Nicole M. Le Douarin

Lateral and Axial Signals Involved in Avian Somite Patterning: A Role for BMP4

In vertebrates, muscles of the limbs and body wall derive from the lateral compartment of the embryonic somites, and axial muscles derive from the medial compartment. Whereas the mechanisms that direct patterning of somites along the dorsoventral axis are beginning to be understood, little is known about the tissue interactions and signaling molecules that direct somite patterning along the mediolateral axis. We report the identification of a specific marker for the lateral somitic compartment and its early derivatives, cSim1, an avian homolog of the Drosophila single minded gene. Using this marker, we provide evidence that specification of the lateral somitic lineage results from the antagonistic actions of a diffusible medializing signal from the neural tube and a diffusible lateralizing signal from the lateral plate mesoderm, and we implicate bone morphogenetic protein 4(BMP4) in directing this lateralization.

Mapping of the early neural primordium in quail-chick chimeras: II. The prosencephalic neural plate and neural folds: Implications for the genesis of cephalic human congenital abnormalities

Mapping of the avian neural primordium was carried out at the early somitic stages by substituting definite regions of the chick embryo by their quail counterpart. The quail nuclear marker made it possible to identify precisely the derivatives of the grafted areas within the chimeric cephalic structures. A fate map of the prosencephalic neural plate and neural folds is presented. Moreover the origin of the forebrain meninges from the pro- and mesencephalic neural crest is demonstrated. In the light of the data resulting from these experiments, we present a rationale for the genesis of malformations of the face and brain and of congenital endocrine abnormalities occurring in man.

Formation of the dorsal root ganglia in the avian embryo segmental origin and migratory behavior of neural crest progenitor cells

The segmental origin and migratory pattern of neural crest cells at the trunk level of avian embryos was studied, with special emphasis on the formation of the dorsal root ganglia (DRG) which organize in the anterior half of each somite. Neural crest cells were visualized using the quail-chick marker and HNK-1 immunofluorescence. The migratory process turned out to be closely correlated with somitic development: when the somites are epithelial in structure few labeled cells were found in a dorsolateral position on the neural tube, uniformly distributed along the craniocaudal axis. Following somitic dissociation into dermomyotome and sclerotome labeled cells follow defined migratory pathways restricted to each anterior somitic half. In contrast, opposite the posterior half of the somites, cells remain grouped in a dorsolateral position on the neural tube. The fate of crest cells originating at the level of the posterior somitic half was investigated by grafting into chick hosts short segments of quail neural primordium, which ended at mid-somitic or at intersomitic levels. It was found that neural crest cells arising opposite the posterior somitic half participate in the formation of the DRG and Schwann cells lining the dorsal and ventral root fibers of the same somitic level as well as of the subsequent one, whereas those cells originating from levels facing the anterior half of a somite participate in the formation of the corresponding DRG. Moreover, crest cells from both segmental halves segregate within each ganglion in a distinct topographical arrangement which reflects their segmental origin on the neural primordium. Labeled cells which relocate from posterior into anterior somitic regions migrate longitudinally along the neural tube. Longitudinal migration of neural crest cells was first observed when the somites are epithelial in structure and is completed after the disappearance of the last cells from the posterior somitic region at a stage corresponding to the organogenesis of the DRG.

Two molecules related to the VEGF receptor are expressed in early endothelial cells during avian embryonic development.

We present the partial cloning and the expression patterns of two putative growth factor receptor molecules named Quek1 and Quek2 (for quail endothelial kinase) in chick and quail embryos from gastrulation to embryonic day 9 (E9). Quek1 and Quek2 show high homology to three interrelated murine and human genes, flk-1, KDR and flt. Flt was recently shown to be the receptor for the endothelial cell mitogen vascular endothelial growth factor (VEGF). In situ hybridization of Quek1 and Quek2 to sections of avian embryos showed that they are both expressed essentially by endothelial cells, that we identified with a monoclonal antibody (Mab) QH1 specific for endothelial and white blood cells of the quail. Quek1 is expressed in the mesoderm from the onset of gastrulation, whereas Quek2 message is first detected on QH1-expressing endothelial cells. The expression pattern of Quek1 suggests that it could identify the putative precursor of both endothelial and hematopoietic lineages, the hemangioblast. Quek1 and Quek2 are not expressed in all endothelial cells throughout life. At E9, after the initial phase of vasculogenesis, these genes are switched off in various compartments of the vascular network.

chapter 2 Migration and Differentiation of Neural Crest Cells

Publisher Summary This chapter reviews the present state of knowledge concerning the cell types derived from the neural crest and discusses recent advances concerning the migratory process. It focuses on the migration and differentiation of the peripheral nervous system. Among the fundamental problems raised by the ontogeny of the neural crest, the molecular basis of crest cell migration and localization still remains a poorly understood question. Because active investigation of this problem has been recently initiated in several laboratories, one can expect some progress to emerge in this field in the near future. In regard to the other basic question concerning segregation of the various cell lines arising from the neural crest, interesting advances have been made. The experimental analysis of autonomic nerve cell differentiation has shown that the choice of transmitter synthesis remains labile for a while during differentiation of the autonomic neuroblasts into fully functional adrenergic or cholinergic neurons. One of the most attractive hypotheses that could account for the experimental data is that the autonomic neuroblast normally goes through a state during which it is able to synthesize both transmitters (catecholamine and ACh). Thereafter, environmental cues stimulate selectively one or the other of these metabolic pathways until the stable state of chemical differentiation is finally reached.

The early development of cranial sensory ganglia and the potentialities of their component cells studied in quail-chick chimeras☆

The quail-chick marker system has been used to study the early developmental stages of the ganglia located along cranial nerves VII, IX, and X. The streams of neural crest cells arising from the rhombencephalic-vagal neural crest were followed from the onset of their migration up to the localization of crest cells in the trunk and root ganglia of these nerves. It was shown that two different populations of crest cells are segregated early as a result of morphogenetic movements in the hypobranchial region. The dorsal population gives rise to the root ganglia of nerves IX and X located close to the encephalic vesicles, where the crest cells differentiate both into neurons and into glia. In contrast, the ventral stream of neural crest cells contributes together with cells from epibranchial placodes to the trunk ganglia (geniculate, petrous, and nodose ganglia) of cranial nerves VII, IX, and X. The successive steps of the invasion of the placodal anlage by crest cells can be followed owing to the selective labeling of the neural crest cells. It appears that the latter give rise to the satellite cells of the geniculate, petrous, and nodose ganglia while the large sensory neurons originate from the placodes. The nodose ganglion has been the subject of further studies aimed to investigate whether neuronal potentialities can be elicited in the neural crest-derived cells that it contains. The ability to label selectively either the neurons or the glia by the quail nuclear marker made this investigation possible in the particular case of the nodose ganglion whose neurons and satellite cells have a different embryonic origin. By the technique already described (N. M. Le Douarin, M. A. Teillet, C. Ziller, and J. Smith, 1978, Proc. Nat. Acad. Sci. USA 75, 2030–2034) of back-transplantation into the neural crest migration pathway of a younger host, it was shown that the presumptive glial cells of the nodose ganglion are able to remigrate when transplanted into a 2-day chick host and to differentiate into autonomic structures (sympathetic ganglion cells, adrenomedullary cells, and enteric ganglia). It is proposed as a working hypothesis that neuronal potentialities contained in the neural crest cells which invade the placodal primordium of the nodose ganglion are repressed through cell-cell interactions occurring between placodal and crest cells.

On the origin of pancreatic endocrine cells

A long-standing debate in embryology concerns the developmental lineage of endocrine or paracrine cells that produce polypeptide hormones and are distributed throughout the body. Included in this group are pancreatic endocrine cells and a variety of endocrine cells of the gastrointestinal mucosa. These cells share several characteristics with neurons, which has led to the speculation that they may originate from the neurectoderm. In this issue of Ce//, an article by Alpert. Hanahan, and Teitelman (p. 295) revives this debate. On the basis of experiments with transgenie mice, these authors report the provocative finding that not only do differentiating pancreatic endocrine cells synthesize a neuronal marker, tyrosine hydroxylase (TH), but that developing neurons in the neural tube transcribe the insulin gene. Here, I briefly recall the historical background of this question and place the emerging data in a contemporary perspective. The Concept of a Diffuse Neuroendocrine System In 1938. Friedrich Feyrter described a system of clear cells dispersed in the gut and various other parts of the body. Feyrter proposed that these cells constituted a sort of diffuse endocrine organ, with some cells acting on their immediate neighbors, and thus being paracrine rather than endocrine in nature. This initial concept was further elaborated by Pearse (Nature 277, 598-600. 1966; Vet. Record 79,587-590, 1966), who noticed that a number of cells, located mainly in the gut and its appendages, share certain cytochemical and ultrastructural characteristics, as well as a common primary function-the production of polypeptide hormones. On the basis of these observations, Pearse postulated that all of these cells arose from the neural crest and were therefore of neurectodermal origin. He later assigned the acronym APUD (Amine content and/or Amine Precursor Uptake and Decarboxylation) to describe them (Pearse, PNAS 770, 71-80, 1968). The list of APUD cells, restricted in 1969 to fourteen cell types (including pituitary corticotrophs and melanotrophs, pancreatic islet cells, calcitonin-producing cells: carotid body type I cells, adrenal medulla, and various endocrine cells of the gut epithelium), increased to forty less than ten years later, by which time Pearse had included the parathyroid and a number of cells in the gut, lung, and skin that had been shown to produce peptides or neuropeptides (Pearse, Nature 262, 92-94, 1976). The crux of Pearse’s theory was that cells of the APUD series constituted a “diffuse neuroendocrine system,” which he viewed as a third branch of the nervous system. “acting with the second, autonomic division in the control of the Minireview

The developmental relationship between osteocytes and osteoclasts: A study using the quail-chick nuclear marker in endochondral ossification☆

Abstract Interspecific grafts of limb buds and femurs on the chorioallantoic membrane of 5-day-old hosts and into the somatopleure of 3-day-old hosts were carried out between quail and chick embryos. Due to their different nuclear features, the cells of the two species can be identified in the chimeric bones resulting from the endochondral ossification which occurs in the explanted tissues. By following the cell lineage in the bone and marrow we were able to show that the hemopoietic and the osteogenic (comprising osteoblasts, osteocytes, and chondrocytes) cell lines have different embryological origins. The osteogenic line is derived from the limb bud mesenchyme, while the hemopoietic cells are brought into the bone marrow via the circulation. In the fixed cells of the marrow two categories have to be distinguished: the reticular cells originating from the bone rudiment and the endothelial cells which invade the cartilage and are of hematogenous origin. The osteoclasts belong to the hemopoietic cell line and are not derived from any cell type of the osteogenic line.

Consequences of neural tube and notochord excision on the development of the peripheral nervous system in the chick embryo

Notochordectomy and neuralectomy were carried out either in one- or in two-step experiments on the chick embryo. The aim of this operation was to study the influence of the axial organs (notochord and neural tube) on the development of the ganglia of the peripheral nervous system. The neural crest cells from which most peripheral ganglion cells arise were labeled through the quail-chick marker system and their fate was followed under various experimental conditions. It appeared that the development of the dorsal root and sympathetic ganglia depends on survival and differentiation of somite-derived structures. In the absence of neural tube and notochord, somitic cells die rapidly, and so do the neural crest cells that are present in the somitic mesenchyme at that time. In contrast, those crest cells which can reach the mesenchymal wall of the aorta, the suprarenal glands, or the gut survive and develop normally into nerve and paraganglion cells. Differentiation of the neural crest- and placode-derived sensory ganglia of the head which develop in the cephalic mesenchyme is not affected by removal of notochord and encephalic vesicles. These results show that the peripheral ganglia are differentially sensitive to the presence of the neural tube and the notochord. Among the various ganglia of the peripheral nervous system, spinal and sympathetic ganglia are the only ones which require the presence of these axial structures. The neural tube allows both the spinal and the sympathetic ganglia to develop in the absence of the notochord. In contrast, if the notochord is left in situ and the neural tube removed, the spinal ganglia fail to differentiate and only sympathetic ganglia can develop.

Development of melanocyte precursors from the vertebrate neural crest.

Pigment cells that differentiate in the vertebral skin arise from the neural crest (NC), a transitory structure formed at the dorsal borders of the neural plate and which gives rise to migratory cells of multiple fates. How NC cells become committed to the melanocytic lineage and what factors control the survival, proliferation and differentiation of melanocyte precursors remain largely unknown. These issues are of great importance for understanding the mechanisms of several pigment cell pathologies including melanomas. Recent in vivo and in vitro analyses of the fate of single NC cells have indicated that multipotent cells yield melanocyte precursors that become spatially and temporally segregated from other, non melanogenic, NC-derived cell types. The proper development of subsets of NC precursors is governed by environmental local cytokines acting in a paracrine manner. The conjunction of recent studies in mammals and birds reviewed here focuses on the action of endothelin 3 in controlling both the emergence and the maintenance of the NC-derived melanocyte phenotype.