In-vivo development of embryos occurs in the absence of light. Time-lapse imaging enables observation of embryo development and uses low energy wavelengths. However, more informative photonic assays like hyperspectral analysis use wavelengths of higher energy light, which can cause DNA damage, mitochondrial degeneration, increased reactive oxygen species production and blastomere apoptosis, thus lowering implantation potential of embryos. We hypothesised that exposing embryos to discrete wavelengths of light delivered at the same energy (1Joule/cm2/day) causes differences in embryo development rates. We assessed the toxicity of these wavelengths by determining cleavage and blastocyst development rates, cell numbers and DNA damage.
CBAF1 mice one cell presumptive zygotes were collected and cultured (5% O2) until day 5. Embryos were exposed to light emitting diodes of Blue (616nm, 52sec), Green (525nm, 105sec), Yellow (590nm, 213sec) and Red (616nm, 83sec) wavelengths, delivering a total 1Joule/cm2/day of energy from days 1-5. Cleavage and blastocyst rates were recorded. To determine inner cell mass and trophectoderm cell numbers, blastocysts were differentially stained. To measure the incidence of DNA strand breaks, histone modification antibody (γH2AX) was used. Area (in pixels) for γH2AX and DAPI positive cells was calculated using FIJI image analysis. Statistical significance (p<0.05) was analysed using GraphPad Prism.
Exposing embryos to the yellow wavelength had a significant impact by reducing cleavage (p<0.01) and blastocyst rates (p<0.05) when compared to control. No significant difference in cell numbers was noted across treatment groups when differentially stained, but DNA damage was evident across all treatments when stained for DNA strand breaks.
Our data demonstrates that yellow light illumination at an equivalent energy level as other wavelengths, impedes embryo development, with reduced cleavage and blastocyst rates. Exposing embryos to all wavelengths of light in this study caused significant cell DNA damage, which may impact implantation potential of embryos.