Department of Obstetrics and Gynecology, Northwestern University Feinberg School of Medicine, Chicago, IL, USA.
Chemistry of Life Processes Institute, Northwestern University, Evanston, IL, USA.
Mol Hum Reprod. 2020 Apr 24;26(4):228-239. doi: 10.1093/molehr/gaaa017.
Zinc dynamics are essential for oocyte meiotic maturation, egg activation, and preimplantation embryo development. During fertilisation and egg activation, the egg releases billions of zinc atoms (Zn2+) in an exocytotic event termed the 'zinc spark'. We hypothesised that this zinc transport and exocytosis is dependent upon the intracellular trafficking of cortical granules (CG) which requires myosin-actin-dependent motors. Treatment of mature mouse and human eggs with ML-7, a myosin light chain kinase inhibitor (MLCK), resulted in an 80% reduction in zinc spark intensity compared to untreated controls when activated with ionomycin. Moreover, CG migration towards the plasma membrane was significantly decreased in ML-7-treated eggs compared with controls when activated parthenogenetically with ionomycin. In sperm-induced fertilisation via intracytoplasmic sperm injection (ICSI), ML-7-treated mouse eggs exhibited decreased labile zinc intensity and cortical CG staining. Collectively, these data demonstrate that ML-7 treatment impairs zinc release from both murine and human eggs after activation, demonstrating that zinc exocytosis requires myosin light chain kinase activity. Further, these results provide additional support that zinc is likely stored and released from CGs. These data underscore the importance of intracellular zinc trafficking as a crucial component of egg maturation necessary for egg activation and early embryo development.
锌动态对于卵母细胞减数分裂成熟、卵子激活和着床前胚胎发育至关重要。在受精和卵子激活过程中，卵子会通过一种称为“锌火花”的胞吐作用释放数十亿个锌原子（Zn2+）。我们假设这种锌的运输和胞吐作用依赖于皮质颗粒（CG）的细胞内运输，这需要肌球蛋白-肌动蛋白依赖性马达。用肌球蛋白轻链激酶抑制剂（MLCK）ML-7 处理成熟的小鼠和人卵，与未处理的对照组相比，在用离子霉素激活时，锌火花强度降低了 80%。此外，与对照组相比，在用离子霉素进行部分激活时，ML-7 处理的卵子中 CG 向质膜的迁移明显减少。在通过胞浆内单精子注射（ICSI）进行的精子诱导受精中，ML-7 处理的小鼠卵子表现出不稳定锌强度和皮质 CG 染色减少。总的来说，这些数据表明，ML-7 处理会在激活后损害来自小鼠和人卵的锌释放，表明锌胞吐作用需要肌球蛋白轻链激酶活性。此外，这些结果进一步支持锌可能来自 CG 存储和释放。这些数据强调了细胞内锌运输作为卵子成熟的关键组成部分的重要性，这对于卵子激活和早期胚胎发育是必要的。
