This work explored whether bovine embryo development relies on signaling from the interleukin-6 (IL6) cytokine family. This was accomplished by interrupting IL6 signal transducer (IL6ST), the common beta-subunit receptor used by the IL6 family. One series of studies cultured in vitro–produced embryos with SC144, a pharmacological IL6ST inhibitor. Providing the inhibitor at a concentration that partially diminished IL6ST signaling reduced development to the 16-cell and blastocyst stages and reduced inner-cell-mass cell numbers. Inhibitor concentrations that completely blocked IL6ST signaling prevented blastocyst development. Another series of studies used CRISPR-Cas9 to disrupt IL6ST. Two electroporation approaches were used to introduce guide RNAs and Cas9 protein into one-cell in vitro–produced embryos. Editing efficiency was ≥82%. Targeting IL6ST did not affect cleavage but reduced development to the 16-cell and blastocyst stages. A reduction in inner-cell-mass cell numbers was detected, and disorganization of the inner cell mass was observed in approximately one-half of the IL6ST-targeted blastocysts. These observations indicate that embryo-derived IL6 family members that signal through IL6ST are needed to support normal in vitro bovine embryo development. These signals are needed by the 16-cell stage and for inner-cell-mass cell development at the blastocyst stage. There is also evidence that these signals support the overall cellular organization of the blastocyst.

Summary Sentence

IL6ST disruption affects in vitro bovine embryo development and specifically development after d 2 post-fertilization, and this disruption also decreases inner cell mass cell numbers in blastocysts.

Graphical Abstract