Site specificity of blastocyst hatching significantly influences pregnancy outcomes in mice

Effect of blastocyst development on hatching and embryo implantation

The mammalian zygote, formed after a sperm fertilizes an egg, undergoes several rounds of mitosis and morphogenesis to form the blastocyst. During the peri-implantation period, the blastocyst hatches out of the zona pellucida (ZP) and invades the receptive uterine endometrium. This process promotes maternal-fetal dialogue at the physiological and molecular level, thereby initiating the implantation process. Blastocyst hatching is a consequence of elevated osmotic pressure due to active Na+/K+ ion transporter in the blastocyst cavity, as well as proteases produced by trophectoderm (TE) that hydrolyze the ZP. This review summarizes the process underpinning blastocyst hatching, such as the hatching schedule, the location of TEs during initial hatching out of the ZP, the molecules involved in blastocyst hatching, and how these processes affect implantation events. Additionally, we focus on identifying crucial molecules that may influence the quality of implantation and predict the outcome of embryo implantation. Further understanding the mechanism of these molecules may help us to improve the efficiency of Assisted reproductive technology (ART) in livestock breeding. This review provides insight into embryonic development, specifically during the short-term process of blastocyst hatching and its effects on the following implantation.

Overcoming the H4K20me3 epigenetic barrier improves somatic cell nuclear transfer reprogramming efficiency in mice

Epigenetic reprogramming during fertilization and somatic cell nuclear transfer (NT) is required for cell plasticity and competent development. Here, we characterize the epigenetic modification pattern of H4K20me3, a repressive histone signature in heterochromatin, during fertilization and NT reprogramming. Importantly, the dynamic H4K20me3 signature identified during preimplantation development in fertilized embryos differed from NT and parthenogenetic activation (PA) embryos. In fertilized embryos, only maternal pronuclei carried the canonical H4K20me3 peripheral nucleolar ring-like signature. H4K20me3 disappeared at the 2-cell stage and reappeared in fertilized embryos at the 8-cell stage and in NT and PA embryos at the 4-cell stage. H4K20me3 intensity in 4-cell, 8-cell, and morula stages of fertilized embryos was significantly lower than in NT and PA embryos, suggesting aberrant regulation of H4K20me3 in PA and NT embryos. Indeed, RNA expression of the H4K20 methyltransferase Suv4-20h2 in 4-cell fertilized embryos was significantly lower than NT embryos. Knockdown of Suv4-20h2 in NT embryos rescued the H4K20me3 pattern similar to fertilized embryos. Compared to control NT embryos, knockdown of Suv4-20h2 in NT embryos improved blastocyst development ratios (11.1% vs. 30.5%) and full-term cloning efficiencies (0.8% vs. 5.9%). Upregulation of reprogramming factors, including Kdm4b, Kdm4d, Kdm6a, and Kdm6b, as well as ZGA-related factors, including Dux, Zscan4, and Hmgpi, was observed with Suv4-20h2 knockdown in NT embryos. Collectively, these are the first findings to demonstrate that H4K20me3 is an epigenetic barrier of NT reprogramming and begin to unravel the epigenetic mechanisms of H4K20 trimethylation in cell plasticity during natural reproduction and NT reprogramming in mice.

Development of a Microfluidic Chip Powered by EWOD for In Vitro Manipulation of Bovine Embryos

Digital microfluidics (DMF) holds great potential for the alleviation of laboratory procedures in assisted reproductive technologies (ARTs). The electrowetting on dielectric (EWOD) technology provides dynamic culture conditions in vitro that may better mimic the natural embryo microenvironment. Thus far, EWOD microdevices have been proposed for in vitro gamete and embryo handling in mice and for analyzing the human embryo secretome. This article presents the development of the first microfluidic chip utilizing EWOD technology designed for the manipulation of bovine embryos in vitro. The prototype sustains the cell cycles of embryos manipulated individually on the chips during in vitro culture (IVC). Challenges related to the chip fabrication as well as to its application during bovine embryo IVC in accordance with the adapted on-chip protocol are thoroughly discussed, and future directions for DMF in ARTs are indicated.