Regulation of Tjp1 mRNA by CPEB2 for tight junction assembly in mouse blastocyst

Cytoplasmic polyadenylation element-binding protein 2 (CPEB2) is an mRNA-binding protein that regulates the cytoplasmic polyadenylation of mRNA and is required for tight junction (TJ) assembly in the trophectoderm epithelium during porcine preimplantation development. However, the regulatory mechanism underlying TJ assembly by CPEB2 has not been examined. The aim of this study was to elucidate how Cpeb2 regulates the subcellular localisation and stabilisation of Tjp1 mRNA for TJ biogenesis during mouse preimplantation. CPEB2 was detected in nuclei during the early stages of development and was localised at apical cell membranes from the morula stage onwards. In the Cpeb2 knockdown (KD), we observed reduced blastocyst formation with impaired TJs, defective inner cell mass development in the blastocyst outgrowth assay, and loss of pregnancy after embryo transfer. More importantly, Tjp1 mRNA was localised apically in the outer cells of control morulae but not in the Cpeb2 KD embryos, indicating that CPEB2 mediated the translocalisation of Tjp1 mRNA from the nuclei. Finally, in the control embryos, the length of the Tjp1 mRNA poly (A) tail was varied, while only a single peak was detected in the Cpeb2 KD embryos. These findings suggest that the binding of CPEB2 to the cytoplasmic polyadenylation element in the 3'-UTR can confer stability on Tjp1 mRNA and translational regulation. In summary, we demonstrated for the first time that CPEB2 mediates Tjp1 mRNA stabilisation and subcellular localisation for TJ assembly during mouse blastocyst formation.