OIVC medium enhances developmental competence in porcine preimplantation embryos

The developmental capacity of in vitro embryos is critical for the success of embryonic biotechnology. However, in vitro embryos often exhibit suboptimal quality, with fewer inner cell mass (ICM) cells and reduced total blastocyst cell counts compared to in vivo embryos. To address this, we optimized the conventional PZM-3 culture medium by supplementing 50% Advanced DMEM/F12 and 5% FBS on the fifth day after embryo activation (Day 5 medium) and resulted in a 2.5-fold increase in the total cell numbers of parthenogenetic activation (PA) derived blastocysts. Further enhancement was achieved by incorporating Activin A in Day 5 medium, creating the OIVC (Optimized In Vitro Culture) medium, which significantly increased both the total cell numbers and the ICM cell counts by 4.5-fold in the blastocyst stage. The OIVC medium also improved the quality of pig somatic cloned and in vitro fertilized (IVF) embryos. RNA sequencing analysis revealed that in the OIVC-treated embryos, most of the differentially expressed genes were downregulated compared to the control group, with the main enriched signaling pathways including Activin A/TGF-β. Notably, among these downregulated genes, PAX6 may be as a potential key gene influencing the number of ICM cells. This study presents a novel culture system that markedly enhances pig in vitro embryo quality, providing an efficient strategy for generating cloned pigs based on somatic cell nuclear transfer (SCNT) technology.