58 Effect of different light sources on the developmental capacity of bovine embryos produced in vitro

Abstract

Under natural conditions, mammalian oocytes and zygotes are never exposed to daylight or artificial light. During assisted reproductive procedures such as in vitro production (IVP), oocytes and pre-implantation embryos are exposed to light from time to time before being transferred to recipients. The detrimental effect of visible light is not directly related to the intensity and exposure time, but is also a function of the spectral composition of the light. Recently, a green pass light filter was used during all steps of bovine IVP. Results indicated the protective effect of the filter against harmful blue and infrared regions of the light (Korhonen et al. 2009 Hum Reprod. 24, 308-314; https://doi.org/10.1093/humrep/den432). Data regarding either blue or infrared light are missing. Therefore, the effect of environmental light will be examined on the developmental capacity of bovine oocytes and pre-implantation embryos produced in vitro. Three different experimental conditions were set during all IVP steps: (i) light from the microscope filtered with a red pass filter, no artificial light, and no daylight, (ii) artificial light without day light, light from the microscope without a filter, and (iii) artificial and daylight, light from the microscope without a filter, as normally used in the laboratory (control). Bovine cumulus-oocyte complexes were recovered from abattoir-derived ovaries by the slicing method. After 24 h of maturation, fertilisation was realised and after 19 h of co-culture of cumulus-oocyte complexes and sperm, presumptive zygotes were cultured in SOFaa for 8 days. Cleavage and developmental rates were recorded at Day 3 and Day 7/8 (Day 0 = IVF, 10 IVP runs). Blastocysts from all groups were individually stored at −80°C until analyses. Then RT-qPCR (at least 12 replicates) was performed as described previously (Stinshoff et al. 2014 Reprod. Fertil. Dev. 26, 502-510; https://doi.org/10.1071/RD12372) for gene transcripts related to cellular stress (BAX, BCL2L1, HSPA1A, SOD1) and embryo developmental capacity (SLC2A3). The morphological quality of expanded blastocyst was assessed via a differential staining procedure (with propidium iodide and Hoechst, 4 replicates) to determine the number of inner cell masses (ICM), trophectoderms (TE), and total cells and to calculate the ICM/TE ratio. Data were analysed by analysis of variance followed by a Tukey test. Cleavage and developmental rates were similar in all groups of embryos (P > 0.05). The relative abundance of all analysed gene transcripts was significantly increased (P ≤ 0.05) in blastocysts stemming from settings (i) and (ii) compared with those from the control group. Blastocysts generated using only artificial light or artificial and daylight did show a significantly increased number of ICM and total cells (86.3 ± 3.2, 56.3 ± 1.4; 183.6 ± 4.0, 161.8 ± 2.8) compared with embryos produced under filtered microscope light without any other light (35.3 ± 0.8; 133.8 ± 1.4; P ≤ 0.05). The number of TE cells was similar (P > 0.05) in blastocysts of all groups (i: 98.5 ± 1.3; ii: 97.3 ± 2.6; iii (control): 105.5 ± 2.4). These data suggest that day light exposure might influence bovine embryos at the molecular level, whereas the morphological quality seems to be unaffected when compared with embryos exposed to only artificial light.