The formation of aggregated chromatin/chromosomes in mouse oocytes treated with high concentration of IBMX as a model for a chromosome transfer in human

Abstract

The presence of cyclic adenosine monophosphate (cAMP) has been considered to be a fundamental factor in ensuring meiotic arrest prior to ovulation. cAMP is regarded as a key molecule in the regulation of oocyte maturation. However, it has been reported that increased levels of intracellular cAMP can result in abnormal cytokinesis, with some MI oocytes leading to symmetrically cleaved 2-cell MII oocytes. Consequently, we aimed to investigate the effects of elevated intracellular cAMP levels on abnormal cytokinesis and oocyte maturation during the meiosis of mouse oocytes. This study found that a high concentration of isobutylmethylxanthine (IBMX) also caused chromatin/chromosomes aggregation (AC) after the first meiosis. The rates of AC increased the greater the concentration of IBMX. In addition, AC formation was found to be reversible, showing that the re-formation of the spindle chromosome complex was possible after the IBMX was removed. In human oocytes, the chromosomes aggregate after the germinal vesicle breakdown and following the first and second polar body extrusions (the AC phase), while mouse oocytes do not have this AC phase. The results of our current study may indicate that the AC phase in human oocytes could be related to elevated levels of intracytoplasmic cAMP.

Keywords:

• Cyclic adenosine monophosphate (cAMP)
• chromosome aggregation
• chromatin
• meiosis
• IBMX

Acknowledgment

We appreciate Ms. Moemi Tsukano for her technical help with transmission electron microscopy.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Authors’ contributions

Conceptualization: JO; funding acquisition: WX; investigation: WX, SA, RO; supervision: JO; writing: WX, JO.

Data availability statement

The data that support the findings of this study are available from the corresponding author, JO, upon reasonable request.

Additional information

Funding

This study was funded by a Guideline Research Grant for the encouragement of students, the Graduate School of Environmental and Life Science, Okayama University.