Background:
The transition of chromatin from a transcriptionally repressive to permissive state is necessary for the onset of gene expression in the embryonic genome. Acetylation of histone 3 lysine 9 (H3K9ace) is involved in this process. H3K9ace is undetectable in oocytes and embryos that have just been fertilised. However, levels rise throughout early embryonic development and during the start of DNA replication. Interventions carried out during an in vitro fertilisation (IVF) process can impact this reprogramming.
Aim:
To investigate factors that may affect the amount of H3K9ace during early embryo development.
Methods:
Using quantitative indirect immunofluorescence, we measured the amount of H3K9ace in zygotes cultured in vitro in single step or sequential media (optimal and suboptimal). Additionally, IVF embryos, and embryos obtained after natural mating with and without fixing the culturing and the insemination time were tested.
Results:
In embryos obtained after natural mating H3K9ace expression was significantly greater in single step media compared to sequential media, irrespective of which media was used (optimal or suboptimal). However, using suboptimal sequential media increased the level of H3K9ace. Embryos obtained after IVF demonstrated a higher H3K9ace level compared to embryos obtained after natural mating. On the other hand, when the culture time between IVF and embryos obtained after natural mating was the same, we found an opposite effect. Additionally, narrowing the insemination period resulted in higher levels of H3K9ace in natural mating embryos.
Conclusion:
Our findings demonstrate that in vitro culture conditions induce disturbances in the epigenetic reprogramming and the impact is exacerbated when suboptimal media is used. This demonstrates that in vitro culture is the main adverse stressor on H3K9ace irrespective of the method of fertilisation, and affirms the usefulness of H3K9ace measurements as a biomarker of stress in the early embryo.