RT Journal Article SR Electronic T1 Dynamic changes in Sox2 spatio-temporal expression direct the second cell fate decision through Fgf4/Fgfr2 signaling in preimplantation mouse embryos JF bioRxiv FD Cold Spring Harbor Laboratory SP 052530 DO 10.1101/052530 A1 Tapan Kumar Mistri A1 Wibowo Arindrarto A1 Wei Ping Ng A1 Choayang Wang A1 Leng Hiong Lim A1 Lili Sun A1 Ian Chambers A1 Thorsten Wohland A1 Paul Robson YR 2016 UL http://biorxiv.org/content/early/2016/11/07/052530.abstract AB Oct4 and Sox2 regulate the expression of target genes such as Nanog, Fgf4 and Utf1, by binding to their respective regulatory motifs. Their functional cooperation is reflected in their ability to heterodimerise on adjacent cis regulatory elements, the composite Sox/Oct motif. Given that Oct4 and Sox2 regulate many developmental genes, a quantitative analysis of their synergistic action on different Sox/Oct motifs would yield valuable insights into the mechanisms of early embryonic development. In this study, we measured binding affinities of Oct4 and Sox2 to different Sox/Oct motifs using fluorescence correlation spectroscopy (FCS). We found that the synergistic binding interaction is driven mainly by the level of Sox2 in the case of the Fgf4 Sox/Oct motif. Taking into account Sox2 expression levels fluctuate more than Oct4, our finding provides an explanation on how Sox2 controls the segregation of the epiblast (EPI) and primitive endoderm (PE) populations within the inner cell mass (ICM) of the developing rodent blastocyst.