A deficiency in the region homologous to human 17q21.33-q23.2 causes heart defects in mice.
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Several constitutional chromosomal rearrangements occur on human chromosome 17. Patients who carry constitutional deletions of 17q21.3-q24 exhibit distinct phenotypic features. Within the deletion interval, there is a genomic segment that is bounded by the myeloperoxidase and homeobox B1 genes. This genomic segment is syntenically conserved on mouse chromosome 11 and is bounded by the mouse homologs of the same genes (Mpo and HoxB1). To attain functional information about this syntenic segment in mice, we have generated a 6.9-Mb deletion [Df(11)18], the reciprocal duplication [Dp(11)18] between Mpo and Chad (the chondroadherin gene), and a 1.8-Mb deletion between Chad and HoxB1. Phenotypic analyses of the mutant mouse lines showed that the Dp(11)18/Dp(11)18 genotype was responsible for embryonic or adolescent lethality, whereas the Df(11)18/+ genotype was responsible for heart defects. The cardiovascular phenotype of the Df(11)18/+ fetuses was similar to those of patients who carried the deletions of 17q21.3-q24. Since heart defects were not detectable in Df(11)18/Dp(11)18 mice, the haplo-insufficiency of one or more genes located between Mpo and Chad may be responsible for the abnormal cardiovascular phenotype. Therefore, we have identified a new dosage-sensitive genomic region that may be critical for normal heart development in both mice and humans. (+info)
Hydrops fetalis, cardiovascular defects, and embryonic lethality in mice lacking the calcitonin receptor-like receptor gene.
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Adrenomedullin (AM) is a multifunctional peptide vasodilator that is essential for life. To date, numerous in vitro studies have suggested that AM can mediate its biological effects through at least three different receptors. To determine the in vivo importance of the most likely candidate receptor, calcitonin receptor-like receptor, a gene-targeted knockout model of the gene was generated. Mice heterozygous for the targeted Calcrl allele appear normal, survive to adulthood, and reproduce. However, heterozygote matings fail to produce viable Calcrl-/- pups, demonstrating that Calcrl is essential for survival. Timed matings confirmed that Calcrl-/- embryos die between embryonic day 13.5 (E13.5) and E14.5 of gestation. The Calcrl-/- embryos exhibit extreme hydrops fetalis and cardiovascular defects, including thin vascular smooth muscle walls and small, disorganized hearts remarkably similar to the previously characterized AM-/- phenotype. In vivo assays of cellular proliferation and apoptosis in the hearts and vasculature of Calcrl-/- and AM-/- embryos support the concept that AM signaling is a crucial mediator of cardiovascular development. The Calcrl gene targeted mice provide the first in vivo genetic evidence that CLR functions as an AM receptor during embryonic development. (+info)
GATA-6 regulates semaphorin 3C and is required in cardiac neural crest for cardiovascular morphogenesis.
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GATA transcription factors play critical roles in restricting cell lineage differentiation during development. Here, we show that conditional inactivation of GATA-6 in VSMCs results in perinatal mortality from a spectrum of cardiovascular defects, including interrupted aortic arch and persistent truncus arteriosus. Inactivation of GATA-6 in neural crest recapitulates these abnormalities, demonstrating a cell-autonomous requirement for GATA-6 in neural crest-derived SMCs. Surprisingly, the observed defects do not result from impaired SMC differentiation but rather are associated with severely attenuated expression of semaphorin 3C, a signaling molecule critical for both neuronal and vascular patterning. Thus, the primary function of GATA-6 during cardiovascular development is to regulate morphogenetic patterning of the cardiac outflow tract and aortic arch. These findings provide new insights into the conserved functions of the GATA-4, -5, and -6 subfamily members and identify GATA-6 and GATA-6-regulated genes as candidates involved in the pathogenesis of congenital heart disease. (+info)
Impaired neurogenesis and cardiovascular development in mice lacking the E3 ubiquitin ligases UBR1 and UBR2 of the N-end rule pathway.
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The N-end rule relates the in vivo half-life of a protein to the identity of its N-terminal residue. A subset of degradation signals recognized by the N-end rule pathway comprises the signals, called N-degrons, whose determinants include destabilizing N-terminal residues. Our previous work identified a family of at least four mammalian E3 ubiquitin ligases, including UBR1 and UBR2, that share the UBR box and recognize N-degrons. These E3 enzymes mediate the multifunctional N-end rule pathway, but their individual roles are just beginning to emerge. Mutations of UBR1 in humans are the cause of Johanson-Blizzard syndrome. UBR1 and UBR2 are 46% identical and appear to be indistinguishable in their recognition of N-degrons. UBR1-/- mice are viable but have defects that include pancreatic insufficiency, similarly to UBR1-/- human patients with Johanson-Blizzard syndrome. UBR2-/- mice are inviable in some strain backgrounds and are defective in male meiosis. To examine functional relationships between UBR1 and UBR2, we constructed mouse strains lacking both of these E3s. We report here that UBR1-/-UBR2-/- embryos die at midgestation, with defects in neurogenesis and cardiovascular development. These defects included reduced proliferation as well as precocious migration and differentiation of neural progenitor cells. The expression of regulators such as D-type cyclins and Notch1 was also altered in UBR1-/-UBR2-/- embryos. We conclude that the functions of UBR1 and UBR2 are significantly divergent, in part because of differences in their expression patterns and possibly also because of differences in their recognition of protein substrates that contain degradation signals other than N-degrons. (+info)
Isl1 is upstream of sonic hedgehog in a pathway required for cardiac morphogenesis.
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The LIM homeodomain transcription factor Islet1 (Isl1) is expressed in both foregut endoderm and cardiogenic mesoderm and is required for earliest stages of heart development. Here, we report that isl1 is also required upstream of Shh. We find that, in isl1 null mice, Sonic hedgehog (Shh) is downregulated in foregut endoderm. Shh signals through the unique activating receptor smoothened (Smo). To investigate the role of hedgehog signaling in the isl1 domain, we ablated smo utilizing isl1-cre. Isl1-cre;smo mutants exhibit cardiovascular defects similar to those observed in Shh null mice, defining a spatial requirement for hedgehog signaling within isl1 expression domains for aortic arch and outflow tract formation. Semaphorin signaling through neuropilin receptors npn1 and npn2 is required for aortic arch and outflow tract formation. We find that expression of npn2 is downregulated in isl1-cre;smo mutants, suggesting an isl1/Shh/npn pathway required to affect morphogenesis at the anterior pole of the heart. (+info)
Aortic valve regurgitation after arterial switch operation for transposition of the great arteries: incidence, risk factors, and outcome.
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OBJECTIVES: The aims of this study were to assess the prevalence and incidence of aortic valve regurgitation (AR) after arterial switch operation (ASO), its outcome, and the risk factors. BACKGROUND: After an ASO, the long-term fate of the aortic valve is a concern as follow-up lengthens. METHODS: Operative and follow-up data on 1,156 hospital survivors after ASOs between 1982 and December 2000 were reviewed. RESULTS: At last follow-up (mean duration 76.2 +/- 60.5 months), 172 patients (14.9%) had an AR. Complex transposition of the great arteries, prior pulmonary banding done in 75 patients (21 with intact ventricular septum), aortic arch anomalies, AR at discharge, older age at ASO, and aortic/pulmonary size discrepancy were associated with AR. On multivariate analysis, the presence of a ventricular septal defect (VSD) or AR at discharge multiplied the risk by 2 and 4, respectively. Freedom from AR was 77.9% and 69.5% at 10 and 15 years, respectively; hazard function for AR declined rapidly and slowly increased thereafter. Reoperation from AR was done in 16 patients with one death, valvuloplasty being unsuccessful. Freedom from reoperation for AR was 97.7% and 96.8% at 10 and 15 years, respectively; hazard function slowly increased from 2 to 16 years. Higher late mortality was not associated with AR. CONCLUSIONS: After ASO, AR was observed and was related to VSD with attending high pressure and flow and AR at discharge. Progression of AR was slow, but incidence increased with follow-up. Reoperation for AR was rare. Late aortic valve function warrants long-term monitoring. (+info)
A common SCN5A polymorphism attenuates a severe cardiac phenotype caused by a nonsense SCN5A mutation in a Chinese family with an inherited cardiac conduction defect.
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The SCN5A mutations have been associated with a variety of arrhythmic disorders, including type 3 long QT syndrome (LQT3), Brugada syndrome and inherited cardiac conduction defects. The relationship between genotype and phenotype in SCN5A mutations is complex. Some SCN5A mutations may cause death or severe manifestations in some people and may not cause any symptoms or arrhythmias in others. The causes of these unpredictable clinical manifestations remain incompletely understood. The molecular basis of a four-generation family with cardiac conduction abnormalities was studied and whether variants in the SCN5A gene could account for the cardiac phenotypic variability observed in this family was determined. A novel mutation (W1421X) of SCN5A was identified in a four-generation family with cardiac conduction abnormalities and several cases of sudden death. Most family members who carry this W1421X mutation have developed major clinical manifestations or electrocardiographic abnormalities, both of which became more prominent as the patients grew older. However, the 73-year-old grandfather, who carried both the W1421X and R1193Q mutations, had thus far remained healthy and presented with only subtle electrocardiographic abnormalities, whereas most of his offspring, who carried a single mutation (W1421X), had died early or had major disease manifestations. This observation suggests that the R1193Q mutation has a complementary role in alleviating the deleterious effects conferred by W1421X in the function of the SCN5A gene. This report provides a good model to explain the mechanism of penetrance of genetic disorders. (+info)
Required, tissue-specific roles for Fgf8 in outflow tract formation and remodeling.
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Fibroblast growth factor 8 (Fgf8) is a secreted signaling protein expressed in numerous temporospatial domains that are potentially relevant to cardiovascular development. However, the pathogenesis of complex cardiac and outflow tract defects observed in Fgf8-deficient mice, and the specific source(s) of Fgf8 required for outflow tract formation and subsequent remodeling are unknown. A detailed examination of the timing and location of Fgf8 production revealed previously unappreciated expression in a subset of primary heart field cells; Fgf8 is also expressed throughout the anterior heart field (AHF) mesoderm and in pharyngeal endoderm at the crescent and early somite stages. We used conditional mutagenesis to examine the requirements for Fgf8 function in these different expression domains during heart and outflow tract morphogenesis. Formation of the primary heart tube and the addition of right ventricular and outflow tract myocardium depend on autocrine Fgf8 signaling in cardiac crescent mesoderm. Loss of Fgf8 in this domain resulted in decreased expression of the Fgf8 target gene Erm, and aberrant production of Isl1 and its target Mef2c in the anterior heart field, thus linking Fgf8 signaling with transcription factor networks that regulate survival and proliferation of the anterior heart field. We further found that mesodermal- and endodermal-derived Fgf8 perform specific functions during outflow tract remodeling: mesodermal Fgf8 is required for correct alignment of the outflow tract and ventricles, whereas activity of Fgf8 emanating from pharyngeal endoderm regulates outflow tract septation. These findings provide a novel insight into how the formation and remodeling of primary and anterior heart field-derived structures rely on Fgf8 signals from discrete temporospatial domains. (+info)