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Synergism between Activin A and BMP4 in directing the formation of definitive endoderm in human embryonic stem cells

ABSTRACT: Human embryonic stem cells (HESCs) herald tremendous promise for the production of clinically useful cell types for the treatment of injury and disease. Numerous reports demonstrate their differentiation into definitive endoderm (DE) cells, the germ layer from which pancreatic β cells and hepatocytes arise, solely from exposure to a high dose of recombinant Activin/Nodal. Here, we show that combining a second related ligand, BMP4, in combination with Activin A yields 15 to 20% more DE as compared to Activin A alone. The addition of recombinant BMP4 accelerates the downregulation of pluripotency factors, particularly SOX2, and results in upregulation of endogenous BMP2 and BMP4, which in turn leads to elevated levels of phospho-SMAD1/5/8 over the next three days of differentiation. Combined Activin A and BMP4 treatment also leads to an increase in the expression of DE genes CXCR4, SOX17 and FOXA2 when compared to Activin A addition alone. Comparative microarray studies between DE cells harvested on day 3 of differentiation further reveal a novel set of genes upregulated in response to initial BMP4 exposure. Several of these, including APLNR, LRIG3, MCC and LZTS1, are expressed either in the mouse primitive streak, the site of DE formation, or in nascent DE itself. Thus, this synergism between Activin A and BMP4 during the in vitro differentiation of HESC into DE suggests a complex interplay between BMP and Activin/Nodal signaling during the in vivo allocation and expansion of the endoderm lineage.

ORGANISM(S): Homo sapiens

PROVIDER: GSE30630 | GEO | 2011/11/10

SECONDARY ACCESSION(S): PRJNA144583

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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Synergism between Activin A and BMP4 in directing the formation of definitive endoderm in human embryonic stem cells

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