Endoplasmic Reticulum Stress Inducer Tunicamycin Reduces Porcine Embryo Development by Disturbing Blastocoel Formation and Expansion

The formation and expansion capacity of blastocysts plays a very important role in successful implantation. During mammalian embryo development derived from in vitro production (IVP), early embryos are highly susceptible to various cellular stresses, including endoplasmic reticulum (ER) stress, which has been identified in IVP embryos, suggesting that ER stress modulation is crucial for IVP embryo development. In this study, we aimed to evaluate the influences of ER stress on preimplantation embryos during blastocyst formation and expansion potential in pigs. Tunicamycin (TM), an ER stress inducer, was employed in porcine embryos, significantly increasing the mRNA levels of ER stress-related markers ATF6, CHOP, and GRP78. When one-cell embryos were cultured in the presence of TM, the blastocyst formation and diameter (reflecting the blastocyst expansion capacity) were significantly inhibited in a dose-dependent manner. When morula-stage porcine embryos were cultured in TM, the blastocyst formation rate, blastocyst diameter, total cells and EdU-positive cell numbers were significantly lower than the TM-free control group. TM reduced the potential of blastocoel recovery (ex-expansion) in blastocysts collapsed by cytochalasin D and impeded blastocyst expansion. In addition, TM reduced the mRNA levels of CDH1 and TJP1 and affected the normal expression pattern of E-cadherin, Oct4, Sox2 and Cdx2 in porcine blastocysts. Taken together, these findings suggest that TM treatment during embryo development in vitro interferes with the formation and expansion capacity of the blastocoel in pigs.