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Patterning of the hepato‐pancreatobiliary boundary by BMP reveals heterogeneity within the murine liver bud
Author(s) -
Palaria Amrita,
Angelo Jesse R.,
Guertin Taylor M.,
Mager Jesse,
Tremblay Kimberly D.
Publication year - 2018
Publication title -
hepatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.488
H-Index - 361
eISSN - 1527-3350
pISSN - 0270-9139
DOI - 10.1002/hep.29769
Subject(s) - biology , endoderm , mesoderm , fibroblast growth factor , bone morphogenetic protein , microbiology and biotechnology , lateral plate mesoderm , sox9 , fgf10 , transcription factor , endocrinology , cellular differentiation , embryonic stem cell , genetics , gene , receptor
During development, the endoderm initiates organ‐restricted gene expression patterns in a spatiotemporally controlled manner. This process, termed induction, requires signals from adjacent mesodermal derivatives. Fibroblast growth factor (FGF) and bone morphogenetic protein (BMP) emanating from the cardiac mesoderm and the septum transversum mesenchyme (STM), respectively, are believed to be simultaneously and uniformly required to directly induce hepatic gene expression from the murine endoderm. Using small molecule inhibitors of BMP signals during liver bud induction in the developing mouse embryo, we found that BMP signaling was not uniformly required to induce hepatic gene expression. Although BMP inhibition caused an overall reduction in the number of induced hepatoblasts, the STM‐bounded posterior liver bud demonstrated the most severe loss of the essential hepatic transcription factor, hepatocyte nuclear factor 4‐α (HNF4α), whereas the sinus venosus–lined anterior liver bud was less affected. We found that the posterior liver bud progenitors were anteriorly displaced and aberrantly activated pancreatobiliary markers, including sex‐determining region Y‐box 9 (SOX9). Additionally, we found that ectopically expressed SOX9 inhibited HNF4α and that BMP was indirectly required for hepatoblast induction. Finally, because previous studies have demonstrated that FGF signals are essential for anterior but not posterior liver bud induction, we examined synchronous BMP and FGF inhibition and found this led to a nearly complete loss of hepatoblasts. Conclusion: BMP signaling is required to maintain the hepato‐pancreatobiliary boundary, at least in part, by indirectly repressing SOX9 in the hepatic endoderm. BMP and FGF signals are each required for the induction of spatially complementary subsets of hepatoblasts. These results underscore the importance of studying early inductive processes in the whole embryo. (H epatology 2018;68:274‐288).