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Trophectoderm (TE) is the first differentiated cell lineage of mammalian embryogenesis.Inner cell mass (ICM) and TE segregation in blastocyst is a hallmark event in early mammalian development, but molecular mechanisms underlying this first differentiation event remain limited.Many studies have provided evidences that the transcription factors Oct4 and Cdx2 are respecticely essential to ICM and TE specification.In preimplantation embryos, Cdx2 is initially coexpressed with Oct4, and by the blastocyst stage, Oct4 and Cdx2 become separately restricted in ICM and TE.Oct4 and Cdx2 are also indispensible for the self-renewal of embryonic stem (ES) cells and trophoblast stem (TS) cells respectively.Both Oct4 repression and Cdx2 overexpression in ES cells could generate proper TS cells;conversaly, Oct4 overexpression in TS cells could form ES cells.Invetigations into molecular mechanism of mutual antagonism between Oct and Cdx2 in ES cells have shown that Oct4 and Cdx2 bind to each other gene regulatory region to reciprocally suppress transcription and they also form a complex for the mutual repression of their target genes.However, this ES-manner of Oct4 and Cdx2 molecular interaction has never been re-examined and investigated in the early embryos.Here, our data from Cdx2 overexpressed porcine embryos showed that Cdx2 and Oct4 interact in a non-ES manner in early embryos.Our finding might renew the prevailing view and provide new insight into the way that Cdx2 and Oct4 interact and participate in ICM-TE segregation.