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Front Physiol 2019 Feb 01;10:155. doi: 10.3389/fphys.2019.00155.
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Liver Specification in the Absence of Cardiac Differentiation Revealed by Differential Sensitivity to Wnt/β Catenin Pathway Activation.

Haworth K , Samuel L , Black S , Kirilenko P , Latinkic B .

Embryonic precursors of liver and heart, whilst not sharing cellular origin, develop in close proximity through a dynamic series of inductive signaling events. During gastrulation anterior endoderm (AE) provides cardiogenic signals that act on adjacent mesoderm, resulting in induction of cardiac precursors. Subsequently cardiogenic mesoderm generates a FGF signal that acts on adjacent AE to induce foregut organ specification. Additional signals such as BMP and Wnt provide further information required for liver specification. Most findings on liver specification were derived from mouse explant studies as well as experiments with Xenopus and zebrafish embryos. To address some of the limitations of these models, here we used two complementary ex vivo models based on Xenopus embryos: pluripotent animal cap explants expressing Gata4 transcription factor and conjugates of gastrula-stage AE with animal caps (AC). We show that in these models liver specification is not sensitive to Wnt signaling manipulation, in contrast to the requirement for Wnt antagonism shown in vivo. FGF pathway is not necessary for Gata4-induced liver specification in animal cap explants but is required for prolonged period in sandwiches of AE and AC. In contrast, BMP signaling is shown to be essential for Gata4-induced liver specification. Our findings may have implications for research on liver differentiation from embryonic stem cells.

PubMed ID: 30890948
PMC ID: PMC6411699
Article link: Front Physiol
Grant support: [+]

Species referenced: Xenopus
Genes referenced: acss2.2 amy2a cer1 ctnnb1 dkk1 fabp1 fabp2 foxa2 gata4 hhex ins myh6 myl3 myl7 nkx2-2 nr1h5 odc1 pdx1 sox17b.1 tbxt tnni3 wnt8a

Article Images: [+] show captions
References [+] :
Amaya, Expression of a dominant negative mutant of the FGF receptor disrupts mesoderm formation in Xenopus embryos. 1991, Pubmed, Xenbase