Regulation of trophectoderm morphogenesis by small GTPase RHOA through HIPPO signaling-dependent and -independent mechanisms in mouse preimplantation development.

The trophectoderm (TE) is the first tissue to differentiate during the preimplantation development of the mammalian embryo. It forms the outer layer of the blastocyst and is responsible for generating the blastocoel, a fluid-filled cavity whose expansion is essential for successful hatching and implantation. Here, we investigated the role of the small GTPase RHOA in the morphogenesis of the TE, particularly its relationship with HIPPO signaling, using mouse embryos as a model. Inhibition of RHOA resulted in the failure to form a blastocoel and significantly altered the expression of numerous genes. Transcriptomic analysis revealed that 330 genes were down-regulated and 168 genes were up-regulated by more than two-fold. Notably, 98.4% of these transcriptional changes were reversed by simultaneous inhibition of LATS kinases, indicating that the transcriptional influence of RHOA is primarily mediated through HIPPO signaling. Many of the down-regulated genes are involved in critical processes of TE morphogenesis, such as apical-basal cell polarization, tight junction formation, and sodium and water transport, suggesting that RHOA supports TE development by enhancing the expression of morphogenesis-related genes through HIPPO signaling, specifically via TEAD transcription factors. However, RHOA inhibition also disrupted apical-basal polarity and tight junctions, effects that were not restored by LATS inhibition, pointing to additional HIPPO signaling-independent mechanisms by which RHOA controls TE morphogenesis. Furthermore, RHOA inhibition impaired cell viability at the late blastocyst stage, with partial rescue observed upon LATS inhibition, suggesting that RHOA maintains cell survival through both HIPPO signaling-dependent and -independent pathways. A deeper knowledge of the molecular mechanisms governing TE morphogenesis, including blastocoel expansion and cell viability, could significantly advance assisted reproductive technologies aimed at producing healthy blastocysts.