An interdisciplinary team invoked chemical principles and methods to demonstrate that the metal zinc plays a crucial role in fertilization in humans and other mammals.  This team, led by Tom O’Halloran (chemistry) and Teresa Woodruff (obstetrics and gynecology), have opened a new window into the process of fertilization – showing that bursts of zinc released within minutes of fertilization stop reproductive chaos by preventing multiple sperm from binding to eggs.

Entry of a second or third sperm is a disaster for the egg as it leads to polyspermy. Polyspermy contributes to miscarriages and birth defects in mammals, as the zygote inherits an unviable amount of DNA.

The team first witnessed the almost immediate efflux of billions of zinc ions upon mammalian egg fertilization with x-ray fluorescence microscopy in 2010. These zinc sparks look like supernovae. Diffusing away from the cell’s membrane, the zinc ions encounter the zona pellucida, a glycoprotein matrix surrounding the egg. Now the team has revealed that zinc retained by the zona pellucida induces changes that harden its protein structure within 30–60 minutes of fertilization, making it more resistant to sperm binding.

The magnitude of zinc fluxes correlates with egg quality and suggests these findings have a number of implications for research on how to improve the success rate of in vitro fertilization [IVF].