GFR alpha3, a component of the artemin receptor, is required for migration and survival of the superior cervical ganglion

Adrenergic nerves regulate intestinal regeneration through IL-22 signaling from type 3 innate lymphoid cells

The intestinal epithelium has high intrinsic turnover rate, and the precise renewal of the epithelium is dependent on the microenvironment. The intestine is innervated by a dense network of peripheral nerves that controls various aspects of intestinal physiology. However, the role of neurons in regulating epithelial cell regeneration remains largely unknown. Here, we investigated the effects of gut-innervating adrenergic nerves on epithelial cell repair following irradiation (IR)-induced injury. We observed that adrenergic nerve density in the small intestine increased post IR, while chemical adrenergic denervation impaired epithelial regeneration. Single-cell RNA sequencing experiments revealed a decrease in IL-22 signaling post IR in denervated animals. Combining pharmacologic and genetic tools, we demonstrate that β-adrenergic receptor signaling drives IL-22 production from type 3 innate lymphoid cells (ILC3s) post IR, which in turn promotes epithelial regeneration. These results define an adrenergic-ILC3 axis important for intestinal regeneration.

Neuro-mesenchymal units control ILC2 and obesity via a brain-adipose circuit

Signals from sympathetic neurons and immune cells regulate adipocytes and thereby contribute to fat tissue biology. Interactions between the nervous and immune systems have recently emerged as important regulators of host defence and inflammation1-4. Nevertheless, it is unclear whether neuronal and immune cells co-operate in brain-body axes to orchestrate metabolism and obesity. Here we describe a neuro-mesenchymal unit that controls group 2 innate lymphoid cells (ILC2s), adipose tissue physiology, metabolism and obesity via a brain-adipose circuit. We found that sympathetic nerve terminals act on neighbouring adipose mesenchymal cells via the β2-adrenergic receptor to control the expression of glial-derived neurotrophic factor (GDNF) and the activity of ILC2s in gonadal fat. Accordingly, ILC2-autonomous manipulation of the GDNF receptor machinery led to alterations in ILC2 function, energy expenditure, insulin resistance and propensity to obesity. Retrograde tracing and chemical, surgical and chemogenetic manipulations identified a sympathetic aorticorenal circuit that modulates ILC2s in gonadal fat and connects to higher-order brain areas, including the paraventricular nucleus of the hypothalamus. Our results identify a neuro-mesenchymal unit that translates cues from long-range neuronal circuitry into adipose-resident ILC2 function, thereby shaping host metabolism and obesity.

Hallmarks of cancer-the new testament

Diagnosis and treatment of disease demand a sound understanding of the underlying mechanisms, determining any Achilles' heel that can be targeted in effective therapies. Throughout history, this endeavour to decipher the origin and mechanism of transformation of a normal cell into cancer has led to various theories-from cancer as a curse to an understanding at the level of single-cell heterogeneity, meaning even among a single sub-type of cancer there are myriad molecular challenges to overcome. With increasing insight into cancer genetics and biology, the disease has become ever more complex to understand. The complexity of cancer as a disease was distilled into key traits by Hanahan and Weinberg in their seminal 'Hallmarks of Cancer' reviews. This lucid conceptualization of complex cancer biology is widely accepted and has helped advance cancer therapeutics by targeting the various hallmarks but, with the advancement in technologies, there is greater granularity in how we view cancer as a disease, and the additional understanding over the past decade requires us to revisit the hallmarks of cancer. Based on extensive study of the cancer research literature, we propose four novel hallmarks of cancer, namely, the ability of cells to regress from a specific specialized functional state, epigenetic changes that can affect gene expression, the role of microorganisms and neuronal signalling, to be included in the hallmark conceptualization along with evidence of various means to exploit them therapeutically.

Development of the Autonomic Nervous System: Clinical Implications

Investigations of the cellular and molecular mechanisms that mediate the development of the autonomic nervous system have identified critical genes and signaling pathways that, when disrupted, cause disorders of the autonomic nervous system. This review summarizes our current understanding of how the autonomic nervous system emerges from the organized spatial and temporal patterning of precursor cell migration, proliferation, communication, and differentiation, and discusses potential clinical implications for developmental disorders of the autonomic nervous system, including familial dysautonomia, Hirschsprung disease, Rett syndrome, and congenital central hypoventilation syndrome.

Roles of the RET Proto-oncogene in Cancer and Development

RET (REarranged during Transfection)is activated by DNA rearrangement of the 3' fragment of the receptor tyrosine kinase gene, namely, RET proto-oncogene, with the 5' fragment of various genes with putative dimerization domains, such as a coiled coil domain, that are necessary for constitutive activation. RET rearrangements have been detected in a variety of human cancers, including thyroid, lung, colorectal, breast, and salivary gland cancers. Moreover, point mutations in RET are responsible for multiple endocrine neoplasia types 2A and 2B, which can develop into medullary thyroid cancer and pheochromocytoma. Substantial effort is currently being exerted in developing RET kinase inhibitors. RET is also responsible for Hirschsprung's disease, a developmental abnormality in the enteric nervous system. Gene knockout studies have demonstrated that RET plays essential roles in the development of the enteric nervous system and kidney as well as in spermatogenesis. Studies regarding RET continue to provide fascinating challenges in the fields of cancer research, neuroscience, and developmental biology.

The role of glial cell line-derived neurotrophic factor family member artemin in neurological disorders and cancers

Artemin (ARTN) is a member of the glial cell line‐derived neurotrophic factor (GDNF) family ligands (GFLs), which encompasses family members, GDNF, neurturin (NRTN) and persephin (PSPN). ARTN is also referred to as Enovin or Neublastin, and bears structural characteristics of the TGF‐β superfamily. ARTN contains a dibasic cleavage site (RXXR) that is predicted to be cleaved by furin to yield a carboxy‐terminal 113 amino acid mature form. ARTN binds preferentially to receptor GFRα3, coupled to a receptor tyrosine kinase RET, forming a signalling complex for the regulation of intracellular pathways that affect diverse outcomes of nervous system development and homoeostasis. Standard signalling cascades activated by GFLs via RET include the phosphorylation of mitogen‐activated protein kinase or MAPK (p‐ERK, p‐p38 and p‐JNK), PI3K‐AKT and Src. Neural cell adhesion molecule (NCAM) is an alternative signalling receptor for ARTN in the presence of GFRα1, leading to activation of Fyn and FAK. Further, ARTN also interacts with heparan sulphate proteoglycan syndecan‐3 and mediates non‐RET signalling via activation of Src kinases. This review discusses the role of ARTN in spinal cord injury, neuropathic pain and other neurological disorders. Additionally, ARTN plays a role in non‐neuron tissues, such as the formation of Peyer's patch‐like structures in the lymphoid tissue of the gut. The emerging role of ARTN in cancers and therapeutic resistance to cancers is also explored. Further research is necessary to determine the function of ARTN in a tissue‐specific manner, including its signalling mechanisms, in order to improve the therapeutic potential of ARTN in human diseases.

Artemin and an Artemin-Derived Peptide, Artefin, Induce Neuronal Survival, and Differentiation Through Ret and NCAM

Artemin (ARTN) is a neurotrophic factor from the GDNF family ligands (GFLs) that is involved in development of the nervous system and neuronal differentiation and survival. ARTN signals through a complex receptor system consisting of the RET receptor tyrosine kinase and a glycosylphosphatidylinositol-anchored co-receptor GFL receptor α, GFRα3. We found that ARTN binds directly to neural cell adhesion molecule (NCAM) and that ARTN-induced neuritogenesis requires NCAM expression and activation of NCAM-associated signaling partners, thus corroborating that NCAM is an alternative receptor for ARTN. We designed a small peptide, artefin, that could interact with GFRα3 and demonstrated that this peptide agonist induces RET phosphorylation and mimics the biological functions of ARTN – neuroprotection and neurite outgrowth. Moreover, artefin mimicked the binding of ARTN to NCAM and required NCAM expression and activation for its neurite elongation effect, thereby suggesting that artefin represents a binding site for NCAM within ARTN. We showed that biological effects of ARTN and artefin can be inhibited by abrogation of both NCAM and RET, suggesting a more complex signaling mechanism that previously thought. As NCAM plays a significant role in neurodevelopment, regeneration, and synaptic plasticity we suggest that ARTN and its mimetics are promising candidates for treatment of neurological disorders and warrant further investigations.

Non-canonical Ret signaling augments p75-mediated cell death in developing sympathetic neurons

Programmed cell death (PCD) is an evolutionarily conserved process critical in sculpting many organ systems, yet the underlying mechanisms remain poorly understood. Here, we investigated the interactions of pro-survival and pro-apoptotic receptors in PCD using the sympathetic nervous system as a model. We demonstrate that Ret, a receptor tyrosine kinase required for the survival of many neuronal populations, is restricted to a subset of degenerating neurons that rapidly undergo apoptosis. Pro-apoptotic conditions induce Ret to associate with the death receptor p75. Genetic deletion of p75 within Ret+ neurons, and deletion of Ret during PCD, inhibit apoptosis both in vitro and in vivo. Mechanistically, Ret inhibits nerve growth factor (NGF)-mediated survival of sympathetic neurons. Removal of Ret disrupts NGF-mediated TrkA ubiquitination, leading to increased cell surface levels of TrkA, thereby potentiating survival signaling. Additionally, Ret deletion significantly impairs p75 regulated intramembrane proteolysis cleavage, leading to reduced activation of downstream apoptotic effectors. Collectively, these results indicate that Ret acts non-canonically to augment p75-mediated apoptosis.

Interactions of the immune and sensory nervous systems in atopy

A striking feature underlying all atopic disorders, such as asthma, atopic dermatitis, and food allergy, is the presence of pathologic sensory responses, reflexes, and behaviors. These symptoms, exemplified by chronic airway irritation and cough, chronic itch and scratching, as well as gastrointestinal discomfort and dysfunction, are often cited as the most debilitating aspects of atopic disorders. Emerging studies have highlighted how the immune system shapes the scope and intensity of sensory responses by directly modulating the sensory nervous system. Additionally, factors produced by neurons have demonstrated novel functions in propagating atopic inflammation at barrier surfaces. In this review, we highlight new studies that have changed our understanding of atopy through advances in characterizing the reciprocal interactions between the immune and sensory nervous systems.

The GDNF Family: A Role in Cancer?

The glial cell line-derived neurotrophic factor (GDNF) family of ligands (GFLs) comprising of GDNF, neurturin, artemin, and persephin plays an important role in the development and maintenance of the central and peripheral nervous system, renal morphogenesis, and spermatogenesis. Here we review our current understanding of GFL biology, and supported by recent progress in the area, we examine their emerging role in endocrine-related and other non-hormone-dependent solid neoplasms. The ability of GFLs to elicit actions that resemble those perturbed in an oncogenic phenotype, alongside mounting evidence of GFL involvement in tumor progression, presents novel opportunities for therapeutic intervention.

Exon Skipping in the RET Gene Encodes Novel Isoforms That Differentially Regulate RET Protein Signal Transduction

Rearranged during transfection (RET), a receptor tyrosine kinase that is activated by the glial cell line-derived neurotrophic factor family ligands (GFLs), plays a crucial role in the development and function of the nervous system and additionally is required for kidney development and spermatogenesis. RET encodes a transmembrane receptor that is 20 exons long and produces two known protein isoforms differing in C-terminal amino acid composition, referred to as RET9 and RET51. Studies of human pheochromocytomas identified two additional novel transcripts involving the skipping of exon 3 or exons 3, 4, and 5 and are referred to as RET(Δ) (E3) and RET(Δ) (E345), respectively. Here we report the presence of Ret(Δ) (E3) and Ret(Δ) (E345) in zebrafish, mice, and rats and show that these transcripts are dynamically expressed throughout development of the CNS, peripheral nervous system, and kidneys. We further explore the biochemical properties of these isoforms, demonstrating that, like full-length RET, RET(ΔE3) and RET(ΔE345) are trafficked to the cell surface, interact with all four GFRα co-receptors, and have the ability to heterodimerize with full-length RET. Signaling experiments indicate that RET(ΔE3) is phosphorylated in a similar manner to full-length RET. RET(ΔE345), in contrast, displays higher baseline autophosphorylation, specifically on the catalytic tyrosine, Tyr(905), and also on one of the most important signaling residues, Tyr(1062) These data provide the first evidence for a physiologic role of these isoforms in RET pathway function.

The Candidate Neuroprotective Agent Artemin Induces Autonomic Neural Dysplasia without Preventing Peripheral Nerve Dysfunction

Artemin (ART) signals through the GFR α—3/RET receptor complex to support sympathetic neuron development. Here we show that ART also influences autonomic elements in adrenal medulla and enteric and pelvic ganglia. Transgenic mice over-expressing Art throughout development exhibited systemic autonomic neural lesions including fusion of adrenal medullae with adjacent paraganglia, adrenal medullary dysplasia, and marked enlargement of sympathetic (superior cervical and sympathetic chain ganglia) and parasympathetic (enteric, pelvic) ganglia. Changes began by gestational day 12.5 and formed progressively larger masses during adulthood. Art supplementation in wild type adult mice by administering recombinant protein or an Art-bearing retroviral vector resulted in hyperplasia or neuronal metaplasia at the adrenal corticomedullary junction. Expression data revealed that Gfr α—3 is expressed during development in the adrenal medulla, sensory and autonomic ganglia and their projections, while Art is found in contiguous mesenchymal domains (especially skeleton) and in certain nerves. Intrathecal Art therapy did not reduce hypalgesia in rats following nerve ligation. These data (1) confirm that ART acts as a differentiation factor for autonomic (chiefly sympathoadrenal but also parasympathetic) neurons, (2) suggest a role for ART overexpression in the genesis of pheochromocytomas and paragangliomas, and (3) indicate that ART is not a suitable therapy for peripheral neuropathy.

7-dehydrocholesterol efficiently supports Ret signaling in a mouse model of Smith-Opitz-Lemli syndrome

Smith-Lemli-Opitz syndrome (SLOS) is a rare disorder of cholesterol synthesis. Affected individuals exhibit growth failure, intellectual disability and a broad spectrum of developmental malformations. Among them, renal agenesis or hypoplasia, decreased innervation of the gut, and ptosis are consistent with impaired Ret signaling. Ret is a receptor tyrosine kinase that achieves full activity when recruited to lipid rafts. Mice mutant for Ret are born with no kidneys and enteric neurons, and display sympathetic nervous system defects causing ptosis. Since cholesterol is a critical component of lipid rafts, here we tested the hypothesis of whether the cause of the above malformations found in SLOS is defective Ret signaling owing to improper lipid raft composition or function. No defects consistent with decreased Ret signaling were found in newborn Dhcr7^−/− mice, or in Dhcr7^−/− mice lacking one copy of Ret. Although kidneys from Dhcr7^−/− mice showed a mild branching defect in vitro, GDNF was able to support survival and downstream signaling of sympathetic neurons. Consistently, GFRα1 correctly partitioned to lipid rafts in brain tissue. Finally, replacement experiments demonstrated that 7-DHC efficiently supports Ret signaling in vitro. Taken together, our findings do not support a role of Ret signaling in the pathogenesis of SLOS.

Inflammatory and neuropathic cold allodynia are selectively mediated by the neurotrophic factor receptor GFRα3

Tissue injury prompts the release of a number of proalgesic molecules that induce acute and chronic pain by sensitizing pain-sensing neurons (nociceptors) to heat and mechanical stimuli. In contrast, many proalgesics have no effect on cold sensitivity or can inhibit cold-sensitive neurons and diminish cooling-mediated pain relief (analgesia). Nonetheless, cold pain (allodynia) is prevalent in many inflammatory and neuropathic pain settings, with little known of the mechanisms promoting pain vs. those dampening analgesia. Here, we show that cold allodynia induced by inflammation, nerve injury, and chemotherapeutics is abolished in mice lacking the neurotrophic factor receptor glial cell line-derived neurotrophic factor family of receptors-α3 (GFRα3). Furthermore, established cold allodynia is blocked in animals treated with neutralizing antibodies against the GFRα3 ligand, artemin. In contrast, heat and mechanical pain are unchanged, and results show that, in striking contrast to the redundant mechanisms sensitizing other modalities after an insult, cold allodynia is mediated exclusively by a single molecular pathway, suggesting that artemin-GFRα3 signaling can be targeted to selectively treat cold pain.

Microarray Analysis Reveals Increased Transcriptional Repression and Reduced Metabolic Activity but Not Major Changes in the Core Apoptotic Machinery during Maturation of Sympathetic Neurons

Postnatal maturation of the neurons whose main phenotype and basic synaptic contacts are already established includes neuronal growth, refinement of synaptic contacts, final steps of differentiation, programmed cell death period (PCD) etc. In the sympathetic neurons, postnatal maturation includes permanent end of the PCD that occurs with the same time schedule in vivo and in vitro suggesting that the process could be genetically determined. Also many other changes in the neuronal maturation could be permanent and thus based on stable changes in the genome expression. However, postnatal maturation of the neurons is poorly studied. Here we compared the gene expression profiles of immature and mature sympathetic neurons using Affymetrix microarray assay. We found 1310 significantly up-regulated and 1151 significantly down-regulated genes in the mature neurons. Gene ontology analysis reveals up-regulation of genes related to neuronal differentiation, chromatin and epigenetic changes, extracellular factors and their receptors, and cell adhesion, whereas many down-regulated genes were related to metabolic and biosynthetic processes. We show that termination of PCD is not related to major changes in the expression of classical genes for apoptosis or cell survival. Our dataset is deposited to the ArrayExpress database and is a valuable source to select candidate genes in the studies of neuronal maturation. As an example, we studied the changes in the expression of selected genes Igf2bp3, Coro1A, Zfp57, Dcx, and Apaf1 in the young and mature sympathetic ganglia by quantitative PCR and show that these were strongly downregulated in the mature ganglia.

Region-specific role of growth differentiation factor-5 in the establishment of sympathetic innervation

BACKGROUND

Nerve growth factor (NGF) is the prototypical target-derived neurotrophic factor required for sympathetic neuron survival and for the growth and ramification of sympathetic axons within most but not all sympathetic targets. This implies the operation of additional target-derived factors for regulating terminal sympathetic axon growth and branching.

RESULTS

Here report that growth differentiation factor 5 (GDF5), a widely expressed member of the transforming growth factor beta (TGFβ) superfamily required for limb development, promoted axon growth from mouse superior cervical ganglion (SCG) neurons independently of NGF and enhanced axon growth in combination with NGF. GDF5 had no effect on neuronal survival and influenced axon growth during a narrow window of postnatal development when sympathetic axons are ramifying extensively in their targets in vivo. SCG neurons expressed all receptors capable of participating in GDF5 signaling at this stage of development. Using compartment cultures, we demonstrated that GDF5 exerted its growth promoting effect by acting directly on axons and by initiating retrograde canonical Smad signalling to the nucleus. GDF5 is synthesized in sympathetic targets, and examination of several anatomically circumscribed tissues in Gdf5 null mice revealed regional deficits in sympathetic innervation. There was a marked, highly significant reduction in the sympathetic innervation density of the iris, a smaller though significant reduction in the trachea, but no reduction in the submandibular salivary gland. There was no reduction in the number of neurons in the SCG.

CONCLUSIONS

These findings show that GDF5 is a novel target-derived factor that promotes sympathetic axon growth and branching and makes a distinctive regional contribution to the establishment of sympathetic innervation, but unlike NGF, plays no role in regulating sympathetic neuron survival.

Loss of the transcription factor Meis1 prevents sympathetic neurons target-field innervation and increases susceptibility to sudden cardiac death

Although cardio-vascular incidents and sudden cardiac death (SCD) are among the leading causes of premature death in the general population, the origins remain unidentified in many cases. Genome-wide association studies have identified Meis1 as a risk factor for SCD. We report that Meis1 inactivation in the mouse neural crest leads to an altered sympatho-vagal regulation of cardiac rhythmicity in adults characterized by a chronotropic incompetence and cardiac conduction defects, thus increasing the susceptibility to SCD. We demonstrated that Meis1 is a major regulator of sympathetic target-field innervation and that Meis1 deficient sympathetic neurons die by apoptosis from early embryonic stages to perinatal stages. In addition, we showed that Meis1 regulates the transcription of key molecules necessary for the endosomal machinery. Accordingly, the traffic of Rab5⁺ endosomes is severely altered in Meis1-inactivated sympathetic neurons. These results suggest that Meis1 interacts with various trophic factors signaling pathways during postmitotic neurons differentiation.

DOI:http://dx.doi.org/10.7554/eLife.11627.001

Nerve cells called sympathetic neurons can control the activity of almost all of our organs without any conscious thought on our part. For example, these nerve cells are responsible for accelerating the heart rate during exercise.

In a developing embryo, there are initially more of these neurons than are needed, and only those that develop correctly and form a connection with a target cell will survive. This is because the target cells provide the growing neurons with vital molecules called neurotrophins, which are trafficked back along the nerve fiber and into the main body of the nerve cell to ensure its survival. However, it is largely unknown which proteins or genes are also involved in this developmental process.

Now, Bouilloux, Thireau et al. show that if a gene called Meis1 is inactivated in mice, the sympathetic neurons start to develop and grow nerve fibers, but then fail to establish connections with their target cells and finally die. The Meis1 gene encodes a transcription factor, which is a protein that regulates gene activity. Therefore, Bouilloux, Thireau et al. looked for the genes that are regulated by this transcription factor in sympathetic neurons. This search uncovered several genes that are involved in the packaging and trafficking of molecules within cells.

Other experiments then revealed that the trafficking of molecules back along the nerve fiber was altered in mutant neurons in which the Meis1 gene had been inactivated. Furthermore, Meis1 mutant mice had problems with their heart rate, especially during exercise, and an increased risk of dying from a sudden cardiac arrest.

These findings reveal a transcription factor that helps to establish a connection between a neuron and its target, and that activates a pattern of gene expression that works alongside the neurotrophin-based signals. Since all neurons undergo similar processes during development, future work could ask if comparable patterns of gene expression exist in other types of neurons, and if problems with such processes contribute to some neurodegenerative diseases.

DOI:http://dx.doi.org/10.7554/eLife.11627.002

Expression and functional studies of the GDNF family receptor alpha 3 in the pancreas

The generation of therapeutic β-cells from human pluripotent stem cells relies on the identification of growth factors that faithfully mimic pancreatic β-cell development in vitro. In this context, the aim of the study was to determine the expression and function of the glial cell line derived neurotrophic factor receptor alpha 3 (GFRα3) and its ligand artemin (Artn) in islet cell development and function. GFRα3 and Artn expression were characterized by in situ hybridization, immunochemistry, and qRT-PCR. We used GFRα3-deficient mice to study GFRα3 function and generated transgenic mice overexpressing Artn in the embryonic pancreas to study Artn function. We found that GFRα3 is expressed at the surface of a subset of Ngn3-positive endocrine progenitors as well as of embryonic α- and β-cells, while Artn is found in the pancreatic mesenchyme. Adult β-cells lack GFRα3 but α-cells express the receptor. GFRα3 was also found in parasympathetic and sympathetic intra-islet neurons as well as in glial cells in the embryonic and adult pancreas. The loss of GFRα3 or overexpression of Artn has no impact on Ngn3 and islet cell formation and maintenance in the embryo. Islet organization and innervation as well as glucose homeostasis is normal in GFRα3-deficient mice suggesting functional redundancy.

Lipid Rafts Are Physiologic Membrane Microdomains Necessary for the Morphogenic and Developmental Functions of Glial Cell Line-Derived Neurotrophic Factor In Vivo

Glial cell line-derived neurotrophic factor (GDNF) promotes PNS development and kidney morphogenesis via a receptor complex consisting of the glycerophosphatidylinositol (GPI)-anchored, ligand binding receptor GDNF family receptor α1 (GFRα1) and the receptor tyrosine kinase Ret. Although Ret signal transduction in vitro is augmented by translocation into lipid rafts via GFRα1, the existence and importance of lipid rafts in GDNF-Ret signaling under physiologic conditions is unresolved. A knock-in mouse was produced that replaced GFRα1 with GFRα1-TM, which contains a transmembrane (TM) domain instead of the GPI anchor. GFRα1-TM still binds GDNF and promotes Ret activation but does not translocate into rafts. In Gfrα1(TM/TM) mice, GFRα1-TM is expressed, trafficked, and processed at levels identical to GFRα1. Although Gfrα1(+/TM) mice are viable, Gfrα1(TM/TM) mice display bilateral renal agenesis, lack enteric neurons in the intestines, and have motor axon guidance deficits, similar to Gfrα1(-/-) mice. Therefore, the recruitment of Ret into lipid rafts by GFRα1 is required for the physiologic functions of GDNF in vertebrates. Significance statement: Membrane microdomains known as lipid rafts have been proposed to be unique subdomains in the plasma membrane that are critical for the signaling functions of multiple receptor complexes. Their existence and physiologic relevance has been debated. Based on in vitro studies, lipid rafts have been reported to be necessary for the function of the Glial cell line-derived neurotrophic factor (GDNF) family of neurotrophic factors. The receptor for GDNF comprises the lipid raft-resident, glycerophosphatidylinositol-anchored receptor GDNF family receptor α1 (GFRα1) and the receptor tyrosine kinase Ret. Here we demonstrate, using a knock-in mouse model in which GFRα1 is no longer located in lipid rafts, that the developmental functions of GDNF in the periphery require the translocation of the GDNF receptor complex into lipid rafts.

Emerging roles of gut microbiota and the immune system in the development of the enteric nervous system

The enteric nervous system (ENS) consists of neurons and glial cells that differentiate from neural crest progenitors. During embryogenesis, development of the ENS is controlled by the interplay of neural crest cell-intrinsic factors and instructive cues from the surrounding gut mesenchyme. However, postnatal ENS development occurs in a different context, which is characterized by the presence of microbiota and an extensive immune system, suggesting an important role of these factors on enteric neural circuit formation and function. Initial reports confirm this idea while further studies in this area promise new insights into ENS physiology and pathophysiology.

Signaling molecules and transcription factors involved in the development of the sympathetic nervous system, with special emphasis on the superior cervical ganglion

The cells that constitute the sympathetic nervous system originate from the neural crest. This review addresses the current understanding of sympathetic ganglion development viewed from molecular and morphological perspectives. Development of the sympathetic nervous system is categorized into three main steps, as follows: (1) differentiation and migration of cells in the neural crest lineage for formation of the primary sympathetic chain, (2) differentiation of sympathetic progenitors, and (3) growth and survival of sympathetic ganglia. The signaling molecules and transcription factors involved in each of these developmental stages are elaborated mostly on the basis of the results of targeted mutation of respective genes. Analyses in mutant mice revealed differences between the superior cervical ganglion (SCG) and the other posterior sympathetic ganglia. This review provides a summary of the similarities and differences in the development of the SCG and other posterior sympathetic ganglia. Relevant to the development of sympathetic ganglia is the demonstration that neuroendocrine cells, such as adrenal chromaffin cells and carotid body glomus cells, share a common origin with the sympathetic ganglia. Neural crest cells at the trunk level give rise to common sympathoadrenal progenitors of sympathetic neurons and chromaffin cells, while progenitors segregated from the SCG give rise to glomus cells. After separation from the sympathetic primordium, the progenitors of both chromaffin cells and glomus cells colonize the anlage of the adrenal gland and carotid body, respectively. This review highlights the biological properties of chromaffin cells and glomus cells, because, although both cell types are derivatives of sympathetic primordium, they are distinct in many respects.

To bud or not to bud: the RET perspective in CAKUT

Congenital anomalies of the kidneys or lower urinary tract (CAKUT) encompass a spectrum of anomalies that result from aberrations in spatio-temporal regulation of genetic, epigenetic, environmental, and molecular signals at key stages of urinary tract development. The Rearranged in Transfection (RET) tyrosine kinase signaling system is a major pathway required for normal development of the kidneys, ureters, peripheral and enteric nervous systems. In the kidneys, RET is activated by interaction with the ligand glial cell line-derived neurotrophic factor (GDNF) and coreceptor GFRα1. This activated complex regulates a number of downstream signaling cascades (PLCγ, MAPK, and PI3K) that control proliferation, migration, renewal, and apoptosis. Disruption of these events is thought to underlie diseases arising from aberrant RET signaling. RET mutations are found in 5-30 % of CAKUT patients and a number of Ret mouse mutants show a spectrum of kidney and lower urinary tract defects reminiscent of CAKUT in humans. The remarkable similarities between mouse and human kidney development and in defects due to RET mutations has led to using RET signaling as a paradigm for determining the fundamental principles in patterning of the upper and lower urinary tract and for understanding CAKUT pathogenesis. In this review, we provide an overview of studies in vivo that delineate expression and the functional importance of RET signaling complex during different stages of development of the upper and lower urinary tracts. We discuss how RET signaling balances activating and inhibitory signals emanating from its docking tyrosines and its interaction with upstream and downstream regulators to precisely modulate different aspects of Wolffian duct patterning and branching morphogenesis. We outline the diversity of cellular mechanisms regulated by RET, disruption of which causes malformations ranging from renal agenesis to multicystic dysplastic kidneys in the upper tract and vesicoureteral reflux or ureteropelvic junction obstruction in the lower tract.

Proliferation and cell cycle dynamics in the developing stellate ganglion

Cell proliferation during nervous system development is poorly understood outside the mouse neocortex. We measured cell cycle dynamics in the embryonic mouse sympathetic stellate ganglion, where neuroblasts continue to proliferate following neuronal differentiation. At embryonic day (E) 9.5, when neural crest-derived cells were migrating and coalescing into the ganglion primordium, all cells were cycling, cell cycle length was only 10.6 h, and S-phase comprised over 65% of the cell cycle; these values are similar to those previously reported for embryonic stem cells. At E10.5, Sox10(+) cells lengthened their cell cycle to 38 h and reduced the length of S-phase. As cells started to express the neuronal markers Tuj1 and tyrosine hydroxylase (TH) at E10.5, they exited the cell cycle. At E11.5, when >80% of cells in the ganglion were Tuj1(+)/TH(+) neuroblasts, all cells were again cycling. Neuroblast cell cycle length did not change significantly after E11.5, and 98% of Sox10(-)/TH(+) cells had exited the cell cycle by E18.5. The cell cycle length of Sox10(+)/TH(-) cells increased during late embryonic development, and ∼25% were still cycling at E18.5. Loss of Ret increased neuroblast cell cycle length at E16.5 and decreased the number of neuroblasts at E18.5. A mathematical model generated from our data successfully predicted the relative change in proportions of neuroblasts and non-neuroblasts in wild-type mice. Our results show that, like other neurons, sympathetic neuron differentiation is associated with exit from the cell cycle; sympathetic neurons are unusual in that they then re-enter the cell cycle before later permanently exiting.

The transcription factor Hmx1 and growth factor receptor activities control sympathetic neurons diversification

The sympathetic nervous system relies on distinct populations of neurons that use noradrenaline or acetylcholine as neurotransmitter. We show that fating of the sympathetic lineage at early stages results in hybrid precursors from which, genetic cell-lineage tracing reveals, all types progressively emerge by principal mechanisms of maintenance, repression and induction of phenotypes. The homeobox transcription factor HMX1 represses Tlx3 and Ret, induces TrkA and maintains tyrosine hydroxylase (Th) expression in precursors, thus driving segregation of the noradrenergic sympathetic fate. Cholinergic sympathetic neurons develop through cross-regulatory interactions between TRKC and RET in precursors, which lead to Hmx1 repression and sustained Tlx3 expression, thereby resulting in failure of TrkA induction and loss of maintenance of Th expression. Our results provide direct evidence for a model in which diversification of noradrenergic and cholinergic sympathetic neurons is based on a principle of cross-repressive functions in which the specific cell fates are directed by an active suppression of the expression of transcription factors and receptors that direct the alternative fate.

Stage specific requirement of Gfrα1 in the ureteric epithelium during kidney development

Glial cell line-derived neurotrophic factor (GDNF) binds a coreceptor GDNF family receptor α1 (GFRα1) and forms a signaling complex with the receptor tyrosine kinase RET. GDNF-GFRα1-RET signaling activates cellular pathways that are required for normal induction of the ureteric bud (UB) from the Wolffian duct (WD). Failure of UB formation results in bilateral renal agenesis and perinatal lethality. Gfrα1 is expressed in both the epithelial and mesenchymal compartments of the developing kidney while Ret expression is specific to the epithelium. The biological importance of Gfrα1's wider tissue expression and its role in later kidney development are unclear. We discovered that conditional loss of Gfrα1 in the WD epithelium prior to UB branching is sufficient to cause renal agenesis. This finding indicates that Gfrα1 expressed in the nonepithelial structures cannot compensate for this loss. To determine Gfrα1's role in branching morphogenesis after UB induction we used an inducible Gfrα1-specific Cre-deletor strain and deleted Gfrα1 from the majority of UB tip cells post UB induction in vivo and in explant kidney cultures. We report that Gfrα1 excision from the epithelia compartment after UB induction caused a modest reduction in branching morphogenesis. The loss of Gfrα1 from UB-tip cells resulted in reduced cell proliferation and decreased activated ERK (pERK). Further, cells without Gfrα1 expression are able to populate the branching UB tips. These findings delineate previously unclear biological roles of Gfrα1 in the urinary tract and demonstrate its cell-type and stage-specific requirements in kidney development.

The severity of neural invasion is associated with shortened survival in colon cancer

PURPOSE

Neural invasion (NI) is a histopathologic feature of colon cancer that receives little consideration. Therefore, we conducted a morphologic and functional characterization of NI in colon cancer.

EXPERIMENTAL DESIGN

NI was investigated in 673 patients with colon cancer. Localization and severity of NI was determined and related to patient's prognosis and survival. The neuro-affinity of colon cancer cells (HT29, HCT-116, SW620, and DLD-1) was compared with pancreatic cancer (T3M4 and SU86.86) and rectal cancer cells (CMT-93) in the in vitro three-dimensional (3D)-neural-migration assay and analyzed via live-cell imaging. Immunoreactivity of the neuroplasticity marker GAP-43, and the neurotrophic-chemoattractant factors Artemin and nerve growth factor (NGF), was quantified in colon cancer and pancreatic cancer nerves. Dorsal root ganglia of newborn rats were exposed to supernatants of colon cancer, rectal cancer, and pancreatic cancer cells and neurite density was determined.

RESULTS

NI was detected in 210 of 673 patients (31.2%). Although increasing NI severity scores were associated with a significantly poorer survival, presence of NI was not an independent prognostic factor in colon cancer. In the 3D migration assay, colon cancer and rectal cancer cells showed much less neurite-targeted migration when compared with pancreatic cancer cells. Supernatants of pancreatic cancer and rectal cancer cells induced a much higher neurite density than those of colon cancer cells. Accordingly, NGF, Artemin, and GAP-43 were much more pronounced in nerves in pancreatic cancer than in colon cancer.

CONCLUSION

NI is not an independent prognostic factor in colon cancer. The lack of a considerable biologic affinity between colon cancer cells and neurons, the low expression profile of colonic nerves for chemoattractant molecules, and the absence of a major neuroplasticity in colon cancer may explain the low prevalence and impact of NI in colon cancer.

The in vivo response of stem and other undifferentiated spermatogonia to the reversible inhibition of glial cell line-derived neurotrophic factor signaling in the adult

Maintaining adequate numbers of spermatogonial stem cells is required for the production of the millions of sperm required for male fertility. To date, however, the mechanisms that regulate the size of this pool in the adult are poorly defined. Glial cell line-derived neurotrophic factor (GDNF) is required for establishing this pool in the prepubertal animal, but its in vivo function in the normal adult testis has never been examined directly. We used a chemical-genetic approach to address this issue. We generated mice carrying a single amino acid mutation (V805A) in Ret, the kinase subunit of the GDNF receptor. This mutation does not affect normal GDNF signaling but renders it susceptible to inhibition by the ATP competitive inhibitor, NA-PP1. When GDNF signaling was blocked in adults for 11 days, only a few cells remained that expressed the stem spermatogonial markers, Gfrα1 and Zbtb16, and testicular Ret mRNA content was reduced markedly. These decreases were associated with depletion of functional stem spermatogonia; some were lost when GDNF signaling was inhibited for only 2 days while others survived for up to 11 days. However, when signaling was restored, the remaining stem cells proliferated, initiating tissue restoration. In conclusion, these results provide the first direct proof that GDNF acutely regulates the number of spermatogonial stem cells in the normal adult testis. Additionally, these results demonstrate different sensitivities among subpopulation of these stem cells to inhibition of GDNF signaling.

Artemin causes hypersensitivity to warm sensation, mimicking warmth-provoked pruritus in atopic dermatitis

BACKGROUND

Itch impairs the quality of life for many patients with dermatoses, especially atopic dermatitis (AD), and is frequently induced by a warm environment.

OBJECTIVE

To determine the mechanism underlying itch induction by warmth, we focused on artemin, a member of glial cell line-derived neurotrophic factors (GDNFs).

METHODS

A gene array assay revealed that artemin was expressed in substance P-treated dermal fibroblasts. The expression of artemin in healthy and AD-lesional skin was evaluated with immunohistochemistry and in situ hybridization. The impact of fibroblast-derived artemin on the proliferation and morphology of neural cell was investigated in vitro. To confirm the involvement of artemin in skin sensibility, wild-type and GDNF family receptor α3 knockout mice were employed for sensory examination.

RESULTS

Artemin-expressing fibroblasts accumulated in skin lesions of patients with AD. Artemin induced cell proliferation of a neuroblastoma cell line in vitro, and intradermal injection of artemin in mice resulted in peripheral nerve sprouting and thermal hyperalgesia. Artemin-treated mice demonstrated scratching behavior in a warm environment, but mice deficient for GDNF family receptor α3, a potent artemin receptor, did not show this behavior. Furthermore, the escaping response to heat stimulus was attenuated in GDNF family receptor α3 knockout mice, suggesting that artemin may contribute to sensitivity to heat.

CONCLUSION

These data suggest that dermal fibroblasts secrete artemin in response to substance P, leading to abnormal peripheral innvervation and thermal hyperalgesia. We hypothesize that artemin lowers the threshold of temperature-dependent itch sensation and might therefore be a novel therapeutic target for treating pruritic skin disorders, including AD.

Hes1 is required for the development of the superior cervical ganglion of sympathetic trunk and the carotid body

Hes1 gene represses the expression of proneural basic helix-loop-helix (bHLH) factor Mash1, which is essential for the differentiation of the sympathetic ganglia and carotid body glomus cells. The sympathetic ganglia, carotid body, and common carotid artery in Wnt1-Cre/R26R double transgenic mice were intensely labeled by X-gal staining, i.e., the neural crest origin. The deficiency of Hes1 caused severe hypoplasia of the superior cervical ganglion (SCG). At embryonic day (E) 17.5-E18.5, the volume of the SCG in Hes1 null mutants was reduced to 26.4% of the value in wild-type mice. In 4 of 30 cases (13.3%), the common carotid artery derived from the third arch artery was absent in the null mutants, and the carotid body was not formed. When the common carotid artery was retained, the organ grew in the wall of the third arch artery and glomus cell precursors were provided from the SCG in the null mutants as well as in wild-types. However, the volume of carotid body in the null mutants was only 52.5% of the value in wild-types at E17.5-E18.5. These results suggest that Hes1 plays a critical role in regulating the development of neural crest derivatives in the mouse cervical region.

Genome-wide analysis of polymorphisms associated with cytokine responses in smallpox vaccine recipients

The role that genetics play in response to infection or disease is becoming increasingly clear as we learn more about immunogenetics and host-pathogen interactions. Here we report a genome-wide analysis of the effects of host genetic variation on cytokine responses to vaccinia virus stimulation in smallpox vaccine recipients. Our data show that vaccinia stimulation of immune individuals results in secretion of inflammatory and Th1 cytokines. We identified multiple SNPs significantly associated with variations in cytokine secretion. These SNPs are found in genes with known immune function, as well as in genes encoding for proteins involved in signal transduction, cytoskeleton, membrane channels and ion transport, as well as others with no previously identified connection to immune responses. The large number of significant SNP associations implies that cytokine secretion in response to vaccinia virus is a complex process controlled by multiple genes and gene families. Follow-up studies to replicate these findings and then pursue mechanistic studies will provide a greater understanding of how genetic variation influences vaccine responses.

Antidepressant-like effect of artemin in mice: a mechanism for acetyl-L-carnitine activity on depression

RATIONALE

Depression may be associated with altered plasticity of the nervous system. The importance of neurotrophic factor levels is strongly suggested, and the neuronal-related family is extensively studied with respect to glial-derived one.

OBJECTIVES

Aimed to contribute to the study of nervous plasticity modulation as therapeutical target in mood disorders, the role of the glial-derived factor artemin (ARTN) in depression and in the pharmacodynamics of the antidepressant and trophic compound acetyl-L: -carnitine (ALCAR) was evaluated.

METHODS

Male mice were treated with 100 mg kg(-1) ALCAR daily for 7 days; 0.6 μg/mouse ARTN was acutely injected intracerebroventricularly. Gene knockdown of ARTN and GDNF family receptor alpha (GFRalpha3) was obtained by oligonucleotide antisense strategy. The forced swimming test was performed to evaluate antidepressant-like effects.

RESULTS

Repeated ALCAR administration increased ARTN levels in spinal cord, hippocampus, and prefrontal cortex. No modulatory effect was detected on BDNF and glial cell line-derived neutrotrophic factor (GDNF). ARTN, 30 min after administration, showed a dose-dependent antidepressant-like effect. ALCAR needed a 7-day treatment to reach a comparable effect; nevertheless, both substances were able to induce a phosphorylation of the GDNF family receptor Ret. A decrease of the free ARTN level by a specific ARTN antibody impaired the antidepressant-like effect of acute ARTN and repeated ALCAR. Gene knockdown of ARTN or, alternatively, of its receptor GFRalpha3 fully prevented ALCAR effectiveness.

CONCLUSIONS

A mechanism for the antidepressant property of ALCAR is proposed, and the novelty of the possible role of ARTN in depression is suggested.

Egr3 dependent sympathetic target tissue innervation in the absence of neuron death

Nerve Growth Factor (NGF) is a target tissue derived neurotrophin required for normal sympathetic neuron survival and target tissue innervation. NGF signaling regulates gene expression in sympathetic neurons, which in turn mediates critical aspects of neuron survival, axon extension and terminal axon branching during sympathetic nervous system (SNS) development. Egr3 is a transcription factor regulated by NGF signaling in sympathetic neurons that is essential for normal SNS development. Germline Egr3-deficient mice have physiologic dysautonomia characterized by apoptotic sympathetic neuron death and abnormal innervation to many target tissues. The extent to which sympathetic innervation abnormalities in the absence of Egr3 is caused by altered innervation or by neuron death during development is unknown. Using Bax-deficient mice to abrogate apoptotic sympathetic neuron death in vivo, we show that Egr3 has an essential role in target tissue innervation in the absence of neuron death. Sympathetic target tissue innervation is abnormal in many target tissues in the absence of neuron death, and like NGF, Egr3 also appears to effect target tissue innervation heterogeneously. In some tissues, such as heart, spleen, bowel, kidney, pineal gland and the eye, Egr3 is essential for normal innervation, whereas in other tissues such as lung, stomach, pancreas and liver, Egr3 appears to have little role in innervation. Moreover, in salivary glands and heart, two tissues where Egr3 has an essential role in sympathetic innervation, NGF and NT-3 are expressed normally in the absence of Egr3 indicating that abnormal target tissue innervation is not due to deregulation of these neurotrophins in target tissues. Taken together, these results clearly demonstrate a role for Egr3 in mediating sympathetic target tissue innervation that is independent of neuron survival or neurotrophin deregulation.

Biomaterials in cochlear implants

The cochlear implant (CI) represents, for almost 25 years now, the gold standard in the treatment of children born deaf and for postlingually deafened adults. These devices thus constitute the greatest success story in the field of ‘neurobionic’ prostheses. Their (now routine) fitting in adults, and especially in young children and even babies, places exacting demands on these implants, particularly with regard to the biocompatibility of a CI’s surface components. Furthermore, certain parts of the implant face considerable mechanical challenges, such as the need for the electrode array to be flexible and resistant to breakage, and for the implant casing to be able to withstand external forces.

As these implants are in the immediate vicinity of the middle-ear mucosa and of the junction to the perilymph of the cochlea, the risk exists – at least in principle – that bacteria may spread along the electrode array into the cochlea. The wide-ranging requirements made of the CI in terms of biocompatibility and the electrode mechanism mean that there is still further scope – despite the fact that CIs are already technically highly sophisticated – for ongoing improvements to the properties of these implants and their constituent materials, thus enhancing the effectiveness of these devices.

This paper will therefore discuss fundamental material aspects of CIs as well as the potential for their future development.

Artemin improves survival of spiral ganglion neurons in vivo and in vitro

Artemin and its receptors are upregulated in the auditory nerve of deafened rats as a possible intrinsic protective mechanism against ototoxicity-related apoptosis. Consequently, we examined the effect of artemin on spiral ganglion neurons in vitro and in vivo. Spiral ganglion neurons were isolated from neonatal rats and cultured in serum-free medium supplemented with artemin and/or brain-derived neurotrophic factor (BDNF). In vitro, the survival rate of spiral ganglion neurons cultivated with artemin or BDNF was significantly improved compared with negative controls. In addition, artemin was delivered to the inner ear of deafened guinea pigs for 28 days. In-vivo artemin was as effective as BDNF in spiral ganglion neuron protection. Therefore, artemin promotes the survival of spiral ganglion neurons in vitro and in vivo.

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.

Behavioral and cellular level changes in the aging somatosensory system

A study of the peripheral sensory system of young and aged Blk6 mice obtained from the National Institutes on Aging mouse colony is described. Behavioral assays showed male and female aged mice had decreased sensitivity to thermal stimuli. The receptor for the growth factor artemin (Artn), GFRalpha3, and the ion channel TRPV1, which is expressed by 95-99% of GFRalpha3-positive primary sensory neurons, was also decreased. Calcium imaging of isolated dorsal root ganglia neurons grown with nerve growth factor was used to test the in vitro effects of Artn on TRPV1 activation by capsaicin in young and old neurons. Artn potentiated initial TRPV1 responses to capsaicin in young and old neurons, but the percent of capsaicin responders following repeated exposure to capsaicin increased only in young neurons. The lack of change in aged neurons suggests that differences in TRPV1 responses occur with aging in the somatosensory system.

Extracellular signals regulating sympathetic neuron survival and target innervation during development

The comparative ease with which paravertebral sympathetic neurons are studied in vitro and in vivo at stages throughout their development has facilitated major advances in our understanding of several key aspects of neuronal development. Detailed anatomical descriptions of the in vivo development of these neurons, studies of the effects of various extracellular signalling molecules on these neurons in vitro and analysis of the sympathetic phenotype of relevant transgenic mice have provided an in-depth understanding of how different extracellular signals orchestrate sequential steps in the establishment and refinement of sympathetic innervation. In this review, I will document the roles of neurotrophic factors, cytokines and other extracellular signals in regulating sympathetic neuron survival and target innervation at sequential stages of development.

Autocrine regulation of early embryonic development by the artemin-GFRA3 (GDNF family receptor-alpha 3) signaling system in mice

Development of early embryos is regulated by autocrine/paracrine factors. Analyzing the expression of polypeptide ligand-receptor pairs using DNA microarray datasets, we identified transcripts for artemin, a member of the GDNF (glial cell line-derived neurotrophic factor) family, its receptor GFRA3 (GDNF family receptor-alpha 3) and coreceptor RET. Here we report an autocrine/paracrine role of the artemin-GFRA3 signaling system in regulating early embryonic development and apoptosis. Possible involvement of the MAP kinase signaling pathway was also demonstrated. The genome-wide survey of ligand-receptor pairs and early embryo cultures provided a better understanding of autocrine/paracrine embryonic factors important for optimal blastocyst development.

HSV-mediated transfer of artemin overcomes myelin inhibition to improve outcome after spinal cord injury

Artemin is a neurotrophic factor of the glial cell line-derived neurotrophic factor (GDNF) family of ligands that acts through the GDNF family receptor alpha3 (GFRalpha3)/ret receptor found predominantly on sensory and sympathetic neurons. In order to explore the potential utility of artemin to improve functional outcome after spinal cord injury (SCI), we constructed a nonreplicating herpes simplex virus (HSV)-based vector to express artemin (QHArt). We found that QHArt efficiently transfects spinal cord neurons to produce artemin. Transgene-mediated artemin supported the extension of neurites by primary dorsal root ganglion neurons in culture, and allowed those cells to overcome myelin inhibition of neurite extension through activation of protein kinase A (PKA) to phosphorylate cyclic adenosine monophosphate (cAMP) response element binding protein (CREB) and increase expression of arginase I. Intraspinal injection of QHArt immediately after thoracic spinal cord dorsal over hemisection produced a statistically significant improvement in motor recovery over the course of four weeks measured by locomotor rating score.

Loss of the Prader-Willi syndrome protein necdin causes defective migration, axonal outgrowth, and survival of embryonic sympathetic neurons

Prader-Willi syndrome is a neurodevelopmental disorder marked by abnormalities in feeding, drinking, thermoregulation, intestinal motility, and reproduction, suggesting disruption of the autonomic nervous system. Necdin, one of several proteins genetically inactivated in individuals with Prader-Willi syndrome, is important for the differentiation of central and sensory neurons. We now show that formation, migration, and survival of sympathetic superior cervical ganglion neurons are impaired in Ndn-null embryos. We observed reduced innervation of superior cervical ganglion target organs, including the submandibular gland, parotid gland, and nasal mucosa. While the formation of other sympathetic chain ganglia is unaffected, axonal extension is impaired throughout the sympathetic nervous system. These results demonstrate a novel role for necdin in cellular migration, in addition to its roles in survival and axon outgrowth. Furthermore, reduced sympathetic function provides a plausible explanation for deficiencies of salivary gland function in individuals with congenital necdin deficiency consequent to Prader-Willi syndrome.

Altered glial cell line-derived neurotrophic factor (GDNF) concentrations in the brain of patients with depressive disorder: a comparative post-mortem study

INTRODUCTION

A growing body of evidence suggests that the glial cell line-derived neurotrophic factor (GDNF) is involved in the aetiopathology of mood disorders. GDNF is a neurotrophic factor from the transforming growth factor-beta-family, playing a role in cell development and function in the limbic system. This is the first study to examine GDNF concentration in different brain regions of patients with depressive disorder (DD).

MATERIAL AND METHODS

We used sandwich-ELISA-technique to ascertain GDNF concentration and Lowry assay for overall protein levels in post-mortem brain tissue of 7 patients with recurrent depressive disorder and 14 individuals without any neurological or psychiatric diagnoses. We included cortical regions as well as limbic area's (hippocampus, entorhinal cortex) basal ganglia (putamen, caudate nucleus), thalamus and cingulated gyrus.

RESULTS

We found a significant increase in GDNF concentration in the parietal cortex of patients with DD compared to the control group. In other regions the trend of an increased GDNF concentration did not reach statistical difference.

DISCUSSION

This proof of concept study supports previous findings of an alteration of the GDNF in patients with depressive disorder. However, for the first time a significant increase of GDNF in a cortical brain area was found in DD.

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.

Plexin-A3 and plexin-A4 restrict the migration of sympathetic neurons but not their neural crest precursors

During development, the semaphorin family of guidance molecules is required for proper formation of the sympathetic nervous system. Plexins are receptors that mediate semaphorin signaling, but how plexins function during sympathetic development is not fully understood. Using phenotypic analyses of mutant mice in vivo, expression pattern studies, and in vitro assays, we show that plexin-A3 and plexin-A4 are essential for normal sympathetic development. This study confirms our previous in vitro findings that the two plexins differentially regulate the guidance of sympathetic axons. In addition, we find that semaphorin signaling through plexin-A3 and plexin-A4 restricts the migration of sympathetic neurons, but these two plexins function redundantly since migration defects are only observed in plexin-A3/-A4 double mutants. Surprisingly, our analysis also indicates that plexin-A3 and plexin-A4 are not required for guiding neural crest precursors prior to reaching the sympathetic anlagen. Immunoprecipitation studies suggest that these two plexins independently mediate secreted semaphorin signaling. Thus, plexin-A3 and plexin-A4 are expressed in newly-differentiated sympathetic neurons, but not their neural crest precursors. They function cooperatively to regulate the migration of sympathetic neurons and then differentially to guide the sympathetic axons.

FRS2 alpha 2F/2F mice lack carotid body and exhibit abnormalities of the superior cervical sympathetic ganglion and carotid sinus nerve

The docking protein FRS2 alpha is an important mediator of fibroblast growth factor (FGF)-induced signal transduction, and functions by linking FGF receptors (FGFRs) to a variety of intracellular signaling pathways. We show that the carotid body is absent in FRS2 alpha(2F/2F) mice, in which the Shp2-binding sites of FRS2 alpha are disrupted. We also show that the carotid body rudiment is not formed in the wall of the third arch artery in mutant embryos. In wild-type mice, the superior cervical ganglion of the sympathetic trunk connects to the carotid body in the carotid bifurcation region, and extends thick nerve bundles into the carotid body. In FRS2 alpha(2F/2F) mice, the superior cervical ganglion was present in the lower cervical region as an elongated feature, but failed to undergo cranio-ventral migration. In addition, few neuronal processes extended from the ganglion into the carotid bifurcation region. The number of carotid sinus nerve fibers that reached the carotid bifurcation region was markedly decreased, and baroreceptor fibers belonging to the glossopharyngeal nerve were absent from the basal part of the internal carotid artery in FRS2 alpha(2F/2F) mutant mice. In some of the mutant mice (5 out of 14), baroreceptors and some glomus cells were distributed in the wall of the common carotid artery, onto which the sympathetic ganglion abutted. We propose that the sympathetic ganglion provides glomus cell precursors into the third arch artery derivative in the presence of sensory fibers of the glossopharyngeal nerve.

Specificity in the crosstalk of TGFbeta/GDNF family members is determined by distinct GFR alpha receptors

Glial cell line-derived neurotrophic factor (GDNF) and neurturin (NRTN) are neurotrophic factors for parasympathetic neurons including ciliary ganglion (CG) neurons. Recently, we have shown that survival and signaling mediated by GDNF in CG neurons essentially requires transforming growth factor beta (TGFbeta). We have provided evidence that TGFbeta regulates the availability of the glycosyl phosphatidylinositol (GPI)-anchored GDNF receptor alpha 1 (GFRalpha1) by promoting the recruitment of the receptor to the plasma membrane. We report now that in addition to GDNF, NRTN, but not persephin (PSPN) or artemin (ARTN), is able to promote survival of CG neurons. Interestingly, in contrast to GDNF, NRTN is not dependent on cooperation with TGFbeta, but efficiently promotes neuronal survival and intracellular signaling in the absence of TGFbeta. Additional treatment with TGFbeta does not further increase the NRTN response. Both NRTN and GDNF exclusively bind to and activate their cognate receptors, GFRalpha2 and GFRalpha1, respectively, as shown by the use of receptor-specific neutralizing antibodies. Immunocytochemical staining for the two receptors on the surface of CG neurons reveals that, in contrast to the effect on GFRalpha1, TGFbeta is not required for recruitment of GFRalpha2 to the plasma membrane. Moreover, binding of radioactively labeled GDNF but not NRTN is increased upon treatment of CG neurons with TGFbeta. Disruption of TGFbeta signaling does interfere with GDNF-, but not NRTN-mediated signaling and survival. We propose a model taking into account data from GFRalpha1 crystallization and ontogenetic development of the CG that may explain the differences in TGFbeta-dependence of GDNF and NRTN.

A hierarchical NGF signaling cascade controls Ret-dependent and Ret-independent events during development of nonpeptidergic DRG neurons

NGF controls survival, differentiation, and target innervation of both peptidergic and nonpeptidergic DRG sensory neurons. The common receptor for GDNF family ligands, Ret, is highly expressed in nonpeptidergic neurons, but its function during development of these neurons is unclear. Here, we show that expression of Ret and its coreceptors GFRalpha1 and GFRalpha2 is dependent on NGF. GFR/Ret signaling, in turn, autoregulates expression of both GFRalpha1 and GFRalpha2 and promotes expression of TrpA1, MrgA1, MrgA3, and MrgB4, acquisition of normal neuronal size, axonal innervation of the epidermis, and postnatal extinction of the NGF receptor TrkA. Moreover, NGF controls expression of several other genes characteristic of nonpeptidergic neurons, such as TrpC3, TrpM8, MrgD, and the transcription factor Runx1, via a Ret-independent signaling pathway. These findings support a model in which NGF controls maturation of nonpeptidergic DRG neurons through a combination of GFR/Ret-dependent and -independent signaling pathways.