ZP3 and Empty ovarian follicle: While early studies of murine Zp3 KO and null mutations showed that it is essential for zona pellucida (ZP) formation and oocyte ovulation along cumulus complexes36,37, recently described Zp3 mutations in human patients led to empty follicle syndrome (EFS), where no oocytes could be retrieved from patients’ ovarian follicles following hormonal stimulation.