Migration and differentiation of neural crest cells

Alternative Balance between Transcriptional and Epigenetic Regulation during Developmental Proliferation of Human Cranial Neural Crest Cells

Cranial neural crest cells are implicated in multiple transcriptional events at the different stages of differentiation during development. The alteration of some transcription factors expressed during neural crest development, like PAX7, could be implicated in the etiology of face malformation in murine models. Epigenetic regulation has been shown to be an important mechanistic actor in the control of timing and the level of gene expression at different stages of neural crest development. During this work, we investigated the interconnection between epigenetics and transcription factors across a diversity of human development cranial neural crest cells. Across a diversity of neural cells from human developing cranial tissues, in accordance with their proliferation stage, an alternative balance of regulation between transcription factors and epigenetic factors was identified.

Single-Cell Characterization of the Frizzled 5 (Fz5) Mutant Mouse and Human Persistent Fetal Vasculature (PFV)

Purpose

Persistent fetal vasculature (PFV) is a pathological condition accounting for 4.8% of children's blindness in the United States. However, the PFV cell composition and pathogenetic mechanisms are poorly understood. This study aims to characterize PFV cell composition and associated molecular features and attempts to lay a foundation for further understanding the disease.

Methods

Immunohistochemistry was conducted to characterize cell types at the tissue level. Single-cell RNA sequencing (sc-RNAseq) was performed on the vitreous cells derived from normal and Fz5 mutant mice at two early postnatal ages and human PFV samples. Bioinformatic tools were used to cluster cells and analyze their molecular features and functions.

Results

The findings of this study are as follows: (1) a total of 10 defined and one undefined cell types were characterized in both the hyaloid vessel system and PFV by sc-RNAseq and immunohistochemistry; (2) neural crest-derived melanocytes, astrocytes, and fibroblasts were specifically retained in the mutant PFV; (3) Fz5 mutants were found to possess more vitreous cells at early postnatal age 3 but returned to similar levels as the wild type at postnatal age 6; (4) altered phagocytic and proliferation environments and cell-cell interactions were detected in the mutant vitreous; (5) the human PFV samples shared fibroblast, endothelial and macrophage cell types with the mouse, but having distinct immune cells including T cells, NK cells and Neutrophils; and last, (6) some neural crest features were also shared between certain mouse and human vitreous cell types.

Conclusions

We characterized PFV cell composition and associated molecular features in the Fz5 mutant mice and two human PFV samples. The excessively migrated vitreous cells, intrinsic molecular properties of these cells, phagocytic environment, and cell-cell interactions may together contribute to PFV pathogenesis. Human PFV shares certain cell types and molecular features with the mouse.

Quantitative Experimental Embryology: A Modern Classical Approach

Experimental Embryology is often referred to as a classical approach of developmental biology that has been to some extent replaced by the introduction of molecular biology and genetic techniques to the field. Inspired by the combination of this approach with advanced techniques to uncover core principles of neural crest development by the laboratory of Roberto Mayor, we review key quantitative examples of experimental embryology from recent work in a broad range of developmental biology questions. We propose that quantitative experimental embryology offers essential ways to explore the reaction of cells and tissues to targeted cell addition, removal, and confinement. In doing so, it is an essential methodology to uncover principles of development that remain elusive such as pattern regulation, scaling, and self-organisation.

Single-cell transcriptomic analysis of zebrafish cranial neural crest reveals spatiotemporal regulation of lineage decisions during development

Neural crest (NC) cells migrate throughout vertebrate embryos to give rise to a huge variety of cell types, but when and where lineages emerge and their regulation remain unclear. We have performed single-cell RNA sequencing (RNA-seq) of cranial NC cells from the first pharyngeal arch in zebrafish over several stages during migration. Computational analysis combining pseudotime and real-time data reveals that these NC cells first adopt a transitional state, becoming specified mid-migration, with the first lineage decisions being skeletal and pigment, followed by neural and glial progenitors. In addition, by computationally integrating these data with RNA-seq data from a transgenic Wnt reporter line, we identify gene cohorts with similar temporal responses to Wnts during migration and show that one, Atp6ap2, is required for melanocyte differentiation. Together, our results show that cranial NC cell lineages arise progressively and uncover a series of spatially restricted cell interactions likely to regulate such cell-fate decisions.

Tatarakis et al. provide a single-cell transcriptomic timeline of cranial neural crest (NC) development in zebrafish and address long-standing questions surrounding the integration of NC cell migration and lineage specification. They find that lineages are specified mid-migration. These fate decisions correspond to shifts in Wnt signaling, and lineages rapidly segregate.

Neogenin-loss in neural crest cells results in persistent hyperplastic primary vitreous formation

Neogenin is a transmembrane receptor critical for multiple cellular processes, including neurogenesis, astrogliogenesis, endochondral bone formation, and iron homeostasis. Here we present evidence that loss of neogenin contributes to pathogenesis of persistent hyperplastic primary vitreous (PHPV) formation, a genetic disorder accounting for ~ 5% of blindness in the USA. Selective loss of neogenin in neural crest cells (as observed in Wnt1-Cre; Neof/f mice), but not neural stem cells (as observed in GFAP-Cre and Nestin-Cre; Neof/f mice), resulted in a dysregulation of neural crest cell migration or delamination, exhibiting features of PHPV-like pathology (e.g. elevated retrolental mass), unclosed retinal fissure, and microphthalmia. These results demonstrate an unrecognized function of neogenin in preventing PHPV pathogenesis, implicating neogenin regulation of neural crest cell delamination/migration and retinal fissure formation as potential underlying mechanisms of PHPV.

The molecular basis of neural crest axial identity

The neural crest is a migratory cell population that contributes to multiple tissues and organs during vertebrate embryonic development. It is remarkable in its ability to differentiate into an array of different cell types, including melanocytes, cartilage, bone, smooth muscle, and peripheral nerves. Although neural crest cells are formed along the entire anterior-posterior axis of the developing embryo, they can be divided into distinct subpopulations based on their axial level of origin. These groups of cells, which include the cranial, vagal, trunk, and sacral neural crest, display varied migratory patterns and contribute to multiple derivatives. While these subpopulations have been shown to be mostly plastic and to differentiate according to environmental cues, differences in their intrinsic potentials have also been identified. For instance, the cranial neural crest is unique in its ability to give rise to cartilage and bone. Here, we examine the molecular features that underlie such developmental restrictions and discuss the hypothesis that distinct gene regulatory networks operate in these subpopulations. We also consider how reconstructing the phylogeny of the trunk and cranial neural crest cells impacts our understanding of vertebrate evolution.

Cadherins function during the collective cell migration of Xenopus Cranial Neural Crest cells: revisiting the role of E-cadherin

Collective cell migration is a process whereby cells move while keeping contact with other cells. The Xenopus Cranial Neural Crest (CNC) is a population of cells that emerge during early embryogenesis and undergo extensive migration from the dorsal to ventral part of the embryo's head. These cells migrate collectively and require cadherin mediated cell-cell contact. In this review, we will describe the key features of Xenopus CNC migration including the key molecules driving their migration. We will also review the role of the various cadherins during Xenopus CNC emergence and migration. Lastly, we will discuss the recent and seemingly controversial findings showing that E-cadherin presence is essential for CNC migration.

Cdc42 regulates the cellular localization of Cdc42ep1 in controlling neural crest cell migration

The member of Rho family of small GTPases Cdc42 plays important and conserved roles in cell polarity and motility. The Cdc42ep family proteins have been identified to bind to Cdc42, yet how they interact with Cdc42 to regulate cell migration remains to be elucidated. In this study, we focus on Cdc42ep1, which is expressed predominantly in the highly migratory neural crest cells in frog embryos. Through morpholino-mediated knockdown, we show that Cdc42ep1 is required for the migration of cranial neural crest cells. Loss of Cdc42ep1 leads to rounder cell shapes and the formation of membrane blebs, consistent with the observed disruption in actin organization and focal adhesion alignment. As a result, Cdc42ep1 is critical for neural crest cells to apply traction forces at the correct place to migrate efficiently. We further show that Cdc42ep1 is localized to two areas in neural crest cells: in membrane protrusions together with Cdc42 and in perinuclear patches where Cdc42 is absent. Cdc42 directly interacts with Cdc42ep1 (through the CRIB domain) and changes in Cdc42 level shift the distribution of Cdc42ep1 between these two subcellular locations, controlling the formation of membrane protrusions and directionality of migration as a consequence. These results suggest that Cdc42ep1 elaborates Cdc42 activity in neural crest cells to promote their efficient migration.

Advances in understanding functional variations in the Hirschsprung disease spectrum (variant Hirschsprung disease)

Hirschsprung disease (HSCR) is a fairly well understood congenital, genetically based functional obstruction due to the congenital absence of ganglion cells in the distal bowel. However, although over 90% of Hirschsprung cases conform to the normally accepted histological diagnostic criteria, it has become increasingly clear that in addition to HSCR, there is a group of functional disturbances relating to a number of other congenital neurodysplastic conditions causing some degree of gastrointestinal tract malfunction. Although these represent a variety of possibly separate conditions of the enteric nervous system, this spectrum it would appear to be also influenced by similar developmental processes. The term "variant Hirschsprung" is commonly used to describe these conditions, but ganglion cells are mostly present if abnormal in number and distribution. These conditions are a problem group being amongst the most difficult to diagnose and treat with possible practical and legal consequences. The problem appears to be possibly one of definition which has proven difficult in the relative paucity of normal values, especially when correlated to age and gestation. It is the purpose of this paper to review the current position on these conditions and to explore possible shared common pathogenetic and genetic mechanisms. This article explores those conditions where a similar pathogenetic mechanisms to HSCR can be demonstrated (e.g. hypoganglionosis) as well as other neural features, which appear to represent separate conditions possibly linked to certain syndromes.

Chicken trunk neural crest migration visualized with HNK1

The development of the nervous system involves cells remaining within the neural tube (CNS) and a group of cells that delaminate from the dorsal neural tube and migrate extensively throughout the developing embryo called neural crest cells (NCC). These cells are a mesenchymal highly migratory group of cells that give rise to a wide variety of cell derivatives: melanocytes, sensory neurons, bone, Schwann cells, etc. But not all NCC can give rise to all derivatives, they have fate restrictions based on their axial level of origin: cranial, vagal, trunk and sacral. Our aim was to provide a thorough presentation on how does trunk neural crest cell migration looks in the chicken embryo, in wholemount and in sections using the unique chicken marker HNK1. The description presented here makes a good guideline for those interested in viewing trunk NCC migration patterns. We show how before HH14 there are few trunk NCC delaminating and migrating, but between HH15 through HH19 trunk NCC delaminate in large numbers. Melanocytes precursors begin to enter the dorsolateral pathway by HH17. We found that by HH20 HNK1 is not a valid good marker for NCC and that HNK1 is a better marker than Sox10 when looking at neural crest cells morphology and migration details.

Glial but not neuronal development in the cochleo-vestibular ganglion requires Sox10

The cochleo-vestibular ganglion contains neural crest-derived glial cells and sensory neurons that are derived from the neurogenic otic placode. Little is known about the molecular mechanisms that regulate the tightly orchestrated development of this structure. Here, we report that Sox10, a high-mobility group DNA-binding domain transcription factor that is required for the proper development of neural crest cell derivatives, is specifically expressed in post-migratory neural crest cells in the cochleo-vestibular ganglion. Using Sox10-deficient mice, we demonstrate that this transcription factor is essential for the survival, but not the generation, of the post-migratory neural crest cells within the inner ear. In the absence of these neural crest-derived cells, we have investigated the survival of the otocyst-derived auditory neurons. Surprisingly, auditory neuron differentiation, sensory target innervation and survival are conserved despite the absence of glial cells. Moreover, brain-derived neurotrophic factor expression is increased in the hair cells of Sox10-deficient mice, a compensatory mechanism that may prevent spiral ganglion neuronal cell death. Taken together, these data suggest that in the absence of neural crest-derived glial cells, an increase trophic support from hair cells promotes the survival of spiral ganglion neurons in Sox10 mutant mice.

Expression of the homeobox gene Pitx2 in neural crest is required for optic stalk and ocular anterior segment development

Heterozygous mutations in the homeobox gene, PITX2, result in ocular anterior segment defects and a high incidence of early-onset glaucoma. Pitx2 is expressed in both the neural crest and the mesoderm-derived precursors of the periocular mesenchyme. Complete loss of function in mice results in agenesis or severe disruption of periocular mesenchyme structures and extrinsic defects in early optic nerve development. However, the specific requirements for Pitx2 in neural crest versus mesoderm could not be determined using these mice, and only roles in the initial stages of eye development could be assessed due to early embryonic lethality. To determine the specific roles of Pitx2 in the neural crest precursor pool, we generated neural crest-specific Pitx2 knockout mice (Pitx2-ncko). Because Pitx2-nkco mice are viable, we also analyzed gene function in later eye development. Pitx2 is intrinsically required in neural crest for specification of corneal endothelium, corneal stroma and the sclera. Pitx2 function in neural crest is also required for normal development of ocular blood vessels. Pitx2-ncko mice exhibit a unique optic nerve phenotype in which the eyes are progressively displaced towards the midline until they are directly attached to the ventral hypothalamus. As Pitx2 is not expressed in the optic stalk, an essential function of PITX2 protein in neural crest is to regulate an extrinsic factor(s) required for development of the optic nerve. We propose a revised model of optic nerve development and new mechanisms that may underlie the etiology of glaucoma in Axenfeld-Rieger patients.

Stem cell biology and neurodegenerative disease

The fundamental basis of our work is that organs are generated by multipotent stem cells, whose properties we must understand to control tissue assembly or repair. Central nervous system (CNS) stem cells are now recognized as a well-defined population of precursors that differentiate into cells that are indisputably neurons and glial cells. Work from our group played an important role in defining stem cells of the CNS. Embryonic stem (ES) cells also differentiate to specific neuron and glial types through defined intermediates that are similar to the cellular precursors that normally occur in brain development. There is convincing evidence that the differentiated progeny of ES cells and CNS stem cells show expected functions of neurons and glia. Recent progress has been made on three fundamental developmental processes: (i) cell cycle control; (ii) the control of cell fate; and (iii) early steps in neural differentiation. In addition, our work on CNS stem cells has developed to a stage where there are clinical implications for Parkinson's and other degenerative disorders. These advances establish that stem cell biology contributes to our understanding of brain development and has great clinical promise.

Unilateral pulmonary agenesis and renal anomalies associated with in situ neuroblastoma of the adrenal gland

An association of unilateral pulmonary agenesis with in situ neuroblastoma of adrenal gland in a newborn having multiple congenital anomalies is being reported. Polycystic right kidney and absent left kidney, leading to severe oligohydramnios with secondary Potter's syndrome and Breech deformation sequence, were additional malformations present in our proposita.

Latent homologues for the neural crest as an evolutionary novelty

The neural crest is a craniate synapomorphy and a bona fide evolutionary novelty. Recently, researchers considering intriguingly similar patterns of gene expression, cell behaviors, and embryogenetic processes in noncraniate deuterostomes have suggested that cephalochordates, urochordates, and echinoderms or their ancestors might have possessed cells that were precursors to the neural crest or its constituent cells. To emphasize the caution with which similarities at genetic, cellular, or embryological levels should be interpreted as substantiations for cell, germ layer, or tissue homologies, we present and evaluate additional tantalizing evidence that could be considered as documenting neural crest precursors in precraniates. Furthermore, we propose an evolutionary context--latent homologue--within which these data should be interpreted.

Embryonic cell lineage of the marine nematode Pellioditis marina

We describe the complete embryonic cell lineage of the marine nematode Pellioditis marina (Rhabditidae) up to somatic muscle contraction, resulting in the formation of 638 cells, of which 67 undergo programmed cell death. In comparison with Caenorhabditis elegans, the overall lineage homology is 95.5%; fate homology, however, is only 76.4%. The majority of the differences in fate homology concern nervous, epidermal, and pharyngeal tissues. Gut and, remarkably, somatic muscle is highly conserved in number and position. Partial lineage data from the slower developing Halicephalobus sp. (Panagrolaimidae) reveal a lineage largely, but not exclusively, built up of monoclonal sublineage blocs with identical fates, unlike the polyclonal fate distribution in C. elegans and P. marina. The fate distribution pattern in a cell lineage could be a compromise between minimizing the number of specification events by monoclonal specification and minimizing the need for migrations by forming the cells close at their final position. The latter could contribute to a faster embryonic development. These results reveal that there is more than one way to build a nematode.

Mesenchymal stem cells from rat visceral fat exhibit multipotential differentiation in vitro

Human subcutaneous fat-derived stem cells were recently shown to have the potential to differentiate in vitro into a variety of cell types, including adipocytes, osteoblasts, chondrocytes, and myoblasts (Zuk et al., Tissue Eng. 2001;7:211-228). Subcutaneous adipose tissue may therefore prove to be an easily acquired and abundant source of stem cells. Presently it is unclear whether mammals such as rats (which possess small or nonexistent subcutaneous fat pads) contain mesenchymal stem cells within the visceral fat of the abdominal cavity, or whether the visceral fat of any species contains stem cells. In this study we isolated and expanded a pool of mesenchymal cells from visceral fat of adult Sprague-Dawley rats and induced their differentiation in vitro into adipocytes, osteoblasts, neural cells, and chondrocytes. The differentiated phenotypes were verified by morphology as well as detection and expression of tissue-specific protein and mRNA. We conclude that despite well-documented differences in the metabolic and biochemical properties among anatomically distinct depots of fat, the visceral fat of rats contains adult mesenchymal stem cells with developmental potential similar to those isolated from subcutaneous fat in humans. Therefore, animals such as rats provide both a source of fat-derived stem cells and an immunocompetent, autologous host animal in which to investigate the capacity of the fat-derived cells to differentiate and form tissues in vivo.

Rosette formation within a proliferative nodule of an atypical combined melanocytic nevus in an adult

Rosette formation is a feature that has not been described as occurring in melanocytic neoplasms. We present such a unique case. A 59-year-old man presented with an asymptomatic, soft, hairy 3.0 x 2.0-cm pigmented lesion that had been present for many years in the right external ear, extending from the conchal bowl onto the antitragus area. Examination of histologic sections showed a proliferation of nonatypical and heavily pigmented melanocytes in the superficial dermis and around deep adnexal structures, characteristic of a congenital nevus. In other areas, pigmented spindled and dendritic cells infiltrated thickened collagen bundles in a pattern of a blue nevus. A nodular proliferation of epithelioid melanocytes was seen within the deep dermis and subcutaneous tissue. The periphery of the nodule merged with the surrounding nevus cells. Neoplastic cells with nuclear atypia, melanin pigment, pseudonuclear inclusions, and balloon cell change were present. In addition, there was rosette formation by the tumor cells, with a central aggregate of coarse cell processes. Neuroid cords were also noted. No prominent mitotic figures, necrosis, or significant inflammatory infiltrate were noted. The neoplastic cells were positive for S-100 protein, Mart-1, tyrosinase, neuron-specific enolase, and vimentin. HMB-45 and Ki-67 (MIB-1) labeled only rare neoplastic cells within the proliferative nodule. The tumor cells were negative for synaptophysin, protein gene product 9.5, CD57, epithelial membrane antigen, CD31, and CD34. The central cell processes of the rosettes were negative for trichome, type IV collagen, neurofilament protein, glial fibrillary acidic protein, and tyrosine hydroxylase. We also retrospectively examined 78 congenital nevi of 65 pediatric patients at our institution. Rosette formation was not seen in any of these cases.

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.

Development of the neuroendocrine hypothalamus

The development of the neuroendocrine hypothalamus has been studied using a variety of neuroanatomical and molecular techniques. Here, the major findings that mold our understanding of hypothalamic development are reviewed. The rat hypothalamus is generated predominantly from the third ventricular neuroepithelium in a "lateral early to medial late" pattern dictated perhaps by the medially receding third ventricle. Neuroendocrine neurons seem to exhibit a delayed migrational strategy, showing relatively early birthdates, although they are located in the latest-generated, periventricular nuclei. Several homeobox genes seem to play a role in hypothalamic development, and gene knockout experiments implicate a number of genes of importance in the generation of the neuroendocrine cell type.

Pattern of cardiovascular anomalies associated with esophageal atresia: support for a caudal pharyngeal arch neurocristopathy

Patients with cephalic neurocristopathy (an abnormality of neural crest differentiation) present a striking pattern of associated cardiovascular anomalies (CVA). Therefore, to support the hypothesis that esophageal atresia (EA) may be related to a defective contribution from the cephalic neural crest, we studied the pattern of CVA associated with EA. Medical records of 99 patients with isolated EA, 101 with isolated anorectal malformations (ARM) and 15 with both EA and ARM, consecutively admitted to our unit, were reviewed. The prevalence and pattern of CVA associated with isolated EA or isolated ARM were compared on the assumption that the cranial or caudal location of a major malformation is related to a different regional patterning of associated anomalies. The prevalence of CVA was 39% in patients with isolated EA and 7% in those with isolated ARM (p < 0.01). Neural crest-related CVA (aortic arch anomalies, conotruncal defects, and superior vena cava malformations) accounted for 72% of all CVA in patients with isolated EA versus 14% in those with isolated ARM (p < 0.02). In patients with isolated EA, anomalies of the fourth and sixth aortic arch derivatives accounted for 75% of all neural crest related CVA. The present pattern of CVA in infants with EA supports the concept that EA may be related to an abnormal contribution from caudal portion of cephalic neural crest.

Ypel1: a novel nuclear protein that induces an epithelial-like morphology in fibroblasts

BACKGROUND

Embryonic development depends on the regulation of cell morphology and behaviour to carry out morphogenesis. One example of this is the development of the face, which is constructed from independent blocks of tissue that must grow in a coordinated way and then fuse to form a continuous tissue.

RESULTS

We have isolated a novel gene of unknown function from mouse and quail embryos in a search for genes involved in craniofacial development. Sequence analysis of this gene, known as Ypel1, demonstrates a striking level of amino acid conservation between vertebrates and invertebrates but no significant homology with any other characterized genes. Ypel1 is expressed in the ventral half of early embryos including the branchial arches from which the face derives. Ypel1 localizes to the nucleus, and transfection into fibroblasts induces an epithelial-like transition, which is accompanied by alterations to the cytoskeleton and cell adhesion machinery. In addition, human YPEL1 localizes to chromosome 22q11.2, a region associated with a number of syndromes involving malformation of the craniofacial complex.

CONCLUSION

These data suggest a role in regulation of cellular morphology and behaviour that is important for development of the craniofacial complex.

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.

Establishment and characterization of a human neuroectodermal cell line (TB) from a cerebrospinal fluid specimen

We have established a cell line (TB) from a cerebrospinal fluid (CSF) specimen of a patient with a primary leptomeningeal melanomatosis. TB cell line was immunoreactive with the antibodies for low molecular weight neurofilament protein, vimentin, neuron-specific enolase, chromogranin, synaptophysin and HMB-45 (an antibody sensitive and specific for melanoma). When TB cells were transplanted into nude mice, the same immunohistochemical pattern present in cultured cells was found but surprisingly, a positive staining for desmin was observed. Significant amounts of serotonin and its metabolite were detectable. Retinoic acid but not nerve growth factor was able to induce differentiation towards a neuronal phenotype. In summary, TB cells represent primitive neuroectodermal cells having the potential for neuronal, myoblastic and possibly melanoblastic differentiation.

Activin A and follistatin influence expression of somatostatin in the ciliary ganglion in vivo

An important developmental question concerns whether neurotransmitter phenotype is an inherent property of neurons or is influenced by target tissues. This issue can be addressed in the avian ciliary ganglion (CG) which contains two cholinergic populations, ciliary and choroid neurons, that differentially express the peptide cotransmitter, somatostatin. The present study tests the hypothesis that differences in the level of expression of activin A and its endogenous inhibitor follistatin in CG neuron target tissues are responsible for selective expression of somatostatin in choroid neurons. Intraocular injection of activin A or follistatin (300 ng injected at E10/E11) in cultured embryos resulted in a 39% increase or a 23% decrease, respectively, in somatostatin-positive neurons relative to controls. Chorioallantoic membrane application of follistatin (1 microgram daily from E7 to E13) reduced somatostatin positive neurons by 54%. Neuron number, size, and target tissue morphology were unaffected by these treatments. Together with our previous studies, these data suggest that activin A and follistatin are target-derived molecules that regulate neuropeptide phenotype in the ciliary ganglion.

Hirschsprung's disease: a search for etiology

In 1967, Okamoto et al suggested that the absence of ganglion cells in Hirschsprung's disease (HD) was attributable to failure of migration of neural crest cells. The earlier the arrest of migration, the longer the aganglionic segment. Since then, this hypothesis generally has been accepted. However, subsequent experiments using mouse models of intestinal aganglionosis indicate that nerve cells may reach the correct position but then fail to develop or survive. An alternative hypothesis has been proposed that the aganglionosis may be caused by failure of differentiation as a result of microenvironmental changes after the migration has occurred. Extracellular matrix proteins are recognized as important microenvironmental factors. It has been shown that enteric neurogenesis is dependent on extracellular matrices, which provide a migration pathway for neural crest-derived cells and promote the maturation of settled neural crest-derived cells. Altered distributions of extracellular matrices have been shown in human HD cases and murine HD models, suggesting the role of extracellular matrices in the pathogenesis of HD. Recent studies suggest that intestinal smooth muscle cells, target cells of enteric neurons, play an important role in guiding and influencing its own innervation. Normal maturation was inhibited in neurons cultured with smooth muscle cells of aganglionic colon in comparison to normal colon. Furthermore, it was demonstrated that levels of neurotrophic factors, crucial in the development and survival of enteric neurons, are decreased in circular muscle layers of aganglionic colon in comparison to normoganglionic colon. The smooth muscle cells of the aganglionic colon may represent an unfavorable microenvironment for neuronal development compared with the normally innervated region. Recently, markedly increased immunoreactivity of major histocompatibility complex (MHC) class II antigens and ICAM-1 was demonstrated in aganglionic bowel, suggesting the immunological mechanisms may be involved in the etiology of HD. Genetic factors have been implicated in the etiology of this condition because HD is known to occur in families and in association with some chromosomal abnormalities. Recent expansion of molecular genetics identified multiple susceptibility genes of HD, including the RET gene, the glial cell line-derived neurotrophic factor gene, the endothelin-B receptor gene, and endothelin-3 gene. Of these, inactivating mutations of the RET gene are the most frequent, occurring in 50% of familial and 15% to 20% of sporadic cases of HD. To date, despite extensive research, the exact etiology of this condition remains poorly understood. The present report describes the authors' current understanding of and recent progress in the etiology of HD.

The spectrum of neurocristic cutaneous hamartoma: clinicopathologic and immunohistochemical study of three cases

Neurocristic cutaneous hamartomas result from aberrant development of the neuromesenchyme. Thus, the elements within these tumors reflect the spectrum of differentiation that results from migration of neural crest-derived cells. We present three cases, in addition to routine hematoxylin-eosin staining, a battery of immunohistochemical staining, including S-100 protein, HMB-45, EMA, CD34, and neurofilament-protein stains, was performed on each specimen. A dermal melanocytic component was the dominant feature of two of these lesions, while neurosusenticular and neuromesenchymal components dominated in one tumor. Both tumors that developed on the scalp showed effects on the overlying epidermis and/or on adnexal development. The melanocytic component was positive for S-100 protein and HMB-45. The surrounding stroma showed tactoid bodies and increased CD34 staining. Neurocristic cutaneous hamartomas represent dysplastic development of neural crest-derived cells. Although melanocytic cells have been previously reported to be the dominant cell population, neurosusentacular and neuromesenchymal cells also may be the principal component. In cephalic areas, the neuromesenchyme may not only be an important component of the tumor, but may also effect the development of the overlying epithelium and adnexal structures. Although none of these cases presents evidence of malignant transformation, identification of these tumors could be important if malignant transformation results in the development of tumors with a distinctive biologic behavior.

Features of DiGeorge syndrome and CHARGE association in five patients

We report on five patients presenting with features of two congenital disorders, DiGeorge syndrome (DGS) and CHARGE association. CHARGE association is usually sporadic and its origin is as yet unknown. Conversely, more than 90% of DGS patients are monosomic for the 22q11.2 chromosomal region. In each of the five patients, both cytogenetic and molecular analysis for the 22q11.2 region were normal. In view of the broad clinical spectrum and the likely genetic heterogeneity of both disorders, these cases are consistent with the extended phenotype of either DGS without 22q11.2 deletion or CHARGE association, especially as several features of CHARGE association have been reported in rare patients with 22q11.2 deletion association phenotypes. On the other hand, these could be novel cases of an independent association involving a complex defect of neural crest cells originating from the pharyngeal pouches.

Bipolar (neural and myoblastic) phenotype in cell lines derived from human germ cell tumours of testis

Non-seminomatous germ cell tumours of the testis (NSGCT) form a heterogeneous group of neoplasms. Cell lines derived from NSGCT may provide useful data concerning the biology of neoplasic precursor germ cells, differentiation of tumour stem cells and the relationship between various tissue components of these tumours. Four NSGCT were studied, two mixed tumours composed of teratocarcinoma, yolk sac and trophoblastic elements, and two malignant teratomas with a massive neuroectodermal component, equivalent to primary neuroectodermal tumours (PNET) of the testis. The explanted tumours gave rise to various cell populations, including epitheloid cells, flattened large cells, spindle cells and tear drop cells of neuroblastic type. Ultrastructurally, cultured cells expressed various degrees of neural and muscular differentiation: neurosecretory granules, intermediate filaments of glial nature, and filaments resembling Z-bands. Cultured cells showed the expression of several neural and muscular markers, including neurofilaments, cytokeratin, actin, desmin, neuron-specific enolase, glial fibrillary acidic protein and HNK-1. In addition, three cases expressed HBA-71 antigen and two expressed MyoD1 protein. All cases were aneuploid, and an isochromosome 12p, i(12p), was detected in three cases. Myoblastic and neural cells are the predominant tumour cells that grow in vitro, independent of the nature and composition of the primary germ cell tumour. A histogenetic relationship between germ cell tumours and small round cell tumours of childhood is suggested.

EWS-FLI1 fusion transcripts identified in patients with typical neuroblastoma

The t(11.22)(q24.q12) results in expression of a chimeric RNA product, EWS-FLI1. This RNA product is expressed in over 85% of tumours belonging to the Ewing's family, and is increasingly used as a definitive characteristic of these tumours. In this study, we evaluated reverse transcriptase-polymerase chain (RT-PCR) for EWS-FLI1 fusion transcripts in 18 neurally derived small round cell tumours. These included six Ewing's family tumours and 12 neuroblastomas. EWS-FLI1 fusion transcripts were identified in all six Ewing's tumours, but also in two of the 12 neuroblastomas. One neuroblastoma contained the classic type 1 fusion transcript, and the second a type 1 transcript containing a 66 bp (base pair) insert that was not derived from the EWS or FLI1 gene. The presence of EWS-FLI1 fusion products in RNA extracted from primary neuroblastoma suggests the identification of EWS-FLI1 fusion transcripts is not pathognomonic for tumours of the Ewing's family. The clinical significance of these fusion transcripts in neuroblastoma is not known.

Cell lineages and genes

Fixed lineages are the extreme manifestation of the interrelations between cell division pattern, spatial organization and cell differentiation occurring in embryonic development. These relationships are discussed in the light of recent new detailed descriptions of lineages, experimental perturbations and genetic analysis. Lineages could be phylogenetically old devices under the control of specific genes that are required to organize the morphological space. Such genes would be different from those involved in the specification of lineage alternatives. Specification genes operate independently from each other and are expressed in a combinatorial way in different cells and lineages. Since their activity is reversible during development the possibility exists for changing these combinatorial associations during development and evolution. The classical notion of a hierarchical cascade segregation of histotypes along lineages is discussed.

Cutaneous malignant melanotic neurocristic tumors arising in neurocristic hamartomas. A melanocytic tumor morphologically and biologically distinct from common melanoma

Cutaneous neurocristic hamartomas (CNH) are pigmented lesions of neural crest origin that involve the skin and superficial soft tissue. They consist of a complex proliferation of nevomelanocytes, schwann cells, and pigmented dendritic and spindled cells. Malignancies can arise within the lesions, but few studies have dealt with this issue. We studied seven cases of CNH in which malignancy supervened. They included four congenital and three acquired lesions that involved the head and neck (five cases) or back (two cases) in patients aged from 11 to 67 (mean, 32) years. Malignant tumors developed 15 to 67 (mean, 32) years after identification of the pigmented lesion in the congenital CNH and after 1 to 6 (mean 3.5) years in the acquired CNH. The malignant tumors had a deep intradermal or subcutaneous origin and lacked a junctional component. Most were circumscribed, multinodular, melanin-containing tumors composed of bland, small, rounded to spindled cells, focally displaying a trabecular or nested growth pattern. Nuclear palisading and perivascular pseudorosettes were present in several tumors. In two examples, the neoplasm consisted predominantly of large pleomorphic epithelioid cells. Tumors contained immunoreactive S-100 protein (all of seven cases), a melanoma-associated antigen (HMB-45)( five of six cases, neuron-specific enolase (five of seven cases) and vimentin (six of six cases). The four patients with congenital lesions tended to have multiple recurrences and died of disease after 2 to 20 (mean, 9) years, three with metastases, one with direct invasion of the posterior fossa. The three patients with acquired lesions are alive after 1 to 5 years two with persistent disease. In contrast to common melanomas, these tumors have a propensity to recur as bulky nodules and to metastasize after many years or decades. Because these tumors exhibit melanocytic differentiation and arise in hamartomatous lesions composed of neural crest derivatives, we have designated them cutaneous malignant melanotic neurocristic tumors.

Olfactory neuroblastoma is a peripheral primitive neuroectodermal tumor related to Ewing sarcoma

Olfactory neuroblastoma (ONB) is a malignant tumor of the nasal mucosa whose histogenesis is unclear. A relationship to neuroblastoma (NB), a pediatric tumor of the sympathetic nervous system, is based on morphologic similarities and the expression of similar neural antigens. However, the clinical presentation of ONB differs from that of NB, and MYCN amplification characteristic of NB is not observed. We have therefore examined the relationship of this malignancy to other classes of neural tumors. In previous studies, two ONB cell lines demonstrated cytogenetic features and patterns of protooncogene expression suggestive of a relationship to the Ewing sarcoma family of childhood peripheral primitive neuroectodermal tumors (pPNETs). The pPNETs show t(11;22)(q24;q12) or t(21;22)(q22;q12) chromosomal translocations fusing the EWS gene from 22q12 with either the FL11 gene on 11q24 or the ERG gene on 21q22. We therefore analyzed ONBs for the presence of pPNET-associated gene fusions. Both cell lines showed rearrangement of the EWS gene, and fluorescence in situ hybridization (FISH) of each case demonstrated fusion of EWS and FL11 genomic sequences. Moreover, both lines expressed EWS/FL11 fusion transcripts with in-frame junctions between exon 7 of EWS and exon 6 of FL11 as described for pPNETs. We identified similar gene fusions in four of six primary ONB cases. None of the cases expressed tyrosine hydroxylase, a catecholamine biosynthetic enzyme widely expressed in NB. Our studies indicate that ONB is not a NB but is a member of the pPNET family.

Ectomesenchymal hamartoma (benign "ectomesenchymoma") of the VIIIth nerve: case report

We report a previously undescribed hamartoma of the VIIIth nerve, consisting of adipose tissue, Schwann cells associated with myelinated nerve fibers, well-differentiated smooth and striated muscle fibers, and rare ganglion cells. The tumor was found in a 35-year-old Caucasian female who presented with right-sided hearing loss. The mass, which we designate an "ectomesenchymal" hamartoma, most likely developed from pluripotent neural crest cells ("ectomesenchyme"), which are capable of differentiating into a variety of neuroectodermal and mesenchymal cell types. The development of the neural crest, the concept of "ectomesenchyme," and the histogenesis of this tumor are reviewed.

Upper limb malformations in DiGeorge syndrome

We report on upper limb anomalies in two children with a complete DiGeorge sequence: conotruncal defects, hypocalcemia, thymic aplasia, and facial anomalies. One child had preaxial polydactyly, and the other had club hands with hypoplastic first metacarpal. In both patients, molecular analysis documented a 22q11 deletion. To our knowledge, limb anomalies have rarely been reported in DiGeorge syndrome, and they illustrate the variable clinical expression of chromosome 22q11 deletions.

Waardenburg syndrome in man and splotch mutants in the mouse: a paradigm of the usefulness of linkage and synteny homologies in mouse and man for the genetic analysis of human congenital malformations

The use of chromosomal segments with conserved homologous linkage groups found in different species provides one method of predicting the location of genes causing congenital malformations in man. For example, homology between man and mouse involves 241 homologous autosomal genes spread on 68 homologous chromosomal segments. In addition, the similarities of phenotypic expression of human congenital malformations and mouse mutations indicate the possible involvement of an homologous gene implicated during ontogeny of the two species. The identification of a single gene defect in the mouse and comparative mouse-human gene mapping provides therefore another approach for selecting candidate loci for inborn error of morphogenesis in man. Further molecular studies can then be performed to show that the loci are identical. The human Waardenburg syndrome and the splotch (Sp) mouse mutant represent the first example of the potential of this approach for the understanding of human congenital malformations at the molecular level.

Identification of a human achaete-scute homolog highly expressed in neuroendocrine tumors

Basic helix-loop-helix transcription factors of the achaete-scute family are instrumental in Drosophila neurosensory development and are candidate regulators of development in the mammalian central nervous system and neural crest. We report the isolation and initial characterization of a human achaete-scute homolog that is highly expressed in two neuroendocrine cancers, medullary thyroid cancer (MTC) and small cell lung cancer (SCLC). The human gene, which we have termed human achaete-scute homology 1 (hASH1), was cloned from a human MTC cDNA library. It encodes a predicted protein of 238 aa that is 95% homologous to mammalian achaete-scute homolog (MASH) 1, a rodent basic helix-loop-helix factor. The 57-residue basic helix-loop-helix domain is identical to that in the rodent gene, and the basic and helical regions, excluding the loop, are 72-80% identical to Drosophila achaete-scute family members. The proximal coding region of the hASH1 cDNA contains a striking 14-copy repeat of the triplet CAG that exhibits polymorphism in human genomic DNA. Thus, hASH1 is a candidate locus for disease-causing mutations via triplet repeat amplification. Analysis of rodent-human somatic cell hybrids permitted assignment of hASH1 to human chromosome 12. Northern blots revealed hASH1 transcripts in RNA from a human MTC cell line, two fresh MTC tumors, fetal brain, and three lines of human SCLC. In contrast, cultured lines of non-SCLC lung cancers and a panel of normal adult human tissues showed no detectable hASH1 transcripts. Expression of hASH1 may provide a useful marker for cancers with neuroendocrine features and may contribute to the differentiation and growth regulation of these cells.

Hirschsprung's disease: clinical and experimental observations

Hirschsprung's disease (HD) is a relatively common cause of intestinal obstruction in the newborn. It is characterized by an absence of ganglion cells in the distal bowel beginning at the internal sphincter and extending proximally for varying distances. The etiology of HD-associated enterocolitis remains a complex issue. This study has provided further support for a possible infectious etiology of enterocolitis complicating HD.

Cell migration from the olfactory neuroepithelium of neonatal and adult rodents

This study reports the presence of olfactory cell clusters in postnatal and adult animals within the lamina propria of the olfactory mucosa and the nerve fiber layer of the olfactory bulb. The results obtained from mice and rats, partially or totally unilaterally bulbectomized, have been compared with observations in intact control animals. Light microscopic observation has shown that, in bulbectomized animals, the clusters are present in both experimental and normal sides and are usually associated with olfactory axon bundles. Moreover, when compared with intact animals, differences are present in terms of number of clusters and regions from where they originate. The morphological identity of the cells of the clusters with the globose basal cell of the olfactory neuroepithelium could be demonstrated with the electron microscope. By autoradiographic means, it was possible to show that they originate from the olfactory neurogenetic matrix and migrate along olfactory axon bundles. Interestingly, the migrating cells do not express olfactory marker protein. Altogether, these observations suggest that the olfactory matrix may be capable of originating neural elements other than olfactory receptor neurons.

Association of rib anomalies and malignancy in childhood

A relationship exists between tumours and malformations both generally and in particular combinations. This is also valid for minor errors of morphogenesis suggesting that embryonic tumours are an expression of aberrant intra-uterine morphogenesis. We speculated that these minor aberrations might also manifest in other morphological defects, especially in minor anomalies and malformations of the ribs. We reviewed chest roentgenographs of 1000 children with malignancies for rib anomalies and compared them to 200 patients with mainly infectious diseases. We found 242 rib anomalies in 218 children with tumours (21.8%) and 11 (5.5%) in children without malignancy. This difference was statistically highly significant (P less than 0.001). A high incidence of cervical ribs was found in neuroblastoma (33%), brain tumour (27.4%), leukaemia (26.8%), soft tissue sarcoma (24.5%), Wilms tumour (23.5%) and Ewing sarcoma (17.1%). Only neuroblastoma showed a high incidence of rib bifurcation (4.5%). The increased incidence of these mesenchymal defects in children with malignancies may be another clue for an altered morphogenesis in tumour origin. In neuroblastoma the rib anomaly may be another expression of neurocristopathy as proposed for the association of congenital heart disease and neuroblastoma.

Splotch locus mouse mutants: models for neural tube defects and Waardenburg syndrome type I in humans

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Effects of injecting fibronectin and antifibronectin antibodies on cushion mesenchyme formation in the chick. An in vivo study

During heart development in the chick some of the endocardial cells that cover the cushion areas leave the cushion endocardium, seed the underlying cardiac jelly, and are transformed into mesenchyme. Cushion mesenchymal (CM) cells migrate from the endocardium toward the myocardium using the cardiac jelly as substratum. Developing cushions have been microinjected with fibronectin (FN), antifibronectin antibodies (AbFN), and four synthetic peptide probes. Two of these peptides (P7 and P10) contained the sequence Arg-Gly-Asp-Ser (RGDS), while the other two (P15 and PColl) did not. Cushion area, individual cell area, cell density, cell orientation and a factor of form were evaluated in both experimental and control cushions. CM cell migration was inhibited by FN and AbFN, only partially inhibited by P10 and unaffected by P7. Cushions injected with P15 and PColl were unaffected. These results can be explained by steric modifications of the extracellular matrix, that may render cardiac jelly nonpermissive for CM cell migration, or by interaction of the substances injected at the endocardial cell surface. Migrating CM cells do not present any preferential orientation in any particular direction. CM cell migration seems to depend upon intrinsic migratory behaviour and the presence of FN at the CM cell surface. The enforcement of the direction of CM cell migration does not appear to rely upon matrix signals but be the result of randomly migrating cells becoming distributed more evenly in the matrix.

Splotch (Sp2H), a mutation affecting development of the mouse neural tube, shows a deletion within the paired homeodomain of Pax-3

The molecular basis of the mouse mutation splotch (Sp), which is associated with spina bifida and exencephaly, was analyzed at three of its alleles, Sp, Sp2H, and Spr. We mapped the paired box gene Pax-3 within the Inha to Akp3 interval, near or at the Sp locus on chromosome 1, and found Pax-3 to be deleted in heterozygous Spr/+ mice. Analysis of genomic DNA and cDNA clones constructed from Sp2H/Sp2H embryos identified a deletion of 32 nucleotides in the Pax-3 mRNA transcript and gene. This deletion maps within the paired homeodomain of PAX-3 and is predicted to create a truncated protein as a result of a newly created termination codon at the deletion breakpoint. Our study provides evidence for a causal link between deletion of the paired homeodomain of Pax-3 and the Sp2H mutation, and infers that Pax-3 plays a key role in normal neural development.

Laminin-binding integrin alpha 7 beta 1: functional characterization and expression in normal and malignant melanocytes

A novel integrin, alpha 7 beta 1, that specifically binds with high affinity to laminin has been identified on melanoma cells. This complex was purified from both human and murine melanoma cells by laminin-affinity chromatography, and the alpha 7 subunit was recovered after gel electrophoresis. N-terminal amino acid sequence analysis of the alpha 7 subunit from both human and mouse cells verifies that this integrin is distinct from other alpha chains in the beta 1 family, although strikingly similar to the alpha 6 subunit. By using specific proteolytically derived fragments of laminin, it was determined that the alpha 7 beta 1 complex binds selectively to the E8 region, which represents part of the long arm of laminin. In contrast, the receptor failed to bind to the P1 fragment, which contains the intersection of the short arms of laminin. Although the alpha 7 beta 1 complex was commonly expressed in melanoma cells, this integrin was not detected in normal melanocytes, suggesting that alpha 7 expression may be associated with malignant transformation. These results establish the existence of a novel integrin that binds to the E8 domain of laminin and appears to mediate cell adhesion to this ligand.