Skip to main content

NUANCE: Nanoscale Characterization Experimental Center

NUANCE Staff Co-Author “Paradigm-Shifting” Research Paper on the Role of Zinc Sparks in Egg Fertilization.

A Northwestern-based team of researchers, led by Teresa Woodruff and Thomas O’Halloran, recently published a paper in Integrative Biology. The article, entitled “Zinc sparks induce physiochemical changes in the egg zona pellucida that prevent polyspermy,” was featured in this month’s issue of Chemistry World.

The research revealed a previously unidentified factor in the prevention of polyspermy (the entrance of multiple sperm, with disastrous consequences for the fertilized egg) in mammals: zinc sparks.

Almost immediately after fertilization, billions of zinc ions are emitted from the egg cell and pass through the zona pellucida (ZP), the glycoprotein matrix immediately surrounding the egg. Using innovative imaging techniques involving SEM and TEM equipment at the NUANCE EPIC facility, Woodruff and O’Halloran’s team was able to show that these zinc sparks alter the structure of the ZP, hardening it and thus preventing sperm from binding to it.

image from paper
SEM image produced using EPIC’s Hitachi SU8030 FE, showing an increase in fiber thickness in the zona pellucida of Methaphase II (MII) eggs.


Previously, the hardening of the zona pellucida was solely attributed to the work of enzymes released in the cortical reaction. The discovery of zinc’s role thus represents a paradigm shift in our understanding of ZP hardening, the authors claim. The findings have already sparked further research and may have considerable practical implications, such as higher success rates in IVF treatments.

Listed among the authors are NUANCE’s Eric W. Roth, Bio-Cryo Electron Microscopy Specialist, and Dr. Reiner Bleher, BioCryo Manager at the EPIC facility.

The full version of the article (available here) is freely accessible until 9 March 2017.