Influence of bisphenol S on quality of mouse oocytes and embryos

Bc. Eliška Koutná

Master's thesis

Abstract:

Well-known endocrine disruptor (ED) bisphenol A (BPA) and its adverse effects were already described and as a result, a lot of plastics are now BPA-free. However, BPA has been replaced with its analogue bisphenol S (BPS), and its effects on reproduction and development are not fully known yet. The aim of the thesis was to test the hypothesis that in vivo exposure to low doses of BPS affects non-genomic and epigenetic markers of murine oocytes, 2-cell embryos, and early blastocysts. 5-week-old female ICR mice were administered with four different BPS concentrations (0; 0.001; 0.1; 10; 100 ng . g bw-1 . day-1) in 4-week exposure window. Oocytes were isolated after hormonal stimulation with eCG and hCG. Alternatively, hormonally stimulated mice were mated and 2-cell embryos/early blastocysts were obtained 1,5/4,5 days after mating, respectively. Oocytes and embryos were subjected to immunocytochemistry staining and imaging on confocal microscope with spinning disc (Olympus, Germany) for visualization of spindle α-tubulin, pericentrin, 5-methylcytosine and specific histone modifications. Fluorescence signal intensity was quantified and assessed in ImageJ software (NIH, USA). The results showed significant affection of meiotic spindle structure as well as altered genome-wide methylation levels in both oocytes and embryos. Methylation levels of histone H3K4 (H3K4me2) in MII oocytes and H3K9 (H3K9me3) in 2-cell embryos, as well as heterochromatin protein 1 (HP1) amount in blastocysts, varied significantly from the control group. All of these effects were the most profound with BPS dose as low as 0.1 ng . g bw-1 . day-1 and manifested in non-linear dose-response manner. Results suggest that the environmentally relevant doses of BPS pose a risk for female reproduction and their offspring through epigenetic-driven transgenerational effect. Further usage of BPA analogues should be critically assessed in concern of global human health and environmental pollution.

Keywords

bisphenol S, oocyte, embryo, fertilization, embryonic development, epigenetics

Language used: English

Date on which the thesis was submitted / produced: 13. 4. 2018

Thesis defence

• Supervisor: prof. Ing. Jaroslav Petr, DrSc.

Czech University of Life Sciences Prague

Faculty of Agrobiology, Food and Natural Resources

Master programme / field:
Genetic Technologies and Breeding / Biotechnology of Reproduction