Tead4 is required for specification of trophectoderm in pre-implantation mouse embryos

During pre-implantation mouse development, embryos form blastocysts with establishment of the first two cell lineages: the trophectoderm (TE) which gives rise to the placenta, and the inner cell mass (ICM) which will form the embryo proper. Differentiation of TE is regulated by the transcription factor Caudal-related homeobox 2 (Cdx2), but the mechanisms which act upstream of Cdx2 expression remain unknown. Here we show that the TEA domain family transcription factor, Tead4, is required for TE development. Tead1, Tead2 and Tead4 were expressed in pre-implantation embryos, and at least Tead1 and Tead4 were expressed widely in both TE and ICM lineages. Tead4-/- embryos died at pre-implantation stages without forming the blastocoel. The mutant embryos continued cell proliferation, and adherens junction and cell polarity were not significantly affected. In Tead4-/- embryos, Cdx2 was weakly expressed at the morula stage but was not expressed in later stages. None of the TE specific genes, including Eomes and a Cdx2 independent gene, Fgfr2, was detected in Tead4-/- embryos. Instead, the ICM specific transcription factors, Oct3/4 and Nanog, were expressed in all the blastomeres. Tead4-/- embryos also failed to differentiate trophoblast giant cells when they were cultured in vitro. ES cells with normal in vitro differentiation abilities were established from Tead4-/- embryos. These results suggest that Tead4 has a distinct role from Tead1 and Tead2 in trophectoderm specification of pre-implantation embryos, and that Tead4 is an early transcription factor required for specification and development of the trophectoderm lineage, which includes expression of Cdx2.