Local ties that bind: The role of perceived neighborhood cohesion and disorder for immigrants' national identification

Immigrants' identification with the receiving society is a core dimension of their integration process. Previous research has much focused on the relevance of language acquisition, job market placement, and intergroup friendship as drivers of identification. At the same time, neighborhoods as immediate living environments reflect a relevant experiential setting in which immigrants learn about the social fabric of the receiving society and to which degree (local) public authorities take their concerns into account. This study examines how perceptions of neighborhood social cohesion and disorder relate to immigrants' identification with the receiving society. Using geo-coded panel data from the Netherlands Longitudinal Lifecourse Study, we find robust empirical evidence that high levels of perceived neighborhood social cohesion predict higher degrees of immigrants' national identification mainly by facilitating intergroup interaction. Our results suggest that perceptions of and experiences in immigrants' immediate living environments are highly relevant for outcomes related to their integration within the receiving society.

Observing many researchers using the same data and hypothesis reveals a hidden universe of uncertainty

This study explores how researchers' analytical choices affect the reliability of scientific findings. Most discussions of reliability problems in science focus on systematic biases. We broaden the lens to emphasize the idiosyncrasy of conscious and unconscious decisions that researchers make during data analysis. We coordinated 161 researchers in 73 research teams and observed their research decisions as they used the same data to independently test the same prominent social science hypothesis: that greater immigration reduces support for social policies among the public. In this typical case of social science research, research teams reported both widely diverging numerical findings and substantive conclusions despite identical start conditions. Researchers' expertise, prior beliefs, and expectations barely predict the wide variation in research outcomes. More than 95% of the total variance in numerical results remains unexplained even after qualitative coding of all identifiable decisions in each team's workflow. This reveals a universe of uncertainty that remains hidden when considering a single study in isolation. The idiosyncratic nature of how researchers' results and conclusions varied is a previously underappreciated explanation for why many scientific hypotheses remain contested. These results call for greater epistemic humility and clarity in reporting scientific findings.

Residential Segregation and Social Trust of Immigrants and Natives: Evidence From the Netherlands

This study examines the relationship between residential segregation and social trust of immigrants and natives in the Netherlands. Building on previous studies that have found evidence for a negative segregation-trust link, we present a nuanced narrative by (i) distinguishing between an ethnic minority and majority perspective, (ii) elaborating theoretical foundations on the moderating role of individual exposure in the form of ethnic minority concentration in the neighborhood, and (iii) taking income segregation into account. In addition to the refined theoretical framework, our study employs a rigorous empirical approach. Using two waves (2009 and 2013) of the Netherlands Longitudinal Lifecourse Study-a geocoded panel study with an oversampling of Moroccan and Turkish immigrants-we are able to study the influence of (changes in) municipality-level segregation patterns for both natives and immigrants, and consider the roles of both neighborhood ethnic minority concentration, as well as income-based segregation. Results from four-level multilevel models show that ethnic segregation is negatively related to the social trust of immigrants. At the same time, this negative relationship is particularly strong in neighborhoods with a low level of minority population concentration, which provides support for the so-called integration paradox where negative intergroup interactions reduce social trust. For respondents of Dutch origin, we find no evidence that their social trust is sensitive to ethnic segregation or that this relationship is conditional on minority concentration at the neighborhood level.

Economic conditions and native-immigrant asymmetries in generalized social trust

Previous research suggests that individual-level factors such as socio-economic disadvantage and discrimination account for lower levels of generalized social trust of immigrants when compared to natives. This study examines how individual and contextual economic conditions impact such trust gaps. We argue that-beyond objective economic circumstances-evaluations of economic opportunities matter for immigrants' integration, and for their social trust. Using data from the European Social Survey 2012, 2016, merged with regional economic conditions, results from two-way fixed effects multilevel models show that gaps in social trust are wider in regions where the state of the economy is predominantly evaluated as being prosperous. Additional tests show that, in those regions, immigrants report higher levels of discrimination and lower levels of satisfaction with social life. This study adds the important finding to the literature on social inequality and immigrant integration that favorable economic conditions may, paradoxically, increase native-immigrant trust asymmetries.

Immigration, social trust, and the moderating role of value contexts

This study examines whether the values prevalent in one's social environment moderate the link between immigration-related ethnic diversity and social trust. Drawing on arguments related to intergroup relations and anomie, we expect that contexts characterized by a comparatively high degree of openness mitigate a trust-eroding effect of immigration. In contrast, we expect that contexts of low openness or high conservation may reinforce a trust-eroding effect. We test these propositions using survey data from Europe and the United States merged with regional indicators on immigration and value contexts. The results show that high levels of contextual openness attenuate trust-eroding consequences of immigration growth. With regard to mechanisms, we find that contextual openness moderates how change in immigration relates to generalized forms of trust rather than outgroup trust. This points to an overall anomie-reducing function of openness norms, especially in times of ethnic change.

Transient blocking of both B7.1 (CD80) and B7.2 (CD86) in addition to CD40-CD40L interaction fully abrogates the immune response following systemic injection of adenovirus vector

Blockade of the CD40-CD40L and CD80/CD86-CD28 costimulatory pathways represents a strategy to inhibit the immune response against Ad vectors designed for gene therapy applications. Since most previous studies have used a CTLA4-Ig fusion molecule binding to both CD80 and CD86, the respective roles of these B7 molecules remained undefined. We have studied the effect of blocking monoclonal Abs (mAbs) directed against the costimulatory molecules CD40L, CD80 and CD86, alone or in different combinations, on the humoral and cellular immune responses against Ad. Groups of mice were transiently treated with each combination of blocking mAbs upon systemic injection of a first Ad vector. Combinations of anti-CD80 + anti-CD86 or anti-CD40L + anti-CD86 mAbs resulted in strong inhibition of the immune response against Ad. Using either of these mAb pairs, a second vector could be administered 1 month after the first injection but with lower efficiency than in naive animals. Thus, CD86 stands as the pivotal B7 molecule involved in the development of the immune response against Ad. However, only the blockade of both CD80 and CD86 in addition to CD40L fully inhibited the humoral and cellular responses against the Ad vector, such that readministration after 1 month was as efficient as in naive animals. At the time of readministration, treated animals had regained their ability to mount a normal immune response to the second Ad vector, showing that tolerance was not induced.

The expression of Quox 1, a homeodomain-containing protein, in sympathetic ganglion cells is regulated in vitro by growth factors

Quox 1, a quail homeobox gene, is the first vertebrate Antp-type homeobox gene to be described that is expressed in the forebrain. We have already shown that the Quox 1 protein is specifically expressed in post-mitotic sensory neurons. A subpopulation of sympathetic ganglion cells was also found to be labelled by anti-Quox 1 in vitro, but it is not clear whether this protein is expressed in sympathetic ganglion cells in vivo and, if so, the conditions which regulate its expression in vitro. In the present study, we used immunocytochemistry to find out whether Quox 1 expression in sympathetic ganglion cells in vitro is regulated by environmental signals. We found that several peptide growth factors can regulate Quox 1 expression in cultured sympathetic ganglion cells, and that they do so at physiological concentration and in a variety of ways. Basic fibroblast growth factor (FGF-2) induces Quox 1 protein expression, whereas insulin and human insulin-like growth factor-I (IGF-I) down-regulate Quox 1 expression.

The developmental potentials of the caudalmost part of the neural crest are restricted to melanocytes and glia

The avian spinal cord is characterized by an absence of motor nerves and sensory nerves and ganglia at its caudalmost part. Since peripheral sensory neurons derive from neural crest cells, three basic mechanisms could account for this feature: (i) the caudalmost neural tube does not generate any neural crest cells; (ii) neural crest cells originating from the caudal part of the neural tube cannot give rise to dorsal root ganglia or (iii) the caudal environment is not permissive for the formation of dorsal root ganglia. To solve this problem, we have first studied the pattern of expression of ventral (HNF3beta) and dorsal (slug) marker genes in the caudal region of the neural tube; in a second approach, we have recorded the emergence of neural crest cells using the HNK1 monoclonal antibody; and finally, we have analyzed the developmental potentials of neural crest cells arising from the caudalmost part of the neural tube in avian embryo in in vitro culture and by means of heterotopic transplantations in vivo. We show here that neural crest cells arising from the neural tube located at the level of somites 47-53 can differentiate both in vitro and in vivo into melanocytes and Schwann cells but not into neurons. Furthermore, the neural tube located caudally to the last pair of somites (i.e. the 53rd pair) does not give rise to neural crest cells in any of the situations tested. The specific anatomical aspect of the avian spinal cord can thus be accounted for by limited developmental potentials of neural crest cells arising from the most caudal part of the neural tube.

Ovarian carcinoma cells are effectively transfected by polyethylenimine (PEI) derivatives

As a prerequisite to nonviral gene therapy approaches of ovarian carcinoma, we evaluated the possibility of transfecting established tumor cell lines (SKOV3, IGROV1) as well as primary mesothelial and tumor cells by various polyethylenimine (PEI) derivatives. Several PEI-based vectors were able to effectively transfect these cells, as shown by high luciferase expression levels (10(8) to 10(9) relative light units per milligram of cell protein) that corresponded with 25-50% of green fluorescent protein-positive cells after 24 hours. However, unpredictable differences were observed among the vectors and cell types that a posteriori justified the screening procedure. We also showed that cells that were not transfected after the first experiment remained transfectable in a subsequent transfection experiment to a level similar to that of the initial population. This experiment does not support the emergence of a transfection-resistant cell population and opens the door to multiple therapeutic gene deliveries. Although efficacy and cell targeting still remain to be improved, PEI derivatives appear to be promising molecules for the development of nonviral gene therapy of ovarian carcinoma.

Regulation of adenovirus-mediated transgene expression by the viral E4 gene products: requirement for E4 ORF3

In a previous study we showed that multiple deletions of the adenoviral regulatory E1/E3/E4 or E1/E3/E2A genes did not influence the in vivo persistence of the viral genome or affect the antiviral host immune response (Lusky et al., J. Virol. 72:2022-2032, 1998). In this study, the influence of the adenoviral E4 region on the strength and persistence of transgene expression was evaluated by using as a model system the human cystic fibrosis transmembrane conductance regulator (CFTR) cDNA transcribed from the cytomegalovirus (CMV) promoter. We show that the viral E4 region is indispensable for persistent expression from the CMV promoter in vitro and in vivo, with, however, a tissue-specific modulation of E4 function(s). In the liver, E4 open reading frame 3 (ORF3) was necessary and sufficient to establish and maintain CFTR expression. In addition, the E4 ORF3-dependent activation of transgene expression was enhanced in the presence of either E4 ORF4 or E4 ORF6 and ORF6/7. In the lung, establishment of transgene expression was independent of the E4 gene products but maintenance of stable transgene expression required E4 ORF3 together with either E4 ORF4 or E4 ORF6 and ORF6/7. Nuclear run-on experiments showed that initiation of transcription from the CMV promoter was severely reduced in the absence of E4 functions but could be partially restored in the presence of either ORF3 and ORF4 or ORFs 1 through 4. These results imply a direct involvement of some of the E4-encoded proteins in the transcriptional regulation of heterologous transgenes. We also report that C57BL/6 mice are immunologically weakly responsive to the human CFTR protein. This observation implies that such mice may constitute attractive hosts for the in vivo evaluation of vectors for cystic fibrosis gene therapy.

Endothelin 3 selectively promotes survival and proliferation of neural crest-derived glial and melanocytic precursors in vitro

Genetic data in the mouse have shown that endothelin 3 (ET3) and its receptor B (ETRB) are essential for the development of two neural crest (NC) derivatives, the melanocytes and the enteric nervous system. We report here the effects of ET3 in vitro on the differentiation of quail trunk NC cells (NCC) in mass and clonal cultures. Treatment with ET3 is highly mitogenic to the undifferentiated NCC population, which leads to expansion of the population of cells in the melanocytic, and to a lesser extent, the glial lineages. The effect of ET3 on these two NC derivatives was confirmed by the quantitative analysis of clones derived from individual NCC subjected to ET3: we found a large increase in the survival and proliferation of unipotent and bipotent precursors for glial cells and melanocytes, with no significant effect on multipotent cells generating neurons. ET3 first stimulates expression of both ETRB and ETRB2 by cultured NCC. Then, under prolonged exposure to ET3, ETRB expression decreases and switches toward an ETRB2-positive melanogenic cell population. We therefore propose that the present in vitro experiments (long-lasting exposure to a high concentration of ET3) mimic the environment encountered by NCC in vivo when they migrate to the skin under the ectoderm that expresses ET3.

Quox 1 homeobox protein is expressed in postmitotic sensory neurons of dorsal root ganglia

The expression of vertebrate homeoproteins has been extensively studied in a variety of normal and cancerous tissues, but little is known on the role of vertebrate homeoproteins in the proliferation and differentiation of cells from these tissues. In the present study, we investigate the relationship between Quox 1 protein (a quail homeodomain containing protein) expression and the proliferation and differentiation of quail dorsal root ganglia (DRG) and neural crest cells. In vivo [3H]TdR labeling experiments demonstrate that the postmitotic sensory neuroblasts appear before the formation of the ganglion, and that more than half of sensory neuroblasts from DRG have already terminated their proliferation in embryos of 2 days of incubation (E2). All DRG neurons have completely ceased to proliferate from E6.5 onwards. By means of immunocytochemistry, we observe that Quox 1 protein is accumulated exclusively in all bipolar neurons in culture of DRG from E9-E11, and in all postmitotic sensory-like neuroblasts during in vitro cell differentiation of the neural crest. The Quox 1 immunoreactive neurons express simultaneously neurofilaments or substance P, and they are never labeled by anti-bromodeoxyuridine. These observations together with the morphology of Quox 1 positive cells, demonstrate that Quox 1 protein is expressed in the postmitotic sensory neurons of DRG. Our previous experiments have shown that between E4 and E6, the accumulation of Quox 1 protein increases in DRG in vivo, but decreases in the central nervous system in which cell proliferation decreases (Xue et al., (1993) Mech. Dev. 43, 149-158). Taken together, our results show that the accumulation of Quox 1 protein in DRG is tightly linked to the increase in the number of postmitotic neurons, whereas in the central nervous system the level of expression of Quox 1 seems concomitant with the extent of cell proliferation.

HERG- and IRK-like inward rectifier currents are sequentially expressed during neuronal development of neural crest cells and their derivatives

Quail neural crest cells were cultured in a differentiative medium to study the inward K+ channel profile in neuronal precursors at various stages of maturation. Between 12 and 24 h of culture, neural crest-derived neurons displayed, in addition to the previously described outward depolarization-activated K+ currents, an inward current enhanced in high K+ medium. A biophysical and pharmacological analysis led us to conclude that this inward K+ current is identical to that previously demonstrated in mouse and human neuroblastoma cell lines (I[IR]). This current (quail I[IR] or ql[IR]), which is active at membrane potentials positive to -35 mV, was blocked by Cs+ and by class III antiarrhythmic drugs, thus resembling the K+ current encoded by the human ether-a-gò-gò-related gene (HERG). At later stages of incubation (>48 h), neural crest-derived neurons underwent morphological and biochemical differentiation and expressed fast Na+ currents. At this stage the cells lost qI[IR], displaying instead a classical inward rectifier K+ (IRK) current (quail I[IRK] = qI[IRK]). This substitution was reflected in the resting potential (VREST), which became hyperpolarized by >20 mV compared with the 24 h cells. Neurons were also harvested from peripheral ganglia and other derivatives originating from the migration of neural crest cells, viz. ciliary ganglia, dorsal root ganglia, adrenal medulla and sympathetic chain ganglia. After brief culture following harvesting from young embryos, ganglionic neurons always expressed qI(IR). On the other hand, when ganglia were explanted from older embryos (7-12 days), briefly cultured neurons displayed the IRK-like current. Again, in all the above derivatives the qI(IR) substitution by qI(IRK) was accompanied by a 20 mV hyperpolarization of VREST. Together, these data indicate that the VREST of normal neuronal precursors is sequentially regulated by HERG- and IRK-like currents, suggesting that HERG-like channels mark an immature and transient stage of neuronal differentiation, probably the same stage frozen in neuroblastomas by neoplastic transformation.

The avian embryo as a model in developmental studies: chimeras and in vitro clonal analysis

The avian embryo is a model in which techniques of experimental embryology and cellular and molecular biology can converge to address fundamental questions of development biology. The first part of the chapter describes two examples of transplantation and cell labeling experiments performed in ovo. Thanks to the distinctive histologic and immunocytochemical characteristics of quail and chick cells, the migration and development of definite cells are followed in suitably constructed chimeric quail-chick embryos. Isotopic transplantations of neural tube portions between quail and chick, combined with in situ hybridization with a nucleic probe specific for a quail oligodendrocyte marker, allowed study of the origin and migration of oligodendroblasts in the spinal cord. Heterotopic transplantations of rhombomeres were performed to establish the degree of plasticity of these segments of the hindbrain regarding Hox gene expression, which was revealed by labeling with chick-specific nucleic probes. The second part describes in vitro cell cloning experiments devised to investigate cell lineage segregation and diversification during development of the NC. An original cloning procedure and optimal culture conditions permitted analysis of the developmental potentials of individual NC cells taken at definite migration stages. The results revealed a striking heterogeneity of the crest cell population, which appeared to be composed of precursors at different states of determination. Clonal cultures also provide a means to identify subsets of cells that are the target of environmental factors and to understand how extrinsic signals influence the development of responsive cells.

Endothelin 3 promotes neural crest cell proliferation and mediates a vast increase in melanocyte number in culture

Mutations in the endothelin 3 (EDN3) gene severely affect the development of neural crest-derived melanocytes. In this paper, we report the action of EDN3 on neural crest cells in vitro. The presence of EDN3 leads to a large increase in the number of cells, the majority of which eventually differentiate into melanocytes that aggregate to form a reproducible pigmentation pattern. Quantitative analysis of the effect of different culture conditions revealed that EDN3 initially promotes neural crest cell proliferation. This phase of expansion, which can be prolonged for a few weeks if the cells are replaced regularly, is followed by both a decrease in cell proliferation and the onset of melanocytic differentiation. Therefore, EDN3 is a potent mitogen for early neural crest cell precursors that can give rise to melanocytes.

Effect of the Steel gene product on melanogenesis in avian neural crest cell cultures

Mutations at the Steel (Sl) and dominant white spotting (W) loci affect three embryonic lineages: primordial germ cells, hemopoietic stem cells and neural-crest-derived melanocytes. The gene products of these loci are a peptide growth factor, called here stem cell factor (SCF), and its tyrosine kinase receptor, the proto-oncogene c-kit. We have studied how chicken recombinant SCF affects the development of melanocytes from quail neural crest cells in secondary culture under defined conditions. We observed that the total number of neural crest cells, of melanocytes and of their precursors was higher in the presence than in the absence of SCF. Labelling with bromodeoxyuridine showed that SCF had a modest and transient mitogenic effect on the neural crest population. SCF also enhanced the differentiation rate of melanocyte precursors, recognized by the "melanocyte early marker" monoclonal antibody (MelEM MAb), and of melanocytes, since the proportion of both subpopulations significantly increased in the presence of SCF. Finally, SCF increased the survival of the neural crest population since in its presence the total number of cells remained stable while it gradually declined in control cultures. Our results support the notion that SCF sustains the survival of the neural crest population and stimulates the rate of the melanogenic differentiation process.

Genetic and epigenetic control in neural crest development

The neural crest is a fascinating structure of the vertebrate embryo; its ontogeny includes a transient period during which its component cells undergo an epithelio-mesenchymal transition and become migratory. This phase was shown recently to be controlled by the 'Slug' gene which belongs to the 'Snail' family of Drosophila transcription factors. After homing to specific sites in the embryo, the crest-derived cells produce a large variety of phenotypes. Recent advances have shown that during migration most crest cells exhibit various degrees of pluripotentiality, some being already committed to a single and definite fate. Moreover, several lines of evidence point to the existence of totipotent stem cells in the neural crest, the progeny of which become progressively diversified through a combination of intrinsic and extrinsic influences. The latter have been documented by the disruption of several neurotrophin genes, which results in severe deficiencies of selected subsets of neural crest derivatives. The neural crest has also been shown to play an important role in the development of the vertebrate head and hypobranchial region. The genetic control of this process depends on the activity of developmental genes, among which the vertebrate Hox genes are essential, particularly at the rhombencephalic level.

Developmental potentials of enteric neural crest-derived cells in clonal and mass cultures

The aim of this work was to test the differentiation capacities of neural crest-derived cells that had already migrated to the gut and were in the process of forming the intrinsic gut plexuses, when they were withdrawn from the gut wall environment. The experiments were performed on the quail bowel of embryos at 4 to 12 days of incubation (E4 to E12), which was dissociated into a single cell suspension. The crest cells invading the gut carry the NC1/HNK1 epitope. This allowed us to select them as singlets under the control of a uv-illuminated inverted microscope. Crest-derived cells from the gizzard were then clonally cultured on a feeder layer of growth-inhibited 3T3 fibroblasts, as described before for cephalic and truncal neural crest cells. The clonal efficiency of these cells reached about 28% from E4 to E7 and decreased sharply at E8. The size of the clones generated by cells taken between E4 to E8 varied considerably. Large clones (> 10(3)) were numerous from E4 and E5 gizzard-derived cells, whereas E7 and E8 cells produced only very small colonies. The phenotypic diversity of the clones decreased similarly during the time period under scrutiny. Two phenotypes never encountered in the enteric plexuses were found in the cultures: adrenergic cells and glial cells expressing SMP, a marker exclusively expressed by Schwann cells in vivo and normally absent in enteric glia. The capacity to yield adrenergic cells was present up to E6 in clonal cultures of gizzard neural crest-derived cells. Mass cultures of cells dissociated from the gizzard and bowel, including gut mesenchymal and epithelial cells in addition to cells of neural crest origin, revealed that both adrenergic and SMP+ cells could arise under these conditions even in a defined culture medium devoid of serum and chick embryo extract. The number of TH+ cells developing in bowel cultures reached a peak at E7, while at this stage no TH+ cells could be obtained from gizzard cultures. A craniocaudal gradient of disappearance of adrenergic precursors in the gut could thus be demonstrated. Finally we point out that these and previous experiments from other laboratories show that precursor cells of the sympathoadrenal lineage are present in all types of avian sensory and autonomic ganglia during development even though, in most of them, these cells never express the adrenergic phenotype.

The tyrosine hydroxylase gene is expressed in endoderm and pancreas of early quail embryos

The initial expression of the gene encoding tyrosine hydroxylase (TH) was studied in the trunk of quail embryos by in situ hybridization. We detected the presence of quail TH mRNA on embryonic day 3.5 (E3.5) in the sympathetic ganglia and aortic plexus, both neural crest derived structures. In contrast, the TH gene was expressed much earlier in the endodermal layer of E2 embryos, i.e. from the 8-somite stage onwards. TH mRNA was found also in the pancreatic bud, an endoderm-derived structure. The TH protein and catecholamines were subsequently looked for in these structures. TH immunoreactivity was found in cells of E2 explanted endoderm, but no catecholamine histofluorescence was observed before or after a few days in culture. TH-positive cells were also detected in cultures of pancreatic rudiments, explanted from E3 to E6 quail embryos. We suggest that the TH-positive cells of the endoderm are the progenitors of the catecholaminergic cells of the pancreas and of the enterochromaffin cells of the gut. The hypothesis that the TH-positive cells of the endoderm are involved in the expression of the catecholaminergic phenotype by neural crest cells is discussed.

Plasticity in neural crest cell differentiation

The neural crest is a pluripotent population of cells that are endowed with migratory capacities. It has long been known that the differentiation pathway taken by cells derived from the neural crest is largely controlled by the microenvironment to which they home after their migration phase, indicating a high degree of plasticity in their developmental fate. Recent progress has been made concerning the factors which influence survival, growth and differentiation of selected sets of precursors in each embryonic site colonised by derivatives of the neural crest.

Patterning of neural crest derivatives in the avian embryo: in vivo and in vitro studies

In this article we review recent findings from our laboratory on the developmental fate of the neural crest as studied in the avian embryo using the quail-chick marker system in vivo. Quail-chick chimeric experiments carried out at the late neurula stage have revealed the contribution of the neural crest to the skull vault, i.e., the frontal and parietal bones, previously thought to be mesodermally derived. At early developmental stages, the fate of the cephalic mesoderm (free of neural crest cells) could be analyzed. The striking result was that the mesoderm does not contribute to the head and face dermis except in the occipital and otic areas where the skull is derived from the cephalic and somitic mesoderm. Thus, the neural crest forms the dermis, the membrane and cartilage bones of the skull vault, the skull basis, and the face. The limit of the mesoderm-derived skeleton in the skull basis is located in the sella turcica between the basipre- and the basipostsphenoid and coincides with the tip of the notochord. We thus define a "chordal" and an "achordal" skull, the latter being all derived from the neural crest. These results are discussed in the framework of the "New Head" concept of Gans and Northcutt (1983). The second part of this review deals with the role of the environment in the morphogenesis and diversification of neural crest derivatives. The role of the rostrocaudal heterogeneity of the somites in establishing the metameric pattern of the truncal neural crest derivatives is analyzed. The respective contributions of the "in embryo" and in vitro approaches to our understanding of the neural crest cell differentiating potentialities are reviewed. It is pointed out that the search for survival and proliferation factors acting locally on neural crest derivatives when they are wandering and/or settling in various embryonic locations constitutes the new challenge for further understanding their complex patterning and the highly diversified variety of their phenotypes.

Novel markers of melanocyte differentiation in the avian embryo

In order to produce markers of melanoblasts and melanocytes, we immunized a mouse with trunk neural crest cells differentiated into melanocytes in culture. We obtained three monoclonal antibodies which react both with pigmented and unpigmented cells in epidermis and in neural crest cultures. These markers are characteristic of distinct differentiation steps. One of them, melanoblast/cyte early marker (MelEM) monoclonal antibody (Mab) detects melanoblasts as soon as they have reached the subectodermal mesenchyme, while the two others, Mel1 and Mel2 Mabs, detect antigens present in melanosomes and promelanosomes later in the differentiation process. Moreover, MelEM is a specific marker of melanoblasts/cytes deriving exclusively from neural crest and not of those from the neural retina. The antigen recognized by MelEM Mab is a protein of M(r) 26,000. The epitopes recognized by Mel1 and Mel2 Mabs are carbohydrate moieties carried by glycoproteins of M(r) 123,000 and 85,000, respectively.

The neural tube/notochord complex is necessary for vertebral but not limb and body wall striated muscle differentiation

The aim of this work was to investigate the role played by the axial organs, neural tube and notochord, on the differentiation of muscle cells from the somites in the avian embryo. Two of us have previously shown that neuralectomy and notochordectomy is followed by necrosis of the somites and consecutive absence of vertebrae and of most muscle cells derived from the myotomes while the limbs develop normally with muscles. Here we have focused our attention on muscle cell differentiation by using the 13F4 mAb that recognizes a cytoplasmic antigen specific of all types of muscle cells. We show that differentiation of muscle cells of myotomes can occur in the absence of notochord and neural tube provided that the somites from which they are derived have been in contact with the axial organs for a defined period of time, about 10 hours for the first somites formed at the cervical level, a duration that progressively reduces caudalward (i.e. for thoracic and lumbar somites). Either one or the other of the two axial organs, the neural tube or the notochord can prevent somitic cell death and fulfill the requirements for myotomal muscle cell differentiation. Separation of the neural tube/notochord complex from the somites by a surgical slit on one side of the embryo gave the same results as extirpation of these organs and provided a perfect control on the non-operated side. A striking finding was that limb and body wall muscles, although derived from the somites, differentiated in the absence of the axial organs. However, limb muscles that develop after excision of the neural tube started to degenerate from E10 onward due to lack of innervation. In vitro explantation of somites from different axial levels confirmed and defined precisely the chronology of muscle cell commitment in the myotomes as revealed by the in vivo experiments.

Developmental potentialities of cells derived from the truncal neural crest in clonal cultures

The developmental potentialities of single truncal neural crest derived cells were analysed in clonal cultures. The clone-forming ability and differentiation potential of crest cells migrating through the somitic mesoderm of 3-day-old embryos (E3) and of non-neuronal cells of dorsal root ganglia taken at E6-14 were compared. Since most of the cells present in the sclerotomal and rostral parts of the somite at E3 become later on incorporated into the spinal ganglia, one can consider that these two cell populations represent the same derivatives of the trunk neural crest at different developmental stages. After 10 days in vitro, the size of clones and their phenotypic composition varied noticeably, revealing a certain heterogeneity in the founder cell populations in terms of developmental potencies. Clones obtained from migrating neural crest cells at E3 were often large (greater than 1000 cells) and many of them contained neuronal and non-neuronal cells. Dorsal root ganglion cells produced mostly small clones (less than 100 cells) in which only non-neuronal (i.e. glial) phenotypes were expressed. Therefore, both the capacity for proliferation and the differentiation ability of cloned neural crest derived cells decrease considerably with increasing embryonic age. This is even more striking if these results are compared with those obtained previously in our laboratory with single cells cultures of E2 cephalic neural crest. In the latter case, both clone sizes and cellular diversity within the colonies were much higher than with E3 truncal crest and dorsal root ganglia (DRG) non-neuronal cells. The second result of the present work concerns the differentiation of the dormant autonomic neuronal precursors of the DRG. It has been established previously that the non-neuronal cells of the DRG include adrenergic precursors than can differentiate in mass culture of dissociated DRG cells. We show that these cells never differentiate in clonal cultures but depend upon the cell density of the culture. This suggests that cell to cell interaction between crest derived cells are critical in eliciting the differentiation of the adrenergic phenotype.

A monoclonal antibody directed against quail tyrosine hydroxylase: description and use in immunocytochemical studies on differentiating neural crest cells

Catecholamine (CA) synthesis is one of the phenotypic traits expressed by some neural crest-derived cells in vivo and in vitro. In the present study, we have evidenced, in quail embryos, the expression of the first enzyme of CA metabolism, tyrosine hydroxylase (TOH), using a monoclonal antibody raised against the quail enzyme. This antibody also recognizes TOH from chick and pleurodele, but not from several mammalian species (rat, human). We have also investigated the extent to which TOH-positive cells, differentiated in neural crest cultures, express structural neuronal markers and display vasoactive intestinal polypeptide (VIP) and substance P (SP) immunoreactivity. Double-immunolabeling experiments show that, in vitro, half of the population of TOH-positive cells exhibits tetanus toxin binding sites but none of them are recognized by a neurofilament antibody. On the other hand, some TOH-positive cells contain VIP or SP. These observations suggest that under our culture conditions autonomic neural crest precursors differentiate only into immature sympathoblasts, but are able to synthesize peptides in addition to CA.

A monoclonal antibody recognizing a common antigen on neurons and fibroblasts in chicken and quail

A monoclonal antibody, FiN1, obtained by immunization of a mouse with homogenates of embryonic quail nodose ganglia, was found to react with a surface antigenic determinant, both in quail and chick, present on practically all neurons of the spinal cord and of the peripheral nervous system and on a subpopulation of fibroblasts. An ontogenetic study performed on tissue sections, cell suspensions and cultures showed that FiN1 defines a differentiation marker which appears relatively late in development, during the second half of embryonic life, and persists after hatching. The onset and evolution of its expression during development varies in a tissue-specific manner.

A surface protein expressed by avian myelinating and nonmyelinating Schwann cells but not by satellite or enteric glial cells

Searching for specific markers of neural crest-derived cell lineages, we immunized mice with glycoproteins purified from adult quail peripheral myelin. We obtained a monoclonal antibody that reacts with myelin and peripheral glial cells. This antibody, to Schwann cell myelin protein (SMP), is specific for the membranes of all Schwann cells, irrespective of whether they are associated with myelinated nerves. SMP persists on Schwann cells in long-term cultures in vitro, but is absent from satellite cells of peripheral ganglia, both in vivo and in vitro. The antigen (a protein doublet of Mr 75,000-80,000) is present in, but not restricted to, the myelin lamellae, since it is distributed along the whole myelinating Schwann cell membrane. In the CNS, SMP appears as a single band of Mr 80,000. SMP is first detectable by immunofluorescence at E6 in the quail, which is at least 6 days earlier than the first appearance of already described markers related to myelination.

A monoclonal antibody specific for avian early myogenic cells and differentiated muscle

A monoclonal antibody raised in mouse in response to homogenates of Remark ganglia and dorsal mesentery of chicken embryos was found to exhibit a unique reactivity towards myogenic cells, heart, striated muscles, and smooth muscles in chicken and quail. Indirect immunofluorescence assays were performed at different stages of chicken and quail embryonic development and, after hatching, on tissue sections and cultured cells. They revealed that the cytoplasmic marker recognized by 13F4 is expressed in early embryonic heart, in somitic myotome (from stage 14 onward), in the skeletal muscles in limbs and trunk, in all muscles in the head and the branchial arches, in the smooth muscles of the digestive tract and blood vessels. In myofibrils of striated muscles, the antigen is localized in the Z lines. The antigenicity of the molecule recognized by 13F4 is not associated with a glycolipid or a glycoprotein. It is of peptidic nature and its molecular weight is 54 kDa. We stress the value of this cell-type-specific marker in studies on ontogenesis and differentiation of all muscular structures, namely, of myocardium and striated muscles, which express 13F4 antigenicity from an early developmental stage.

In vivo and in vitro expression of vasoactive intestinal polypeptide-like immunoreactivity by neural crest derivatives

Qualitative and quantitative in vivo studies were performed on the development of the neuropeptide vasoactive intestinal polypeptide (VIP) in the peripheral nervous system of quail embryos. VIP-like immunoreactivity (VIPLI) was found by radioimmunoassay (RIA) from the sixth day of embryonic life onward in the sympathetic chain, the esophagus and duodenum, and from day 15 of incubation onward in the adrenal glands and the nodose ganglia. By using immunocytochemistry, we identified cells expressing VIPLI in sensory spinal ganglia of 13- to 15-day-old embryos. In neural crest cultures, cells expressing the VIP phenotype differentiated constantly under various culture conditions, in contrast to other phenotypes which had specific medium requirements, i.e. adrenergic cells or substance P-containing neurons.

Cell lineages in peripheral nervous system ontogeny: medium-induced modulation of neuronal phenotypic expression in neural crest cell cultures

Neural crest, taken from cephalic and trunk levels of quail embryos, was grown in vitro in conventional tissue culture medium (Dulbecco's modified Eagle's medium containing 15% fetal calf serum and either 2 or 15% chick embryo extract (CEE] or in a chemically defined serum- and CEE-free medium. Depending on the conditions employed, different types of neuronal or neuronlike cells developed in the cultures. Thus, in medium containing 15% CEE, adrenergic cells (identified by tyrosine hydroxylase immunoreactivity and catecholamine histofluorescence) emerged after 5-6 days. These cells lacked tetanus toxin binding sites and did not react with an antibody directed against 70-kDa neurofilament protein. In the fully defined medium, a neuronal cell type exhibiting neurofilament and substance P (SP) immunoreactivity differentiated from noncycling precursors within 1 or 2 days of culture. If serum was added to the medium, the neurites disintegrated and the neuronal cells ultimately died. By sequentially culturing neural crest, first in the wholly synthetic medium for 1-3 days and then in the conventional medium supplemented with serum and 15% CEE, the disappearance of the SP-positive neurons was followed, several days later, by the emergence of adrenergic cells. The majority of these cells and/or their precursors were found to undergo cell division in culture. We conclude that the cells expressing the adrenergic phenotype (characteristic of the sympathetic nervous system) and those displaying SP immunoreactivity, comparable to a category of neurons in dorsal root and cranial sensory ganglia, derive from distinct sets of precursors. Our results reinforce the contention, deduced from in ovo transplantation experiments (see N. M. Le Douarin, (1984) In Cellular and Molecular Biology of Neuronal Development (I. Black, Ed.), pp. 3-28. Plenum, New York), that at least two lineages, from which sensory and autonomic cell types are derived respectively, are segregated early during neural crest ontogeny and have extremely different survival and trophic requirements.

Heterogeneity in migrating neural crest cells revealed by a monoclonal antibody

A monoclonal antibody, GlN1, obtained by immunization with extracts of the 14 d embryonic quail nodose ganglion, is described. GlN1 recognizes an antigenic determinant present in virtually all the satellite cells of the peripheral ganglia, all Schwann cells of the peripheral nerves, and in subpopulations of sensory and autonomic neurons of embryonic and adult quails and chickens. The molecular weight of the antigen(s) revealed by GlN1 in embryonic day 12 quail dorsal root ganglion (DRG) cultures is around 80 kDa. In the neural crest, GlN1 determinant is found as soon as the crest cells leave the neural primordium. Only a proportion (25%) of the migrating neural crest cells carry the antigen. This demonstrates that the neural crest is composed of a heterogeneous population of cells from its early migratory stages. Being selectively distributed on neural crest cells and its derivatives, the GlN1 determinant may be considered as a "differentiation antigen" that will be useful in further studies on cell-line segregation during the ontogeny of the PNS.

Quail neural crest cells transformed by Rous sarcoma virus can be established into differentiating permanent cell cultures

Quail neural crest cells derived from the truncal neural primordium, infected in vitro by Rous sarcoma virus (RSV) in January 1978, were induced to multiply and have been established into permanent cultures. These cultures contain cells that differentiate into melanocytes, neuron-like cells and flat cells. About 50% of these different cell types are tetanus-toxin positive. Electrophysiological studies have shown that some cells can generate action potentials similar to those reported in quail neural crest primary cultures. Taken together these data show that the RSV-transformed quail neural crest permanent cultures are composed of stem cells which can differentiate into cell types specific for neural crest.

Early segregation of a neuronal precursor cell line in the neural crest as revealed by culture in a chemically defined medium

This article addresses the problem of the segregation of cell lines during the development of peripheral nervous system components from the neural crest. We show here that committed precursors of peripheral neurons are present in the crest before the migration of its cells has started. If cultured in a serum-deprived medium, a subpopulation of the crest cells readily differentiates into neurons without dividing. Neuronal markers such as neurofilament proteins and receptor sites for tetanus toxin are not expressed in the committed neuronal precursors, but appear after a few hours in culture. They are coexpressed in neurons with the mesenchymal intermediate filament protein, vimentin, which is common to all neural crest cells regardless of their prospective fate. A strong inhibitory effect of serum factor(s) on neurite outgrowth is demonstrated. We show also that conditions stimulating proliferation of crest cells are incompatible with promotion of neuronal differentiation and vice-versa.

Migration and differentiation of neural crest cells and their derivatives: in vivo and in vitro studies on the early development of the avian peripheral nervous system

After a period of extensive migration through the vertebrate embryo, neural crest cells differentiate into a great variety of cell types, including all the elements of the peripheral nervous system. We have studied crest cell migration in quail-chick chimeras in which quail cells can be identified by means of a stable natural nuclear marker. The results of interspecific grafts of neural primordium, performed systematically at different levels of the neuraxis, have established the sites of origin of the principal peripheral ganglia. In addition, they suggest that the cholinergic and adrenergic phenotypes are not predetermined in the neural crest before migration, but are the result of multiple cellular interactions. Furthermore, the phenotype expression of young differentiating autonomic ganglia is labile and can be modified if the latter are subjected to an appropriate cellular environment by grafting into a younger host embryo. The results of experiments in which fragments of neural crest, sensory and autonomic ganglia were transplanted are presented in terms of a model of crest cell-line segregation. As a step towards the analysis of the cellular interactions occurring during autonomic neuron differentiation, we have also studied neuronal development in tissue cultures of neural crest, taken from the cranial and trunk levels of quail embryos and grown in the presence or absence of other embryonic tissues. The results confirm that both levels of the crest are potentially able to give rise to cells that can make acetylcholine and catecholamines. However, whereas acetylcholine-synthesizing ability is apparently a very early feature of autonomic neuron precursors, the ability to produce catecholamines is acquired later as a result of interactions with other cell types, in particular with mesenchymal derivatives. Although production of both neurotransmitters can be considerably stimulated by associating crest with any of several young embryonic rudiments, only when trunk crest is cultured with the sclerotomal moiety of the somite is biochemical differentiation accompanied by extensive morphological and cytochemical neuronal maturation.

[Neuronal differentiation of neural crest cells cultured in a defined medium]

Mesencephalic neural crest cells from Quail embryos, cultivated in a defined serum free medium, exhibit neurite extension and typical neuronal traits. This differentiation is never achieved in the presence of serum. Addition of serum into the culture medium after neuronal differentiation has occurred, induces complete regression of the neurites.

Differentiation of autonomic neuron precursors in vitro: cholinergic and adrenergic traits in cultured neural crest cells

The development of autonomic neuronal precursors was studied in cultures of microsurgically excised quail neural crest grown alone and associated with other young embryonic tissues. Biochemical differentiation in the cultures was followed by measuring their ability to synthesize acetylcholine (ACh) and catecholamines (CA) from radioactive precursors; cytochemical aspects of their differentiation were examined by techniques including electron microscopy, cholinesterase histochemistry, and CA cytofluorescence. Mesencephalic crest, which can make ACh before explantation, always synthesized ACh after 7 d in culture and often, but not invariably, elaborated small quantities of CA as well. Association with 2-d somite and notochord, 2-d heart, or 4-d hindgut, in medium supplemented with horse serum, resulted in the synthesis of increased amounts of both transmitters. ACh-synthesizing activity was lower and the cholinergic-stimulating effects of somite and heart were abolished in the presence of fetal calf serum. Cervicothoracic (trunk) crest, taken from the level where the dorsal mesoderm is still unsegmented, always produced ACh after culture, but CA was detectable only when the cultures were obtained by initially explanting the entire neural primordium. Co-culture of trunk crest with young embryonic tissue increased ACh-synthesizing ability and initiated CA production. Despite their capacity to elaborate neurotransmitter, cultures of either type of neural crest, alone or in association with the above-mentioned tissues, contained very few cells resembling neurons in their phase contrast appearance and none that reacted positively to any of the cytological tests applied. On the other hand, when the sclerotomic moiety of 3-d somite was cultured, trunk neural crest cells that had already migrated into the rudiment in vivo but which had not yet begun to produce detectable amounts of CA underwent rapid differentiation into neurons that synthesized and accumulated large quantities of CA. Stores of CA were detectable cytochemically as early as 24 hr after explantation and the presence of many small, dense core vesicles in neurons and processes was revealed by electron microscopy. ACh-synthesizing activity, demonstrable in freshly dissected sclerotomes, was also present in all of the cultures examined. These results show that (1) during ontogeny, cholinergic traits appear earlier than adrenergic ones in the neuronal precursors contained in the neural crest; (2) some decisive step in the differentiation of the precursor cells of the sympathetic ganglia takes place in vivo within a few hours of the onset of trunk neural crest migration. This coincides with a maturation of the somitic mesenchyme. A similar developmental process does not occur in vitro when 2-d somites and neural crest are associated in histiotypic cultures.

Acetylcholine synthesis by mesencephalic neural crest cells in the process of migration in vivo

Specific to the vertebrate embryo, the neural crest is a transitory structure whose constituent cells migrate extensively through the developing animal and ultimately give rise to many distinct cell types, including the components of the peripheral nervous system. The earliest clear indices of their differentiation have so far been detected only when cells from the crest have reached their destination. This is exemplified by the acquisition of the ability to synthesise and store catecholamines; absent from crest cells before and during their dorso-ventral migration, this ability appears concomitantly with their aggregation into the primary sympathetic ganglia. The chronology of cholinergic maturation, however, is less well defined. Appropriate biochemical markers are demonstrable as soon as parasympathetic or enteric ganglia are formed, but the lack of a suitable cytochemical method is a major obstacle to the identification of any cholinergic cells before then. Although acetylcholinesterase (AChE) is present in migrating neural crest, choline acetyltransferase (CAT), the enzyme catalysing acetylcholine (ACh) synthesis, is a much more relevant correlate, and definitive evidence for cholinergic differentiation should include the demonstration of ACh-synthesising activity in intact cells or their extracts. We show here that neural crest, as soon as it begins migration, can synthesise ACh.

Adrenergic differentiation of cells of the cholinergic ciliary and Remak ganglia in avian embryo after in vivo transplantation

We have previously shown that the neural crest is regionalized early into "adrenergic" and "cholinergic" areas from which arise, respectively, the sympathetic and parasympathetic ganglioblasts of the autonomic nervous system. This regionalization does not correspond, however, to an irreversible determination of the neural crest cells since, under certain experimental conditions, cholinergic cells can arise from the adrenergic region of the crest and vice versa. The phenotypic expression of the presumptive ganglion cells appears to be responsive to the environmental conditions they encounter during and/or after their migration. In the present study we show that the developmental behavior of parasympathetic ganglion cells which have stopped migrating and at least some of which have started to differentiate into cholinergic neurons can be profoundly modified if they are transplanted into a younger embryo at the trunk neural crest level. The crest level. The grafted ganglion cells start migrating and stop in the same sites as the host neural crest cells. Their further differentiation depends on their localization. When situated in the adrenergic ganglia and in the suprarenal gland they synthesize catehcolamines, whereas they differentiate into nonfluorescent, silver-staining ganglion cells if they migrate in the gut wall. Thus, the differentiation of autonomic neurons is dependent on tissue interactions even after the neural crest cells have grouped to form ganglionic structures in which biochemical differentiation is already in progress.

[The effect of repeated amputations on planarian regeneration in the presence of the heat-stable toxin from Bacillus thuringiensis]

The exotoxin of Bacillus thuringiensis, which is an inhibitor of RNA synthesis, inhibits Planarian regeneration. Planarians which have been cut twice at the same level are able to regenerate after the second section in the presence of the toxin. This indicates that the first amputation stimulates a synthesis of stable RNAs which thus are available for regeneration at the moment of the second section.

[Effect of actinomycin D and cycloheximide on planarian regeneration after repeated amputation]

A Planaria deprived of its head twice at an interval of a few days can regenerate in the presence of actinomycin D, even if the second amputation takes place 13 days after the first one, but it cannot regenerate in the presence of cyclohemixide. This indicates that at the moment of the second amputation, stable RNAs are available for regeneration in the tissues behind the level of section, whereas proteins have to be synthesized in situ in the blastema.