Neural crest and normal development: a new perspective

Xenopus embryos to study fetal alcohol syndrome, a model for environmental teratogenesis

Vertebrate model systems are central to characterize the outcomes of ethanol exposure and the etiology of fetal alcohol spectrum disorder (FASD), taking advantage of their genetic and morphological closeness and similarity to humans. We discuss the contribution of amphibian embryos to FASD research, focusing on Xenopus embryos. The Xenopus experimental system is characterized by external development and accessibility throughout embryogenesis, large clutch sizes, gene and protein activity manipulation, transgenesis and genome editing, convenient chemical treatment, explants and conjugates, and many other experimental approaches. Taking advantage of these methods, many insights regarding FASD have been obtained. These studies characterized the malformations induced by ethanol including quantitative analysis of craniofacial malformations, induction of fetal growth restriction, delay in gut maturation, and defects in the differentiation of the neural crest. Mechanistic, biochemical, and molecular studies in Xenopus embryos identified early gastrula as the high alcohol sensitivity window, targeting the embryonic organizer and inducing a delay in gastrulation movements. Frog embryos have also served to demonstrate the involvement of reduced retinoic acid production and an increase in reactive oxygen species in FASD. Amphibian embryos have helped pave the way for our mechanistic, molecular, and biochemical understanding of the etiology and pathophysiology of FASD.

Probing the Electrophysiology of the Developing Heart

Many diseases that result in dysfunction and dysmorphology of the heart originate in the embryo. However, the embryonic heart presents a challenging subject for study: especially challenging is its electrophysiology. Electrophysiological maturation of the embryonic heart without disturbing its physiological function requires the creation and deployment of novel technologies along with the use of classical techniques on a range of animal models. Each tool has its strengths and limitations and has contributed to making key discoveries to expand our understanding of cardiac development. Further progress in understanding the mechanisms that regulate the normal and abnormal development of the electrophysiology of the heart requires integration of this functional information with the more extensively elucidated structural and molecular changes.

Connecting teratogen-induced congenital heart defects to neural crest cells and their effect on cardiac function

Neural crest cells play many key roles in embryonic development, as demonstrated by the abnormalities that result from their specific absence or dysfunction. Unfortunately, these key cells are particularly sensitive to abnormalities in various intrinsic and extrinsic factors, such as genetic deletions or ethanol-exposure that lead to morbidity and mortality for organisms. This review discusses the role identified for a segment of neural crest in regulating the morphogenesis of the heart and associated great vessels. The paradox is that their derivatives constitute a small proportion of cells to the cardiovascular system. Findings supporting that these cells impact early cardiac function raises the interesting possibility that they indirectly control cardiovascular development at least partially through regulating function. Making connections between insults to the neural crest, cardiac function, and morphogenesis is more approachable with technological advances. Expanding our understanding of early functional consequences could be useful in improving diagnosis and testing therapies.

[Embryology of the heart walls]

Although anatomically simple structures, the atrial septum and the ventricular septum have complex embryological origins. Recent findings in molecular biology allowed better comprehension of their formation. As soon as the heart tube is formed, cells migrate from several cardiogenic fields to take part in the septation. Elongation, ballooning, and later inflexion of the heart tube create chamber separating grooves, facing the future septa. The systemic venous tributaries conflate at the venous pole of the heart; it will partially involute while contributing to the atrial septum. The primary atrial septum grows from the atrial roof towards the atrioventricular canal. It fuses there with the atrioventricular cushions, while its upper margin breaks down to form the ostium secundum. Then a deep fold develops from the atrial roof and partly covers the ostium secundum, leaving a flap-like interatrial communication through the oval foramen. It will close at birth. The interventricular septum has three embryological origins. The ventricular septum primum, created during the ballooning process, origins from the primary heart tube. It will form the trabecular septum and the inlet septum. The interventricular ring, surrounding the interventricular foramen, will participate in the inlet septum and also form the atrioventricular conduction axis. The outflow cushions will separate the outflow tract in the aorta and pulmonary artery, and grow to create the outlet septum. After merging with the atrioventricular cushions, they will also be part of the membranous septum.

Immunoregulation of follicular renewal, selection, POF, and menopause in vivo, vs. neo-oogenesis in vitro, POF and ovarian infertility treatment, and a clinical trial

The immune system plays an important role in the regulation of tissue homeostasis ("tissue immune physiology"). Function of distinct tissues during adulthood, including the ovary, requires (1) Renewal from stem cells, (2) Preservation of tissue-specific cells in a proper differentiated state, which differs among distinct tissues, and (3) Regulation of tissue quantity. Such morphostasis can be executed by the tissue control system, consisting of immune system-related components, vascular pericytes, and autonomic innervation. Morphostasis is established epigenetically, during morphogenetic (developmental) immune adaptation, i.e., during the critical developmental period. Subsequently, the tissues are maintained in a state of differentiation reached during the adaptation by a "stop effect" of resident and self renewing monocyte-derived cells. The later normal tissue is programmed to emerge (e.g., late emergence of ovarian granulosa cells), the earlier its function ceases. Alteration of certain tissue differentiation during the critical developmental period causes persistent alteration of that tissue function, including premature ovarian failure (POF) and primary amenorrhea. In fetal and adult human ovaries the ovarian surface epithelium cells called ovarian stem cells (OSC) are bipotent stem cells for the formation of ovarian germ and granulosa cells. Recently termed oogonial stem cells are, in reality, not stem but already germ cells which have the ability to divide. Immune system-related cells and molecules accompany asymmetric division of OSC resulting in the emergence of secondary germ cells, symmetric division, and migration of secondary germ cells, formation of new granulosa cells and fetal and adult primordial follicles (follicular renewal), and selection and growth of primary/preantral, and dominant follicles. The number of selected follicles during each ovarian cycle is determined by autonomic innervation. Morphostasis is altered with advancing age, due to degenerative changes of the immune system. This causes cessation of oocyte and follicular renewal at 38 +/-2 years of age due to the lack of formation of new granulosa cells. Oocytes in primordial follicles persisting after the end of the prime reproductive period accumulate genetic alterations resulting in an exponentially growing incidence of fetal trisomies and other genetic abnormalities with advanced maternal age. The secondary germ cells also develop in the OSC cultures derived from POF and aging ovaries. In vitro conditions are free of immune mechanisms, which prevent neo-oogenesis in vivo. Such germ cells are capable of differentiating in vitro into functional oocytes. This may provide fresh oocytes and genetically related children to women lacking the ability to produce their own follicular oocytes. Further study of "immune physiology" may help us to better understand ovarian physiology and pathology, including ovarian infertility caused by POF or by a lack of ovarian follicles with functional oocytes in aging ovaries. The observations indicating involvement of immunoregulation in physiological neo-oogenesis and follicular renewal from OSC during the fetal and prime reproductive periods are reviewed as well as immune system and age-independent neo-oogenesis and oocyte maturation in OSC cultures, perimenopausal alteration of homeostasis causing disorders of many tissues, and the first OSC culture clinical trial.

Effect of culture age on the susceptibility of differentiating neuroblastoma cells to retinoid cytotoxicity

The cytotoxic effects of retinoids on neuroblastoma cells at various times during electrophysiological differentiation were evaluated. We used N1E-115, a clone of the murine neuroblastoma C1300 derived from the neural crest, and three retinoids: vitamin A (retinol), all-trans retinoic acid (tretinoin), and 13-cis-retinoic acid (isotretinoin). Differentiating N1E-115 cells exposed to retinoids at an isotretinoin EC(50) of 16 microM exhibited the greatest vulnerability in terms of cell death during a period (8 to 10 days) that was previously found to be the most sensitive for induction of gross malformations in rodents. This finding suggested possible similarities between the in vivo and in vitro retinoid mechanism(s) of action. The greatest period of vulnerability to retinoid cytotoxicity was also found to coincide with the rapid resting membrane potential (V(m)) development period, suggesting a linkage between neuronal V(m) and/or electrical excitability development and vulnerability to retinoid cytotoxicity.

DiGeorge anomaly in the absence of chromosome 22q11.2 deletion

OBJECTIVE

To test the hypothesis that the prevalence of deletion 22q11.2 among individuals who meet criteria for DiGeorge anomaly (DGA) is lower than the 90% commonly cited.

STUDY DESIGN

Participants were identified through retrospective chart reviews on all patients who underwent testing for deletion 22q11.2 and all patients with a diagnosis of "DiGeorge" or any of the major criteria associated with DGA at a large pediatric hospital over a period of 6 years. DGA was confirmed in 64 individuals, based on the presence of at least 2 of the following features: (1) cellular immune deficiency and/or absence of part or all of the thymus; (2) hypocalcemia and/or parathyroid deficiency; (3) congenital heart disease.

RESULTS

Of the 64 individuals with DGA, 29 (45%) did not have a chromosome 22q11.2 deletion. Among this deletion-negative subset, diabetic embryopathy and other chromosome abnormalities were the most commonly recognized underlying etiologies.

CONCLUSIONS

These findings challenge a widely held belief that nearly 90% of DGA is due to chromosome 22q11.2 deletion. This study also calls attention to the heterogeneity of DGA, highlights similarities and differences between those with and without a chromosome 22q11.2 deletion, and attempts to resolve some confusing features of conditions associated with DGA.

Autonomic innervation of the developing heart: origins and function

Maintenance of homeostatic circulation in mammals and birds is reliant upon autonomic innervation of the heart. Neural branches of mixed cellular origin and function innervate the heart at the arterial and venous poles as it matures, eventually coupling autonomic output to the cardiac components, including the conduction system. The development of neural identity is controlled by specific networks of genes and growth factors, whereas functional properties are governed by the use of different neurotransmitters. In this review, we summarize briefly the anatomic arrangement of the vertebrate autonomic nervous system and describe, in detail, the innervation of the heart. We discuss the timing of cardiac innervation in the chick and mouse, emphasizing the relationship of the cardiac neural networks to the anatomical structures within the heart. We also discuss the variable contribution of the neural crest to vagal cardiac nerves, and summarize the main neurotransmitters secreted by the developing sympathetic and parasympathetic autonomic divisions. We provide an overview of the main growth factor and gene families involved in neural development, discussing how these factors may impact upon the development of cardiac abnormalities in congenital syndromes associated with autonomic dysfunction.

Immune physiology in tissue regeneration and aging, tumor growth, and regenerative medicine

The immune system plays an important role in immunity (immune surveillance), but also in the regulation of tissue homeostasis (immune physiology). Lessons from the female reproductive tract indicate that immune system related cells, such as intraepithelial T cells and monocyte-derived cells (MDC) in stratified epithelium, interact amongst themselves and degenerate whereas epithelial cells proliferate and differentiate. In adult ovaries, MDC and T cells are present during oocyte renewal from ovarian stem cells. Activated MDC are also associated with follicular development and atresia, and corpus luteum differentiation. Corpus luteum demise resembles rejection of a graft since it is attended by a massive influx of MDC and T cells resulting in parenchymal and vascular regression. Vascular pericytes play important roles in immune physiology, and their activities (including secretion of the Thy-1 differentiation protein) can be regulated by vascular autonomic innervation. In tumors, MDC regulate proliferation of neoplastic cells and angiogenesis. Tumor infiltrating T cells die among malignant cells. Alterations of immune physiology can result in pathology, such as autoimmune, metabolic, and degenerative diseases, but also in infertility and intrauterine growth retardation, fetal morbidity and mortality. Animal experiments indicate that modification of tissue differentiation (retardation or acceleration) during immune adaptation can cause malfunction (persistent immaturity or premature aging) of such tissue during adulthood. Thus successful stem cell therapy will depend on immune physiology in targeted tissues. From this point of view, regenerative medicine is more likely to be successful in acute rather than chronic tissue disorders.

Temporal-spatial ablation of neural crest in the mouse results in cardiovascular defects

Neural crest cells are thought to play a critical role in human conotruncal morphogenesis and dysmorphogenesis. Much of our understanding of the contribution of neural crest to cardiovascular patterning comes from ablation and transplantation experiments in avian species. Although fate mapping experiments in mice suggests a conservation of function, the functional requirement for neural crest in cardiovascular development in mammals has not been formally tested. We used a novel two component genetic system for the temporal-spatial ablation of neural crest in the mouse. Affected embryos displayed a spectrum of cardiovascular outflow tract defects and aortic arch patterning abnormalities. We show that the severity of the cardiovascular phenotype is directly related to the level and extent of neural crest ablation. This is the first report of cardiac neural crest ablation in mammals, and it provides important insight into the role of the mammalian neural crest during cardiovascular development.

Differentially expressed genes in embryonic cardiac tissues of mice lacking Folr1 gene activity

BACKGROUND

Heart anomalies are the most frequently observed among all human congenital defects. As with the situation for neural tube defects (NTDs), it has been demonstrated that women who use multivitamins containing folic acid peri-conceptionally have a reduced risk for delivering offspring with conotruncal heart defects 123. Cellular folate transport is mediated by a receptor or binding protein and by an anionic transporter protein system. Defective function of the Folr1 (also known as Folbp1; homologue of human FRalpha) gene in mice results in inadequate transport, accumulation, or metabolism of folate during cardiovascular morphogenesis.

RESULTS

We have observed cardiovascular abnormalities including outflow tract and aortic arch arterial defects in genetically compromised Folr1 knockout mice. In order to investigate the molecular mechanisms underlying the failure to complete development of outflow tract and aortic arch arteries in the Folr1 knockout mouse model, we examined tissue-specific gene expression difference between Folr1 nullizygous embryos and morphologically normal heterozygous embryos during early cardiac development (14-somite stage), heart tube looping (28-somite stage), and outflow track septation (38-somite stage). Microarray analysis was performed as a primary screening, followed by investigation using quantitative real-time PCR assays. Gene ontology analysis highlighted the following ontology groups: cell migration, cell motility and localization of cells, structural constituent of cytoskeleton, cell-cell adhesion, oxidoreductase, protein folding and mRNA processing. This study provided preliminary data and suggested potential candidate genes for further description and investigation.

CONCLUSION

The results suggested that Folr1 gene ablation and abnormal folate homeostasis altered gene expression in developing heart and conotruncal tissues. These changes affected normal cytoskeleton structures, cell migration and motility as well as cellular redox status, which may contribute to cardiovascular abnormalities in mouse embryos lacking Folr1 gene activity.

Immune system involvement in the regulation of ovarian function and augmentation of cancer

Increasing evidence indicates a role for the immune system and mesenchymal-epithelial interactions in the regulation of ovarian function. Cytokines produced by mesenchymal cells can stimulate development and regression of ovarian structures. We report here that mesenchymal cells releasing surface molecules among epithelial cells--namely vascular pericytes and monocyte-derived cells (MDC)--and intraepithelial T lymphocytes are associated with oogenesis and formation of new primary follicles in both fetal and adult human ovaries. These activated mesenchymal cells interact with the ovarian surface epithelium, which appears to be a source of secondary germ cells and granulosa cells. Activated pericytes and MDC are also associated with stimulation of thecal development during selection of growing secondary follicles from the cohort of primary follicles. However, survival of the dominant follicle during mid-follicular phase selection is associated with a lack of activity of mesenchymal cells and retardation of thecal development, since immature granulosa cells lacking aromatase are unable to resist high levels of thecal androgens. Once the selected follicle matures (late follicular phase), it shows enhanced activity of thecal mesenchymal cells and advanced thecal development. Corpus luteum (CL) development is accompanied by a high activity of vascular pericytes and MDC. In mature CL and CL of pregnancy, luteal MDC and pericytes show a stable (inactive) state. Regression of the CL is associated with regression of pericytes, transformation of MDC into dendritic cells, infiltration by T lymphocytes, and binding of immunoglobulin G to the luteal cells. The immunoglobulin M (IgM) binds to young but not mature luteal cells. In the CL of pregnancy, IgM binds to luteal vessels, but not to luteal cells. Regressing CL shows IgM binding to both luteal cells and vessels. In ovarian cancers, highly activated MDC and sometimes activated pericytes (poorly differentiated carcinomas) are present. IgM binding is similar to that seen in the CL of pregnancy. These data indicate that vascular pericytes, MDC, T cells, and immunoglobulins may play an important role in the regulation of ovarian physiology and contribute to the augmentation of ovarian cancer growth.

Persistent Fifth Aortic Arch Associated with 22q11.2 Deletion Syndrome

BACKGROUND

Chromosome 22q11.2 deletion is frequently associated with conotruncal malformations and aortic arch anomalies. This study investigated the association of chromosome 22q11.2 deletion with clinical manifestations in four pediatric patients with persistent fifth aortic arch.

METHODS

Four patients with persistent fifth aortic arch treated between July 1997 and June 2004 were included in this retrospective study. There were two girls and two boys, aged 2 days to 11.3 years, with persistent fifth aortic arch and cardiac conotruncal malformations. Chart recordings, plain chest films, two-dimensional and Doppler echocardiograms, cardiac catheterization with angiograms, surgical findings, and cytogenetic study were analyzed.

RESULTS

Clinically, all four patients had the cardinal phenotypic features of 22q11.2 deletion syndrome, including cardiovascular malformations (conotruncal malformations and aortic arch anomalies), abnormal facies, thymic hypoplasia, canopy anomaly of the palate (high-arched palate, rather than cleft palate), and hypocalcemia (or hypoparathyroidism). All four patients were confirmed to have chromosome 22q11.2 deletion.

CONCLUSION

Congenital conotruncal malformations, including tetralogy of Fallot with pulmonary atresia or stenosis, and aortic arch anomalies including a persistent fifth aortic arch or a right aortic arch, should lead to suspicion of chromosome 22q11.2 deletion when manifested together with any one of the other four cardinal phenotypic features.

Prenatal alcohol exposure and fetal programming: effects on neuroendocrine and immune function

Alcohol abuse is known to result in clinical abnormalities of endocrine function and neuroendocrine regulation. However, most studies have been conducted on males. Only recently have studies begun to investigate the influence of alcohol on endocrine function in females and, more specifically, endocrine function during pregnancy. Alcohol-induced endocrine imbalances may contribute to the etiology of fetal alcohol syndrome. Alcohol crosses the placenta and can directly affect developing fetal cells and tissues. Alcohol-induced changes in maternal endocrine function can disrupt maternal-fetal hormonal interactions and affect the female's ability to maintain a successful pregnancy, thus indirectly affecting the fetus. In this review, we focus on the adverse effects of prenatal alcohol exposure on neuroendocrine and immune function, with particular emphasis on the hypothalamic-pituitary-adrenal (HPA) axis and the concept of fetal programming. The HPA axis is highly susceptible to programming during fetal development. Early environmental experiences, including exposure to alcohol, can reprogram the HPA axis such that HPA tone is increased throughout life. We present data that demonstrate that maternal alcohol consumption increases HPA activity in both the maternal female and the offspring. Increased exposure to endogenous glucocorticoids throughout the lifespan can alter behavioral and physiologic responsiveness and increase vulnerability to illnesses or disorders later in life. Alterations in immune function may be one of the long-term consequences of fetal HPA programming. We discuss studies that demonstrate the adverse effects of alcohol on immune competence and the increased vulnerability of ethanol-exposed offspring to the immunosuppressive effects of stress. Fetal programming of HPA activity may underlie some of the long-term behavioral, cognitive, and immune deficits that are observed following prenatal alcohol exposure.

Immunohistochemical assessment of the neurosecretory cells of the chicken thymus using a novel monoclonal antibody against avian chromogranin A

An immunocytochemical approach to the identification of neuroendocrine cells in the thymus of the chicken was taken based on a novel monoclonal antibody against turkey chromogranin A (CgA), a classic marker protein for neuroendocrine cells. CgA-immunoreactive cells were readily observed in the thymus, and were typically confined to the medullary side of the corticomedullary junction of the thymic lobules. Reversed transcription PCR confirmed local production of CgA in the thymus. The majority of CgA+ cells were small and round or oval in shape but some cells were larger and had conspicuous extensions. Immunofluorescent double staining experiments with antibodies against Neuron-specific enolase and with a neural crest marker (HNK-1) indicated no demonstrable overlap between the CgA-positive cells and either of the above cell populations, demonstrating the existence of three distinct neuronal/neuroendocrine cell populations in the avian thymus.

AP-2 and HNK-1 define distinct populations of cranial neural crest cells

OBJECTIVE

To determine if distinct populations of cranial neural crest cells (CNCC) exist by characterization of their divergent gene expression patterns.

DESIGN

Identification of unique populations of CNCC was determined by a combination of lineage and immunohistochemical analyses.

SETTING

Department of Pathology, Children's Hospital of Philadelphia and the University of Pennsylvania School of Medicine, Philadelphia, PA 19104.

RESULTS

We found antibodies of two proteins previously described as identifying all CNCC, label three populations of CNCC at specific time-points. Furthermore, the activating protein 2 (AP-2) expressing CNCC become neural or mesenchymal NCC derivatives whereas the HNK-1 labeled cells do not participate in the mesenchymal lineage.

CONCLUSION

These data provide molecular markers for unique CNCC fates and thus will be invaluable in the characterizing of craniofacial anomalies related to defects in NCCS. In addition, our data suggest AP-2 may function in determining the unique mesenchymal fate of CNCCs.

The role of chordin/Bmp signals in mammalian pharyngeal development and DiGeorge syndrome

The chordin/Bmp system provides one of the best examples of extracellular signaling regulation in animal development. We present the phenotype produced by the targeted inactivation of the chordin gene in mouse. Chordin homozygous mutant mice show, at low penetrance, early lethality and a ventralized gastrulation phenotype. The mutant embryos that survive die perinatally, displaying an extensive array of malformations that encompass most features of DiGeorge and Velo-Cardio-Facial syndromes in humans. Chordin secreted by the mesendoderm is required for the correct expression of Tbx1 and other transcription factors involved in the development of the pharyngeal region. The chordin mutation provides a mouse model for head and neck congenital malformations that frequently occur in humans and suggests that chordin/Bmp signaling may participate in their pathogenesis.

Septation and separation within the outflow tract of the developing heart

The developmental anatomy of the ventricular outlets and intrapericardial arterial trunks is a source of considerable confusion. First, major problems exist because of the multiple names and definitions used to describe this region of the heart as it develops. Second, there is no agreement on the boundaries of the described components, nor on the number of ridges or cushions to be found dividing the outflow tract, and the pattern of their fusion. Evidence is also lacking concerning the role of the fused cushions relative to that of the so-called aortopulmonary septum in separating the intrapericardial components of the great arterial trunks. In this review, we discuss the existing problems, as we see them, in the context of developmental and postnatal morphology. We concentrate, in particular, on the changes in the nature of the wall of the outflow tract, which is initially myocardial throughout its length. Key features that, thus far, do not seem to have received appropriate attention are the origin, and mode of separation, of the intrapericardial portions of the arterial trunks, and the formation of the walls of the aortic and pulmonary valvar sinuses. Also as yet undetermined is the formation of the free-standing muscular subpulmonary infundibulum, the mechanism of its separation from the aortic valvar sinuses, and its differentiation, if any, from the muscular ventricular outlet septum.

Neural crest and cardiovascular development: a 20-year perspective

BACKGROUND

Twenty years ago this year was the first publication describing a region of neural crest cells necessary for normal cardiovascular development. Ablation of this region in chick resulted in persistent truncus arteriosus, mispatterning of the great vessels, outflow malalignments, and hypoplasia or aplasia of the pharyngeal glands.

METHODS

We begin with a historical perspective and then review the progress that has been made in the ensuing 20 years in determining the direct and indirect contributions of the neural crest cells, now termed cardiac neural crest cells, in cardiovascular and pharyngeal arch development. Many of the molecular pathways that are now known to influence the specification, migration, patterning and final targeting of the cardiac neural crest cells are also reviewed.

RESULTS

Although much knowledge has been gained by using many genetic manipulations to understand the cardiac neural crest cells' role in cardiovascular development, most models fail to explain the phenotypes seen in syndromic and non-syndromic human congenital heart defects, such as the DiGeorge syndrome.

CONCLUSIONS

We propose that the cardiac neural crest exists as part of a larger cardiocraniofacial morphogenetic field and describe several human syndromes that result from abnormal development of this field.

Hensen's node gives rise to the ventral midline of the foregut: implications for organizing head and heart development

Patterning of the ventral head has been attributed to various cell populations, including endoderm, mesoderm, and neural crest. Here, we provide evidence that head and heart development may be influenced by a ventral midline endodermal cell population. We show that the ventral midline endoderm of the foregut is generated directly from the extreme rostral portion of Hensen's node, the avian equivalent of the Spemann organizer. The endodermal cells extend caudally in the ventral midline from the prechordal plate during development of the foregut pocket. Thus, the prechordal plate appears as a mesendodermal pivot between the notochord and the ventral foregut midline. The elongating ventral midline endoderm delimits the right and left sides of the ventral foregut endoderm. Cells derived from the midline endoderm are incorporated into the endocardium and myocardium during closure of the foregut pocket and fusion of the bilateral heart primordia. Bilateral ablation of the endoderm flanking the midline at the level of the anterior intestinal portal leads to randomization of heart looping, suggesting that this endoderm is partitioned into right and left domains by the midline endoderm, thus performing a function similar to that of the notochord in maintaining left-right asymmetry. Because of its derivation from the dorsal organizer, its extent from the forebrain through the midline of the developing face and pharynx, and its participation in formation of a single midline heart tube, we propose that the ventral midline endoderm is ideally situated to function as a ventral organizer of the head and heart.

Conotruncal anomalies in the trisomy 16 mouse: an immunohistochemical analysis with emphasis on the involvement of the neural crest

The trisomy 16 (Ts16) mouse is generally considered a model for human Down's syndrome (trisomy 21). However, many of the cardiac defects in the Ts16 mouse do not reflect the heart malformations seen in patients suffering from this chromosomal disorder. In this study we describe the conotruncal malformations in mice with trisomy 16. The development of the outflow tract was immunohistochemically studied in serially sectioned hearts from 34 normal and 26 Ts16 mouse embryos ranging from 8.5 to 14.5 embryonic days. Conotruncal malformations observed in the Ts 16 embryos included double outlet right ventricle, persistent truncus arteriosus, Tetralogy of Fallot, and right-sided aortic arch. This spectrum of malformations is remarkably similar to that seen in humans suffering from DiGeorge syndrome (DGS). As perturbation of neural crest development has been proposed in the pathogenesis of DGS we specifically focussed on the fate of neural crest derived cells during outflow tract development of the Ts16 mouse using an antibody that enabled us to trace these cells during development. Severe perturbation of the neural crest-derived cell population was observed in each trisomic specimen. The abnormalities pertained to: 1) the size of the columns of neural crest-derived cells (or prongs); 2) the spatial orientation of these prongs within the mesenchymal tissues of the outflow tract; and 3) the location in which the neural crest cells interact with the myocardium. The latter abnormality appeared to be responsible for ectopic myocardialization found in trisomic embryos. Our observations strongly suggest that abnormal neural crest cell behavior is involved in the pathogenesis of the conotruncal malformations in the Ts16 mouse.

Mouse fzd4 maps within a region of chromosome 7 important for thymus and cardiac development

The cardiac neural crest (CNC) plays a central role in development of the thymus gland and cardiovascular system. Through morphological and histological characterization of embryos homozygous for the Del(7)Tyr(c-112K) and Del(7)Tyr(c-3H) albino deletions, we identified abnormalities that are consistent with aberrant development of tissues requiring CNC contributions. The defects include incompletely penetrant heart and great vessel patterning defects and hypoplastic thymus glands. The CNC phenotype is complemented by the partially overlapping deletion Del(7)Tyr(c-23DVT). Combined, these results suggest that a functional region necessary for development of CNC derived tissues is located between the Del(7)Tyr(c-23DVT) and Del(7)Tyr(c-112K) distal deletion breakpoints. This interval encompasses a functional region previously identified as important for juvenile survival (juvenile development and fertility, jdf). Using deletion mapping, we localized the Frizzled4 (Fzd4) gene to the jdf/thymus and cardiac development intervals.

Malformations in offspring of diabetic rats: morphometric analysis of neural crest-derived organs and effects of maternal vitamin E treatment

BACKGROUND

We have previously reported on a malformation-prone Sprague-Dawley rat substrain (U), which presents a high frequency of micrognathia in the offspring of diabetic mothers. This malformation is related to impaired development of the cranial neural crest cells (NCC); the defect may be prevented by antioxidative treatment of the mother.

METHODS

We have therefore investigated whether fetuses of diabetic rats display other malformations associated with altered cranial NCC development and whether maternal vitamin E supplementation may affect such malformations.

RESULTS

Fetuses of diabetic rats showed low-set external ears, severely malformed Meckel's cartilage, small thyroid and thymus, and absence of parathyroid glands. Cardiac anomalies were frequently observed, including rightward displacement of the aorta, double outlet right ventricle (DORV), persistent truncus arteriosus (PTA) combined with ventricular septal defects due to a malaligned outlet septum. The malformations in the outflow tract included abnormalities of the great arteries; right-sided aortic arch/descending aorta, and double aortic arches. These defects tended to occur together within individual fetuses. Maternal dietary treatment with 2% vitamin E markedly reduced the severity of the malformations.

CONCLUSIONS

The phenotypic appearance of these defects is strikingly similar to the DiGeorge anomaly in humans, which has been found in children of diabetic mothers together with an overrepresentation of PTA and DORV. The malformations associated with defective NCC development in the offspring of diabetic U rats show several morphological similarities to those in humans; hence the teratogenic mechanisms may be similar and accessible for study.

Clinicopathologic study of ectomesenchymomas from Intergroup Rhabdomyosarcoma Study Groups III and IV

Ectomesenchymomas (EM) are rare malignant neoplasms usually consisting of rhabdomyosarcoma (RMS) with a neural component. Only 21 cases have been previously reported. Here we extend the clinicopathologic spectrum of EM by describing our findings in 15 cases. Only 5 patients were infants; 10 were < or =3 years old and 5 were > or =6 years old. No male predilection was observed; 7 were female. The originating institutional diagnoses were; RMS (12), undifferentiated sarcoma (1), or EM (2), suggesting underdiagnosis of this entity. The primary tumor sites included external genital (5), pelvis/abdomen (6), head and neck (3), and extremity (1). The size of the primary neoplasm was usually > or =5 cm at diagnosis but dissemination only occurred in a minority. Local infiltration was not uncommon. These neoplasms were typically multilobate, thinly encapsulated, hemorrhagic, and necrotic. Light microscopic features were highly variable, but embryonal RMS with scattered or clustered ganglion cells, often in lacunae, was characteristic. In some cases, primitive neuroblastic or neuroectodermal areas were found and/or a component of alveolar RMS was seen. Focal anaplasia was occasionally observed. Mitotic activity appears higher than previously appreciated and some necrosis was invariably present. Electron microscopy was performed in 11 cases, which confirmed skeletal muscle +/- neural differentiation. Cytogenetic studies performed in five cases revealed no specific abnormality. Monoclonal neuron-specific enolase was the best marker of ganglion cells and primitive neural elements. MIC-2 (CD99) membrane expression was not definitively present in any of the six cases examined. A number of the above parameters appear to be of some prognostic significance, but overall, these neoplasms appear to have a similar outcome as would be predicted for their RMS element alone (exclusive of any neural component), with respect to the RMS subtype, age of the patient, and anatomic location of the neoplasm.

Contribution of the cervical sympathetic ganglia to the innervation of the pharyngeal arch arteries and the heart in the chick embryo

In the chick heart, sympathetic innervation is derived from the sympathetic neural crest (trunk neural crest arising from somite level 10-20). Since the trunk neural crest gives rise to sympathetic ganglia of their corresponding level, it suggests that the sympathetic neural crest develops into cervical ganglia 4-14. We therefore tested the hypothesis that, in addition to the first thoracic ganglia, the cervical ganglia might contribute to cardiac innervation as well. Putative sympathetic nerve connections between the cervical ganglia and the heart were demonstrated using the differentiation markers tyrosine hydroxylase and HNK-1. In addition, heterospecific transplantation (quail to chick) of the cardiac and trunk neural crest was used to study the relation between the sympathetic neural crest and the cervical ganglia. Quail cells were visualized using the quail nuclear antibody QCPN. The results by immunohistochemical study show that the superior and the middle cervical ganglia and possibly the carotid paraganglia contribute to the carotid nerve. This nerve subsequently joins the nodose ganglion of the vagal nerve via which it contributes to nerve fibers in cardiac vagal branches entering the arterial and venous pole of the heart. In addition, the carotid nerve contributes to nerve fibers connected to putative baro- and chemoreceptors in and near the wall of pharyngeal arch arteries suggesting a role of the superior and middle cervical ganglia and the paraganglia of the carotid plexus in sensory afferent innervation. The lower cervical ganglia 13 and 14 contribute predominantly to nerve branches entering the venous pole via the anterior cardinal veins. We did not observe a thoracic contribution. Heterospecific transplantation shows that the cervical ganglia 4-14 as well as the carotid paraganglia are derived from the sympathetic neural crest. The cardiac neural crest does not contribute to the neurons of the cervical ganglia. We conclude that the cervical ganglia contribute to cardiac innervation which explains the contribution of the sympathetic neural crest to the innervation of the chick heart.

Cloning, chromosome mapping and expression analysis of the HIRA gene from Drosophila melanogaster

The human HIRA gene was identified as a putative transcriptional regulator mapping within the DiGeorge syndrome critical region at 22q11. HIRA-related proteins have been described in a number of species, but functional information concerning family members is only available in Saccharomyces cerevisiae, where the Hir1p and Hir2p proteins are known to be transcriptional corepressors. In order to analyse conservation of HIRA-related genes and to provide resources for functional studies in another model organism we have isolated the HIRA gene from Drosophila melanogaster (dhira). The 3374 nucleotide cDNA encodes a protein of 1047 aa, showing 42% identity with the human protein. Alignment with the predicted HIRA proteins from human, mouse, chick and pufferfish reveals strong conservation within the N-terminal region which contains seven WD domains, with less conservation of C-terminal sequences. In situ hybridisation to salivary gland chromosomes indicates that the gene resides in region 7B2-3 of the X chromosome. Dhira is expressed through embryonic development and at lower levels during larval and pupal development. The expression of dhira is dramatically increased in early embryos and in females, suggesting that the dhira mRNA could be maternally deposited in the embryos.

Gscl, a gene within the minimal DiGeorge critical region, is expressed in primordial germ cells and the developing pons

Gscl, a paired-type homeobox gene, has been implicated in the pathology of DGS/VCFS by virtue of its genomic location and its structural similarity to the Gsc gene family. Immunohistochemical and in situ studies were performed to examine the expression pattern of this gene during embryonic development. A polyclonal antibody, generated to the full-length protein and shown to be specific for GSCL by both Western blotting and immunofluorescence, was used for immunohistochemical localization. Both in situ and antibody staining localized GSCL expression to a cluster of cells in the pons region of the developing brain. This GSCL expression pattern showed partial overlap with that of Pax6. More detailed immunohistochemistry revealed the GSCL in primordial germ cells during migration from the epithelium of the hindgut and later as they colonize the developing gonads. GSCL was not detected in tissues affected in DGS/VCSF.

Characterization and mutation analysis of goosecoid-like (GSCL), a homeodomain-containing gene that maps to the critical region for VCFS/DGS on 22q11

Velocardiofacial syndrome (VCFS) is a developmental disorder characterized by conotruncal heart defects, craniofacial anomalies, and learning disabilities. VCFS is phenotypically related to DiGeorge syndrome (DGS) and both syndromes are associated with hemizygous 22q11 deletions. Because many of the tissues and structures affected in VCFS/DGS derive from the pharyngeal arches of the developing embryo, it is believed that haploinsufficiency of a gene(s) involved in embryonic development may be responsible for its etiology. A homeodomain-containing gene, Goosecoidlike (GSCL), has been recently described, and it resides in the critical region for VCFS/DGS on 22q11. GSCL is related to the Goosecoid gene (GSC) in both sequence of the homeodomain and genomic organization. Gsc in the mouse is expressed during early and midembryogenesis and is required for craniofacial rib, and limb development. The chick homolog of GSCL, termed GSX, is expressed during early chick embryogenesis. We detected GSCL expression in human embryos and biphasic expression in mouse embryos. It is possible that the vertebrate GSCL gene is also required for embryonic development. Due to its location in the critical region on 22q11, GSCL is an excellent candidate gene for VCFS/DGS. The vertebrate GSC protein has the same DNA binding specificity as the Drosophila morphogen, bicoid. Upon examination of the putative GSCL promoter, we found three sequence elements with an exact match to the reverse complement of the bicoid DNA recognition motif, suggesting that GSC, or possibly GSCL itself, regulates the transcription of GSCL. Sequence analysis of the putative promoter and the coding region of GSCL was performed on the DNA template from 17 VCFS patients who did not have a detectable 22q11 deletion to identify mutations. We did not detect a mutation in this set of VCFS patients. A polymorphism was detected in codon 47 of exon 1.

Development of the thymus

Proper development of the thymus is critical for an individual to acquire full immune capability. A full complement of the components that participate in thymic development, interacting with each other at the correct time, is required for maturation. In order to establish the microenvironment necessary for T-cell differentiation, the epithelial primordium of the thymus must expand from pharyngeal endoderm with the aid of contributions from the ectoderm. Experimental studies have established the importance of mesenchymal derivatives from the neural crest in functional development of the epithelial primordium. Interfering with this process inhibits thymic development in a manner similar to that observed in congenital conditions such as the DiGeorge syndrome and the fetal alcohol syndrome. These observations provide clues to understanding the origin of defects in thymus-dependent immunity, and point the way to studies that will expand our understanding of the controls that are involved in genetic and environmental factors impacting on this process.

Conotruncal cardiac anomalies and otitis media

BACKGROUND

The neural crest influences the differentiation of the branchial arches, including the precursor tissue of the cardiac outflow tract and the eustachian tubes. Abnormal eustachian tubes are associated with otitis media. We hypothesized a relationship between conotruncal anomalies and eustachian tube anomalies.

METHODS

We surveyed 115 nonsyndromic patients, aged 5 to 20 years, attending a state-run pediatric cardiology clinic. The cardiac anomalies were conotruncal (transposition of the great arteries, tetralogy of Fallot, or aortic stenosis) or nonconotruncal (atrial septal defect, tricuspid atresia, atrioventricular canal). Tympanic membrane photographs were categorized independently by two physicians as to normal, abnormal (scarred or other indication of otitis proneness), or indeterminate.

RESULTS

For the 37 patients who had both ears categorized as normal or abnormal by both physicians, 20 of the 26 with a conotruncal anomaly had evidence of otitis media. In contrast, only 4 of 11 with nonconotruncal cardiac anomaly had evidence of otitis (p < 0.03; relative risk [conotruncal vs nonconotruncal], 5.83; 95% confidence interval, 1.26 to 26.95).

CONCLUSION

The concept is supported that a neural crest determined branchial field defect influences the development of the cardiac outflow tract and the eustachian tubes. Children with congenital cardiac conotruncal anomalies are otitis media prone.

Absence of neural crest cell regeneration from the postotic neural tube

The preotic neural tube has a variable ability for regeneration of neural crest depending on the neuraxial level. There is robust regeneration of neural crest in the caudal midbrain/rostral hindbrain. In contrast, removal of the cardiac neural crest results in cardiovascular abnormalities suggesting the lack of regeneration in this area, although the regenerative capacity of the cardiac crest region has never been tested directly. Premigratory cardiac neural crest was ablated bilaterally using laser irradiation or extirpation by tungsten needle, and the remaining ventral neural tube was labeled with DiI to examine any neural crest regeneration from the neural tube. The results indicate that there is very little regeneration of crest cells from the cardiac region of the neural tube if the ablation is done prior to the 5-somite stage and no regeneration after the 6-somite stage with either ablation procedure. Furthermore no compensatory response occurs from the adjacent regions of the neural crest. By contrast, we were able to confirm that regeneration of neural crest occurs in the preotic rhombencephalic neural tube even after laser irradiation. An analysis in the trunk region suggests that the trunk neural tube is similar to the cardiac region in that it does not regenerate crest cells in the ventral migratory pathway after ablation. However, melanocytes generated cranial and caudal to the ablated region migrate radially and fill in the ablated region so that there is no interruption of the normal pigment pattern. This study indicates that even though there is a variable capacity for crest regeneration in the preotic neural tube, the postotic neural tube does not have such regenerative ability.

A region of mouse chromosome 16 is syntenic to the DiGeorge, velocardiofacial syndrome minimal critical region

DGS and VCFS, haploinsufficiencies characterized by multiple craniofacial and cardiac abnormalities, are associated with a microdeletion of chromosome 22q11.2. Here we document synteny between a 150-kb region on mouse chromosome 16 and the most commonly deleted portion of 22q11.2. Seven genes, all of which are transcribed in the early mouse embryo, have been identified. Of particular interest are two serine/threonine kinase genes and a novel goosecoid-like homeobox gene (Gscl). Comparative sequence analysis of a 38-kb segment reveals similarities in gene content, order, exon composition, and transcriptional direction. Therefore, if deletion of these genes results in DGS/VCFS in humans, then haploinsufficiencies involving this region of chromosome 16 should recapitulate the developmental field defects characteristic of this syndrome.

Developmental toxicity of concanavalin A in rats: association with restricted migration of neural crest cells

Concanavalin A (Con A), a plant lectin, was injected iv into pregnant rats as a single dose of 5, 10 or 20 mg/kg on gestational day (GD) 8, to investigate developmental toxicity in foetuses at term and to examine histologically embryos between GD 10 and 12. There were high incidences of various malformations in the 10 and 20 mg/kg groups: externally, craniofacial dysplasia and closure defects of the ventral body wall; internally, anophthalmia and cardiovascular malformations; and in the skeleton, anomalies of the anterior region of the vertebrae and ribs. Histological examination revealed that neural crest cells (NCC) in the control embryos appeared to be streaming from the neural crest towards the ventral region on GD 10, 11 and 12, and reached the region of the branchial arches on GD 12. By contrast, those in the Con A-treated embryos were aggregated near the dorsal region on GD 10 and 11, and had not reached the destination even on GD 12. These findings suggest that pathogenesis of developmental toxicity of Con A in rats is associated with disturbance of NCC migration and inhibition of their pluripotentiality at the destination.

Cardiac neural crest is essential for the persistence rather than the formation of an arch artery

Double-label immunohistochemistry was used to compare early aortic arch artery development in cardiac neural crest-ablated and sham-operated quail embryos ranging from stage 13 to stage 18. The monoclonal antibody QH-1 labeled endothelial cells and their precursors, and HNK-1 labeled migrating neural crest cells. In the sham-operated embryos, the third aortic arch artery developed from a lumenizing strand of endothelial precursors that became separated from the pharyngeal endoderm by migrating cardiac neural crest cells as they ensheathed the artery. The arch artery of the neural crest-ablated embryos lumenized but failed to become separated from the pharyngeal endoderm, indicating that neural crest is unnecessary for the early formation of the aortic arch artery. However, once blood flow was initiated through the third arch artery of crest-ablated embryos at stage 16, the artery became misshapen and sinusoidal. By embryonic day 3, abnormal connections to the dorsal aorta occurred and bilateral symmetry was lost, suggesting that the loss of neural crest-derived ectomesenchyme destabilizes the nascent artery. Although here we show no loss of the third arch artery, past studies have reported hypoplasia or missing carotids in older neural crest-ablated embryos (Bockman et al. [1987] Am. J. Anat. 180:332-341; Bockman et al. [1989] Anat. Rec. 225:209-217; Nishibatake et al. [1987] Circulation 75:255-264; Tomita et al. [1991] Circulation 84:1289-1295). We suggest that the cardiac neural crest is essential for the persistence of an arch artery, but not its formation. Furthermore, since changes in the development of the arch artery are seen prior to the formation of the tunica media, it is suggested that a critical period is reached in the development of the arch artery, after lumenization, but prior to the formation of the tunica media, which necessitates the presence of the cardiac neural crest.

Cloning a balanced translocation associated with DiGeorge syndrome and identification of a disrupted candidate gene

DiGeorge syndrome (DGS), a developmental defect, is characterized by cardiac defects and aplasia or hypoplasia of the thymus and parathyroid glands. DGS has been associated with visible chromosomal abnormalities and microdeletions of 22q11, but only one balanced translocation--ADU/VDU t(2;22)(q14;q11.21). We now report the cloning of this translocation, the identification of a gene disrupted by the rearrangement and the analysis of other transcripts in its vicinity. Transcripts were identified by direct screening of cDNA libraries, exon amplification, cDNA selection and genomic sequence analysis using GRAIL. Disruption of a gene in 22q11.2 by the breakpoint and haploinsufficiency of this locus in deleted DGS patients make it a strong candidate for the major features associated with this disorder.

Midline maxillofacial skeleton in human anencephalic fetuses

The purpose of this study was to describe the midline maxillofacial skeleton (the axial skeleton anterior to the sella turcica) in 15 human anencephalic fetuses (14-19 weeks of gestation) by radiography and histology, and to relate the findings to skeletal patterns in the remaining part of the axial skeleton. Four patterns in the maxillofacial skeleton were recognized: normal structures, slightly deformed (6 cases); cleft palate (3 cases); incomplete nasal septum (3 cases); multilocular ethmoid cartilage (3 cases). No association was found between skeletal patterns in the different parts of the axial skeleton. The study demonstrates the existence of a developmental borderline in the anencephalic axial skeleton in the region of the sella turcica. It is presumed that this borderline indicates the boundary between skeletal tissue developed around the notochord (posterior axial skeleton) and the anterior skeletal components derived from neural crest cells.

Familial interruption of the aortic arch

Interruption of the aortic arch (IAA) is an important congenital cardiac malformation occurring in 1.4% of cases with a congenital cardiac malformation. Only two reports have described IAA in siblings, each with type B and an anomalous right subclavian artery. We report the occurrence of IAA type B with an anomalous right subclavian artery in two siblings and their half-sibling, each of whom had additional conotruncal cardiac malformations. Recent evidence suggests that conotruncal cardiac malformations, including IAA type B, are related to abnormalities of neural crest cell migration. Thus, the family reported herein may manifest a syndrome related to alterations in mesenchymal tissue/neural crest cell migration.

Congenital heart disease in CHARGE association

This study reviews the spectrum of congenital heart disease and associated anomalies in 59 patients with the CHARGE association. We have analyzed our clinical experience in managing the cardiovascular anomalies and have reviewed outcome and risk factors for mortality. This study also highlights problems of cardiac management in children born with multiple system involvement. Twenty patients have died; actuarial survival was 78% at 1 year and 60% at 10 years. In only four of the nonsurvivors could their demise be ascribed to their underlying congenital heart disease. We found the outlook for survival was poor if more than one of the following three features were present; cyanotic cardiac lesions, bilateral posterior choanal atresia, or tracheoesophageal fistula. However, mortality was largely due not to the structural heart or choanal abnormalities, but instead reflected the underlying pharyngeal and laryngeal incoordination which resulted in aspiration of secretions. Furthermore, outcome is likely to be improved if collaboration between specialist surgical teams allows necessary procedures to be performed using the minimum of anesthetics. Examination of both the short- and long-term management of these children has stressed the importance of a multidisciplinary approach to their care. The pattern of cardiac defects was not random; lesions within the Fallot spectrum accounted for 33% of their congenital heart disease. Atrioventricular septal defects were also overrepresented. Not all cardiovascular defects could be explained by hypothesizing a neural crest etiology.

Differentiation of neurogenic precursors within the neural crest cell lineage

It has been suggested that many, if not all crest-derived neurons develop from a limited subpopulation of neurogenic precursors. To develop cell-type specific markers that identify these precursors directly we have used differential screening of crest-derived cell populations known to have, or not to have, neurogenic ability. We have determined that the neuron-specific human auto-antibodies designated Anti-Hu bind to cytoplasmic and nuclear determinants not only in mature avian neurons and neuroendocrine cells but also in subpopulations of morphologically non-neuronal avian crest-derived cells. Significantly, these Anti-Hu+ non-neuronal crest-derived cells are present only in populations that have neurogenic ability and are absent from populations that lack neurogenic ability. Moreover, following additional development in vivo or in vitro, Anti-Hu+ non-neuronal crest-derived cells appear to express other neuronal traits. These results suggest that Anti-Hu-immunoreactivity is an early indicator of neurogenesis among crest-derived cells, and that Anti-Hu+ non-neuronal cells are either neurogenic precursors or immature neurons. Similarly, using the same differential screening paradigm, we have identified two monoclonal antibodies, designated 12E10 and 17F5, which also label both neurons and some apparently nonneuronal cells in neurogenic populations of neural crest cells. Anti-Hu-IR appears to precede expression of either of these two markers.

Association of Hirschsprung's disease and Müllerian inhibiting substance deficiency

An infant who presented with Hirschsprung's disease was found to also have the clinical features of persistent Müllerian duct syndrome and on testing to have Müllerian inhibiting substance deficiency. This association has not been previously reported. While this may be a coincidence, recent reports indicate intersex conditions can be associated with Hirschsprung's disease.

Anomalous right coronary artery associated with sudden death: an example of a neural crest migration defect

A unique right coronary artery anomaly of hemodynamic significance was discovered in a young adult who suddenly died. In addition, abnormally migrated, or supernumerary, thymic tissue with embedded parathyroid glands was present. This combination of congenital malformations suggests that the pathogenesis of this rare cardiac anomaly may be explained by a cranial neural crest defect.

Inhibition of epibranchial placode-derived ganglia in the developing rat by bisdiamine

Although bisdiamine has been shown to affect the development of mammals, its effect on the nervous system has gone largely unrecognized. In the present study, rats were given bisdiamine by gavage on days 9 and 10 of pregnancy. They were sacrificed at intervals and the fetuses were prepared for study of serial sections stained with hematoxylin and eosin, or by immunohistochemical reaction with HNK-1 monoclonal antibody. HNK-1 reacted strongly with the nervous system, allowing precise analysis of the components and their relationships. Controls receiving no bisdiamine were prepared and studied in parallel with the experimental fetuses. Administration of bisdiamine inhibited development of the petrosal and nodose ganglia, altered associations of the glossopharyngeal, vagus, and hypoglossal nerves, and inhibited contributions of vagal nerve fibers to the developing enteric system. The proximal ganglia of the glossopharyngeal and vagus nerves developed normally. It is concluded that bisdiamine affects, directly or indirectly, the differentiation of nervous components derived from the epibranchial placodes. It seems likely that these placode-derived components serve as pioneer neurons in establishing the pathway for the posteriorly extending trunks of the glossopharyngeal and vagus nerves. The early changes in congenital conditions such as the DiGeorge syndrome may not be limited to alterations in neural crest derivatives. It may be worthwhile to investigate more closely whether there are alterations in the nervous system associated with these syndromes.

Identification of early neurogenic cells in the neural crest lineage

Pluripotent neural crest cells are restricted progressively during development. The sequence of restrictions and the time(s) in early development at which such restrictions are imposed on crest-derived cells are largely unknown. We have used a human autoantibody (Anti-Hu) to characterize neurogenic populations of avian neural crest-derived cells. Anti-Hu binds specifically to neurons and neuroendocrine cells in older (greater than E4) quail embryos. Early in development, Anti-Hu also binds a subpopulation of neural crest-derived cells that lack neuronal morphology and do not express other neuronal traits. These cells may represent a putative neurogenic precursor subpopulation within the early crest cell lineage. To test this hypothesis, we have characterized Anti-Hu immunoreactivity within crest-derived populations known to have, or to lack, the ability to give rise to new neurons. We report that the presence of Anti-Hu+ nonneuronal cells is correlated with the neurogenic ability of a given cell population. Moreover, Anti-Hu+ nonneuronal cells are transient and appear to be replaced by Anti-Hu+ neuronal cells. We conclude that Anti-Hu is a very early indicator of neurogenesis among crest-derived cells and that Anti-Hu+ nonneuronal cells are either neurogenic precursors or immature neurons.

A tissue culture model for studying ethanol toxicity on embryonic heart cells

A tissue system in which fibroblasts and myocytes from chick embryonic hearts were separately maintained was used to study the toxicity of ethanol. To reproduce the teratogenic effects of acute, high concentrations of ethanol typical of "binge" drinking, an open tissue culture system was employed. With open cultures, the cells were initially exposed to peak alcohol levels for approximately 6 hr and were exposed to decreasing concentrations of ethanol for the remainder of each 24 hr period. After the first day of ethanol exposure, there was substantial cell loss in both fibroblast and myocyte cultures. Alcohol-induced cell loss was dose-dependent. Despite decreased cell density after the first day of ethanol exposure, the surviving cells differentiated into monolayers of fibroblasts or beating cardiac muscle fibers. However, both ethanol-exposed fibroblasts and myocytes appeared atrophic, that is, smaller and shrunken. Electrophoretic analysis or these ethanol-exposed fibroblast and myocyte cultures revealed specific reduction in the cellular contents of alpha-actinin, myosin, and actin. These decreases in cytoskeletal proteins may be responsible for the morphological abnormalities noted in these cells.

Hirschsprung's disease: associated abnormalities and demography

We here examine the demographic parameters of patients with Hirschsprung's disease. The study population includes all patients with histologically confirmed disease treated at the Children's Hospital Medical Center of Boston over the 25-year period extending from 1961 through the first quarter of 1986. There were 179 cases. Overall, children with Hirschsprung's disease were found less likely to be first born (P less than .01). This relationship was seen to persist irrespective of maternal age, maternal race, or type of disease. The implications of this finding are discussed. Overall, 22% of these children had one or more associated abnormalities involving the neurological, cardiovascular, urological, and gastrointestinal systems. Many of the disorders appeared to be related to neurocrestopathies. Frequent associations included Down's syndrome, defects in cardiac septation, tetralogy of Fallot, and Dandy-Walker syndrome. These conditions occurred more frequently than would have been predicted through chance alone. This study found no association between an increased maternal age and the occurrence of Hirschsprung's disease. This study also found that approximately 7% of the affected children had been born prematurely.