Signaling via the Tgf-beta type I receptor Alk5 in heart development.
ABSTRACT Trophic factors secreted both from the endocardium and epicardium regulate appropriate growth of the myocardium during cardiac development. Epicardially-derived cells play also a key role in development of the coronary vasculature. This process involves transformation of epithelial (epicardial) cells to mesenchymal cells (EMT). Similarly, a subset of endocardial cells undergoes EMT to form the mesenchyme of endocardial cushions, which function as primordia for developing valves and septa. While it has been suggested that transforming growth factor-betas (Tgf-beta) play an important role in induction of EMT in the avian epi- and endocardium, the function of Tgf-betas in corresponding mammalian tissues is still poorly understood. In this study, we have ablated the Tgf-beta type I receptor Alk5 in endo-, myo- and epicardial lineages using the Tie2-Cre, Nkx2.5-Cre, and Gata5-Cre driver lines, respectively. We show that while Alk5-mediated signaling does not play a major role in the myocardium during mouse cardiac development, it is critically important in the endocardium for induction of EMT both in vitro and in vivo. Moreover, loss of epicardial Alk5-mediated signaling leads to disruption of cell-cell interactions between the epicardium and myocardium resulting in a thinned myocardium. Furthermore, epicardial cells lacking Alk5 fail to undergo Tgf-beta-induced EMT in vitro. Late term mutant embryos lacking epicardial Alk5 display defective formation of a smooth muscle cell layer around coronary arteries, and aberrant formation of capillary vessels in the myocardium suggesting that Alk5 is controlling vascular homeostasis during cardiogenesis. To conclude, Tgf-beta signaling via Alk5 is not required in myocardial cells during mammalian cardiac development, but plays an irreplaceable cell-autonomous role regulating cellular communication, differentiation and proliferation in endocardial and epicardial cells.
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ABSTRACT: The majority of congenital heart defects arise from abnormal development of valvuloseptal tissue. The primordia of the valve leaflets and membranous septa of the heart are the cardiac cushions. Remodeling of the cushions is associated with a transitional extracellular matrix that includes sulfated proteoglycans and the microfibrillar proteins fibulin and fibrillin. Cushion formation is restricted to the AV canal and ventricular outflow tract regions of the primary heart tube. The proper placement of the cushions may be the result of the development of the primary heart tube as a segmented organ, as well as the subsequent looping of the heart. Segmentation of the heart tube may be demonstrated by the alternating molecular expression pattern along the longitudinal axis. In support of this hypothesis is the restricted expression of BMP-4 and msx-2 to the AV canal and ventricular outflow tract. The importance of looping for cushion positioning may imply that the iv and inv genes and retinoic acid are important for the proper patterning of the heart. The cells of the cushions evolve from endocardial cells that undergo an epithelial-to-mesenchymal transformation. This developmental event is regulated by the myocardium and is probably due to the production of protein complexes, present within the cardiac jelly of the cushion-forming regions, that consist of fibronectin and the ES proteins. Both the cushion mesenchyme and its endocardial cell antecedents express JB3, an ECM protein. JB3 expression is also featured within the heart-forming fields of the primary mesoderm, from which the endocardial progenitors of the cushion cells originate.(ABSTRACT TRUNCATED AT 250 WORDS)Circulation Research 08/1995; 77(1):1-6. · 9.49 Impact Factor
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ABSTRACT: Cardiac neural crest cells undergo extensive cell rearrangements during the formation of the aorticopulmonary septum in the outflow tract. However, the morphogenetic mechanisms involved in this fundamental process remain poorly understood. To determine the function of the Ca2+-dependent cell adhesion molecule, N-cadherin, in murine neural crest, we applied the Cre/loxP system and created mouse embryos genetically mosaic for N-cadherin. Specifically, deletion of N-cadherin in neural crest cells led to embryonic lethality with distinct cardiovascular defects. Neural crest cell migration and homing to the cardiac outflow tract niche were unaffected by loss of N-cadherin. However, N-cadherin-deficient neural crest cells were unable to undergo the normal morphogenetic changes associated with outflow tract remodeling, resulting in persistent truncus arteriosus in the majority of mutant embryos. Other mutant embryos initiated aorticopulmonary septum formation; however, the neural crest cells were unable to elongate and align properly along the midline and remained rounded with limited contact with their neighbors. Interestingly, rotation of the outflow tract was incomplete in these mutants suggesting that alignment of the channels is dependent on N-cadherin-generated cytoskeletal forces. A second cardiac phenotype was observed where loss of N-cadherin in the epicardium led to disruption of heterotypic cell interactions between the epicardium and myocardium resulting in a thinned ventricular myocardium. Thus, we conclude that in addition to its role in myocardial cell adhesion, N-cadherin is required for neural crest cell rearrangements critical for patterning of the cardiac outflow tract and in the maintenance of epicardial-myocardial cell interactions.Developmental Biology 12/2006; 299(2):517-28. · 4.07 Impact Factor
Article: Targeted disruption of the mouse transforming growth factor-beta 1 gene results in multifocal inflammatory disease.[show abstract] [hide abstract]
ABSTRACT: Transforming growth factor-beta 1 (TGF-beta 1) is a multifunctional growth factor that has profound regulatory effects on many developmental and physiological processes. Disruption of the TGF-beta 1 gene by homologous recombination in murine embryonic stem cells enables mice to be generated that carry the disrupted allele. Animals homozygous for the mutated TGF-beta 1 allele show no gross developmental abnormalities, but about 20 days after birth they succumb to a wasting syndrome accompanied by a multifocal, mixed inflammatory cell response and tissue necrosis, leading to organ failure and death. TGF-beta 1-deficient mice may be valuable models for human immune and inflammatory disorders, including autoimmune diseases, transplant rejection and graft versus host reactions.Nature 11/1992; 359(6397):693-9. · 36.28 Impact Factor