In vitro Activation of Mouse Oocytes through Intracellular Ca2+ Regulation

J Hum Reprod Sci. Apr-Jun 2020;13(2):138-144. doi: 10.4103/jhrs.JHRS_122_19. Epub 2020 Jul 9.

Abstract

Background: Ca2+ signaling pathway is suggested to play an essential role in mediating oocyte maturation.

Aims: The aim of this study was to evaluate intracellular Ca2+ of resistant immature oocytes that failed to resume meiosis following subsequent in vitro culture reach metaphase II after calcium ionophore A23187 activation.

Settings and design: This in vitro analytical experimental study was conducted at Animal Science Laboratory of Indonesian Medical Education and Research Institute (IMERI), Human Reproductive Infertility and Family Planning of IMERI, and Electrophysiology Imaging of Terpadu Laboratory, Faculty of Medicine, University of Indonesia.

Methods: A total of 308 oocytes classed as resistant immature following in vitro culture were randomly allocated to control (n = 113) and treatment groups (n = 195). The oocyte activation group was exposed to A23187 solution for 15 min and then washed extensively. Maturation was evaluated by observing the first polar body extrusion 20‒24 h after A23187 exposure. Ca2+ imaging was conducted using a confocal laser scanning microscope to identify the dynamic of Ca2+ response.

Statistical analysis: SPSS 20, Chi-square, and Mann-Whitney U-test were used in this study.

Results: Activation of resistant immature oocytes with A23187 significantly increased the number of oocyte maturation compared with the control group (P < 0.001). Furthermore, fluorescent intensity measurements exhibited a significant increase in the germinal vesicle stage when activated (P = 0.005), as well as the metaphase I stage, even though differences were not significant (P = 0.146).

Conclusion: Artificial activation of resistant immature oocyte using chemical A23187/calcimycin was adequate to initiate meiosis progress.

Keywords: Artificial oocyte activation; Ca2+ signaling; calcimycin; calcium ionophore A23187; meiotic arrest.