Dynamic changes in Sox2 spatio-temporal expression direct the second cell fate decision throughFgf4/Fgfr2signaling in preimplantation mouse embryos

Abstract

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.

Journey of the mouse primitive endoderm: from specification to maturation

“…SOX2 expression by uncommitted ICM cells regulates the initial expression of FGF4 at the morula stage [70], which is necessary for the later expression of PrE genes [33]. SOX2 regulates the expression of FGF4 and FGFR2 through binding cis regulatory motifs in the genes encoding these proteins [71]. This interaction could likely lead to early asymmetries in FGF4 signalling within the blastocyst.…”

Analysis of pluripotency transcription factor interactions reveals preferential binding of NANOG to SOX2 rather than NANOG or OCT4

“…A dichroic mirror (560DRLP) and bandpass emission filters (500-550nm for Alexa 488/GFP and 607-683 nm for Atto 565/mCherry, (Chroma Technology, VT) were used to separate the excitation light coming from the fluorescence emission. A standard calibration approach was used to determine the absolute concentration of the fusion proteins in the crude nuclear lysate (Mistri et al 2018, Mistri et al 2015). Appropriately chosen dyes with known diffusion coefficients were employed to determine the confocal volume accurately.…”