Synaptotagmin 1 regulates cortical granule exocytosis during mouse oocyte activation.

Xiu-Lan Zhu,Ying-Chun Ouyang,Shi-Fen Li,Hong Xu,Feng-Hua Liu,Yan-Hong Yi,Chun-Hui Zhang,Yi Hou,Yan-Qun Luo,Heide Schatten,Zhen-Bo Wang,Xi-Qian Zhang,Li-Juan Lv

doi:10.1017/s0967199419000704

Abstract

Synaptotagmin 1 (Syt1) is an abundant and important presynaptic vesicle protein that binds Ca2+ for the regulation of synaptic vesicle exocytosis. Our previous study reported its localization and function on spindle assembly in mouse oocyte meiotic maturation. The present study was designed to investigate the function of Syt1 during mouse oocyte activation and subsequent cortical granule exocytosis (CGE) using confocal microscopy, morpholinol-based knockdown and time-lapse live cell imaging. By employing live cell imaging, we first studied the dynamic process of CGE and calculated the time interval between [Ca2+]i rise and CGE after oocyte activation. We further showed that Syt1 was co-localized to cortical granules (CGs) at the oocyte cortex. After oocyte activation with SrCl2, the Syt1 distribution pattern was altered significantly, similar to the changes seen for the CGs. Knockdown of Syt1 inhibited [Ca2+]i oscillations, disrupted the F-actin distribution pattern and delayed the time of cortical reaction. In summary, as a synaptic vesicle protein and calcium sensor for exocytosis, Syt1 acts as an essential regulator in mouse oocyte activation events including the generation of Ca2+ signals and CGE.

Highlights

Synaptotagmins (Syts) are a highly conserved family of proteins in many species (Glavan et al, 2009)
We found that Synaptotagmin 1 (Syt1) depletion affected intracellular [Ca2þ]i oscillations, the filamentous actin (F-actin) distribution pattern and cortical granules (CGs) exocytosis
Syt1 was distributed in the same pattern as that at of CGs. Both were located beneath the oolemma except for the area under which the spindle was located at the animal pole

Summary

Introduction

Synaptotagmins (Syts) are a highly conserved family of proteins in many species (Glavan et al, 2009). Syt is an abundant protein in synaptic vesicle membrane and plays an essential role in neurotransmitter release by Ca2þ-binding to the C2B domain (Perin et al, 1990; Leguia et al, 2006). The C2AB portion of Syt was determined and it was shown that it could self-assemble into Ca2þ-sensitive ring-like oligomers on membranes to regulate neurotransmitter release (Zanetti et al, 2016). Syt regulates the neuronal polarity and axon differentiation in hippocampal neurons (Inoue et al, 2015). These findings show that Syt plays an important role in the exocytosis of neurotransmitter and endocrine granules in neurons and neuroendocrine cells. We hypothesized that Syt is involved in the exocytosis of cortical granules (CGs) during mouse egg activation

Methods

Results

Discussion

Conclusion