Mammalian implantation requires the proliferation of embryonic trophoblast stem cells (TSCs) to form the trophectoderm. Most studies on TSCs have been carried out in mice, but it has been challenging to extrapolate these findings to other species. Now, Vimal Selvaraj and colleagues decipher the key factors that facilitate TSC renewal in cattle. Through systematic transcriptome and proteome analyses, the authors identify Rho GTPase signalling as a candidate for bovine TSC self-renewal. Indeed, toxin-mediated inhibition of Rho activity or ectopic expression of a dominative-negative RhoA increases bovine TSC proliferation. Furthermore, inhibition of Rock (Rocki), a RhoA target, phenocopies Rho loss-of-function experiments, increases TSC and blastocyst size, and sustains TSCs in vitro. The researchers show that TGFβ1 is associated with spontaneous TSC differentiation, with TGFβ1 treatment suppressing TSC proliferation, altering cell morphology and increasing differentiation gene expression. They identify Rock targets: a regulatory network of five transcription factors, highlighting the role of the NF𝜅B pathway. Finally, Rock2 gain-of-function is sufficient to induce TSC differentiation, as shown by binucleate morphology. Together, these data show that TGFβ1 and RhoA-Rock regulate bovine TSC proliferation and differentiation, and that Rocki promotes TSC derivation and renewal in vitro.
