Genetic studies place Tbx5 at the apex of the sinoatrial node (SAN) transcriptional program. To understand its role in SAN differentiation, clonal embryonic stem (ES) cell lines were made that conditionally overexpress Tbx5, Tbx3, Tbx18, Shox2, Islet-1, and MAP3k7/TAK1. Cardiac cells differentiated using embryoid bodies (EBs).
View Article and Find Full Text PDFSpecification of the primary heart field in mouse embryos requires signaling from the anterior visceral endoderm (AVE). The nature of these signals is not known. We hypothesized that the TGFβ-activated kinase (TAK1/Map3k7) may act as a cardiogenic factor, based on its expression in heart-inducing endoderm and its requirement for cardiac differentiation of p19 cells.
View Article and Find Full Text PDFThe cardiac transcription factor Nkx2-5 is essential for normal outflow tract (OFT) and right ventricle (RV) development. Nkx2-5 null mouse embryos display severe OFT and RV hypoplasia and a single ventricle phenotype due to decreased proliferation of Second Heart Field (SHF) cells, a pool of cardiac progenitors present in anterior pharyngeal arch mesoderm at mid-gestation. However, definition of the precise role of Nkx2-5 in facilitating SHF expansion is incomplete.
View Article and Find Full Text PDFIn vivo, cardiomyocytes comprise a heterogeneous population of contractile cells defined by unique electrophysiologies, molecular markers and morphologies. The mechanisms directing myocardial cells to specific sub-lineages remain poorly understood. Here we report that overexpression of TGFβ-Activated Kinase (TAK1/Map3k7) in mouse embryonic stem (ES) cells faithfully directs myocardial differentiation of embryoid body (EB)-derived cardiac cells toward the sinoatrial node (SAN) lineage.
View Article and Find Full Text PDFPhilos Trans R Soc Lond B Biol Sci
December 2014
Despite the importance of the gut and its accessory organs, our understanding of early endoderm development is still incomplete. Traditionally, endoderm has been difficult to study because of its small size and relative fragility. However, recent advances in live cell imaging technologies have dramatically expanded our understanding of this tissue, adding a new appreciation for the complex molecular and morphogenetic processes that mediate gut formation.
View Article and Find Full Text PDFObjective: Preeclampsia (PE) affects 2-8% of pregnancies worldwide and is a significant source of maternal and neonatal morbidity and mortality. However, the mechanisms underlying PE are poorly understood and major questions regarding etiology and risk factors remain to be addressed. Our objective was to examine whether abnormal expression of the cardiovascular developmental transcription factor, Nkx2-5, was associated with early onset and severe preeclampsia (EOSPE).
View Article and Find Full Text PDFInteractions between the endoderm and mesoderm that mediate myocardial induction are difficult to study in vivo because of the small size of mammalian embryos at relevant stages. However, we and others have demonstrated that signals from endodermal cell lines can influence myocardial differentiation from both mouse and human embryoid bodies (EBs), and because of this, assays that utilize embryonic stem (ES) cells and endodermal cell lines provide excellent in vitro models to study early cardiac differentiation. Extraembryonic endoderm (XEN) stem cells have a particular advantage over other heart-inducing cell lines in that they can easily be derived from both wild type and mutant mouse blastocysts.
View Article and Find Full Text PDFThe transfer of nutrients from the mother through the chorioallantoic placenta meets the nutritional needs of the embryo during human prenatal development. Although all amniotes start with a similar "tool kit" of extraembryonic tissues, an enormous diversity of extraembryonic tissue formation has evolved to accommodate embryological and physiological constraints unique to their developmental programs. A comparative knowledge of these extraembryonic tissues and their role in nutrient uptake during development is required to fully appreciate the adaptive changes in placental mammals.
View Article and Find Full Text PDFBackground: Initial specification of cardiomyocytes in the mouse results from interactions between the extraembryonic anterior visceral endoderm (AVE) and the nascent mesoderm. However the mechanism by which AVE activates cardiogenesis is not well understood, and the identity of specific cardiogenic factors in the endoderm remains elusive. Most mammalian studies of the cardiogenic potential of the endoderm have relied on the use of cell lines that are similar to the heart-inducing AVE.
View Article and Find Full Text PDFCardiomyocyte differentiation is a complex multistep process requiring the proper temporal and spatial integration of multiple signaling pathways. Previous embryological and genetic studies have identified a number of signaling pathways that are critical to mediate the initial formation of the mesoderm and its allocation to the cardiomyocyte lineage. It has become clear that some of these signaling networks work autonomously, in differentiating myocardial cells whereas others work non-autonomously, in neighboring tissues, to regulate cardiac differentiation indirectly.
View Article and Find Full Text PDFWe have characterized two signaling pathways that induce heart tissue during embryonic development. The first is initiated by the Wnt antagonist Dickkopf1 (Dkk1) and involves the homeodomain transcription factor Hex. Other Wnt antagonists are less effective and the potency of Dkk1 might be due to synergy between Wnt antagonizing and another, novel activity emanating from its amino terminal cysteine-rich domain.
View Article and Find Full Text PDFThe TGFbeta family member Nodal has been implicated in heart induction through misexpression of a dominant negative version of the type I Nodal receptor (Alk4) and targeted deletion of the co-receptor Cripto in murine ESCs and mouse embryos; however, whether Nodal acts directly or indirectly to induce heart tissue or interacts with other signaling molecules or pathways remained unclear. Here we present Xenopus embryological studies demonstrating an unforeseen role for the DAN family protein Cerberus within presumptive foregut endoderm as essential for differentiation of cardiac mesoderm in response to Nodal. Ectopic activation of Nodal signaling in non-cardiogenic ventroposterior mesendoderm, either by misexpression of the Nodal homologue XNr1 together with Cripto or by a constitutively active Alk4 (caAlk4), induced both cardiac markers and Cerberus.
View Article and Find Full Text PDFInhibition of canonical Wnt/beta-catenin signaling by Dickkopf-1 (Dkk-1) or Crescent initiates cardiogenesis in vertebrate embryos. However, nearly nothing is known about the downstream effectors of these secreted Wnt antagonists or the mechanism by which they activate heart formation. Here we show that Wnt antagonists in Xenopus stimulate cardiogenesis non-cell-autonomously, up to several cells away from those in which canonical Wnt/beta-catenin signaling is blocked, indicative of an indirect role in heart induction.
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