MS-681c

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.

Myosin light-chain kinase (MLCK) is a widely known kinase that controls the contraction of muscle cells. Whether MLCK is involved in the endocytosis of nanoparticles (NPs) has not been reported yet. NPs attract interest in many fields; most of them can induce autophagy and cytotoxicity after entering cells via endocytosis. In this study, we found that MLCK inhibitors, ML-7 and ML-9, abolished the endocytosis of silver NPs and yttrium oxide NPs in HeLa cells, and subsequently attenuated the autophagy induction and cytotoxicity caused by the NPs treatment. This is the first report that MLCK inhibitors acted as an endocytosis inhibitor and abolished the cell entry of NPs, which provided a new method for inhibiting the endocytosis of NPs.