['Mammalian first lineage segregation generates trophectoderm (TE) and pluripotent inner cell mass (ICM), which provides an ideal model for studying the mechanisms of maintenance and loss of pluripotency. In mouse, the transcription factor OCT4 restricts to ICM and plays a key role in TE/ICM specification and pluripotent regulatory networks. However, in pig, OCT4 does not restrict to ICM cells, suggesting a different molecular basis in TE/ICM specification and pluripotent regulatory networks.', 'To explore molecular basis of porcine TE/ICM specification and pluripotent regulatory networks, we examined expression pattern of pluripotency factors, including SOX2, REX1, SALL4, ESG1, NANOG, TBX3, LIN28, KLF2, and KLF5, in porcine blastocysts. We found that SOX2 is a faithful pluripotent marker that anchored to the pluripotent cells including embryonic part cells, ICM cells and newly EPI cells along with developmental progress, whereas OCT4 expressed in almost all the cells at the same time. Consistently, analysis of spatiotemporal distribution of SOX2 and the TE marker CDX2 revealed an exclusive expression pattern in D6 blastocysts, whereas no correlation was observed between OCT4 and CDX2 at the same stage.'] Is sox2 the faithful marker for pluripotency in pig : evidence from embryonic studies?