Preimplantation Developmental Competence of Bovine and Porcine Oocytes Activated by Zinc Chelation

SIMPLE SUMMARY: Although naturally triggered by sperm, oocyte activation can be achieved artificially to improve the development of fertilized eggs, produce nuclear transfer embryos, and induce parthenogenetic development. Calcium and zinc are known to play an essential role in this process. Exploring the impact of oocyte artificial activation protocols on development across different mammalian models is critical before application to humans. Here, we report the production of bovine and porcine blastocysts by using a novel zinc chelator. Developmental rates and the expression of key transcription factors were compromised in bovine when using the zinc chelator compared to calcium-induced embryos. On the contrary, a new concentration and incubation time of the zinc chelator allowed higher developmental rates without affecting embryo quality in porcine. Our results contribute to understanding the role of zinc during oocyte activation and preimplantation embryo development across different mammalian species. ABSTRACT: After sperm-oocyte fusion, intracytoplasmic rises of calcium (Ca) induce the release of zinc (Zn) out of the oocyte (Zn sparks). Both phenomena are known to play an essential role in the oocyte activation process. Our work aimed to explore different protocols for activating bovine and porcine oocytes using the novel zinc chelator 1,10-phenanthroline (PHEN) and to compare developmental rates and quality to bovine IVF and parthenogenetic ionomycin-induced embryos in both species. Different incubation conditions for the zinc chelator were tested, including its combination with ionomycin. Embryo quality was assessed by immunofluorescence of SOX2, SOX17, OCT4, and CDX2 and total cell number at the blastocyst stage. Even though blastocyst development was achieved using a zinc chelator in bovine, bypassing calcium oscillations, developmental rates, and blastocyst quality were compromised compared to embryos generated with sperm-induced or ionomycin calcium rise. On the contrary, zinc chelation is sufficient to trigger oocyte activation in porcine. Additionally, we determined the optimal exposure to PHEN for this species. Zinc chelation and artificial induction of calcium rise combined did not improve developmental competence. Our results contribute to understanding the role of zinc during oocyte activation and preimplantation embryo development across different mammalian species.