Role of neural crest in congenital heart disease

Ventrally emigrating neural tube cells contribute to the normal development of heart and great vessels

We investigated the contributions of a recently described population of neural tube cells, which participates in the development of a variety of tissues, to the development of the heart and great vessels. These cells, termed as the ventrally emigrating neural tube (VENT) cells, originate in the ventral part of the hindbrain neural tube, emigrate at the site of attachment of the cranial nerves, and populate their respective target tissues. VENT cells of the caudal hindbrain neural tube at the level of the vagus nerve, which were previously reported to migrate into the heart, were tagged with replication-deficient retroviruses containing the LacZ gene in chick embryos, after the emigration of neural crest from this region. In older embryos, VENT cells were detected in a variety of locations including the ventricles, atria, their septa, aorticopulmonary septum, and great vessels of the heart. Immunostaining with a specific marker revealed that VENT cells differentiated into smooth muscle cells of great vessels. Differentiation of VENT cells into cardiac muscle cells was reported previously. Extirpation of the VENT cells prior to their departure from the neural tube resulted in some common cardiovascular malformations: thin-walled ventricles and atria, ventricular and atrial septal defects, persistent truncus arteriosus, and stenosis of the great vessels. These results suggest that a novel population of neural tube cells also contributes to the normal development of the heart and great vessels. Thus, the heart and great vessels develop from three sources of cells: mesoderm, neural crest, and VENT cells.

Cell autonomous requirement for PDGFRalpha in populations of cranial and cardiac neural crest cells

Cardiac and cephalic neural crest cells (NCCs) are essential components of the craniofacial and aortic arch mesenchyme. Genetic disruption of the platelet-derived growth factor receptor alpha (PDGFRalpha) results in defects in multiple tissues in the mouse, including neural crest derivatives contributing to the frontonasal process and the aortic arch. Using chimeric analysis, we show that loss of the receptor in NCCs renders them inefficient at contributing to the cranial mesenchyme. Conditional gene ablation in NCCs results in neonatal lethality because of aortic arch defects and a severely cleft palate. The conotruncal defects are first observed at E11.5 and are consistent with aberrant NCC development in the third, fourth and sixth branchial arches, while the bone malformations present in the frontonasal process and skull coincide with defects of NCCs from the first to third branchial arches. Changes in cell proliferation, migration, or survival were not observed in PDGFRalpha NCC conditional embryos, suggesting that the PDGFRalpha may play a role in a later stage of NCC development. Our results demonstrate that the PDGFRalpha plays an essential, cell-autonomous role in the development of cardiac and cephalic NCCs and provides a model for the study of aberrant NCC development.

Genetic and comparative mapping of genes dysregulated in mouse hearts lacking the Hand2 transcription factor gene

The helix-loop-helix transcription factor HAND2 plays a vital role in the development of the heart, limb, facies, and other neural crest-derived structures. We used differential display analysis to identify 33 putative HAND2-regulated ESTs that are differentially expressed in Hand2(-/-) vs wild-type mice. We determined the positions on mouse and human genetic maps of 29 of these by using the T31 mouse Radiation Hybrid panel, comparison to human genomic sequence, and comparative mapping. We examined the conserved chromosomal locations for phenotypes that involve development of heart, face, and limb structures that are affected by HAND2. One EST mapped to a region of conserved synteny between mouse chromosome 2 and human chromosome 10p. RACE analysis extended the sequence and identified this cDNA as the mouse ortholog of human nebulette, an actin-binding protein expressed in fetal heart. Nebulette was shown to be deleted in DiGeorge Syndrome 2 patients with the proximal deletion of human 10p13-p14 that is associated with cardiac and craniofacial abnormalities.

The role of neural crest during cardiac development in a mouse model of DiGeorge syndrome

The velo-cardio-facial syndrome (VCFS)/DiGeorge syndrome (DGS) is a genetic disorder characterized by phenotypic abnormalities of the derivatives of the pharyngeal arches, including cardiac outflow tract defects. Neural crest cells play a major role in the development of the pharyngeal arches, and defects in these cells are likely responsible for the syndrome. Most patients are hemizygous for a 1.5- to 3.0-Mb region of 22q11, that is suspected to be critical for normal pharyngeal arch development. Mice hemizygous for a 1.5-Mb homologous region of chromosome 16 (Lgdel/+) exhibit conotruncal cardiac defects similar to those seen in affected VCFS/DGS patients. To investigate the role of Lgdel genes in neural crest development, we fate mapped neural crest cells in Lgdel/+ mice and we performed hemizygous neural crest-specific inactivation of Lgdel. Hemizygosity of the Lgdel region does not eliminate cardiac neural crest migration to the forming aortic arches. However, neural crest cells do not differentiate appropriately into smooth muscle in both fourth and sixth aortic arches and the affected aortic arch segments develop abnormally. Tissue-specific hemizygous inactivation of Lgdel genes in neural crest results in normal cardiovascular development. Based on our studies, we propose that Lgdel genes are required for the expression of soluble signals that regulate neural crest cell differentiation.

Intracranial aneurysms associated with unsuspected aortic coarctation

Intracranial aneurysms (IAs) are found more often in patients with aortic coarctation (AC) than in the general population and aneurysm rupture occurs much earlier in the lives of these patients when there is coexistent AC. The diagnosis of AC is frequently made only after a serious cerebrovascular complication has developed. The aim of this paper is to call attention to AC in patients presenting with aneurysmal subarachnoid hemorrhage. The literature is reviewed, the key clinical features are highlighted, and the proposed pathogenesis of this association is discussed. The authors present clinical information and imaging data obtained in three young patients with ruptured IAs that were associated with initially unnoticed AC. Abnormal results of cardiovascular examinations led the authors to consider an underlying AC, which was later confirmed by aortography. These aneurysms were successfully treated prior to correction of the ACs. The diagnosis of AC should be considered in adolescent and young adult patients presenting with IAs.

AnFgf8mouse mutant phenocopies human 22q11 deletion syndrome

Deletion of chromosome 22q11, the most common microdeletion detected in humans, is associated with a life-threatening array of birth defects. Although 90% of affected individuals share the same three megabase deletion, their phenotype is highly variable and includes craniofacial and cardiovascular anomalies, hypoplasia or aplasia of the thymus with associated deficiency of T cells, hypocalcemia with hypoplasia or aplasia of the parathyroids, and a variety of central nervous system abnormalities. Because ablation of neural crest in chicks produces many features of the deletion 22q11 syndrome, it has been proposed that haploinsufficiency in this region impacts neural crest function during cardiac and pharyngeal arch development. Few factors required for migration, survival, proliferation and subsequent differentiation of pharyngeal arch neural crest and mesoderm-derived mesenchyme into their respective cardiovascular, musculoskeletal, and glandular derivatives have been identified. However, the importance of epithelial-mesenchymal interactions and pharyngeal endoderm function is becoming increasingly clear.

Fibroblast growth factor 8 is a signaling molecule expressed in the ectoderm and endoderm of the developing pharyngeal arches and known to play an important role in survival and patterning of first arch tissues. We demonstrate a dosage-sensitive requirement for FGF8 during development of pharyngeal arch, pharyngeal pouch and neural crest-derived tissues. We show that FGF8 deficient embryos have lethal malformations of the cardiac outflow tract, great vessels and heart due, at least in part, to failure to form the fourth pharyngeal arch arteries, altered expression of Fgf10 in the pharyngeal mesenchyme, and abnormal apoptosis in pharyngeal and cardiac neural crest.

The Fgf8 mutants described herein display the complete array of cardiovascular, glandular and craniofacial phenotypes seen in human deletion 22q11 syndromes. This represents the first single gene disruption outside the typically deleted region of human chromosome 22 to fully recapitulate the deletion 22q11 phenotype. FGF8 may operate directly in molecular pathways affected by deletions in 22q11 or function in parallel pathways required for normal development of pharyngeal arch and neural crest-derived tissues. In either case, Fgf8 may function as a modifier of the 22q11 deletion and contribute to the phenotypic variability of this syndrome.

Bicuspid aortic valve stenosis complicated by descending aortic dissection mimicking coarctation of the aorta

We report a rare case of bicuspid aortic stenosis complicated by an ascending aortic aneurysm and aortic dissection of DeBakey type IIIb. A 35-year-old woman was admitted to our hospital to examine her systolic murmur identified at birth. Severe aortic stenosis, dilatation of the ascending aorta, and the narrow color flow signal in the descending aorta were detected by transthoracic echocardiography. Initially, coarctation of the descending aorta was suspected, but aortic dissection, DeBakey type IIIb, was revealed by transesophageal echocardiography. Transesophageal echocardiography is indicated when only insufficient information is available on valve and aortic morphology in patients with bicuspid aortic valve.

Congenital heart disease and neuroblastoma: just coincidence?

The clinical history of a neonate with simple transposition of the great arteries in whom a metastatic neuroblastoma was diagnosed incidentally at autopsy is described, and the literature containing all 66 previously reported cases of neuroblastoma associated with congenital cardiac malformations is reviewed. One third of the described cases were classified as in situ neuroblastoma; neural crest derived cardiac lesions were present in 31%. Several possible aetiological mechanisms are discussed, and we conclude that the association of neuroblastoma with congenital cardiac malformations is multifactorial in origin. The described case represents the first reported example in which catecholamine release may have contributed to the fatal outcome of definitive congenital cardiac surgery.

Generation of a complete thymic microenvironment by MTS24(+) thymic epithelial cells

The epithelial component of the thymic microenvironment is indispensable for the generation of T lymphocytes. Although the heterogeneity of this epithelium is well documented, little is known about precursor-progeny relationships between distinct thymic epithelial lineages. Here we characterized a thymic epithelial cell subpopulation identified by the cell surface glycoprotein MTS24. These cells contained epithelial progenitor cells that were competent and sufficient to fully reconstitute the complex thymic epithelial microenvironment that supported normal T cell development.

Transposition of the great arteries and hypocalcemia in a patient with fetal hydantoin syndrome

We report a patient with fetal hydantoin syndrome (FHS) with associated d-transposition of the great arteries (d-TGA) and persistent hypocalcemia. d-TGA and hypocalcemia have each been individually reported once in association with FHS, but these patients were also prenatally exposed to phenobarbital. To our knowledge, this is the first report of these problems occurring after prenatal exposure to hydantoin alone. The combination of congenital heart disease and hypocalcemia in our patient raises the possibility of a hydantoin effect on neural crest migration.

A common cis-acting sequence in the DiGeorge critical region regulates bi-directional transcription of UFD1L and CDC45L

Two to three megabase deletions on chromosome 22q11 are the cytogenetic findings most commonly associated with cardiac and craniofacial defects in humans. The constellation of clinical findings associated with these deletions is termed the 22q11 deletion syndrome. We had earlier described a patient with the 22q11 deletion phenotype who was hemizygous for an atypical 20 kb microdeletion in this region. The deletion included coding regions of two genes organized head-to-head, UFD1L and CDC45L, along with an 884 bp CpG-rich intervening region. Based on this genomic organization, we hypothesized that both genes may be co-expressed and co-regulated by sequences within this region. We demonstrate that expression of both genes is enhanced in a similar pattern in precursors of structures affected by the deletion. The intergenic region is sufficient to direct transcription most strongly in the developing pharyngeal arches and limb buds of transgenic mice and can also direct bi-directional transcriptional activation in a neural crest-derived cell line. Deletion analyses revealed that a 404 bp fragment closest to UFD1L is necessary and sufficient to direct this bi-directional transcriptional activity. These results reveal the presence of a conserved regulatory region in the 22q11 deletion locus that can direct simultaneous transcription of genes involved in ubiquitin mediated protein processing (UFD1L) and cell cycle control (CDC45L).

Cloning and characterization of the gene encoding human NPL4, a protein interacting with the ubiquitin fusion-degradation protein (UFD1L)

The ubiquitin fusion-degradation gene (UFD1L) encodes the human homologue of the yeast ubiquitin fusion-degradation 1 protein, an essential component of the ubiquitin-dependent proteolytic turnover and mRNA processing. Although the UFD1L gene has been mapped in the region commonly deleted in patients with DiGeorge syndrome (DGS)/velocardiofacial syndrome (VCFS), correlation between its haploinsufficiency and the phenotype has not yet been established. The only functional data available about mammalian Ufd1p is the ability to form a complex with the rat Npl4 protein, a component of the nuclear pore complex. In this paper we report the cloning and molecular characterization of the human NPL4 gene. This gene encodes for a protein 96% homologous to the rat Npl4, and 44 and 34% homologous to the C. elegans and S. cerevisiae Npl4 gene products, respectively. Fluorescence in situ hybridization experiments on human metaphases localized the NPL4 gene on the most telomeric region of chromosome 17q. Northern blots analysis on foetal and adult human tissues revealed a major approximately 4.5 kb transcript most abundant in heart, brain, kidney and skeletal muscle. In order to test a potential relationship between nuclear transport defects and some aspect of the DGS/VCFS phenotype, we also exclude the presence of mutations in the NPL4 coding sequence in a subset of patients with DGS/VCFS and no detectable 22q11 deletion or mutations at the UFD1L locus.

The molecular basis of congenital cardiac disease

Today, congenital cardiovascular disease is virtually always amenable to corrective or palliative surgical interventions. However, the mechanisms causing developmental anomalies of the heart and vessels have remained obscure until recently. This review presents genetic defects causing the pediatric vasculopathies; Marfan's syndrome, inherited supravalvar aortic stenosis, and Williams' syndrome. A synopsis of known mutations causing human cardiomyopathies in nuclear genes encoding contractile proteins, cardiomyocyte structural proteins, and mitochondrial proteins essential for cardiac energy production is provided. The molecular genetic evidence implicating single gene mutations in the pathogenesis of conotruncal anomalies (the 22q11 monosomy or "cardiac defects, abnormal facies, thymic hypoplasia, cleft palate, and hypocalcemia with deletions on chromosome 22" [CATCH-22] syndrome), heterotaxy syndromes, trisomies and atrioventricular canal defects, and secundum atrial septal defects is presented. The consequences of these genetic causes for diagnostic evaluation and perioperative care are emphasized. Single gene defects are a common cause of congenital cardiac disease. Copyright 1998 by W.B. Saunders Company

Fetal heart rate and umbilical artery velocity variability in fetuses with congenital cardiac defects: a preliminary study

OBJECTIVE

To examine whether variabilities in fetal heart rate and umbilical artery flow velocity are possible markers for hemodynamic dysfunction in fetuses with a congenital heart defect.

METHODS

Doppler studies of the umbilical artery velocity waveform were performed at 20-35 weeks of gestation in 13 patients with a congenital heart defect. We determined absolute and variability values for heart rate and flow velocities from umbilical artery velocity waveforms of at least 18 s duration. We compared these findings with normal controls matched for gestational age.

RESULTS

Fetuses with a congenital heart defect displayed decreased umbilical artery peak systolic and time-averaged velocities. However, variability in peak systolic and time-averaged velocities and fetal heart rate variability were increased compared with normal controls. Absolute fetal heart rates were similar between the two groups.

CONCLUSIONS

Marked cardiovascular changes occur in the fetus with a congenital heart defect compared with the normal healthy fetus. We propose that variability in fetal heart rate and umbilical artery blood flow velocity could be additional markers for impaired homeostasis in the presence of fetal congenital heart disease.

Tbx1, a DiGeorge syndrome candidate gene, is regulated by sonic hedgehog during pharyngeal arch development

Appropriate interactions between the epithelium and adjacent neural crest-derived mesenchyme are necessary for normal pharyngeal arch development. Disruption of pharyngeal arch development in humans underlies many of the craniofacial defects observed in the 22q11.2 deletion syndrome (del22q11), but the genes responsible remain unknown. Tbx1 is a T-box transcription factor that lies in the 22q11.2 locus. Tbx1 transcripts were found to be localized to the pharyngeal endoderm and the mesodermal core of the pharyngeal arches, but were not present in the neural crest-derived mesenchyme of the pharyngeal arches. Sonic hedgehog (Shh) is also expressed in the pharyngeal arches and is necessary for normal craniofacial development. We found that Tbx1 expression was dependent upon Shh signaling in mouse embryos, consistent with their overlapping expression in the pharyngeal arches. Furthermore, Shh was sufficient to induce Tbx1 expression when misexpressed in selected regions of chick embryos. These studies reveal a Shh-mediated pathway that regulates Tbx1 during pharyngeal arch development.

Genetic assembly of the heart: implications for congenital heart disease

More children die from congenital heart defects (CHD) each year than are diagnosed with childhood cancer, yet the causes remain unknown. The remarkable conservation of genetic pathways regulating cardiac development in species ranging from flies to humans provides an opportunity to experimentally dissect the role of critical cardiogenic factors. Utilization of model biological systems has resulted in a molecular framework in which to consider the etiology of CHD. As whole genome sequencing and single nucleotide polymorphism data become available, identification of genetic mutations predisposing to CHD may allow preventive measures by modulation of secondary genetic or environmental factors. In this review, genetic pathways regulating cardiogenesis revealed by cross-species studies are reviewed and correlated with human CHD.

Isolation and characterization of a novel gene from the DiGeorge chromosomal region that encodes for a mediator subunit

Hemizygous deletions on chromosome 22q11.2 result in developmental disorders referred to as DiGeorge syndrome (DGS)/velocardiofacial syndrome (VCFS). We report the isolation of a novel gene, PCQAP (PC2 glutamine/Q-rich-associated protein), that maps to the DiGeorge typically deleted region and encodes a protein identified as a subunit of the large multiprotein complex PC2. PC2 belongs to the family of the human Mediator complexes, which exhibit coactivator function in RNA polymerase II transcription. Furthermore, we cloned the homologous mouse Pcqap cDNA. There is 83% amino acid identity between the human and the mouse predicted protein sequences, with 96% similarity at the amino- and carboxy-terminal ends. To assess the potential involvement of PCQAP in DGS/VCFS, its developmental expression pattern was analyzed. In situ hybridization of mouse embryos at different developmental stages revealed that Pcqap is ubiquitously expressed. However, higher expression was detected in the frontonasal region, pharyngeal arches, and limb buds. Moreover, analysis of subjects carrying a typical 22q11 deletion revealed that the human PCQAP gene was deleted in all patients. Many of the structures affected in DGS/VCFS evolve from Pcqap-expressing cells. Together with the observed haploinsufficiency of PCQAP in DGS/VCFS patients, this finding is consistent with a possible role for this novel Mediator subunit in the development of some of the structures affected in DGS/VCFS.

Cell biology of cardiac development

Building a vertebrate heart is a complex task and involves several tissues, including the myocardium, endocardium, neural crest, and epicardium. Interactions between these tissues result in the changes in function and morphology (and also in the extracellular matrix, which serves as a substrate for morphological change) that are requisite for development of the heart. Some of the signaling pathways that mediate these changes have now been identified and several investigators are now filling in the missing pieces in these pathways in hopes of ultimately understanding the molecular mechanisms that govern healthy heart development. In addition, transcription factors that regulate various aspects of heart development have been identified. Transcription factors of the GATA and Nkx2 families are of particular importance for early specification of the heart field and for regulating expression of genes that encode proteins of the contractile apparatus. This chapter highlights some of the most significant discoveries made in the rapidly expanding field of heart development.

Isolation of novel cDNA encompassing the ADU balanced translocation break point in the DiGeorge critical region

DiGeorge syndrome (DGS) is a developmental field defect of the third and fourth pharyngeal pouches that are associated with congenital heart defects, hypoparathyroidism, cell-mediated immunodeficiency, velopharyngeal insufficiency, and craniofacial anomalities. Approximately 90% of patients exhibit monosomy in the 22q11 region. In order to isolate the critical gene responsible for DGS, the cDNA libraries were screened with a probe containing the ADU balanced translocation break point, that is a locus reported in one patient (ADU) caused by a balanced translocation between chromosomes 22 and 2. Out of 10(6) clones, three independent overlapping clones were isolated, which were assumed to have originated from a single transcript, DGCR7. This transcript contained a 175-aa long open reading frame (ORF), encoding an acidic (pI = 5.81) and a proline-rich peptide, which are often found in the activation domain of several transcription factors. Also, it was predicted to be a nuclear protein. Northern hybridization detected an approx 1.9 kb transcript in all fetal and adult tissues tested, with strong expression in the fetal liver and kidney. In the case of adult tissues, strong expression was also detected in areas such as the heart, skeletal muscle, liver, and kidney.

TBX1 is responsible for cardiovascular defects in velo-cardio-facial/DiGeorge syndrome

Velo-cardio-facial syndrome (VCFS)/DiGeorge syndrome (DGS) is a human disorder characterized by a number of phenotypic features including cardiovascular defects. Most VCFS/DGS patients are hemizygous for a 1.5-3.0 Mb region of 22q11. To investigate the etiology of this disorder, we used a cre-loxP strategy to generate mice that are hemizygous for a 1.5 Mb deletion corresponding to that on 22q11. These mice exhibit significant perinatal lethality and have conotruncal and parathyroid defects. The conotruncal defects can be partially rescued by a human BAC containing the TBX1 gene. Mice heterozygous for a null mutation in Tbx1 develop conotruncal defects. These results together with the expression patterns of Tbx1 suggest a major role for this gene in the molecular etiology of VCFS/DGS.

Molecular determinants of left and right outflow tract obstruction

Congenital heart defects represent the most common group of human birth defects; they occur in 0.8-1% of live births and in 10% of spontaneously aborted fetuses. Heart defects seen in newborns typically represent specific morphogenetic defects of individual chambers or regions of the heart, with the remaining portions of the heart developing relatively normally. These developmental defects are commonly compatible with the intrauterine circulation, where the pulmonary circulation and systemic circulation work in concert, resulting in adequate embryonic growth and development. After delivery, however, significant cardiac symptoms develop. In many of these disorders, cyanosis is the earliest feature, while in others, cardiovascular collapse occurs before diagnosis. In this review, obstruction of the left and right sides of the heart are discussed. In these disorders, ventricular hypoplasia resulting in single ventricle physiologic characteristics is typical. The unaffected ventricle in these cases is usually morphologically and physiologically normal. These conditions include hypoplastic left heart syndrome and aortic coarctation on the left side, pulmonary stenosis, tetralogy of Fallot, and other complex right ventricle obstructive disorders. Many of these disorders occur in association with genetic syndromes identifiable by dysmorphic features. In some cases, the gene(s) has been identified or the genetic pathway has been defined. The purpose of this review is to discuss the molecular determinants of these obstructive disorders.

Variability in the phenotypic expression of fryns syndrome: A report of two sibships

We report on two sibships with four fetuses of 12, 15, 17, and 20 weeks of gestation, respectively, and 1 preterm baby of 31 weeks of gestation affected by a multiple congenital disorder with manifestation suggestive of Fryns syndrome. In addition to the characteristic malformation pattern in Fryns syndrome, they presented with fetal hydrops, cystic hygroma, and multiple pterygias, allowing prenatal ultrasound diagnosis as early as in the 11th week of gestation. The two affected fetuses of family 1 showed severe craniofacial anomalies with bilateral cleft lip and palate, acral hypoplasia, postaxial oligodactyly, persistent truncus arteriosus, and interrupted aortic arch, asplenia sequence, and complex central nervous system midline malformations. In family 2 with three affected sibs, ear anomalies with atresia of the auditory canals, postaxial hexadactyly, intestinal atresias, callosal defects, and eye colobomas were the most outstanding features. On the basis of the present findings and former reports, the inter- and intrafamiliar phenotypic variability in Fryns syndrome, possible pathogenetic mechanisms, and the value of prenatal diagnosis are discussed. In the pathogenetic discussion, a special emphasis is put on the neural crest cell developmental field.

Neuroblastoma cell lines showing smooth muscle cell phenotypes

Neuroblastoma is a tumor that is derived from the neural crest. Recent studies demonstrated that several human neuroblastoma cell lines exhibit at least three morphologic types: neuroblastic (N)-type, substrate-adhesive (S)-type and intermediate (I)-type cells. However, the origin of the S-type cells has not been clearly identified. In this study, the expressions of smooth muscle-specific proteins (desmin, alpha-smooth muscle actin, basic calponin and the smooth muscle myosin heavy-chain isoforms of SM1 and SM2) in three parent and four cloned neuroblastoma cell lines, composed of S-type cells, were examined by indirect immunofluorescence, Western blot and/or by reverse transcription-polymerase chain reaction (RT-PCR). Desmin was found in two of the seven cell lines, and alpha-smooth muscle actin and basic calponin were detected in all of seven of the cell lines. In three parent cell lines and one cloned cell line composed of N-type cells, none of three smooth muscle-specific proteins were detected. In smooth muscle myosin heavy-chain isoforms, SM1 was detected in two parent cell lines composed of S-type cells (MP-N-MS and KP-N-YS) by immunofluorescence, Western blot and/or by RT-PCR, whereas the SM2 isoform was detected in one parent cell line (MP-N-MS) by RT-PCR. These findings indicate that S-type cells have either the immature or mature smooth muscle cell phenotype, and neural crest cells very likely have the ability of to differentiate into smooth muscle cells in the human system.

Ventricular septal defect associated with microdeletions of chromosome 22q11.2

Microdeletions of chromosome 22q11.2 (del.22q11) cause DiGeorge syndrome, velo-cardio-facial syndrome, and conotruncal anomaly face syndrome, which are commonly associated with conotruncal heart anomalies. Approximately 15% of the patients manifest ventricular septal defect (VSD), and the conal septal type of VSD has been proposed to be associated with del.22q11, since it is categorized as a conotruncal anomaly. However, the types of VSD associated with del.22q11 remain poorly studied. The purpose of this study is to assess whether conal septal VSD or other types of VSDs are associated with del.22q11. We analyzed the chromosomes of 22 consecutive patients with conal-septal VSD, prospectively, and evaluated the types of VSD observed in 3 patients with del.22q11, retrospectively. Del.22q11 was not detected in any of the 22 patients with conal septal VSD. All the VSDs observed in the 3 patients with del.22q11 were a perimembranous type of VSD, which is not a conotruncal anomaly. Our results suggest that perimembranous VSD can be associated with del.22q11, but del.22q11 is not a common cause of conal-septal VSD.

Characterization of a Xenopus laevis CXC chemokine receptor 4: implications for hematopoietic cell development in the vertebrate embryo

Previous reports have shown that the Gi-protein-coupled CXC chemokine receptor 4 is activated by stromal cell-derived factor 1 (SDF-1). The receptor is present in many cell types and regulates a variety of cellular functions, including chemotaxis, adhesion, hematopoiesis, and organogenesis. To examine the role of CXCR4 as a regulator of organogenesis in the vertebrate embryo, we have isolated a cDNA encoding the Xenopus laevis homologue of CXCR4 (xCXCR4). The encoded polypeptide was functionally reconstituted with recombinant Gi2 in baculovirus-infected insect cells. Although xCXCR4 shares only 42% of its extracellular residues with mammalian CXCR4, it is indistinguishable from human CXCR4 in terms of its activation by human SDF-1alpha and SDF-1beta. The fact that only 19 of these residues are specifically present in the extracellular portions of CXCR4 suggests that these residues may be involved in recognizing SDF-1 and/or mediating CXCR4 activation by SDF-1. Xenopus CXCR4 mRNA expression was up-regulated during early neurula stages and remained high during early organogenesis. Whole mount in situ hybridization analysis showed abundant expression of xCXCR4 mRNA in the nervous system, including forebrain, hindbrain, and sensory organs, and in neural crest cells. xCXCR4 mRNA was also detected in the dorsal lateral plate, the first site of definitive hematopoiesis in the amphibian embryo corresponding to aorta-gonad-mesonephros or para-aortic splanchnopleura in mammals. This observation suggests that SDF-1 and CXCR4 are involved in regulating the migratory behavior of hematopoietic stem cells colonizing the larval or fetal liver. The hematopoietic defects observed in mice lacking SDF-1 or CXCR4 may, at least in part, be explained by a disturbance of this migration.

Normal cardiovascular development in mice deficient for 16 genes in 550 kb of the velocardiofacial/DiGeorge syndrome region

Hemizygous interstitial deletions in human chromosome 22q11 are associated with velocardiofacial syndrome and DiGeorge syndrome and lead to multiple congenital abnormalities, including cardiovascular defects. The gene(s) responsible for these disorders is thought to reside in a 1.5-Mb region of 22q11 in which 27 genes have been identified. We have used Cre-mediated recombination of LoxP sites in embryonic stem cells and mice to generate a 550-kb deletion encompassing 16 of these genes in the corresponding region on mouse chromosome 16. Mice heterozygous for this deletion are normal and do not exhibit cardiovascular abnormalities. Because mice with a larger deletion on mouse chromosome 16 do have heart defects, the results allow us to exclude these 16 genes as being solely, or in combination among themselves, responsible for the cardiovascular abnormalities in velocardiofacial/DiGeorge syndrome. We also generated mice with a duplication of the 16 genes that may help dissect the genetic basis of "cat eye" and derivative 22 syndromes that are characterized by extra copies of portions of 22q11, including these 16 genes. We also describe a strategy for selecting cell lines with defined chromosomal rearrangements. The method is based on reconstitution of a dominant selection marker after Cre-mediated recombination of LoxP sites. Therefore it should be widely applicable to many cell lines.

Retinoid signaling is essential for patterning the endoderm of the third and fourth pharyngeal arches

The requirement of retinoic acid (RA) in the initial formation of the pharyngeal arches was investigated by treating headfold-stage mouse embryos with a pan-RAR antagonist in vitro and in vivo. This results in a complete absence of mesenchyme, arteries, nerves and epibranchial placodes of the 3rd and 4th pharyngeal arches, complete agenesis of the 3rd and 4th pouches and consistent lack of the 6th arch artery. Mesodermally derived endothelial cells are absent from the 3rd and 4th pharyngeal arch region and the distribution domain of EphA2 transcripts in mesodermal cells is shifted caudally. In situ hybridization with CRABPI, kreisler and EphA4 probes and the pattern of expression of a Wnt1-lacZ transgene show that neural crest cells (NCC) normally destined to the 3rd and 4th arches migrate ectopically. Most interestingly, the appearance of the 3rd and 4th arches is prevented by the antagonist only during a very narrow window of time, which does not correspond to the period of post-otic NCC migration. Both the timing of appearance and the nature of the defects in RAR antagonist-treated embryos indicate that migrating NCC and mesodermal cells destined to the caudal pharyngeal arches do not represent primary targets of RA action. Alterations in the endodermal expression pattern of Hoxa1, Hoxb1, Pax1, Pax9, Fgf3 and Fgf8 in response to the antagonist-induced block in RA signal transduction demonstrate for the first time that RA signaling is indispensable for the specification of the pharyngeal endoderm and suggest that this signaling is necessary to provide a permissive environment locally for the migration of NCC and mesodermal cells. Our study also indicates that the formation of the 2nd pharyngeal arch and that of the 3rd and 4th pharyngeal arches probably involve distinct RA-dependent developmental processes.

Fate of the mammalian cardiac neural crest

A subpopulation of neural crest termed the cardiac neural crest is required in avian embryos to initiate reorganization of the outflow tract of the developing cardiovascular system. In mammalian embryos, it has not been previously experimentally possible to study the long-term fate of this population, although there is strong inference that a similar population exists and is perturbed in a number of genetic and teratogenic contexts. We have employed a two-component genetic system based on Cre/lox recombination to label indelibly the entire mouse neural crest population at the time of its formation, and to detect it at any time thereafter. Labeled cells are detected throughout gestation and in postnatal stages in major tissues that are known or predicted to be derived from neural crest. Labeling is highly specific and highly efficient. In the region of the heart, neural-crest-derived cells surround the pharyngeal arch arteries from the time of their formation and undergo an altered distribution coincident with the reorganization of these vessels. Labeled cells populate the aorticopulmonary septum and conotruncal cushions prior to and during overt septation of the outflow tract, and surround the thymus and thyroid as these organs form. Neural-crest-derived mesenchymal cells are abundantly distributed in midgestation (E9.5-12.5), and adult derivatives of the third, fourth and sixth pharyngeal arch arteries retain a substantial contribution of labeled cells. However, the population of neural-crest-derived cells that infiltrates the conotruncus and which surrounds the noncardiac pharyngeal organs is either overgrown or selectively eliminated as development proceeds, resulting for these tissues in a modest to marginal contribution in late fetal and postnatal life.

Benzofuranyl ureas with potent cardiovascular teratogenicity in rats

Studies of embryo-fetal development in rats were conducted with two 5-lipoxygenase inhibitors. SB-202235 (1,000 mg/kg/day) or SB-210661 (50, 100, or 500 mg/kg/day) was administered orally by gavage to female rats on days 6-17 postcoitus (pc) or days 7-16 pc. SB-202235 (1,000 mg/kg/day) and SB-210661 (100 mg/kg/day) reduced maternal body weight gain for the treatment period by 16% and 21%, respectively, relative to controls. SB-202235 (1,000 mg/kg/day) or SB-210661 (50 or 100 mg/kg/day), did not affect numbers of resorptions, dead or live fetuses/litter, but 500 mg/kg/day of SB-210661 caused 100% embryo lethality. SB-202235 (1,000 mg/kg/day) and SB-210661 (50 and 100 mg/kg/day) reduced fetal body weight by 15-30% and produced extensive cardiovascular malformations, as well as diaphragmatic hernias. SB-210661 also caused thymic abnormalities and cryptorchidism. Cardiovascular defects included abnormalities in aorticopulmonary septation, the aortic arch, pulmonary trunk, and ventricular septal defects are discussed relative to comparable human syndromes of cardiovascular malformation.

Neural crest-derived defects in experimental esophageal atresia

Esophageal atresia (EA) is often associated with cardiovascular and other malformations that are likely neural crest derived. The present study tests the hypothesis that the heart and great vessels and the thymus and parathyroids may be abnormal in the rat model of EA as a result of disturbed neural crest development. Time-mated pregnant rats received intraperitoneally on d 8 and 9 of gestation either 2 mg/kg adriamycin or vehicle. Esophageal, heart, and thymic malformations were sought under the microscope in term fetuses. The parathyroids were histologically investigated. Control fetuses had no malformations, whereas 69 of 109 fetuses exposed to adriamycin had EA and 45 of 69 had 15 right aortic arches, nine aberrant right subclavia, eight ventricular septal defects, six narrow pulmonary outflow tracts, five tetralogies of Fallot, three double outflow right ventricles, three double aortic arches, three atrial septal defects, three right ductus arteriosus, and two truncus. The thymus was absent in 19, hypoplastic in 12, and ectopic in five out of 36 fetuses with EA in which it was studied, whereas the parathyroid glands were absent in 16, single in four, and ectopic in one of the 23 fetuses with EA in which they were studied. In conclusion, the nature of the cardiovascular, thymic, and parathyroid malformations associated with EA in rats is consistent with the hypothesis of neural crest participation in their pathogenesis. Mechanisms simultaneously disturbing foregut septation, somitic segmentation, and neural crest development should be sought to explain the combined occurrence of malformations in EA.

Distribution of different regions of cardiac neural crest in the extrinsic and the intrinsic cardiac nervous system

In this study we focused upon whether different levels of postotic neural crest as well as the right and left cardiac neural crest show a segmented or mixed distribution in the extrinsic and intrinsic cardiac nervous system. Different parts of the postotic neural crest were labeled by heterospecific replacement of chick neural tube by its quail counterpart. Quail-chick chimeras (n = 21) were immunohistochemically evaluated at stage HH28+, HH29+, and between HH34-37. In another set of embryos, different regions of cardiac neural crest were tagged with a retrovirus containing the LacZ reporter gene and evaluated between HH35-37 (n = 13). The results show a difference in distribution between the right- and left-sided cardiac neural crest cells at the arterial pole and ventral cardiac plexus. In the dorsal cardiac plexus, the right and left cardiac neural crest cells mix. In general, the extrinsic and intrinsic cardiac nerves receive a lower contribution from the right cardiac neural crest compared with the left cardiac neural crest. The right-sided neural crest from the level of somite 1 seeds only the cranial part of the vagal nerve and the ventral cardiac plexus. Furthermore, the results show a nonsegmented overlapping contribution of neural crest originating from S1 to S3 to the Schwann cells of the cranial and recurrent nerves and the intrinsic cardiac plexus. Also the Schwann cells along the distal intestinal part of the vagal nerve are derived exclusively from the cardiac neural crest region. These findings and the smaller contribution of the more cranially emanating cardiac neural crest to the dorsal cardiac plexus compared with more caudal cardiac neural crest levels, suggests an initial segmented distribution of cardiac neural crest cells in the circumpharyngeal region, followed by longitudinal migration along the vagal nerve during later stages.

A population-based case-control teratologic study of oral oxytetracycline treatment during pregnancy

OBJECTIVE

To study human teratogenic potential of oral oxytetracycline treatment during pregnancy.

MATERIALS AND METHODS

The pair analysis of cases with congenital abnormalities and matched healthy controls in the large population-based dataset of the Hungarian Case-Control Surveillance of Congenital Abnormalities, 1980-1996.

RESULTS

Of 38,151 pregnant women who had babies without any defects in the study period (control group), 214 (0.6%) were treated with oral oxytetracycline. Of 22,865 pregnant women who had offspring with congenital abnormalities, 216 (0.9%) were treated with oxytetracycline (OR with 95%: 1.7, 1.4-2.0). Different approaches in the study showed a higher rate of medically documented oxytetracycline treatment in the second months of gestation in neural-tube defects (OR with 95%: 9.7, 2.0-47.1), cleft palate (17.2, 3.5-83.5) and multiple congenital abnormalities (12.9, 3.8-44.3) including mainly the combination of neural-tube defects and cardiovascular malformations.

CONCLUSION

Treatment with oxytetracycline during the second months of pregnancy presents a teratogenic risk to the fetus.

Key roles of retinoic acid receptors alpha and beta in the patterning of the caudal hindbrain, pharyngeal arches and otocyst in the mouse

Mouse fetuses carrying targeted inactivations of both the RAR(α) and the RARbeta genes display a variety of malformations in structures known to be partially derived from the mesenchymal neural crest originating from post-otic rhombomeres (e.g. thymus and great cephalic arteries) (Ghyselinck, N., Dupe, V., Dierich, A., Messaddeq, N., Garnier, J.M., Rochette-Egly, C., Chambon, P. and Mark M. (1997). Int. J. Dev. Biol. 41, 425–447). In a search for neural crest defects, we have analysed the rhombomeres, cranial nerves and pharyngeal arches of these double null mutants at early embryonic stages. The mutant post-otic cranial nerves are disorganized, indicating that RARs are involved in the patterning of structures derived from neurogenic neural crest, even though the lack of RARalpha and RARbeta has no detectable effect on the number and migration path of neural crest cells. Interestingly, the double null mutation impairs early developmental processes known to be independent of the neural crest e.g., the initial formation of the 3rd and 4th branchial pouches and of the 3rd, 4th and 6th arch arteries. The double mutation also results in an enlargement of rhombomere 5, which is likely to be responsible for the induction of supernumerary otic vesicles, in a disappearance of the rhombomere 5/6 boundary, and in profound alterations of rhombomere identities. In the mutant hindbrain, the expression domain of kreisler is twice its normal size and the caudal stripe of Krox-20 extends into the presumptive rhombomeres 6 and 7 region. In this region, Hoxb-1 is ectopically expressed, Hoxb-3 is ectopically up-regulated and Hoxd-4 expression is abolished. These data, which indicate that retinoic acid signaling through RARalpha and/or RARbeta is essential for the specification of rhombomere identities and for the control of caudal hindbrain segmentation by restricting the expression domains of kreisler and of Krox-20, also strongly suggest that this signaling plays a crucial role in the posteriorization of the hindbrain neurectoderm.

Ventrally emigrating neural tube cells differentiate into vascular smooth muscle cells

A multipotential cell population originating in the ventral part of the hindbrain neural tube, the ventrally emigrating neural tube cells (VENT cells), has recently been shown to migrate into the craniofacial mesenchyme. Because vascular smooth muscle cells develop from this mesenchyme, we sought to determine if the VENT cells contributed to their differentiation. VENT cells were tagged with replication-deficient retroviral vector with LacZ by microinjection into the lumen of the rostral hindbrain of chick embryos on day 2. Embryos were processed for the detection of LacZ positive cells on day 7. LacZ-positive cells were present in the wall of craniofacial arteries and veins. Immunostaining with the smooth muscle alpha-actin confirmed the labeled cells to be smooth muscle cells. It is concluded that some vascular smooth muscle cells differentiate from neural tube cells. the developmental and functional significance of which remains to be established.

Audiological findings in patients with microdeletion 22q11 (di George/velocardiofacial syndrome)

Microdeletion 22q11 (del22q11) is one of the most frequent causes of genetic syndromes. The majority of cases of di George and velocardiofacial syndromes are due to del22q11. These conditions are considered to be developmentally related to neural crest anomalies influencing the differentiation of the branchial arches, including the percursor tissue of the ear. In addition, the UFDIL gene, an ubiquination gene being expressed during embryogenesis in the inner ear primordia, has been identified in the 22q11 critical region. The aim of this study was to evaluate the prevalence of hearing impairment in del22q11 syndrome. Admittance audiometry, behavioural pure tone audiometry and auditory brainstem response (ABR) were performed in 27 children studied at our hospital between 1997 and 1998. Results were related to clinical history, frequency otitis media and immune status. Sensorineural hearing loss was found in 4/27 (15%) patients (severe in three cases, mild in one), conductive hearing impairment in 12/27 (45%) (moderate in four cases, mild in eight) and normal hearing in 11/27 (40%). Interestingly, three of the patients with sensorineural hearing loss had cerebral lesions due to neonatal distress, to hydrocephalus and to post-surgical ischaemia each in one. The prevalence of speech delay, otitis media and low CD3 values was higher among patients with conductive hearing impairment in comparison with those with normal hearing. In conclusion, hearing impairment was documented in 60% of the patients and must be included among the clinical features of del22q11 syndrome. Audiological evaluation is recommended in patients with del22q11 in order to reduce the risk of speech deficit.

Cardiovascular malformations in congenital diaphragmatic hernia: human and experimental studies

BACKGROUND/PURPOSE

Cardiovascular malformations (CVM) associated with congenital diaphragmatic hernia (CDH) account in part for the high mortality caused by this defect. The aim of this study is to examine the nature of these malformations in a large series of autopsies and to assess if similar defects are also present in rat fetuses with experimental CDH.

METHODS

The incidence of CVM and their nature were examined in the autopsy records of 136 stillborns and neonates with CDH admitted to our institution in the last 30 years. Experimental CDH was induced in rat fetuses by giving 100 mg of nitrofen to their mothers on gestational day 9.5, and the fetuses were harvested on day 21 (near full term). The presence of CDH and the anatomy of the heart and great vessels were studied under dissecting microscope after formalin fixation. Unexposed fetuses were used as controls.

RESULTS

Thirty-three newborns with CDH (24%) had CVM, either isolated or associated with other defects, and 7 had heart hypoplasia. Most CVM (ventricular septal defect, tetralogy of Fallot, transposition of the great vessels, double-outlet right ventricle) involved the outflow tract. In our animal experiments, no malformations were found in 21 control pups. Conversely, 80 of 130 nitrofen-exposed fetuses (61%) had CDH, and 59 of them (74%) had CVM. A significant association (Fisher's Exact test, P<.01) was found between CDH and CVM because only 25 of the 50 exposed animals without CDH (50%) had CVM. Again, most defects involved the outflow tract and were similar to those seen in human CDH (tetralogy of Fallot, persistent truncus, ventricular septal defect, double-outlet right ventricle, aberrant right subclavian artery, agenetic ductus, and interrupted aortic arch). Animals with CDH had significantly decreased heart weight to fetal weight ratio in comparison with controls and with those without CDH.

CONCLUSIONS

The similar nature of the cardiovascular defects found in babies succumbing to CDH and in nitrofen-exposed rats suggests that a similar disturbance of the regional organogenesis related to the neural crest might be involved in both settings, and further validates the use of this animal model for clarifying the cellular and molecular pathogenetic mechanisms.

Interruption of the aortic arch associated with deletion of chromosome 22q11 is associated with a subarterial and doubly committed ventricular septal defect in Japanese patients

OBJECTIVES

The purpose of this study was to clarify the clinical characteristics of interruption of the aortic arch associated with chromosome 22q11deletion.

BACKGROUND

About half of patients with interruption of the aortic arch between the left common carotid and the left subclavian artery have deletion of chromosome 22q11.

METHODS

In total, 20 patients with interruption of the aortic arch were studied with fluorescence in situ hybridization using peripheral lymphocytes and a DiGeorge syndrome chromosomal probe (Oncor N25). Cardiovascular anomalies in these patients were diagnosed by cross-sectional echocardiography and angiocardiography, and were confirmed at intracardiac repair.

RESULTS

Of 13 patients with interruption between the left common carotid artery and the left subclavian artery, seven had the deletion. All 7 also showed thymic hypoplasia and hypocalcemia, together with a nasal voice and peculiar facies. Six of the seven patients had complete deficiency of the muscular outlet septum, with the defect extending to the perimembranous area. Such complete absence of the muscular outlet septum was not present in any of the patients without the deletion.

CONCLUSIONS

Interruption of the aortic arch between the left common carotid and the left subclavian artery, absence of the thymus, and complete absence of the muscular outlet septum, were characteristic in Japanese patients with interruption of the aortic arch associated with deletion of chromosome 22q11.

Synergistic activities of alpha3 and alpha6 integrins are required during apical ectodermal ridge formation and organogenesis in the mouse

Integrins alpha6beta1 and alpha6beta4 are cell surface receptors for laminins. Integrin alpha6-null mice die at birth with severe skin blistering and defects in the cerebral cortex and in the retina. Integrin alpha3beta1 can associate with laminins and other ligands. Integrin alpha3-null mice also die at birth, with kidney and lung defects at late stages of development, and moderate skin blistering. To investigate possible overlapping functions between alpha3 and alpha6 integrins, we analyzed the phenotype of compound alpha3−/−/alpha6−/− mutant embryos. Double homozygous mutant embryos were growth-retarded and displayed several developmental defects not observed in the single mutant animals. First, limb abnormalities characterized by an absence of digit separation and the fusion of preskeletal elements were observed. Further analyses indicated a defect in the apical ectodermal ridge, an essential limb organizing center. In the double mutant, the ridge appeared flattened, and ridge cells did not show a columnar morphology. A strong reduction in ridge cell proliferation and alterations of the basal lamina underlying the ectoderm were observed. These results suggest that alpha3 and alpha6 integrins are required for the organization or compaction of presumptive apical ectodermal ridge cells into a distinct differentiated structure. Additional defects were present: an absence of neural tube closure, bilateral lung hypoplasia, and several abnormalities in the urogenital tract. Finally, an aggravation of brain and eye lamination defects was observed. The presence of novel phenotypes in double mutant embryos demonstrates the synergism between alpha3 and alpha6 integrins and their essential roles in multiple processes during embryogenesis.

Malignant rhabdoid-tumor cell line showing neural and smooth-muscle-cell phenotypes

Malignant rhabdoid tumor (MRT) is a rare and extremely aggressive malignant tumor in childhood. In this study, an MRT cell line, designated KP-MRT-NS, was established from the ascitic fluid taken from an 11-month-old girl, whose tumor had originated from the left kidney. Ultrastructural findings demonstrated the typical aggregation of whorls of intermediate filaments. Chromosome constitution was described as 46, XX, add (10)(q26)[17]/46, idem, dis (1;2)(q22;q31)[3] based on ISCN (1995) and a del (22)(q11.2) was not found in this cell line. The origin of MRT is controversial, various cellular origins having been proposed because of the phenotypic diversity of MRT. Therefore, in this study, to clarify the origin of MRT, the expressions of cytoplasmic proteins including smooth-muscle-specific proteins (alpha-smooth-muscle actin, basic calponin, smooth-muscle-myosin-heavy-chain isoforms of SM1 and SM2) in the primary-MRT tissue and cell line were analyzed. In the primary-tumor tissue, the expressions of neurofilament, vimentin and alpha-smooth-muscle actin were demonstrated by indirect immunofluorescence. In the KP-MRT-NS cell line, the expression of neurofilament, alpha-smooth-muscle actin, basic calponin and smooth-muscle-myosin heavy chain of SM1 and SM2 isoforms was revealed by immunofluorescence, Western blot and/or reverse transcriptase-polymerase chain reaction (RT-PCR). MyoD1 mRNA, determined as a skeletal-muscle-cell lineage marker, was not expressed in the primary-tumor tissue or in the KP-MRT-NS cell line. According to our findings, the MRT cells are of both neural and smooth-muscle cell phenotypes, and support the neural-crest origin of MRT.

Cardiovascular malformations in experimental congenital diaphragmatic hernia

BACKGROUND/PURPOSE

Newborns with congenital diaphragmatic hernia (CDH) frequently have associated anomalies that have a major impact on survival rate independent of pulmonary hypoplasia and pulmonary hypertension. Cardiovascular malformations (CVM) represent a major group of lethal extrapulmonary abnormalities that often assume greatest prognostic significance in most CDH studies. Animal models resembling human CDH may aid knowledge of the basic embryology that leads to the coexpression of CDH and CVM. This study, therefore, analyzed the incidence and spectrum of CVM in fetal rats with CDH.

METHODS

Left-sided CDH (LCDH) was induced in fetal rats by the maternal administration of 100 mg of nitrofen by gavage on day 9.5 gestation (term, day 22). Control animals received olive oil (OO) and were used for comparative analysis. Fetal rats were harvested by cesarean section on day 21.5 or day 22, histologically processed and examined for CVM.

RESULTS

A significant number of CVM were observed in 15 of 60 (25%) LCDH rats compared with 4 of 60 (6.7%) nitrofen non-CDH rats (P = .01). The spectrum of abnormalities in CDH included ventricular septal (VSD) defects (n = 6), vascular rings (n = 4), anomalous subclavian arteries (n = 3), atrioventricular septal defects (n = 1) and Fallot's tetralogy (n = 1). A VSD (n = 1), double-outlet right ventricle VSD (n = 1) and Fallot's tetralogy (n = 2) were noted in nitrofen non-CDH rats. Control (OO) fetal rats (n = 60) displayed no malformations.

CONCLUSIONS

These results confirm a significant incidence and spectrum of CVM in a teratogenic CDH model similar to that seen in humans with CDH. The findings of this study reinforce the validity of the nitrofen model as a research tool to uncover the genetic and molecular mechanisms responsible for the genesis of CDH and allied malformations.

A novel role for cardiac neural crest in heart development

Ablation of premigratory cardiac neural crest results in defective development of the cardiac outflow tract. The purpose of the present study was to correlate the earliest functional and morphological changes in heart development after cardiac neural crest ablation. Within 24 hours after neural crest ablation, the external morphology of the hearts showed straight outflow limbs, tighter heart loops, and variable dilations. Incorporation of bromodeoxyuridine in myocytes, an indication of proliferation, was doubled after cardiac neural crest ablation. The myocardial calcium transients, which are a measure of excitation-contraction coupling, were depressed by 50% in both the inflow and outflow portions of the looped heart tube. The myocardial transients could be rescued by replacing the cardiac neural crest. The cardiac jelly produced by the myocardium was distributed in an uneven, rather than uniform, pattern. An extreme variability in external morphology could be attributed to the uneven distribution of cardiac jelly. In the absence of cardiac neural crest, the myocardium was characterized by somewhat disorganized myofibrils that may be a result of abnormally elevated proliferation. In contrast, endocardial development appeared normal, as evidenced by normal expression of fibrillin-2 protein (JB3 antigen) and normal formation of cushion mesenchyme and trabeculae. The signs of abnormal myocardial development coincident with normal endocardium suggest that the presence of cardiac neural crest cells is necessary for normal differentiation and function of the myocardium during early heart development. These results indicate a novel role for neural crest cells in myocardial maturation.

Functions of c-Jun in liver and heart development

Mice lacking the AP-1 transcription factor c-Jun die around embryonic day E13.0 but little is known about the cell types affected as well as the cause of embryonic lethality. Here we show that a fraction of mutant E13.0 fetal livers exhibits extensive apoptosis of both hematopoietic cells and hepatoblasts, whereas the expression of 15 mRNAs, including those of albumin, keratin 18, hepatocyte nuclear factor 1, beta-globin, and erythropoietin, some of which are putative AP-1 target genes, is not affected. Apoptosis of hematopoietic cells in mutant livers is most likely not due to a cell-autonomous defect, since c-jun-/- fetal liver cells are able to reconstitute all hematopoietic compartments of lethally irradiated recipient mice. A developmental analysis of chimeras showed contribution of c-jun-/- ES cell derivatives to fetal, but not to adult livers, suggesting a role of c-Jun in hepatocyte turnover. This is in agreement with the reduced mitotic and increased apoptotic rates found in primary liver cell cultures derived from c-jun-/- fetuses. Furthermore, a novel function for c-Jun was found in heart development. The heart outflow tract of c-jun-/- fetuses show malformations that resemble the human disease of a truncus arteriosus persistens. Therefore, the lethality of c-jun mutant fetuses is most likely due to pleiotropic defects reflecting the diversity of functions of c-Jun in development, such as a role in neural crest cell function, in the maintenance of hepatic hematopoiesis and in the regulation of apoptosis.

Developmental and genetic aspects of congenital heart disease

Congenital heart defects (CHDs) are the result of abnormal cardiac mesoderm or cardiac neural crest development. The molecular cause of most congenital heart disease remains unknown, although numerous cardiac regulatory factors have recently been described. dHAND and eHAND are basic helix-loop-helix transcription factors expressed differentially in the right and left ventricles, respectively, and in the cardiac neural crest. Mice lacking dHAND have a hypoplastic right ventricle and abnormal development of vessels arising from the heart and cell death of craniofacial precursors. By searching for dHAND-dependent genes, a gene likely responsible for the cardiac and craniofacial defects associated with chromosome 22q11 deletion has been identified. A systematic dissection of molecular pathways involved in cardiogenesis should allow for further identification of genes responsible for CHD.