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Activin/Nodal signalling controls divergent transcriptional networks in pluripotent and endoderm progenitors.

ABSTRACT: Activin/Nodal signalling is necessary to maintain pluripotency of human Embryonic Stem Cells (hESCs) and to induce their differentiation towards endoderm. However, the mechanisms by which Activin/Nodal signalling achieves these opposite functions remain unclear. To unravel these mechanisms, we examined the transcriptional network controlled in hESCs by Smad2 and Smad3 which represent the direct effectors of Activin/Nodal signalling. These analyses reveal that Smad2/3 participate in the control of the core transcriptional network characterising pluripotency which includes Oct-4, Nanog, FoxD3, Dppa4, Tert, Myc and UTF-1. In addition, similar experiments performed on endoderm cells confirm that a broad part of the transcriptional network directing differentiation is downstream of Smad2/3. Therefore, Activin/Nodal signalling appears to control divergent transcriptional networks in hESCs and in endoderm. Importantly, we observed an overlap between the transcriptional network downstream of Nanog and Smad2/3 in hESCs while functional studies showed that both factors cooperate to control the expression of pluripotency genes. Therefore, the effect of Activin/Nodal signalling on pluripotency and differentiation could be dictated by tissue specific Smad2/3 partners such as Nanog, explaining the mechanisms by which signalling pathways can orchestrate divergent cell fate decisions.

ORGANISM(S): Homo sapiens

PROVIDER: GSE19461 | GEO | 2011/11/11

SECONDARY ACCESSION(S): PRJNA120331

REPOSITORIES: GEO

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Project description:Nodal and Activin are morphogens of the TGFbeta superfamily of signaling molecules that direct differential cell fate decisions in a dose- and distance-dependent manner. During early embryonic development the Nodal/Activin pathway is responsible for the specification of mesoderm, endoderm, node and mesendoderm. In contradiction to this drive towards cellular differentiation, the pathway also plays important roles in the maintenance of self-renewal and pluripotency in embryonic and epiblast stem cells. The molecular basis behind stem cell interpretation of Nodal/Activin signaling gradients and the undertaking of disparate cell fate decisions remains poorly understood. Here, we show that any perturbation of endogenous signaling levels in mouse ES cells leads to their exit from self renewal towards divergent differentiation programs. Increasing Nodal signals above basal levels by direct stimulation with Activin promotes differentiation towards the mesendodermal lineages while repression of signaling with the specific Nodal/Activin receptor inhibitor SB431542 induces trophectodermal differentiation. To address how quantitative Nodal/Activin signals are translated qualitatively into distinct cell fates decisions, we performed chromatin immunoprecipitation of phospho-Smad2 the primary downstream transcriptional factor of the Nodal/Activin pathway followed by massively parallel sequencing and show that phospho-Smad2 binds to and regulates distinct subsets of target genes in a dose-dependent manner. Crucially, Nodal/Activin signaling directly controls the Oct4 master regulator of pluripotency by graded phospho-Smad2 binding in the promoter region. Hence stem cells interpret and carry out differential Nodal/Activin signaling instructions via a corresponding gradient of Smad2 phosphorylation that selectively titrates self-renewal against alternative differentiation programs by direct regulation of distinct target gene subsets and Oct4 expression. Four biological replicates consisting of 4 different passages of E14TG2a ES cells at P20, P21, P23 and P24

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Activin/Nodal signalling controls divergent transcriptional networks in pluripotent and endoderm progenitors.

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