinic space and in the blastocoele, indicating loss of blastomeres. The use of PES was able to reduce lipid droplets and increase the mitochondrial number in serum-produced embryos. Therefore, the PES decreased lipid content and increased mitochondrial number without affecting the development and ultrastructure of IVP bovine embryos.
FAPESP 09/54513-3, 10/09922-0.
Evaluation of Culture Media Limited in Nitrogen and Silicates on the Production Response and Lipid Content of the Diatom Chaetoceros muelleri
