The expression of dopamine beta-hydroxylase, tyrosine hydroxylase, and Phox2 transcription factors in sympathetic neurons: evidence for common regulation during noradrenergic induction and diverging regulation later in development

Neural crest origin of sympathetic neurons at the dawn of vertebrates

The neural crest is an embryonic stem cell population unique to vertebrates1 whose expansion and diversification are thought to have promoted vertebrate evolution by enabling emergence of new cell types and structures such as jaws and peripheral ganglia2. Although jawless vertebrates have sensory ganglia, convention has it that trunk sympathetic chain ganglia arose only in jawed vertebrates3-8. Here, by contrast, we report the presence of trunk sympathetic neurons in the sea lamprey, Petromyzon marinus, an extant jawless vertebrate. These neurons arise from sympathoblasts near the dorsal aorta that undergo noradrenergic specification through a transcriptional program homologous to that described in gnathostomes. Lamprey sympathoblasts populate the extracardiac space and extend along the length of the trunk in bilateral streams, expressing the catecholamine biosynthetic pathway enzymes tyrosine hydroxylase and dopamine β-hydroxylase. CM-DiI lineage tracing analysis further confirmed that these cells derive from the trunk neural crest. RNA sequencing of isolated ammocoete trunk sympathoblasts revealed gene profiles characteristic of sympathetic neuron function. Our findings challenge the prevailing dogma that posits that sympathetic ganglia are a gnathostome innovation, instead suggesting that a late-developing rudimentary sympathetic nervous system may have been characteristic of the earliest vertebrates.

Conditional c-MYC activation in catecholaminergic cells drives distinct neuroendocrine tumors: neuroblastoma vs somatostatinoma

The MYC proto-oncogenes (c-MYC, MYCN , MYCL ) are among the most deregulated oncogenic drivers in human malignancies including high-risk neuroblastoma, 50% of which are MYCN -amplified. Genetically engineered mouse models (GEMMs) based on the MYCN transgene have greatly expanded the understanding of neuroblastoma biology and are powerful tools for testing new therapies. However, a lack of c-MYC-driven GEMMs has hampered the ability to better understand mechanisms of neuroblastoma oncogenesis and therapy development given that c-MYC is also an important driver of many high-risk neuroblastomas. In this study, we report two transgenic murine neuroendocrine models driven by conditional c-MYC induction in tyrosine hydroxylase (Th) and dopamine β-hydroxylase (Dbh)-expressing cells. c-MYC induction in Th-expressing cells leads to a preponderance of Pdx1 + somatostatinomas, a type of pancreatic neuroendocrine tumor (PNET), resembling human somatostatinoma with highly expressed gene signatures of δ cells and potassium channels. In contrast, c-MYC induction in Dbh-expressing cells leads to onset of neuroblastomas, showing a better transforming capacity than MYCN in a comparable C57BL/6 genetic background. The c-MYC murine neuroblastoma tumors recapitulate the pathologic and genetic features of human neuroblastoma, express GD2, and respond to anti-GD2 immunotherapy. This model also responds to DFMO, an FDA-approved inhibitor targeting ODC1, which is a known MYC transcriptional target. Thus, establishing c-MYC-overexpressing GEMMs resulted in different but related tumor types depending on the targeted cell and provide useful tools for testing immunotherapies and targeted therapies for these diseases.

Human iPSC modeling recapitulates in vivo sympathoadrenal development and reveals an aberrant developmental subpopulation in familial neuroblastoma

Studies defining normal and disrupted human neural crest cell development have been challenging given its early timing and intricacy of development. Consequently, insight into the early disruptive events causing a neural crest related disease such as pediatric cancer neuroblastoma is limited. To overcome this problem, we developed an in vitro differentiation model to recapitulate the normal in vivo developmental process of the sympathoadrenal lineage which gives rise to neuroblastoma. We used human in vitro pluripotent stem cells and single-cell RNA sequencing to recapitulate the molecular events during sympathoadrenal development. We provide a detailed map of dynamically regulated transcriptomes during sympathoblast formation and illustrate the power of this model to study early events of the development of human neuroblastoma, identifying a distinct subpopulation of cell marked by SOX2 expression in developing sympathoblast obtained from patient derived iPSC cells harboring a germline activating mutation in the anaplastic lymphoma kinase (ALK) gene.

A description of the bat star nervous system throughout larval ontogeny

Larvae represent a distinct life history stage in which animal morphology and behavior contrast strongly to adult organisms. This life history stage is a ubiquitous aspect of animal life cycles, particularly in the marine environment. In many species, the structure and function of the nervous system differ significantly between metamorphosed juveniles and larvae. However, the distribution and diversity of neural cell types in larval nervous systems remains incompletely known. Here, the expression of neurotransmitter and neuropeptide synthesis and transport genes in the bat star Patiria miniata is examined throughout larval development. This characterization of nervous system structure reveals three main neural regions with distinct but overlapping territories. These regions include a densely innervated anterior region, an enteric neural plexus, and neurons associated with the ciliary band. In the ciliary band, cholinergic cells are pervasive while dopaminergic, noradrenergic, and GABAergic cells show regional differences in their localization patterns. Furthermore, the distribution of some neural subtypes changes throughout larval development, suggesting that changes in nervous system structure align with shifting ecological priorities during different larval stages, before the development of the adult nervous system. While past work has described aspects of P. miniata larval nervous system structure, largely focusing on early developmental timepoints, this work provides a comprehensive description of neural cell type localization throughout the extensive larval period.

Sympathetic innervation of the development, maturity, and aging of the gastrointestinal tract

The sympathetic nervous system inhibits gut motility, secretion, and blood flow in the gut microvasculature and can modulate gastrointestinal inflammation. Sympathetic neurons signal via catecholamines, neuropeptides, and gas mediators. In the current review, we summarize the current understanding of the mature sympathetic innervation of the gastrointestinal tract with a focus mainly on the prevertebral sympathetic ganglia as the main output to the gut. We also highlight recent work regarding the developmental processes of sympathetic innervation. The anatomy, neurochemistry, and connections of the sympathetic prevertebral ganglia with different parts of the gut are considered in adult organisms during prenatal and postnatal development and aging. The processes and mechanisms that control the development of sympathetic neurons, including their migratory pathways, neuronal differentiation, and aging, are reviewed.

A topographic atlas defines developmental origins of cell heterogeneity in the human embryonic lung

The lung contains numerous specialized cell types with distinct roles in tissue function and integrity. To clarify the origins and mechanisms generating cell heterogeneity, we created a comprehensive topographic atlas of early human lung development. Here we report 83 cell states and several spatially resolved developmental trajectories and predict cell interactions within defined tissue niches. We integrated single-cell RNA sequencing and spatially resolved transcriptomics into a web-based, open platform for interactive exploration. We show distinct gene expression programmes, accompanying sequential events of cell differentiation and maturation of the secretory and neuroendocrine cell types in proximal epithelium. We define the origin of airway fibroblasts associated with airway smooth muscle in bronchovascular bundles and describe a trajectory of Schwann cell progenitors to intrinsic parasympathetic neurons controlling bronchoconstriction. Our atlas provides a rich resource for further research and a reference for defining deviations from homeostatic and repair mechanisms leading to pulmonary diseases.

Exploring the neurogenic differentiation of human dental pulp stem cells

Human dental pulp stem cells (hDPSCs) have increasingly gained interest as a potential therapy for nerve regeneration in medicine and dentistry, however their neurogenic potential remains a matter of debate. This study aimed to characterize hDPSC neuronal differentiation in comparison with the human SH-SY5Y neuronal stem cell differentiation model. Both hDPSCs and SH-SY5Y could be differentiated to generate typical neuronal-like cells following sequential treatment with all-trans retinoic acid (ATRA) and brain-derived neurotrophic factor (BDNF), as evidenced by significant expression of neuronal proteins βIII-tubulin (TUBB3) and neurofilament medium (NF-M). Both cell types also expressed multiple neural gene markers including growth-associated protein 43 (GAP43), enolase 2/neuron-specific enolase (ENO2/NSE), synapsin I (SYN1), nestin (NES), and peripherin (PRPH), and exhibited measurable voltage-activated Na⁺ and K⁺ currents. In hDPSCs, upregulation of acetylcholinesterase (ACHE), choline O-acetyltransferase (CHAT), sodium channel alpha subunit 9 (SCN9A), POU class 4 homeobox 1 (POU4F1/BRN3A) along with a downregulation of motor neuron and pancreas homeobox 1 (MNX1) indicated that differentiation was more guided toward a cholinergic sensory neuronal lineage. Furthermore, the Extracellular signal-regulated kinase 1/2 (ERK1/2) inhibitor U0126 significantly impaired hDPSC neuronal differentiation and was associated with reduction of the ERK1/2 phosphorylation. In conclusion, this study demonstrates that extracellular signal-regulated kinase/Mitogen-activated protein kinase (ERK/MAPK) is necessary for sensory cholinergic neuronal differentiation of hDPSCs. hDPSC-derived cholinergic sensory neuronal-like cells represent a novel model and potential source for neuronal regeneration therapies.

Sympathetic tales: subdivisons of the autonomic nervous system and the impact of developmental studies

Remarkable progress in a range of biomedical disciplines has promoted the understanding of the cellular components of the autonomic nervous system and their differentiation during development to a critical level. Characterization of the gene expression fingerprints of individual neurons and identification of the key regulators of autonomic neuron differentiation enables us to comprehend the development of different sets of autonomic neurons. Their individual functional properties emerge as a consequence of differential gene expression initiated by the action of specific developmental regulators. In this review, we delineate the anatomical and physiological observations that led to the subdivision into sympathetic and parasympathetic domains and analyze how the recent molecular insights melt into and challenge the classical description of the autonomic nervous system.

Human axial progenitors generate trunk neural crest cells in vitro

The neural crest (NC) is a multipotent embryonic cell population that generates distinct cell types in an axial position-dependent manner. The production of NC cells from human pluripotent stem cells (hPSCs) is a valuable approach to study human NC biology. However, the origin of human trunk NC remains undefined and current in vitro differentiation strategies induce only a modest yield of trunk NC cells. Here we show that hPSC-derived axial progenitors, the posteriorly-located drivers of embryonic axis elongation, give rise to trunk NC cells and their derivatives. Moreover, we define the molecular signatures associated with the emergence of human NC cells of distinct axial identities in vitro. Collectively, our findings indicate that there are two routes toward a human post-cranial NC state: the birth of cardiac and vagal NC is facilitated by retinoic acid-induced posteriorisation of an anterior precursor whereas trunk NC arises within a pool of posterior axial progenitors.

Enhanced expression of MycN/CIP2A drives neural crest toward a neural stem cell-like fate: Implications for priming of neuroblastoma

Neuroblastoma is a neural crest-derived childhood tumor of the peripheral nervous system in which MycN amplification is a hallmark of poor prognosis. Here we show that MycN is expressed together with phosphorylation-stabilizing factor CIP2A in regions of the neural plate destined to form the CNS, but MycN is excluded from the neighboring neural crest stem cell domain. Interestingly, ectopic expression of MycN or CIP2A in the neural crest domain biases cells toward CNS-like neural stem cells that express Sox2. Consistent with this, some forms of neuroblastoma have been shown to share transcriptional resemblance with CNS neural stem cells. As high MycN/CIP2A levels correlate with poor prognosis, we posit that a MycN/CIP2A-mediated cell-fate bias may reflect a possible mechanism underlying early priming of some aggressive forms of neuroblastoma. In contrast to MycN, its paralogue cMyc is normally expressed in the neural crest stem cell domain and typically is associated with better overall survival in clinical neuroblastoma, perhaps reflecting a more "normal" neural crest-like state. These data suggest that priming for some forms of aggressive neuroblastoma may occur before neural crest emigration from the CNS and well before sympathoadrenal specification.

Studying the peripheral sympathetic nervous system and neuroblastoma in zebrafish

The zebrafish serves as an excellent model to study vertebrate development and disease. Optically clear embryos, combined with tissue-specific fluorescent reporters, permit direct visualization and measurement of peripheral nervous system formation in real time. Additionally, the model is amenable to rapid cellular, molecular, and genetic approaches to determine how developmental mechanisms contribute to disease states, such as cancer. In this chapter, we describe the development of the peripheral sympathetic nervous system (PSNS) in general, and our current understanding of genetic pathways important in zebrafish PSNS development specifically. We also illustrate how zebrafish genetics is used to identify new mechanisms controlling PSNS development and methods for interrogating the potential role of PSNS developmental pathways in neuroblastoma pathogenesis in vivo using the zebrafish MYCN-driven neuroblastoma model.

PHOX2A and PHOX2B are differentially regulated during retinoic acid-driven differentiation of SK-N-BE(2)C neuroblastoma cell line

PHOX2B and its paralogue gene PHOX2A are two homeodomain proteins in the network regulating the development of autonomic ganglia that have been associated with the pathogenesis of neuroblastoma (NB), because of their over-expression in different NB cell lines and tumour samples. We used the SK-N-BE(2)C cell line to show that all-trans retinoic acid (ATRA), a drug that is widely used to inhibit growth and induce differentiation in NBs, regulates both PHOX2A and PHOX2B expression, albeit by means of different mechanisms: it up-regulates PHOX2A and down-regulates PHOX2B. Both mechanisms act at transcriptional level, but prolonged ATRA treatment selectively degrades the PHOX2A protein, whereas the corresponding mRNA remains up-regulated. Further, we show that PHOX2A is capable of modulating PHOX2B expression, but this mechanism is not involved in the PHOX2B down-regulation induced by retinoic acid. Our findings demonstrate that PHOX2A expression is finely controlled during retinoic acid differentiation and this, together with PHOX2B down-regulation, reinforces the idea that they may be useful biomarkers for NB staging, prognosis and treatment decision making.

Neuroblastoma and Its Zebrafish Model

Neuroblastoma, an important developmental tumor arising in the peripheral sympathetic nervous system (PSNS), accounts for approximately 10 % of all cancer-related deaths in children. Recent genomic analyses have identified a spectrum of genetic alterations in this tumor. Amplification of the MYCN oncogene is found in 20 % of cases and is often accompanied by mutational activation of the ALK (anaplastic lymphoma kinase) gene, suggesting their cooperation in tumor initiation and spread. Understanding how complex genetic changes function together in oncogenesis has been a continuing and daunting task in cancer research. This challenge was addressed in neuroblastoma by generating a transgenic zebrafish model that overexpresses human MYCN and activated ALK in the PSNS, leading to tumors that closely resemble human neuroblastoma and new opportunities to probe the mechanisms that underlie the pathogenesis of this tumor. For example, coexpression of activated ALK with MYCN in this model triples the penetrance of neuroblastoma and markedly accelerates tumor onset, demonstrating the interaction of these modified genes in tumor development. Further, MYCN overexpression induces adrenal sympathetic neuroblast hyperplasia, blocks chromaffin cell differentiation, and ultimately triggers a developmentally-timed apoptotic response in the hyperplastic sympathoadrenal cells. In the context of MYCN overexpression, activated ALK provides prosurvival signals that block this apoptotic response, allowing continued expansion and oncogenic transformation of hyperplastic neuroblasts, thus promoting progression to neuroblastoma. This application of the zebrafish model illustrates its value in rational assessment of the multigenic changes that define neuroblastoma pathogenesis and points the way to future studies to identify novel targets for therapeutic intervention.

Sympathetic neurons and chromaffin cells share a common progenitor in the neural crest in vivo

BACKGROUND

The neural crest (NC) is a transient embryonic structure unique to vertebrates, which generates peripheral sensory and autonomic neurons, glia, neuroendocrine chromaffin and thyroid C-cells, melanocytes, and mesenchymal derivatives such as parts of the skull, heart, and meninges. The sympathoadrenal (SA) cell lineage is one major sub-lineage of the NC that gives rise to sympathetic neurons, chromaffin cells, and the intermediate small intensely fluorescent (SIF) cells. A key question is when during NC ontogeny do multipotent progenitors segregate into the different NC-derived lineages. Recent evidence suggested that sympathetic, sensory, and melanocyte progenitors delaminate from the thoracic neural tube (NT) in successive, largely non-overlapping waves and that at least certain NC progenitors are already fate-restricted within the NT. Whether sympathetic neurons and chromaffin cells, suggested by cell culture studies to share a common progenitor, are also fate segregated in ovo prior to emigration, is not known.

RESULTS

We have conducted single cell electroporations of a GFP-encoding plasmid into the dorsal midline of E2 chick NTs at the adrenomedullary level of the NC. Analysis of their derivatives, performed at E6, revealed that in most cases, labelled progeny was detected in both sympathetic ganglia and adrenal glands, where cells co-expressed characteristic marker combinations.

CONCLUSIONS

Our results show that sympathetic neurons and adrenal chromaffin cells share a common progenitor in the NT. Together with previous findings we suggest that phenotypic diversification of these sublineages is likely to occur after delamination from the NT and prior to target encounter.

Autonomic neurocristopathy-associated mutations in PHOX2B dysregulate Sox10 expression

The most common forms of neurocristopathy in the autonomic nervous system are Hirschsprung disease (HSCR), resulting in congenital loss of enteric ganglia, and neuroblastoma (NB), childhood tumors originating from the sympathetic ganglia and adrenal medulla. The risk for these diseases dramatically increases in patients with congenital central hypoventilation syndrome (CCHS) harboring a nonpolyalanine repeat expansion mutation of the Paired-like homeobox 2b (PHOX2B) gene, but the molecular mechanism of pathogenesis remains unknown. We found that introducing nonpolyalanine repeat expansion mutation of the PHOX2B into the mouse Phox2b locus recapitulates the clinical features of the CCHS associated with HSCR and NB. In mutant embryos, enteric and sympathetic ganglion progenitors showed sustained sex-determining region Y (SRY) box10 (Sox10) expression, with impaired proliferation and biased differentiation toward the glial lineage. Nonpolyalanine repeat expansion mutation of PHOX2B reduced transactivation of wild-type PHOX2B on its known target, dopamine β-hydroxylase (DBH), in a dominant-negative fashion. Moreover, the introduced mutation converted the transcriptional effect of PHOX2B on a Sox10 enhancer from repression to transactivation. Collectively, these data reveal that nonpolyalanine repeat expansion mutation of PHOX2B is both a dominant-negative and gain-of-function mutation. Our results also demonstrate that Sox10 regulation by PHOX2B is pivotal for the development and pathogenesis of the autonomic ganglia.

NPARM in PHOX2B: why some things just should not be expanded

Although the neural crest and its derivatives have been studied for a very long time, disorders of derivatives of the crest, the neurocristopathies, are not well understood. In this issue of the JCI, Nagashimada et al. provide an elegant analysis of one neurocristopathy, the association of neuroblastoma (NB) with Hirschsprung disease (HSCR) (aganglionosis of the terminal bowel) and congenital central hypoventilation syndrome (CCHS) (also known as NB-HSCR-CCHS), linked to mutations in PHOX2B. In a mouse model, Nagashimada et al. demonstrate that a disease-linked mutation promotes tumorigenesis and disrupts neurogenesis, sympathetic gangliogenesis, and crest cell colonization of the terminal bowel. They also show that mutant PHOX2B results in decreased proliferation of crest-derived cells and the development of glia at the expense of neurons. The work raises intriguing issues about the possible common origin of sympathetic and enteric nervous systems and provides new hope that we may someday understand the vexing abnormalities in gastrointestinal function that persist after the surgical treatment of HSCR.

Neuronal activity regulates expression of tyrosine hydroxylase in adult mouse substantia nigra pars compacta neurons

Striatal delivery of dopamine (DA) by midbrain substantia nigra pars compacta (SNc) neurons is vital for motor control and its depletion causes the motor symptoms of Parkinson's disease. While membrane potential changes or neuronal activity regulates tyrosine hydroxylase (TH, the rate limiting enzyme in catecholamine synthesis) expression in other catecholaminergic cells, it is not known whether the same occurs in adult SNc neurons. We administered drugs known to alter neuronal activity to mouse SNc DAergic neurons in various experimental preparations and measured changes in their TH expression. In cultured midbrain neurons, blockade of action potentials with 1 μM tetrodotoxin decreased TH expression beginning around 20 h later (as measured in real time by green fluorescent protein (GFP) expression driven off TH promoter activity). By contrast, partial blockade of small-conductance, Ca(2+) -activated potassium channels with 300 nM apamin increased TH mRNA and protein between 12 and 24 h later in slices of adult midbrain. Two-week infusions of 300 nM apamin directly to the adult mouse midbrain in vivo also increased TH expression in SNc neurons, measured immunohistochemically. Paradoxically, the number of TH immunoreactive (TH+) SNc neurons decreased in these animals. Similar in vivo infusions of drugs affecting other ion-channels and receptors (L-type voltage-activated Ca(2+) channels, GABA(A) receptors, high K(+) , DA receptors) also increased or decreased cellular TH immunoreactivity but decreased or increased, respectively, the number of TH+ cells in SNc. We conclude that in adult SNc neurons: (i) TH expression is activity-dependent and begins to change ∼20 h following sustained changes in neuronal activity; (ii) ion-channels and receptors mediating cell-autonomous activity or synaptic input are equally potent in altering TH expression; and (iii) activity-dependent changes in TH expression are balanced by opposing changes in the number of TH+ SNc cells.

Development of the autonomic nervous system: a comparative view

In this review we summarize current understanding of the development of autonomic neurons in vertebrates. The mechanisms controlling the development of sympathetic and enteric neurons have been studied in considerable detail in laboratory mammals, chick and zebrafish, and there are also limited data about the development of sympathetic and enteric neurons in amphibians. Little is known about the development of parasympathetic neurons apart from the ciliary ganglion in chicks. Although there are considerable gaps in our knowledge, some of the mechanisms controlling sympathetic and enteric neuron development appear to be conserved between mammals, avians and zebrafish. For example, some of the transcriptional regulators involved in the development of sympathetic neurons are conserved between mammals, avians and zebrafish, and the requirement for Ret signalling in the development of enteric neurons is conserved between mammals (including humans), avians and zebrafish. However, there are also differences between species in the migratory pathways followed by sympathetic and enteric neuron precursors and in the requirements for some signalling pathways.

Studying peripheral sympathetic nervous system development and neuroblastoma in zebrafish

The combined experimental attributes of the zebrafish model system, which accommodates cellular, molecular, and genetic approaches, make it particularly well-suited for determining the mechanisms underlying normal vertebrate development as well as disease states, such as cancer. In this chapter, we describe the advantages of the zebrafish system for identifying genes and their functions that participate in the regulation of the development of the peripheral sympathetic nervous system (PSNS). The zebrafish model is a powerful system for identifying new genes and pathways that regulate PSNS development, which can then be used to genetically dissect PSNS developmental processes, such as tissue size and cell numbers, which in the past haves proved difficult to study by mutational analysis in vivo. We provide a brief review of our current understanding of genetic pathways important in PSNS development, the rationale for developing a zebrafish model, and the current knowledge of zebrafish PSNS development. Finally, we postulate that knowledge of the genes responsible for normal PSNS development in the zebrafish will help in the identification of molecular pathways that are dysfunctional in neuroblastoma, a highly malignant cancer of the PSNS.

Generating diversity: Mechanisms regulating the differentiation of autonomic neuron phenotypes

Sympathetic and parasympathetic postganglionic neurons innervate a wide range of target tissues. The subpopulation of neurons innervating each target tissue can express unique combinations of neurotransmitters, neuropeptides, ion channels and receptors, which together comprise the chemical phenotype of the neurons. The target-specific chemical phenotype shown by autonomic postganglionic neurons arises during development. In this review, we examine the different mechanisms that generate such a diversity of neuronal phenotypes from the pool of apparently homogenous neural crest progenitor cells that form the sympathetic ganglia. There is evidence that the final chemical phenotype of autonomic postganglionic neurons is generated by both signals at the level of the cell body that trigger cell-autonomous programs, as well as signals from the target tissues they innervate.

The bHLH transcription factor Hand2 is essential for the maintenance of noradrenergic properties in differentiated sympathetic neurons

The basic helix-loop-helix transcription factor Hand2 is essential for the proliferation and noradrenergic differentiation of sympathetic neuron precursors during development. Here we address the function of Hand2 in postmitotic, differentiated sympathetic neurons. Knockdown of endogenous Hand2 in cultured E12 chick sympathetic neurons by siRNA results in a significant (about 60%) decrease in the expression of the noradrenergic marker genes dopamine-beta-hydroxylase (DBH) and tyrosine hydroxylase (TH). In contrast, expression of the pan-neuronal genes TuJ1, HuC and SCG10 was not affected. To analyze the in vivo role of Hand2 in differentiated sympathetic neurons we used mice harboring a conditional Hand2-null allele and excised the gene by expression of Cre recombinase under control of the DBH promotor. Mouse embryos homozygous for Hand2 gene deletion showed decreased sympathetic neuron number and TH expression was strongly reduced in the residual neuron population. The in vitro Hand2 knockdown also enhances the CNTF-induced expression of the cholinergic marker genes vesicular acetylcholine transporter (VAChT) and choline acetyltransferase (ChAT). Taken together, these findings demonstrate that the Hand2 transcription factor plays a key role in maintaining noradrenergic properties in differentiated neurons.

The role of GDNF family ligand signalling in the differentiation of sympathetic and dorsal root ganglion neurons

The diversity of neurons in sympathetic ganglia and dorsal root ganglia (DRG) provides intriguing systems for the analysis of neuronal differentiation. Cell surface receptors for the GDNF family ligands (GFLs) glial cell-line-derived neurotrophic factor (GDNF), neurturin and artemin, are expressed in subpopulations of these neurons prompting the question regarding their involvement in neuronal subtype specification. Mutational analysis in mice has demonstrated the requirement for GFL signalling during embryonic development of cholinergic sympathetic neurons as shown by the loss of expression from the cholinergic gene locus in ganglia from mice deficient for ret, the signal transducing subunit of the GFL receptor complex. Analysis in mutant animals and transgenic mice overexpressing GFLs demonstrates an effect on sensitivity to thermal and mechanical stimuli in DRG neurons correlating at least partially with the altered expression of transient receptor potential ion channels and acid-sensitive cation channels. Persistence of targeted cells in mutant ganglia suggests that the alterations are caused by differentiation effects and not by cell loss. Because of the massive effect of GFLs on neurite outgrowth, it remains to be determined whether GFL signalling acts directly on neuronal specification or indirectly via altered target innervation and access to other growth factors. The data show that GFL signalling is required for the specification of subpopulations of sensory and autonomic neurons. In order to comprehend this process fully, the role of individual GFLs, the transduction of the GFL signals, and the interplay of GFL signalling with other regulatory pathways need to be deciphered.

Target-dependent inhibition of sympathetic neuron growth via modulation of a BMP signaling pathway

Target-derived factors modulate many aspects of peripheral neuron development including neuronal growth, survival, and maturation. Less is known about how initial target contact regulates changes in gene expression associated with these developmental processes. One early consequence of contact between growing sympathetic neurons and their cardiac myocyte targets is the inhibition of neuronal outgrowth. Analysis of neuronal gene expression following this contact revealed coordinate regulation of a bone morphogenetic protein (BMP)-dependent growth pathway in which basic helix-loop-helix transcription factors and downstream neurofilament expression contribute to the growth dynamics of developing sympathetic neurons. BMP2 had dose-dependent growth-promoting effects on sympathetic neurons cultured in the absence, but not the presence, of myocyte targets, suggesting that target contact alters neuronal responses to BMP signaling. Target contact also induced the expression of matrix Gla protein (MGP), a regulator of BMP function in the vascular system. Increased MGP expression inhibited BMP-dependent neuronal growth and MGP expression increased in sympathetic neurons during the period of target contact in vivo. These experiments establish MGP as a novel regulator of BMP function in the nervous system, and define developmental transitions in BMP responses during sympathetic development.

The sympathoadrenal cell lineage: specification, diversification, and new perspectives

During the past years considerable progress has been made in understanding the generation of cell diversity in the neural crest (NC). Sympathoadrenal (SA) cells constitute a major lineage among NC derivatives; they give rise to sympathetic neurons, neuroendocrine chromaffin cells, and the intermediate small intensely fluorescent (SIF) cells. The classic perception of how this diversification is achieved implies that (i) there is a common progenitor cell for sympathetic neurons and chromaffin cells, (ii) NC cells are instructed to a SA cell fate by signals derived from the wall of the dorsal aorta, especially bone morphogenetic proteins (BMP), and (iii) the local environments of secondary sympathetic ganglia and adrenal gland, respectively, are crucial for inducing differentiation of SA cells into sympathetic neurons and adrenal chromaffin cells. However, recent studies have suggested that the adrenal cortex is dispensable for the acquisition of a chromaffin cell fate. This review summarizes the current understanding of the development of SA cells. It covers the specification of SA cells from multipotent NC crest cells, the role of transcription factors during their development, the classic model of their subsequent diversification as well as alternative views for explaining the generation of endocrine versus neuronal SA derivatives.

Delays in neuronal differentiation in Mash1/Ascl1 mutants

The inactivation of a developmental transcription factor may lead to the complete absence of a specific cell type. More commonly, though, it only partially impairs its generation. The modalities of this partial effect have rarely been documented in any detail. Here, we report a novel function for the bHLH transcription factor Ascl1/Mash1 in the generation of the nucleus of the solitary tract (nTS). In Mash1(-/-) late embryos, the nTS is markedly atrophic. Tracing back the origin of this atrophy, we show that nTS precursors appear in the mutants 1 day later than in the wild type and then accumulate at a slower pace. We also show that the previously reported atrophy of the sympathetic chain in Mash1 mutants is similarly preceded by a delay of 1 to 2 days in the appearance of differentiated ganglionic cells. Finally, we provide evidence that the acceleration imposed by Mash1, regardless of the production of post-mitotic cells, affects differentiation itself, both generic and type-specific.

Loss of leukemia inhibitory factor receptor beta or cardiotrophin-1 causes similar deficits in preganglionic sympathetic neurons and adrenal medulla

Leukemia inhibitory factor (LIF) receptor beta (LIFRbeta) is a receptor for a variety of neurotrophic cytokines, including LIF, ciliary neurotrophic factor (CNTF), and cardiotrophin-1 (CT-1). These cytokines play an essential role for the survival and maintenance of developing and postnatal somatic motoneurons. CNTF may also serve the maintenance of autonomic, preganglionic sympathetic neurons (PSNs) in the spinal cord, as suggested by its capacity to prevent their death after destruction of one of their major targets, the adrenal medulla. Although somatic motoneurons and PSNs share a common embryonic origin, they are distinct in several respects, including responses to lesions. We have studied PSNs in mice with targeted deletions of the LIFRbeta or CT-1 genes, respectively. We show that LIF, CNTF, and CT-1 are synthesized in embryonic adrenal gland and spinal cord and that PSNs express LIFRbeta. In embryonic day 18.5 LIFRbeta (-/-) and CT-1 (-/-) mice, PSNs were reduced by approximately 20%. PSNs projecting to the adrenal medulla were more severely affected (-55%). Although LIFRbeta (-/-) mice revealed normal numbers of adrenal chromaffin cells and axons terminating on chromaffin cells, levels of adrenaline and numbers of adrenaline-synthesizing cells were significantly reduced. We conclude that activation of LIFRbeta is required for normal development of PSNs and one of their prominent targets, the adrenal medulla. Thus, both somatic motoneurons and PSNs in the spinal cord depend on LIFRbeta signaling for their development and maintenance, although PSNs seem to be overall less affected than somatic motoneurons by LIFRbeta deprivation.

Locus coeruleus neurons originate in alar rhombomere 1 and migrate into the basal plate: Studies in chick and mouse embryos

We investigated in the mouse and chick the neuroepithelial origin and development of the locus coeruleus (LoC), the most important noradrenergic neuronal population in the brain. We first studied the topography of the developing LoC in the hindbrain, using as markers the key noradrenergic marker gene Dbh and the transcription factors Phox2a and Phox2b (upstream of Dbh). In both mouse and chicken, LoC neurons first appear arranged linearly along the middle one-third of the alar plate of rhombomere 1 (r1), collinear to a reference ventricular longitudinal band that early on expresses Phox2a and Phox2b in the alar plate of r2 and later expands to r1. Double-labeling experiments with LoC markers (Dbh or Phox2a) and either alar (Pax7 and Rnx3) or basal (Otp) genetic markers suggested that LoC cells migrate from their origin in the alar plate to a final position in the lateral basal plate. To corroborate these suggestions experimentally and determine the precise origin of the LoC, we fate mapped the LoC in the chick at stage HH11 by using quail-chick homotopic grafts. The experimental results confirmed that the LoC originates in the alar plate throughout the rostrocaudal extent of r1 and ruled out a rostrocaudal translocation. They also corroborated a ventralward tangential migration of LoC cells into the lateral basal plate, where the postmigratory LoC primordium is located. Comparisons with neighboring alar r1-derived cell populations established that LoC neurons originate outside the cerebellum, in a matrix area intercalated dorsoventrally between the sources of the prospective vestibular and trigeminal columns.

Cholinergic differentiation occurs early in mouse sympathetic neurons and requires Phox2b

The generation of neurotransmitter identity in the autonomic nervous system is a classical model system to study the development of neuronal diversity. Analysis of the expression of genes coding for enzymes of noradrenaline biosynthesis in the sympathoadrenal system allowed the characterization of factors involved in the differentiation of the noradrenergic transmitter phenotype. The development of cholinergic properties in the autonomic system is less well understood. Here we show that expression of mRNAs for choline acetyltransferase (ChAT) and the vesicular acetylcholine transporter (VAChT), both encoded by the cholinergic gene locus, is induced in mouse sympathetic ganglia at embryonic day 11 (E11). Positive cells amount to more than 50% of Phox2b-positive sympathetic cells at cervical levels. The proportion declines caudally, decreasing to approximately 20% of Phox2b-positive cells at lower thoracic levels. In the adrenal anlage, ChAT and VAChT mRNA are largely undetectable at E11 and E13. In mice homozygous for a mutational inactivation of the transcription factor Phox2b, ChAT and VAChT mRNA expression is absent from sympathetic ganglia. The data show that expression from the cholinergic gene locus is regulated differently in sympathetic neurons and adrenal chromaffin cells. Phox2b is required for development of cholinergic neurons but does not suffice to support cholinergic properties in chromaffin cells.

Regulation of neural development by glial cell line-derived neurotrophic factor family ligands

Glial cell line-derived neurotrophic factor (GDNF) and its three relatives constitute a novel family of neurotrophic factors, the GDNF family ligands. These factors signal through a multicomponent receptor complex comprising a glycosylphosphatidylinositol-anchored cell surface molecule (GDNF family receptor (GFR) alpha) and RET tyrosine kinase, triggering the activation of multiple signaling pathways in responsive cells. Recent gene-targeting studies have demonstrated that GDNF family ligands are essential for the development of a diverse set of neuronal populations and we have now started to understand how these ligands uniquely regulate the formation and sculpting of the nervous system. Recent studies have also revealed interactions by multiple extracellular signals during neural development. The deciphering of GDNF family ligand signaling in neural cells promises to provide vital new insights into the development and pathology of the nervous system.

The role of Phox2B in chromaffin cell development

Phox2B, a homeodomain transcription factor closely related to Phox2A, is expressed in peripheral and central noradrenergic neurons. In neural crest (NC) derivatives Phox2B is restricted to sympathetic and parasympathetic ganglia, enteric neurons, and adrenal and extraadrenal chromaffin cells. Similar to MASH-1, Phox2B has been implicated in synchronizing pan-neuronal and catecholaminergic phenotype-specific aspects of neurogenesis. The role of Phox2B for the differentiation of the neuroendocrine NC derivatives, the adrenal medullary chromaffin cells, has not been explored. We have previously reported that in MASH-1-deficient mice most chromaffin cells are arrested at the early neuroblast stage and lack catecholaminergic differentiation. We show now that in Phox2B knockout/lacZ knockin mice the maturation of presumptive chromaffin cells is arrested at an even earlier stage of development. The cells lack the catecholaminergic marker enzyme TH and fail to form a centrally located medulla. In contrast to MASH-1 (-/-) mice they do not express dHand, Phox2A, c-ret, neurofilament, neuron-specific tubulin, and NCAM and appear ultrastructurally more immature. Many of these cells die by apoptosis. Despite the complete lack of differentiation, few lacZ-positive adrenal cells can still be found at E16.5. We conclude that Phox2B regulates very early events in the differentiation of adrenal chromaffin cells distinct to steps, which essentially require MASH-1.

Nicotinamide promotes long-term survival and extensive neurite outgrowth in ultimobranchial C cells cultured from chick embryos

In avian species, the ultimobranchial anlage is populated with neuronal cells derived from the distal vagal ganglion. We found that ultimobranchial C cells of chick embryos cultured in the presence of nicotinamide continued to grow for at least 60 days and exhibited profound morphological changes, resulting in the formation of dense networks of neuronal fibers. Nicotinamide, thus, facilitated the manifestation of neuronal features in C cells. The neuronal phenotypes of cultured C cells were analyzed in detail by both scanning and transmission electron microscopy. Their neural nature was also positively established by immunostaining with monoclonal antibodies to the neuronal markers neuron-specific class III beta-tubulin (TuJ1), microtubule-associated protein (MAP) 2, and synaptophysin. Confocal laser scanning microscopy confirmed that these neuron-specific proteins are colocalized with calcitonin in both the somata and the neuronal processes of C cells. Furthermore, reverse transcriptase-polymerase chain reaction analyses, performed at various times up to 30 days in culture, indicated that the C cells have persistent gene expression of calcitonin, the catecholamine-synthesizing enzyme tyrosine hydroxylase, proenkephalin, proopiomelanocortin, neuron-specific beta-tubulin (cbeta4), SCG10, and Bcl-2. The morphological responses of C cells to nicotinamide treatment were analyzed quantitatively over a period of 60 days. The area of C-cell colonies, number of processes per colony, and length of processes continued to increase until culture day 45. In conclusion, nicotinamide stimulates long-term survival and neuronal differentiation of chick embryo C cells, and this culture system may provide a useful model for studying neuronal differentiation mechanisms.

Expression of neuronal markers suggests heterogeneity of chick sympathoadrenal cells prior to invasion of the adrenal anlagen

We have analyzed the distribution of neural crest-derived precursors and the expression of catecholaminergic and neuronal markers in developing adrenal tissue of chick embryos. Undifferentiated neural crest cells are found in presumptive adrenal regions from embryonic day 3 (E3) onward. An increasing proportion of cells expressing tyrosine hydroxylase (TH) mRNA indicates catecholaminergic differentiation of precursors not only in primary sympathetic ganglia, but also in presumptive adrenal regions. Whereas precursors and differentiating cells show mesenchymal distribution until E5, discrete adrenal anlagen form during E6. Even during E5, catecholaminergic cells with low or undetectable neurofilament M (NF-M) mRNA expression prevail in positions at which adrenal anlagen become distinct during E6. The predominance of TH-positive and NF-M-negative cells is maintained throughout embryogenesis in adrenal tissue. RNA encoding SCG10, a pan-neuronal marker like NF-M, is strongly expressed throughout adrenal anlagen during E6 but is found at reduced levels in chromaffin cells compared with neuronal cells at E15. Two additional neuronal markers, synaptotagmin 1 and neurexin 1, are expressed at low to undetectable levels in developing chromaffin cells throughout embryogenesis. The developmental regulation of neuronal markers shows at least three different patterns among the four mRNAs analyzed. Importantly, there is no generalized downregulation of neuronal markers in developing adrenal anlagen. Thus, our observations question the classical concept of chromaffin differentiation from a common sympathoadrenal progenitor expressing neuronal properties and suggest alternative models with changing instructive signals or separate progenitor populations for sympathetic neuronal and chromaffin endocrine cells.

Molecular cloning and characterization of the promoter region of the human Phox2b gene

The closely related homeodomain transcription factors, Phox2a and Phox2b, are restrictively expressed in central and peripheral noradrenergic (NA) neurons in an overlapping but distinct manner, and critically regulate the differentiation and neurotransmitter identity of NA neurons. The structure and function of the human Phox2a (hPhox2a) promoter has recently been reported. Towards the long-term goal of delineating the regulatory cascade of NA neuron differentiation, we isolated a human Phox2b (hPhox2b) genomic clone encompassing approximately 7.8 kb of the 5' upstream promoter region, the entire exon-intron structure and 4.5 kb of the 3' flanking region. Two transcription start sites are identified to reside 115 and 110 nucleotides upstream of the start codon, based on both primer extension and 5'-rapid amplification of the cDNA ends analyses. In addition, transient transfection assays indicate that 1.1 kb or longer upstream sequences of the hPhox2b gene may confer cell type-specific gene expression in certain, but not all cell lines. The promoter activity of the hPhox2b gene is modestly transactivated by forced co-expression of Phox2b and the hPhox2b gene promoter contains a high-affinity binding site at -320 to -295 bp. This study provides a frame to further elucidate the molecular mechanisms underlying the regulation of Phox2a and Phox2b gene expression and its relation to NA differentiation.

c-ret regulates cholinergic properties in mouse sympathetic neurons: evidence from mutant mice

The search for signalling systems regulating development of noradrenergic and cholinergic sympathetic neurons is a classical problem of developmental neuroscience. While an essential role of bone morphogenetic proteins for induction of noradrenergic properties is firmly established, factors involved in the development of cholinergic traits in vivo are still enigmatic. Previous studies have shown that the c-ret receptor and cholinergic properties are coexpressed in chick sympathetic neurons. Using in situ hybridization we show now that a loss-of-function mutation of the c-ret receptor in mice dramatically reduces numbers of cells positive for choline acetyltransferase (ChAT) and the vesicular acetylcholine transporter (VAChT) in stellate ganglia of homozygous newborn animals. The number of neurons positive for tyrosine hydroxylase (TH) mRNA, the rate-limiting enzyme of noradrenaline synthesis, is reduced to a smaller degree and expression levels are not detectably altered. Already at embryonic day 16 (E16), ChAT and VAChT-positive cells are affected by the c-ret mutation. At E14, however, ChAT and VAChT mRNAs are detectable at low levels and no difference is observed between wildtype and mutant mice. Our data suggest that c-ret signalling is necessary for the maturation of cholinergic sympathetic neurons but dispensable for de novo induction of ChAT and VAChT expression.

Monooxygenase X, a member of the copper-dependent monooxygenase family localized to the endoplasmic reticulum

Based on sequence comparisons, MOX (monooxygenase X), is a member of the copper monooxygenase family that includes dopamine beta-monooxygenase (DBM) and peptidylglycine alpha-hydroxylating monooxygenase (PHM). MOX has all of the residues expected to be critical for copper binding, and its cysteine residues can yield the intramolecular disulfide bond pattern observed in DBM. Although DBM and PHM function within the lumen of the secretory pathway, the published sequence for human MOX lacks a signal sequence, suggesting that it does not enter this compartment. We identified an upstream exon that encodes the signal sequence of human MOX. A retained intron yields minor amounts of transcript encoding MOX without a signal sequence. MOX transcripts are widely expressed, with the highest levels in the salivary gland and ovary and moderate levels in brain, pituitary, and heart. Despite the presence of a signal sequence, exogenous MOX is not secreted, and it localizes throughout the endoplasmic reticulum in both endocrine or nonendocrine cells. Neither appending green fluorescent protein to its C terminus nor deleting the hydrophobic domain near its C terminus facilitates secretion of MOX. MOX is N-glycosylated, is tightly membrane-associated, and forms oligomers that are not disulfide-linked. Based on its sequence and localization, MOX is predicted to hydroxylate a hydrophobic substrate in the endoplasmic reticulum.

Sympathetic cholinergic target innervation requires GDNF family receptor GFRα2

Many cholinergic parasympathetic and enteric neurons require neurturin signaling through GDNF family receptor GFRalpha2 for target innervation. Since a distinct minority of sympathetic neurons are cholinergic, we examined whether GFRalpha2 is important for their development. We detected GFRalpha2 in neonatal sympathetic cholinergic neurons and neurturin mRNA in their target tissues, sweat glands in footpads, and periosteum. Lack of GFRalpha2 in mice did not affect the number of sympathetic cholinergic neurons, but their soma size was decreased in comparison to wild types. In adult and in 3-week-old GFRalpha2 knockout mice, the density of sympathetic cholinergic innervation was reduced by 50-70% in the sweat glands, and was completely absent in the periosteum. Sympathetic noradrenergic innervation of blood vessels in the footpads was unchanged. The density of sympathetic axons in sweat glands was unaffected at postnatal day P4 reflecting successful growth into the target area. Our results indicate that the cholinergic subpopulation of sympathetic neurons requires GFRalpha2 signaling for soma size and for growth or maintenance of target innervation. Thus, neurturin may be a general target-derived innervation factor for postganglionic cholinergic neurons in all parts of the autonomic nervous system.

Interaction of Mash1 and Phox2b in sympathetic neuron development

The transcription factors Mash1 and Phox2b are both essential for sympathetic neuron development. To understand in more detail their function and interaction, Phox2b and Mash1 were ectopically expressed in vivo, in peripheral nerve precursors. Here, we demonstrate that the Phox2b-induced generation of ectopic noradrenergic neurons in chick peripheral nerve involves the induction of Cash1, the chick homolog of Mash1. All Phox2-induced neurons coexpress the noradrenergic marker genes TH and DBH. Conversely, Mash1 induces neuronal differentiation characterized by the expression of generic neuronal genes SCG10, Hu and NF160; however, only a subpopulation of these neurons also displays an autonomic, noradrenergic phenotype. This context-dependent action of Mash1 implicates autonomic codeterminants, required for noradrenergic differentiation in response to Mash1. In contrast, Phox2b coordinates generic and noradrenergic gene expression, recruiting Mash1/Cash1, which may have a major function in the control of pan-neuronal gene expression during noradrenergic neuron development.

Increased adrenergic contractility and decreased mRNA expression of NOS III in aging rat urinary bladders

Our objective was to study age-related changes in adrenergic contractility and gene expression profile in the rat urinary bladder. Young (3-month old), adult (10-month old) and senescent (30-month old) male WAG/Rij rats were used. Gene expression profile in the rat urinary bladder was defined using Atlas microarray technology. In vitro contractile responses induced by KCl, phenylephrine (PHE) and norepinephrine (NE) were compared in isolated urinary bladders dissected from young, adult and senescent rats. Among a total of 1176 genes present on the arrays, 15 genes showed an increase in expression and 10 genes a decrease with age. Four genes related to nerve growth factor were upregulated whereas NOS type III was downregulated in aging rats. Intrinsic contractility of isolated rat urinary bladders was not changed between adult and aging rats as judged by the response curves to KCl. In contrast, an age-related increase in the maximal contractile responses to NE, but not PHE, was noticed (13 +/- 1, 48 +/- 2% and 59 +/- 2% at 3, 10 and 30 months, respectively). The alpha1D-adrenoceptor antagonist BMY7378 antagonized NE-induced contractions with low potency in both groups suggesting the involvement of the alpha1A-adrenoceptor subtype. This was confirmed by microarray, which demonstrated mRNA expression for the alpha1A-adrenoceptor subtype only. These results suggest that aging of the urinary bladder is associated with an increase in the maximal contractile response to NE which could be due to NO shortage resulting from downregulation of urothelial NOS III.

Molecular control of ciliary neuron development: BMPs and downstream transcriptional control in the parasympathetic lineage

The generation of noradrenergic sympathetic neurons is controlled by BMPs and the downstream transcription factors Mash1, Phox2b, Phox2a and dHand. We examined the role of these signals in developing cholinergic parasympathetic neurons. The expression of Mash1 (Cash1), Phox2b and Phox2a in the chick ciliary ganglion is followed by the sequential expression of panneuronal, noradrenergic and cholinergic marker genes. BMPs are expressed at the site where ciliary ganglia form and are essential and sufficient for ciliary neuron development. Unlike sympathetic neurons, ciliary neurons do not express dHand; noradrenergic gene expression is eventually lost but can be maintained by ectopic dHand expression. Together, these results demonstrate a common BMP dependence of sympathetic neurons and parasympathetic ciliary neurons and implicate dHand in the maintenance of noradrenergic gene expression in the autonomic nervous system.

Development of chromaffin cells depends on MASH1 function

The sympathoadrenal (SA) cell lineage is a derivative of the neural crest (NC), which gives rise to sympathetic neurons and neuroendocrine chromaffin cells. Signals that are important for specification of these two types of cells are largely unknown. MASH1 plays an important role for neuronal as well as catecholaminergic differentiation. Mash1 knockout mice display severe deficits in sympathetic ganglia, yet their adrenal medulla has been reported to be largely normal suggesting that MASH1 is essential for neuronal but not for neuroendocrine differentiation. We show now that MASH1 function is necessary for the development of the vast majority of chromaffin cells. Most adrenal medullary cells in Mash1–/– mice identified by Phox2b immunoreactivity, lack the catecholaminergic marker tyrosine hydroxylase. Mash1 mutant and wild-type mice have almost identical numbers of Phox2b-positive cells in their adrenal glands at embryonic day (E) 13.5; however, only one-third of the Phox2b-positive adrenal cell population seen in Mash1+/+ mice is maintained in Mash1–/– mice at birth. Similar to Phox2b, cells expressing Phox2a and Hand2 (dHand) clearly outnumber TH-positive cells. Most cells in the adrenal medulla of Mash1–/– mice do not contain chromaffin granules, display a very immature, neuroblast-like phenotype, and, unlike wild-type adrenal chromaffin cells, show prolonged expression of neurofilament and Ret comparable with that observed in wild-type sympathetic ganglia. However, few chromaffin cells in Mash1–/– mice become PNMT positive and downregulate neurofilament and Ret expression. Together, these findings suggest that the development of chomaffin cells does depend on MASH1 function not only for catecholaminergic differentiation but also for general chromaffin cell differentiation.

Opposing functions of GDNF and NGF in the development of cholinergic and noradrenergic sympathetic neurons

We identified a population of mature sympathetic neurons in which Ret, the receptor for glial cell line-derived neurotrophic factor (GDNF), is coexpressed with the neurotrophin-3 (NT3) receptor TrkC and choline acetyltransferase. In a complementary population the nerve growth factor receptor TrkA is coexpressed with the norepinephrine transporter. In accordance with these in vivo results, GDNF and neurturin promote the expression of cholinergic marker genes in sympathetic chain explants, similar to NT3 and ciliary neuronotrophic factor (CNTF). To define intracellular signaling mechanisms commonly activated by NT3, GDNF, or CNTF to promote cholinergic differentiation, we have analyzed the activation of intracellular signaling cascades. Signal transducer and activator of transcription-3 (STAT3) was strongly activated by CNTF but not by GDNF or NT3 and hence is not essential for cholinergic differentiation. We conclude that cholinergic properties can be regulated by neurotrophic factors from three different protein families, whereas noradrenergic properties are promoted by NGF.

The developmental expression of vasoactive intestinal peptide (VIP) in cholinergic sympathetic neurons depends on cytokines signaling through LIFRβ-containing receptors

Sympathetic ganglia are composed of noradrenergic and cholinergic neurons. Cholinergic sympathetic neurons are characterized by the expression of choline acetyl transferase (ChAT), vesicular acetylcholine transporter (VAChT) and the vasoactive intestinal peptide (VIP). To investigate the role of cytokine growth factor family members in the development of cholinergic sympathetic neurons, we interfered in vivo with the function of the subclass of cytokine receptors that contains LIFRβ as essential receptor subunit. Expression of LIFRβ antisense RNA interfered with LIFRβ expression and strongly reduced the developmental induction of VIP expression. By contrast, ganglion size and the number of ChAT-positive cells were not reduced. These results demonstrate a physiological role of cytokines acting through LIFRβ-containing receptors in the control of VIP expression in sympathetic neurons.

The specification of noradrenergic locus coeruleus (LC) neurones depends on bone morphogenetic proteins (BMPs)

The role of BMPs in the development of the major noradrenergic centre of the brain, the locus coeruleus (LC), was investigated. LC generation is reflected by initial expression of the transcription factors Phox2a and Phox2b in dorsal rhombomere1 (r1), followed by expression of dopamine-β-hydroxylase and tyrosine hydroxylase. Bmp5 is expressed in the dorsal neuroepithelium in proximity to Phox2-expressing cells. BMP inhibition in stage 10 chick embryos resulted in the lack of LC neurones or in their generation at the dorsal midline, and loss of roof plate and rhombic lip, but it did not affect neural crest development. These results reveal late essential BMP functions in the specification of dorsal neuronal phenotypes in r1, including LC neurones, and in the development of dorsal midline structures.

Upregulation of acetylcholine synthesis by bone morphogenetic protein 9 in a murine septal cell line

Previous studies showed that bone morphogenetic protein 9 (BMP-9) induces the expression of choline acetyltransferase and the vesicular acetylcholine (ACh) transporter, and upregulates ACh synthesis in cultured primary neurons from embryonic mouse septum [I. López-Coviella, B. Berse, R. Krauss, R.S. Thies, J.K. Blusztajn, Induction and maintenance of the neuronal cholinergic phenotype in the central nervous system by BMP-9. Science 289 (2000) 313-316]. In the present studies we investigated the effects of BMP-9 on ACh synthesis in the cholinergic mouse SN56T17 septal cell line. BMP-9 increased ACh synthesis in these cells up to 2.5-fold in a time- and dose-dependent, saturable manner. The maximal effect of BMP-9 was observed after a 3-day treatment and the median effective concentration of BMP-9 was 0.5 ng/ml. These data show that SN56T17 cells are a useful model for studies of the effects of BMPs on the cholinergic phenotype.