Abstract
During fertilization or chemically-induced egg activation, the mouse egg releases billions of zinc atoms in brief bursts known as ‘zinc sparks.' The zona pellucida (ZP), a glycoprotein matrix surrounding the egg, is the first structure zinc ions encounter as they diffuse away from the plasma membrane. Following fertilization, the ZP undergoes changes described as ‘hardening', which prevent multiple sperm from fertilizing the egg and thereby establish a block to polyspermy. A major event in zona hardening is cleavage of ZP2 proteins by ovastacin; however, the overall physiochemical changes contributing to zona hardening are not well understood. Using X-ray fluorescence microscopy, transmission and scanning electron microscopy, and biological function assays, we tested the hypothesis that zinc release contributes to ZP hardening. We found that the zinc content in the ZP increases by 300% following activation and that zinc exposure modulates the architecture of the ZP matrix. Importantly, zinc-induced structural changes of the ZP have a direct biological consequence; namely, they reduce the ability of sperm to bind to the ZP. These results provide a paradigm-shifting model in which fertilization-induced zinc sparks contribute to the polyspermy block by altering conformations of the ZP matrix. This adds a previously unrecognized factor, namely zinc, to the process of ZP hardening.
Original language | English (US) |
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Pages (from-to) | 135-144 |
Number of pages | 10 |
Journal | Integrative Biology (United Kingdom) |
Volume | 9 |
Issue number | 2 |
DOIs | |
State | Published - Feb 2017 |
Funding
We thank the Oncofertility Academy programs (https://oncofertility.northwestern.edu/oncofertility-saturday-academies) and science teacher Carole Namowicz and her students from Lindblom Math and Science Academy (Chicago, IL) for help with XFM experiments, Jurrien Dean for providing us with ZP2 antibody, and Luca Jovine for discussions of ZP3 structural data. Electron microscopy was performed in the EPIC facility (NUANCE Center-Northwestern University), which has received support from the MRSEC program (NSF DMR-1121262) at the Materials Research Center; the International Institute for Nanotechnology (IIN); and the State of Illinois, through the IIN. This work was supported by a Medical Research Award from the W. M. Keck Foundation, the Chemistry of Life Processes Cornew Innovation Fund a SPARK Award from the Chicago Biomedical Consortium, and the National Institutes of Health (P01 HD021921, GM38784, GM115848, GM038784, U54P50HD076188, and T32GM105538). This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357
ASJC Scopus subject areas
- Biophysics
- Biochemistry