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Purpose: TRK inhibitors achieve marked tumor-agnostic efficacy in TRK fusion–positive cancers and consequently are now an established standard of care. Little is known, however, about the demographics, outcomes, response to alternative standard therapies, or genomic characteristics of TRK fusion–positive cancers. Experimental Design: Utilizing a center-wide screening program involving more than 26,000 prospectively sequenced patients, genomic and clinical data from all cases with TRK fusions were extracted. An integrated analysis was performed of genomic, therapeutic, and phenomic outcomes. Results: We identified 76 cases with confirmed TRK fusions (0.28% overall prevalence) involving 48 unique rearrangements and 17 cancer types. The presence of a TRK fusion was associated with depletion of concurrent oncogenic drivers (P < 0.001) and lower tumor mutation burden (P < 0.001), with the exception of colorectal cancer where TRK fusions cooccur with microsatellite instability (MSI-H). Longitudinal profiling in a subset of patients indicated that TRK fusions were present in all sampled timepoints in 82% (14/17) of cases. Progression-free survival on first-line therapy, excluding TRK inhibitors, administered for advanced disease was 9.6 months [95% confidence interval (CI), 4.8–13.2]. The best overall response rate achieved with chemotherapy containing–regimens across all lines of therapy was 63% (95% CI, 41–81). Among 12 patients treated with checkpoint inhibitors, a patient with MSI-H colorectal cancer had the only observed response. Conclusions: TRK fusion–positive cancers can respond to alternative standards of care, although efficacy of immunotherapy in the absence of other predictive biomarkers (MSI-H) appears limited. TRK fusions are present in tumors with simple genomes lacking in concurrent drivers that may partially explain the tumor-agnostic efficacy of TRK inhibitors.

Peripheral nerve regeneration relies on the ability of Schwann cells to support the regrowth of damaged axons. Schwann cells re-differentiate when reestablishing contact with the sprouting axons, with large fibers becoming remyelinated and small nociceptive fibers ensheathed and collected into Remak bundles. We have previously described how the receptor sortilin facilitates neurotrophin signaling in peripheral neurons via regulated trafficking of Trk receptors. This study aims to characterize the effects of sortilin deletion on nerve regeneration following sciatic crush injury. We found that Sort1–/– mice displayed functional motor recovery like that of WT mice, with no detectable differences in relation to nerve conduction velocities and morphological aspects of myelinated fibers. In contrast, we found abnormal ensheathment of regenerated C-fibers in injured Sort1–/– mice, demonstrating a role of sortilin for Remak bundle formation following injury. Further studies on Schwann cell signaling pathways showed a significant reduction of MAPK/ERK, RSK, and CREB phosphorylation in Sort1–/– Schwann cells after stimulation with neurotrophin-3 (NT-3), while Schwann cell migration and myelination remained unaffected. In conclusion, our results demonstrate that loss of sortilin blunts NT-3 signaling in Schwann cells which might contribute to the impaired Remak bundle regeneration after sciatic nerve injury.

The first hematopoietic stem cells (HSCs) emerge in the Aorta-Gonad-Mesonephros (AGM) region in the vertebrate embryo. This process takes place during a short developmental period, between days 10.5 and 12.5 in the mouse embryo. More specifically, HSCs arise from so-called hemogenic aortic endothelial cells in the ventral region of the dorsal aorta. In order to better characterize the hematopoietic microenvironment of the AGM, we explored the molecular signature of the tissues surrounding the dorsal aorta by combining approaches of laser microdissection, DNA chips and bioinformatics analyses. This study showed that the Ntrk2 and Ntrk3 genes, encoding two neurotrophin receptors (the TRKB and TRKC proteins), are preferentially expressed in the cells underlying the dorsal aorta. The main objective of my project is to comprehensively map the neurotrophin-mediated pathway in AGM using single-cell molecular biology, imaging and transcriptomic approaches. My results suggest that 1) TRKB and TRKC receptor expression is dynamic along the anteroposterior axis of the mouse embryo, 2) TRKB+ and TRKC+ populations exhibit phenotypic and molecular differences, and 3) the Expression of genes encoding neurotrophins (Bdnf, Ntf3 and Ntf5) is heterogeneous and associated with neural (Bdnf), mesenchymal (Bdnf, Ntf3 and Ntf5) and smooth muscle (Bdnf) cells. My results also support the existence of a population of neuro-mesenchymal cells in the subaortic region. Functional approaches are now being considered to study the functional role of the neurotrophin-mediated pathway in aortic hematopoiesis., Les premières cellules souches hématopoïétiques (CSH) émergent dans la région Aorte-Gonades-Mésonéphros (AGM) chez l’embryon de vertébrés. Ce processus se déroule au cours d’une courte période développementale, entre les jours 10,5 et 12,5 chez l’embryon de souris. Plus précisément, les CSH naissent à partir de cellules endothéliales aortiques dites hémogéniques dans la région ventrale de l’aorte dorsale. Afin de mieux caractériser le microenvironnement hématopoïétique de l’AGM, nous avons exploré la signature moléculaire des tissus entourant l’aorte dorsale en combinant des approches de microdissection laser, de puces à ADN et d’analyses bioinformatiques. Cette étude a montré que les gènes Ntrk2 et Ntrk3, codant deux récepteurs aux neurotrophines (les protéines TRKB et TRKC), sont préférentiellement exprimés dans les cellules sous-jacentes à l’aorte dorsale. Mon projet a pour objectif principal de cartographier de façon approfondie la voie médiée par les neurotrophines dans l’AGM à l’aide d’approches de biologie moléculaire, d’imagerie et de transcriptomique à l’échelle cellule unique. Mes résultats suggèrent que 1) l’expression des récepteurs TRKB et TRKC est dynamique le long de l’axe antéro-postérieur de l’embryon de souris, 2) les populations TRKB+ et TRKC+ présentent des différences phénotypiques et moléculaires et 3) l’expression des gènes codant les neurotrophines (Bdnf, Ntf3 et Ntf5) est hétérogène et associée à des cellules neurales (Bdnf), mésenchymateuses (Bdnf, Ntf3 et Ntf5) et musculaires lisses (Bdnf). Mes résultats renforcent également l’existence d’une population de cellules neuro-mésenchymateuses dans la région sous-aortique. Des approches fonctionnelles sont maintenant envisagées pour étudier le rôle fonctionnel de la voie médiée par les neurotrophines dans l’hématopoïèse aortique.

Neurotrophins (NTs) and their signal-transducing Trk receptors play a crucial role in the development and maintenance of specific neuronal subpopulations in nervous and sensory systems. NTs are supposed to regulate two sensory systems in fish, the inner ear and the lateral line system (LLS). The latter is one of the major mechanosensory systems in fish. Considering that annual fishes of the genus Nothobranchius, with their short life expectancy, have become a suitable model for aging studies and that the occurrence and distribution of neurotrophin Trk receptors have never been investigated in the inner ear and LLS of killifish (Nothobranchius guentheri), our study aimed to investigate the localization of neurotrophin-specific Trk receptors in mechanosensory systems of N. guentheri. For histological and immunohistochemical analysis, adult specimens of N. guentheri were processed using antibodies against Trk receptors and S100 protein. An intense immunoreaction for TrkA and TrkC was found in the sensory cells of the inner ear as well as in the hair cells of LLS. Moreover, also the neurons localized in the acoustic ganglia displayed a specific immunoreaction for all Trk receptors (TrkA, B, and C) analyzed. Taken together, our results demonstrate, for the first time, that neurotrophins and their specific receptors could play a pivotal role in the biology of the sensory cells of the inner ear and LLS of N. guentheri and might also be involved in the hair cells regeneration process in normal and aged conditions.

Neurotrophins and their receptors are relevant factors in controlling neuroblastoma growth and progression. The histone deacetylase (HDAC) inhibitor valproic acid (VPA) has been shown to downregulate TrkB and upregulate the p75NTR/sortilin receptor complex. In the present study, we investigated the VPA effect on the expression of the neurotrophin-3 (NT-3) receptor TrkC, a favorable prognostic marker of neuroblastoma. We found that VPA induced the expression of both full-length and truncated (TrkC-T1) isoforms of TrkC in human neuroblastoma cell lines without (SH-SY5Y) and with (Kelly, BE(2)-C and IMR 32) MYCN amplification. VPA enhanced cell surface expression of the receptor and increased Akt and ERK1/2 activation by NT-3. The HDAC inhibitors entinostat, romidepsin and vorinostat also increased TrkC in SH-SY5Y, Kelly and BE(2)-C but not IMR 32 cells. TrkC upregulation by VPA involved induction of RUNX3, stimulation of ERK1/2 and JNK, and ERK1/2-mediated Egr1 expression. In SH-SY5Y cell monolayers and spheroids the exposure to NT-3 enhanced the apoptotic cascade triggered by VPA. Gene silencing of both TrkC-T1 and p75NTR prevented the NT-3 proapoptotic effect. Moreover, NT-3 enhanced p75NTR/TrkC-T1 co-immunoprecipitation. The results indicate that VPA upregulates TrkC by activating epigenetic mechanisms and signaling pathways, and sensitizes neuroblastoma cells to NT-3-induced apoptosis.

Traumatic brain injury (TBI) remains the leading cause of long-term disability, which annually involves millions of individuals. Several studies on mammals reported that neurotrophins could play a significant role in both protection and recovery of function following neurodegenerative diseases such as stroke and TBI. This protective role of neurotrophins after an event of TBI has also been reported in the zebrafish model. Nevertheless, reparative mechanisms in mammalian brain are limited, and newly formed neurons do not survive for a long time. In contrast, the brain of adult fish has high regenerative properties after brain injury. The evident differences in regenerative properties between mammalian and fish brain have been ascribed to remarkable different adult neurogenesis processes. However, it is not clear if the specific role and time point contribution of each neurotrophin and receptor after TBI is conserved during vertebrate evolution. Therefore, in this review, I reported the specific role and time point of intervention for each neurotrophic factor and receptor after an event of TBI in zebrafish and mammals.

// Min Soo Kim 1 , Kwang Wook Suh 2 , Suntaek Hong 3 and Wook Jin 1, 4 1 Laboratory of Molecular Disease and Cell Regulation, Department of Biochemistry, School of Medicine, Gachon University, Incheon 406-840, Korea 2 Department of Surgery, Ajou University School of Medicine, Yeongto-gu, Suwon 443-380, Korea 3 Laboratory of Cancer Cell Biology, Department of Biochemistry, School of Medicine, Gachon University, Incheon 406-840, Korea 4 Gachon Medical Research Institute, Gil Medical Center, Incheon 405-760, Korea Correspondence to: Wook Jin, email: jinwo@gachon.ac.kr Keywords: TrkC, colorectal cancer, tumorigenicity, metastasis, EMT program Received: August 05, 2016 Accepted: April 03, 2017 Published: April 20, 2017 ABSTRACT The current work reveals that TrkC receptor is crucial to many aspects of tumorigenicity and metastasis of cancer. However, with only a few exceptions, such as colorectal cancer (CRC), where suppressing tumorigenic and metastatic ability via expression of TrkC as tumor suppressor have been proposed. These diverse lines of evidence led us to investigate whether TrkC is involved in CRC progression. By using mouse models and molecular biology analyses, we demonstrate that TrkC acts as an activator in tumorigenicity and metastasis of colorectal cancer. In this study, TrkC was frequently overexpressed in CRC cells, patients’ tumor samples and an azoxymethane/dextran sulphate sodium-induced mouse model of colitis-associated CRCs. TrkC expression was associated with a high-grade CRC phenotype, leading to significantly poorer survival. Also, TrkC expression promoted the acquisition of motility and invasiveness in CRC. Moreover, TrkC increased the ability to form tumor spheroids, a property associated with cancer stem cells. Importantly, knockdown of TrkC in malignant mouse or human CRC cells inhibited tumor growth and metastasis in a mouse xenograft model. Furthermore, TrkC enhanced metastatic potential and induced proliferation by aberrant gain of AKT activation and suppression of transforming growth factor (TGF)-β signalling. Interestingly, TrkC not only modulated the actions of TGF-β type II receptor, but also attenuated expression of this receptor. These findings reveal an unexpected physiological role of TrkC in the pathogenesis of CRC. Therefore, TrkC is a potential target for designing effective therapeutic strategies for CRC development.

Summary The vasculature is innervated by a network of peripheral afferents that sense and regulate blood flow. Here, we describe a system of non-peptidergic sensory neurons with cell bodies in the spinal ganglia that regulate vascular tone in the distal arteries. We identify a population of mechanosensitive neurons, marked by tropomyosin receptor kinase C (TrkC) and tyrosine hydroxylase in the dorsal root ganglia, which projects to blood vessels. Local stimulation of TrkC neurons decreases vessel diameter and blood flow, whereas systemic activation increases systolic blood pressure and heart rate variability via the sympathetic nervous system. Ablation of the neurons provokes variability in local blood flow, leading to a reduction in systolic blood pressure, increased heart rate variability, and ultimately lethality within 48 h. Thus, a population of TrkC+ sensory neurons forms part of a sensory-feedback mechanism that maintains cardiovascular homeostasis through the autonomic nervous system., Graphical abstract, Highlights • TrkC+/Th+ DRG neurons project to blood vessels • Local stimulation of TrkC+ DRG neurons decreases vessel diameter and blood flow • Systemic activation of TrkC+ DRG neurons increases blood pressure and heart rate • Ablation of TrkC+ neurons dysregulates cardiovascular homeostasis and is lethal, Morelli et al. identify a subpopulation of peripheral sensory neurons marked by TrkC and Th that projects to distal blood vessels. They demonstrate that these neurons regulate peripheral perfusion, blood pressure, and heart rate.

Tropomyosin receptor kinase (Trk) C contributes to the clinicopathology of a variety of human cancers, and new chimeric oncoproteins containing the tyrosine kinase domain of TrkC occur after fusion to the partner genes. Overexpression of TrkC and TrkC fusion proteins was observed in patients with a variety of cancers, including mesenchymal, hematopoietic, and those of epithelial cell lineage. Both microRNAs (miRNAs) and long non-coding RNAs (lncRNAs) were involved in the regulation of TrkC expression through transcriptional and posttranscriptional alteration. Aberrant activation of TrkC and TrkC fusion proteins markedly induces the epithelial-mesenchymal transition (EMT) program, growth rate, tumorigenic capacity via constitutive activation of Ras-MAP kinase (MAPK), PI3K-AKT, and the JAK2-STAT3 pathway. The clinical trial of TrkC or TrkC fusion-positive cancers with newly developed Trk inhibitors demonstrated that Trk inhibitors were highly effective in inducing tumor regression in patients who do not harbor mutations in the kinase domain. Recently, there has been a progressive accumulation of mutations in TrkC or the TrkC fusion protein detected in the clinic and its related cancer cell lines caused by high-throughput DNA sequencing. Despite given the high overall response rate against Trk or Trk fusion proteins-positive solid tumors, acquired drug resistance was observed in patients with various cancers caused by mutations in the Trk kinase domain. To overcome acquired resistance caused by kinase domain mutation, next-generation Trk inhibitors have been developed, and these inhibitors are currently under investigation in clinical trials.

Developmental cell death plays an important role in the construction of functional neural circuits. In vertebrates, the canonical view proposes a selection of the surviving neurons through stochastic competition for target-derived neurotrophic signals, implying an equal potential for neurons to compete. Here we show an alternative cell fitness selection of neurons that is defined by a specific neuronal heterogeneity code. Proprioceptive sensory neurons that will undergo cell death and those that will survive exhibit different molecular signatures that are regulated by retinoic acid and transcription factors, and are independent of the target and neurotrophins. These molecular features are genetically encoded, representing two distinct subgroups of neurons with contrasted functional maturation states and survival outcome. Thus, in this model, a heterogeneous code of intrinsic cell fitness in neighboring neurons provides differential competitive advantage resulting in the selection of cells with higher capacity to survive and functionally integrate into neural networks., Programmed cell death is an important part of tissue development, and traditionally it is considered that neuronal death is a stochastic process in response to neurotrophic factor deprivation. Here the authors show that for TrkC+ proprioreceptors, which neurons die is predetermined molecularly by how much TrkC is present, as well as by a gene expression signature.

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer worldwide and often has a poor prognosis. The present study investigated the role of the low affinity nerve growth factor receptor CD271 as a putative therapy target in HNSCC. Neurotrophins that bind to CD271 also have a high affinity for the tropomyosin receptor kinase family (Trk), consisting of TrkA, TrkB, and TrkC, which must also be considered in addition to CD271. A retrospective study and functional in vitro cell line tests (migration assay and cell sorting) were conducted in order to evaluate the relevance of CD271 expression alone and with regard to Trk expression. CD271 and Trks were heterogeneously expressed in human HNSCC. The vast majority of tumors exhibited CD271 and TrkA, whereas only half of the tumors expressed TrkB and TrkC. High expression of CD271-positive cells predicted a bad clinical outcome of patients with HNSCC and was associated with distant metastases. However, the human carcinomas that also expressed TrkC had a reduced correlation with distant metastases and better survival rates. In vitro, CD271 expression marked a subpopulation with higher proliferation rates, but proliferation was lower in tumor cells that co-expressed CD271 and TrkC. The CD271 inhibitor LM11A 31 suppressed cell motility in vitro. However, neither TrkA nor TrkB expression were linked to prognosis or cell proliferation. We conclude that CD271 is a promising candidate that provides prognostic information for HNSCC and could be a putative target for HNSCC treatment.

The 30-amino acid peptide Y-P30 corresponds to the N-terminus of the primate-specific, sweat gland-derived dermcidin prepropeptide. Previous work has revealed that Y-P30 enhances the interaction of pleiotrophin and syndecans-2/3, and thus represents a natural ligand to study this signaling pathway. In immature neurons, Y-P30 activates the c-Src and p42/44 ERK kinase pathway, increases the amount of F-actin in axonal growth cones, and promotes neuronal survival, cell migration and axonal elongation. The action of Y-P30 on axonal growth requires syndecan-3 and heparan sulfate side chains. Whether Y-P30 has the potential to influence dendrites and dendritic protrusions has not been explored. The latter is suggested by the observations that syndecan-2 expression increases during postnatal development, that syndecan-2 becomes enriched in dendritic spines, and that overexpression of syndecan-2 in immature neurons results in a premature morphological maturation of dendritic spines. Here, analysing rat cortical pyramidal and non-pyramidal neurons in organotypic cultures, we show that Y-P30 does not alter the development of the dendritic arborization patterns. However, Y-P30 treatment decreases the density of apical, but not basal dendritic protrusions at the expense of the filopodia. Analysis of spine morphology revealed an unchanged mushroom/stubby-to-thin spine ratio and a shortening of the longest decile of dendritic protrusions. Whole-cell recordings from cortical principal neurons in dissociated cultures grown in the presence of Y-P30 demonstrated a decrease in the frequency of glutamatergic mEPSCs. Despite these differences in protrusion morphology and synaptic transmission, the latter likely attributable to presynaptic effects, calcium event rate and amplitude recorded in pyramidal neurons in organotypic cultures were not altered by Y-P30 treatment. Together, our data suggest that Y-P30 has the capacity to decelerate spinogenesis and to promote morphological, but not synaptic, maturation of dendritic protrusions.

The present study was aimed to investigate the role and mechanism of neurotrophin-3 (NT-3) and its specific receptor tropomyosin receptor kinase C (TrkC) in the perineural invasion (PNI) process of the salivary adenoid cystic carcinoma (SACC). The co-cultured system between SACC cells and Schwann cells (SCs) was employed to detect the expression of NT-3 and TrkC. The results of ELISA, qRT-PCR and western blot showed that NT-3 was noticeably elevated in the co-cultured SACC-83 cells, while TrkC was increased in the co-cultured SCs. The results of scratch wound healing, migration, and 3D co-culture assays showed that the directional migration abilities of the co-cultured SACC-83 cells and SCs were significantly increased. Under the stimulation of NT-3, the directional motor ability of SACC-83 cells and SCs was significantly improved, and the apoptosis of SACC-83 cells and SCs were obviously inhibited. In addition, blocking TrkC by its specific inhibitor AZD7451 could significantly inhibit these effects. Immunohistochemistry staining showed that the positive expression of NT-3 (88.5%) and TrkC (92.3%) was significantly correlated with the PNI in SACC specimens (P < 0.05). Additionally, the high expression of NT-3 was significantly associated with the poor prognosis of SACC patients (P < 0.05). The present study indicated that NT-3/TrkC axis contributed to the PNI progression and the poor prognosis of SACC via regulating the interaction between SACC cells and SCs. Interruption of the interaction between SACC cells and SCs by blocking the NT-3/TrkC axis might be an effective strategy for anti-PNI therapy in SACC.

The neurotrophic tyrosine receptor kinase (NTRK) gene family encodes three tropomyosin receptor kinases (TRKA, TRKB, TRKC) that contribute to central and peripheral nervous system development and function.NTRKgene fusions are oncogenic drivers of various adult and paediatric tumours. Several methods have been used to detectNTRKgene fusions including immunohistochemistry, fluorescence in situ hybridisation, reverse transcriptase polymerase chain reaction, and DNA- or RNA-based next-generation sequencing. For patients with TRK fusion cancer, TRK inhibition is an important therapeutic target. Following the FDA approval of the selective TRK inhibitor, larotrectinib, as well as the ongoing development of multi-kinase inhibitors with activity in TRK fusion cancer, testing forNTRKgene fusions should become part of the standard diagnostic process. In this review we discuss the biology ofNTRKgene fusions, and we present a testing algorithm to aid detection of these gene fusions in clinical practice and guide treatment decisions.

INTRODUCTION: The maldevelopmental model of schizophrenia postulates pathological alterations in embryonal neurogenesis as the etiopathogenetic basis of schizophrenic psychoses. The neurotrophic factor hypothesis explains these neuropathological abnormalities as the result of alterations of the neurotrophin system caused by different mechanisms such as a genetic, infectious and traumatic factors. The tyrosine-kinase containing receptors trkB and trkC mediate growth-promoting effects of neurotrophins and respond to changes in neurotrophic factors availability. AIM: The aim of the present study was to establish the expression pattern of trkB and trkC in rat brain structures by a developmental model of schizophrenia. MATERIALS AND METHODS: On cryostat coronal brain sections of control and lesioned rats (after infusion of ibotenic acid solution bilaterally into the hippocampal formation), immunoreactions for trkB and trkC were performed. RESULTS: We found diminished expression of trkB and trkC in the hippocampal formation of lesioned animals compared to the controls. Quantitative measurements of immunohistochemical reactions intensity and statistical analysis confi rmed the reduced immunoreactivity for antigens under study (trkB and trkC) in the positive hippocampal neurons of 56-day-old lesioned rats compared to the control animals. CONCLUSION: The observed downregulation of neurotrophic factor receptors expression may compromise the function and plasticity of hippocampal formation in schizophrenic brains.

Trk neurotrophin receptors are transmembrane tyrosine kinase proteins known as TrkA, TrkB, and TrkC. TrkA is the high affinity receptor for nerve growth factor, TrkB is the one for both brain-derived neurotrophic factor and neurotrophin-4, and TrkC is the preferred receptor for neurotrophin-3. In the adult mammalian brain, neurotrophins are important regulators of neuronal function and plasticity. This study is based on Nothobranchius furzeri, a teleost fish that is becoming an ideal candidate as animal model for aging studies because its life expectancy in captivity is of just 3 months. In adult N. furzeri, all three investigated neurotrophin Trk receptors were immunohistochemically detected in each brain region. TrkA positive neuronal perikarya were localized in the dorsal and ventral areas of the telencephalon and in the cortical nucleus; TrkB immunoreactivity was observed in neuronal perikarya of the dorsal and ventral areas of the telencephalon, the diffuse inferior lobe of the hypothalamus, and Purkinje cells; TrkC positive neuronal perikarya were detected in the most aboral region of the telencephalon, in the magnocellular preoptic nucleus and in few neurons dispersed in the hypothalamus. Numerous positive fibers were widely distributed throughout the brain. Radial glial cells lining the mesencephalic and rhombencephalic ventricles showed immunoreactivity to all three Trks. These findings suggest an involvement of neurotrophins in many aspects of biology of adult N. furzeri. Microsc. Res. Tech Trk neurotrophin receptors are transmembrane tyrosine kinase proteins known as TrkA, TrkB, and TrkC. TrkA is the high affinity receptor for nerve growth factor, TrkB is the one for both brain-derived neurotrophic factor and neurotrophin-4, and TrkC is the preferred receptor for neurotrophin-3. In the adult mammalian brain, neurotrophins are important regulators of neuronal function and plasticity. This study is based on Nothobranchius furzeri, a teleost fish that is becoming an ideal candidate as animal model for aging studies because its life expectancy in captivity is of just 3 months. In adult N. furzeri, all three investigated neurotrophin Trk receptors were immunohistochemically detected in each brain region. TrkA positive neuronal perikarya were localized in the dorsal and ventral areas of the telencephalon and in the cortical nucleus; TrkB immunoreactivity was observed in neuronal perikarya of the dorsal and ventral areas of the telencephalon, the diffuse inferior lobe of the hypothalamus, and Purkinje cells; TrkC positive neuronal perikarya were detected in the most aboral region of the telencephalon, in the magnocellular preoptic nucleus and in few neurons dispersed in the hypothalamus. Numerous positive fibers were widely distributed throughout the brain. Radial glial cells lining the mesencephalic and rhombencephalic ventricles showed immunoreactivity to all three Trks. These findings suggest an involvement of neurotrophins in many aspects of biology of adult N. furzeri. © 2011 Wiley Periodicals, Inc.

Gene rearrangements resulting in the aberrant activity of tyrosine kinases have been identified as drivers of oncogenesis in a variety of cancers. The tropomyosin receptor kinase (TRK) family of tyrosine receptor kinases is emerging as an important target for cancer therapeutics. The TRK family contains three members, TRKA, TRKB, and TRKC, and these proteins are encoded by the genes NTRK1, NTRK2, and NTRK3, respectively. To activate TRK receptors, neurotrophins bind to the extracellular region stimulating dimerization, phosphorylation, and activation of downstream signaling pathways. Major known downstream pathways include RAS/MAPK/ERK, PLCγ, and PI3K/Akt. While being rare in most cancers, TRK fusions with other proteins have been well-established as oncogenic events in specific malignancies, including glioblastoma, papillary thyroid carcinoma, and secretory breast carcinomas. TRK protein amplification as well as alternative splicing events have also been described as contributors to cancer pathogenesis. For patients harboring alterations in TRK expression or activity, TRK inhibition emerges as an important therapeutic target. To date, multiple trials testing TRK-inhibiting compounds in various cancers are underway. In this review, we will summarize the current therapeutic trials for neoplasms involving NTKR gene alterations, as well as the promises and setbacks that are associated with targeting gene fusions.

BETA2/NeuroD1 has been shown to play a major role in terminal differentiation of the pancreatic and enteroendocrine cells, as well as for the survival of photoreceptors. Here, we report that the loss of BETA2/NeuroD1 affected the cerebellar development with a major reduction of granule cell number. However, there is a differential reduction of granule cells along the anterior and posterior axis of the cerebellum; while the reduction of granule cells in the anterior lobes is substantial, there is an almost complete loss of granule cells in the posterior compartment. To understand the mechanism for this anterior–posterior difference, we carried out detailed analyses. We found that both BETA2/NeuroD1 and its direct target TrkC, expression commence earlier in the posterior part than those in the anterior part during cerebellum development. Consequently, loss of BETA2/NeuroD1 enhances granule cell death in the posterior 2 days earlier than the anterior. Furthermore, the higher rate of cell death in the posterior of the cerebellum is concomitant with the reduction of TrkC expression in knockout mice. Thus, our data indicate that preferential expression of BETA2/NeuroD1 and TrkC in posterior lobes explains the earlier start of cell apoptosis and preferential loss of granule cells in the posterior lobes.

There is little information about neurotrophic regulation in the developing rat hypothalamus. In the present study, we therefore examined the expression of neurotrophin receptor TrkC in the developing forebrain and hypothalamus. In situ hybridization of coronal sections revealed that on the 15th day of gestation, trkC messenger RNA expression is homogeneously distributed over the neocortex, septum, thalamus, hypothalamus, hippocampus, rhinencephalon and the amygdala. Exceptions were the anteroventral nucleus of the hypothalamus and the striatum, which showed higher levels of trkC messenger RNA expression, and the germinal zones which were devoid of trkC messenger RNA. After birth, the homogeneous staining pattern changes into a heterogeneous staining pattern like that found in adulthood. TrkC expression is observed in the area of the suprachiasmatic nucleus as early as E17 and continues until adulthood. The presence of the TrkC receptor in the E17 suprachiasmatic nucleus suggests that neurotrophin-3 plays a role in development of this structure and that application of neurotrophin-3 could stimulate neuronal survival and neuritic outgrowth in a suprachiasmatic nucleus transplantation model.

NEUROTROPHIN-3 (NT3) or TrkC null mutant mice were examined for the presence of muscle spindles. Muscles of mastication, but not limbs, contained spindles in newborn and adolescent mutants. The intramuscular distribution and morphological properties of spindles in mutant masticatory muscles were indistinguishable from those of wild-type spindles. Intrafusal fibers of NT3- or trkC-deficient spindles expressed the slow-tonic isoform of myosin heavy chains, characteristic of wild-type spindles. Sensory nerve endings were observed in spindles of mutants by electron microscopy. Thus, NT3 or trkC, which is expressed in wild-type spindles, may serve functions other than those related to spindle assembly. Presumably, proprioceptive neurons innervating jaw muscles are dependent on factors other than NT3 for survival and maintenance. (C) 1998 Rapid Science Ltd.

The neurotrophin receptor TrkC was recently identified as a dependence receptor, and, as such, it triggers apoptosis in the absence of its ligand, NT-3. Indeed cells that express these receptors are thought to be dependent on ligand availability for their survival, a mechanism that inhibits uncontrolled tumor cell proliferation and migration. TrkC, as a classic tyrosine kinase receptor, is generally considered to be a proto-oncogene. We show that TrkC expression is down-regulated in a large fraction of human colorectal cancers, mainly through promoter methylation. Moreover, we show that TrkC silencing by promoter methylation is a selective advantage for colorectal cell lines to limit tumor cell death. Furthermore, reestablished TrkC expression in colorectal cancer cell lines is associated with tumor cell death and inhibition of in vitro characteristics of cell transformation, as well as in vivo tumor growth. Together, these data support the conclusion that TrkC is a colorectal cancer tumor suppressor. TrkC triggers apoptosis in the absence of its ligand NT-3 : the molecular mechanism for apoptotic engagement involves the double cleavage of the receptor's intracellular domain, leading to the formation of a proapoptotic fragment (TrkC KF). We show that TrkC KF interfacts with Cobra1, a putative cofactor of BRCA1, and that Cobra1 is required for TrkC-induced apoptosis. Cobra1 shuttles TrkC KF to the mitochondria, where it promotes apoptosome-dependent apoptosis. Thus, we propose that, in the absence of NT-3, the proteolytic cleavage of TrkC leads to the release of a killer fragment that triggers mitochondria-dependent apoptosis via the recruitment of Cobra1, Le récepteur à neurotrophine TrkC a été identifié comme étant un récepteur à dépendance : en l'absence de son ligand NT-3, il déclenche l'apoptose. En effet, la survie des cellules qui expriment ces récepteurs dépend de la disponibilité en ligand, un mécanisme qui inhibe la prolifération incontrôlée et la migration des cellules tumorales. TrkC, en tant que récepteur à tyrosine kinase, est généralement considéré comme un proto-oncogène. Or nous montrons que l'expression TrkC est diminuée dans une grande fraction des cancers colorectaux humains, principalement par méthylation du promoteur de TrkC. En outre, ce mécanisme confère un avantage sélectif aux lignées cellulaires colorectales pour inhiber la mort des cellules tumorales. De plus, la réexpression de TrkC dans les lignées tumorales colorectales est associée à la mort des cellules tumorales et à l'inhibition in vitro des caractéristiques de transformation cellulaire, et in vivo de la croissance tumorale. Ensemble, ces données permettent de conclure que TrkC est un gène suppresseur de tumeur dans le cancer colorectal. Le mécanisme moléculaire par lequel TrkC déclenche l'apoptose implique le clivage de son domaine intracellulaire, ce qui libère un fragment pro-apoptotique (TrkC KF). Nous montrons que TrkC KF interagit avec Cobra1, un cofacteur de BRCA1, et que Cobra1 est nécessaire à l'apoptose induite par TrkC. Cobra1 conduit TrkC KF à la mitochondrie, où il favorise l'apoptose apoptosome-dépendante. Ainsi, nous proposons qu'en l'absence de NT-3, le clivage protéolytique de TrkC conduit à la libération d'un fragment tueur qui déclenche l'apoptose mitochondriale, via le recrutement de Cobra1

The neurotrophin receptor TRKC was initially shown to induce apoptosis in settings of lackof its ligand, NT-3. This cell death was described to be important in the regulation of neuronalsurvival during sympathetic nervous system formation and finally it was linked with severaltypes of cancer. During my thesis I focused on the molecular characterization of the signaling cascade leadingto TRKC-induced apoptosis. Importantly, in order to kill, TRKC is double-cleaved bycaspases in its intracellular domain releasing a pro-apoptotic fragment, named TRKC KF(Killer Fragment). Using a yeast two-hybrid screen we identified several potential interactingpartners for TRKC KF. Initially, i focused on COBRA1, a cofactor of BRCA1.I show here that COBRA1 is requisite for TRKC-induced cell death both in vitro and in vivo,on primary neurons. COBRA1 seems to stabilize and accumulate TRKC KF at themitochondria, where TRKC KF induces the activation of BAX and therefore cytochrome crelease. Therefore, it looks that TRKC-induced cell death is dependent on the intrinsicpathway of apoptosis. During my thesis, I also took part in two projects characterizing the role of TRKC as aconditional tumor suppressor in neuroblastoma and colon cancer. We showed that inneuroblastoma tumors the pro-apoptotic function of TRKC is impaired due to an autocrineproduction loop of NT-3, which can be targeted as a therapeutic strategy. In colon cancer, wedescribed another mechanism by which tumor cells evade TRKC-induced apoptosis, morespecifically a loss of TRKC expression due to promoter hypermethylation, Le récepteur à neurotrophine TRKC a initialement été montré comme induisant la mortcellulaire par apoptose en l’absence de son ligand, NT-3. Cette mort cellulaire a tout d’abordété décrite comme étant importante dans la régulation de la survie neuronale, pendant laformation du système nerveux sympathique. Plus tard, elle a été montrée comme étantimpliquée dans différents types de cancer.Au cours de ma thèse, je me suis concentré sur la caractérisation moléculaire de la cascade designalisation conduisant à l’induction de l’apoptose par TRKC. Afin d’induire l’apoptose, ledomaine intracellulaire de TRKC est clivé par les caspases en deux sites, ce qui entraine lagénération d’un fragment pro-apoptotique, TRKC KF (Killer Fragment). Plusieurs partenairespotentiels de TRKC KF ont été identifiés lors d’un crible double-hybride. Initialement, je mesuis focalisé sur l’un d’eux, COBRA1, un cofacteur de BRCA1.Je montre ici que COBRA1 est requis pour la mort cellulaire induite par TRKC, à la fois invitro et in vivo, dans des neurones primaires. COBRA1 semble stabiliser et accumuler TRKCKF à la mitochondrie, où TRKC KF entraine l’activation de BAX et ensuite le relargage ducytochrome c. En conclusion, il semblerait que la mort cellulaire induite par TRKC estdépendante de la voie apoptotique intrinsèque. J’ai aussi pris part à deux autres projets décrivant le rôle de TRKC comme un suppresseur de tumeur potentiel dans le neuroblastome et le cancer colorectal. Nous avons montré dans leneuroblastome que la fonction pro-apoptotique de TRKC est invalidée par une boucleautocrine de production de NT3, qui peut être ciblée lors d’une approche thérapeutique. Dansle cancer colorectal, nous avons décrit un second mécanisme par lequel les cellules tumoraleséchappent à l’apoptose induite par TrkC. Il s’agit d’une perte de l’expression de TrkC due àune hypermethylation du promoteur.

The trk family of tyrosine protein kinase genes serves crucial roles for the development of the nervous system and the survival of neurons. The members of this gene family, trk, trkB and trkC, bind a distinct neurotrophin of the nerve growth factor (NGF) gene family, and trigger the intracellular signals which elicit trophic and differentiating effects on neurons. Adding to these neurotrophic receptor kinases, the truncated forms without the tyrosine kinase domain have been cloned and characterized. It has been thought that the existence of truncated forms is limited to trkB; however, very recently the truncated trkC has been cloned in rat [(1993) Neuron 10, 963-974; (1993) Neuron 10, 975-990]. We independently approached and molecularly cloned a truncated form which belongs to the chicken trkC. The truncated trkC possesses the binding and the transmembrane domains but not the tyrosine kinase domain. Northern blot analysis shows that the truncated form is preferentially expressed in the adult central nervous system. The truncated form is scarcely expressed during the embryonic stages. The conservation of the truncated trkC beyond species suggests they have specific functions.

This is an open-access article subject to an exclusive license agreement between the authors and the Frontiers Research Foundation., Panic disorder is a highly prevalent neuropsychiatric disorder that shows co-occurrence with substance abuse. Here, we demonstrate that TrkC, the high-affinity receptor for neurotrophin-3, is a key molecule involved in panic disorder and opiate dependence, using a transgenic mouse model (TgNTRK3). Constitutive TrkC overexpression in TgNTRK3 mice dramatically alters spontaneous firing rates of locus coeruleus (LC) neurons and the response of the noradrenergic system to chronic opiate exposure, possibly related to the altered regulation of neurotrophic peptides observed. Notably, TgNTRK3 LC neurons showed an increased firing rate in saline-treated conditions and profound abnormalities in their response to met5-enkephalin. Behaviorally, chronic morphine administration induced a significantly increased withdrawal syndrome in TgNTRK3 mice. In conclusion, we show here that the NT-3/TrkC system is an important regulator of neuronal firing in LC and could contribute to the adaptations of the noradrenergic system in response to chronic opiate exposure. Moreover, our results indicate that TrkC is involved in the molecular and cellular changes in noradrenergic neurons underlying both panic attacks and opiate dependence and support a functional endogenous opioid deficit in panic disorder patients., This work was funded by the Spanish Ministry of Education and Sciences SAF2007-31093-E, SAF2007-60827, and SAF2008-03612, 2009SGR1313 and Health (PI082038), Fundación Areces, Marató TV3, Phecomp (EU LSHM-CT-2007-037669; 037627-AnEUploidy), Ministerio de Salud y Consumo (RTA G03/005 and PI05/0513, PI082038), University of the Basque Country (1/UPV 0026.327-E-15924/2004 and GIU07/46), Plan Nacional sobre Drogas (PNDMSC 2005) and CIBERER. Patricia Murtra is a scientific researcher supported by the Juan de la Cierva program of Ministerio de Ciencia y Tecnología. Teresa Zamalloa was supported by a predoctoral fellowship from the Basque Government.

The basic-helix-loop-helix transcription factor HeyL is expressed at high levels by neural crest progenitor cells (NCPs) that give rise to neurons and glia in dorsal root ganglia (DRG). Since HeyL expression was observed in these NCPs during the period of neurogenesis, we generated HeyL null mutants to help examine the factor's role in ganglion neuronal specification. Homozygous null mutation of HeyL reduced the number of TrkC+ neurons in DRG at birth including the subpopulation that expresses the ETS transcription factor ER81. Conversely, null mutation of the Hey paralog, Hey1, increased the number of TrkC+ neurons. Null mutation of HeyL increased expression of the Hey paralogs Hey1 and Hey2, suggesting that HeyL normally inhibits their expression. Double null mutation of both Hey1 and HeyL rescued TrkC+ neuron numbers to control levels. Thus, the balance between HeyL and Hey1 expression regulates the differentiation of a subpopulation of TrkC+ neurons in the DRG.

Neurotrophins and their receptors are key molecules in the development of thenervous system. Neurotrophin-3 binds preferentially to its high-affinity receptorNTRK3, which exists in two major isoforms in humans, the full-length kinaseactiveform (150 kDa) and a truncated non-catalytic form (50 kDa). The twovariants show different 3'UTR regions, indicating that they might be differentiallyregulated at the post-transcriptional level. In this work we explore howmicroRNAs take part in the regulation of full-length and truncated NTRK3,demonstrating that the two isoforms are targeted by different sets of microRNAs.We analyze the physiological consequences of the overexpression of some of theregulating microRNAs in human neuroblastoma cells. Finally, we providepreliminary evidence for a possible involvement of miR-124 - a microRNA with noputative target site in either NTRK3 isoform - in the control of the alternativespicing of NTRK3 through the downregulation of the splicing repressor PTBP1., Las neurotrofinas y sus receptores constituyen una familia de factores crucialespara el desarrollo del sistema nervioso. La neurotrofina 3 ejerce su funciónprincipalmente a través de una unión de gran afinidad al receptor NTRK3, del cualse conocen dos isoformas principales, una larga de 150KDa con actividad de tipotirosina kinasa y una truncada de 50KDa sin dicha actividad. Estas dos isoformasno comparten la misma región 3'UTR, lo que sugiere la existencia de unaregulación postranscripcional diferente. En el presente trabajo se ha exploradocomo los microRNAs intervienen en la regulación de NTRK3, demostrando que lasdos isoformas son reguladas por diferentes miRNAs. Se han analizado lasconsecuencias fisiológicas de la sobrexpresión de dichos microRNAs utilizandocélulas de neuroblastoma. Finalmente, se ha estudiado la posible implicación delmicroRNA miR-124 en el control del splicing alternativo de NTRK3 a través de laregulación de represor de splicing PTBP1.

Neurotrophins (NTs) belong to a family of growth factors, which control the development, maintenance, and apoptotic death of neurons and also fulfill multiple regulatory functions outside the nervous system. Biological effects induced by NTs strongly depend on the pattern of NT receptor/co-receptors expression in target cells, as well as on the set of intracellular adaptor molecules that link NT signalling to distinct biochemical pathways. In this review, we summarize data on the molecular mechanisms underlying the involvement of NTs in the control of non-neuronal functions in normal skin (e.g. keratinocyte proliferation, melanocyte development and apoptosis, hair growth). We also review the data on the role for NTs and their receptors in a number of pathological skin conditions (stress-induced hair loss, psoriasis, atopic dermatitis). Although additional efforts are required to fully understand mechanisms underlying the involvement of NTs and their receptors in controlling functions of normal and pathologically altered skin cells, substantial evidence suggests that modulation of NT signalling by NTs receptor agonists/antagonists may be developed as intervention modalities in distinct skin and hair growth pathologies.

The zinc finger protein Klf7 and POU homeodomain protein Brn3a are each required for efficient transcription of TrkA in primary sensory neurons. In this study, we examined whether these transcription factors act in concert to regulate TrkA expression. In vitro, Brn3a and Klf7 can synergistically activate the TrkA enhancer. In vivo, precursor cells that are destined to become TrkA(+) neurons are born. However, both Brn3a and Klf7 are dispensable for the initiation of TrkA expression. At E12.5, while TrkA expression is unaffected in Brn3a−/− trigeminal ganglia and only slightly decreased in Klf7−/− trigeminal ganglia, it is severely reduced in the double mutant Brn3a−/−;Klf7−/− trigeminal ganglia. At birth, all Trk(+) neurons are lost in Brn3a−/−;Klf7−/− trigeminal ganglia. We further demonstrate that the TrkA enhancer is inactive in Brn3a−/−;Klf7−/− trigeminal ganglia. Thus, cooperation between these two transcription factors is required for endogenous TrkA gene expression and the survival of nociceptive sensory neurons.

Previous studies have analyzed the expression of different members of the neurotrophin family and theirtrk receptors in glial cultures composed mainly or exclusively of type-1 astrocytes, whereas only partial data have been published on other cultured glial types. In this article we compare the mRNA levels for neurotrophins (NGF, BDNF, NT-3, NT-4) and their high-affinity receptors (trkA,trkB,trkC) in cultures enriched in specific glial types, such as microglia, type-1 astroglia, and cells of the O/2A lineage (type-2 astroglia and oligodendroglia). Relatively high levels of NGF mRNA (comparable to those observed in adult rat cerebral cortex) are present in all types of cultured glial cells, except for a low level of expression in cultures enriched in microglial cells. In contrast, BDNF mRNA is undetectable in all cultures examined. NT-3 and NT-4 mRNA molecules, at a level equal to that observed in adult rat cerebral cortex, are easily detected in type-1 astrocyte cultures, whereas their hybridization signals are undetectable in cells of the O/2A lineage and in microglial cultures. The analysis of neurotrophin receptor mRNAs confirms the absence oftrkA mRNA, the presence of relatively high levels oftrkB mRNA (70–100% of cerebral cortex values), and low levels oftrkC mRNA (10–18% of cerebral cortex values) in both cultured astroglial and oligodendroglial cells. Only very low levels oftrkB andtrkC mRNAs are observed in microglial cultures. Although cultured glial cells express mainly mRNAs encoding for the truncated form oftrkB andtrkC, a low level of mRNA encoding for the full-length catalytic form of these receptors is detected by the sensitive ribonuclease protection assay. However, NT-3 and NT-4 increasezif/268 expression in oligodendroglial cultures, but not in type-1 astroglial cultures. The presence of these transcripts has been also examined in white matter regions that are devoid of neuronal cell bodies and enriched in glial cells (optic nerve and the corpus callosum). Both corpus callosum and optic nerve show the presence of NGF, NT-3, and NT-4 mRNA, whereas BDNF mRNA level is very low or undetectable;trkA mRNA is absent, although both the truncated and full-lengthtrkB andtrkC mRNA are detected. In conclusion, in vivo (central nervous system white matter) and in vitro (glial cultures) results support the hypothesis that cells of the glial lineage can be both a source of neurotrophins and a cellular target for their actions.

In the present work we determined, by Northern blotting, ribonuclease assay and in situ hybridization, the level of multiple trkB and trkC transcripts at different times after ibotenic acid-induced neuronal injury in the rat hippocampus. All the transcripts (7.0-7.5, 2.4 and 1.8 kb) encoding the truncated TrkB receptor are coordinately up-regulated following neurotoxic injury, with a time-course similar to that observed for the glial fibrillary acidic protein mRNA, a molecular marker of reactive astrocytes. The highest level of induction was observed for the 2.4 kb mRNA level. The 1.8 kb mRNA, whose relative level is higher in astroglial cultures compared to normal brain tissue, is detectable only in the gliotic hippocampus. The 9 kb trkB mRNA, which encodes the full-length TrkB receptor, rapidly decreases with a time-course similar to that previously observed for other neuronal markers. In situ hybridization studies show that the increased mRNA level per cell is a major determinant in the up-regulation of truncated trkB expression. A decrease of truncated and full-length trkC mRNA was observed in the neuron-depleted astroglia-enriched hippocampus, suggesting that this mRNA is mainly localized in the neuronal layers and that no induction of its expression occurs in reactive astrocytes.

In this study we have shown, by in situ hybridization and RNase protection assay, a significant trkC mRNA increase confined to the dentate gyrus of hippocampus, both after seizures induced by intracerebroventricular injection of kainic acid and bicuculline. Moreover, after bicuculline treatment we observed an earlier increase of trkC mRNA level, which peaked after 3 h and returned back to normal levels by 12 h. In contrast, the kainic acid treatment produced a delayed increase of trkC mRNA, which initiated after 6 h, peaked at 12 h, and returned to normal levels at 24 h. This increase, which involves also trkC mRNA receptor with tyrosine kinase activity, was mediated by non-NMDA receptors and counteracted by GABA potentiating agent diazepam. Using embryonic neuronal cultures from cerebral hemispheres, including hippocampus, we found that glutamate receptor agonists, including glutamate, kainate, NMDA, and t-ACPD, increase trkC mRNA levels with the following rank order of efficacy: NMDA > t-ACPD > kainic acid > glutamate. In conclusion, our data show that trkC mRNA expression in granule cells of the hippocampus dentate gyrus is increased during seizure activity and that it is mediated by non-NMDA receptors.

By northern blot analysis and ribonuclease protection assay, we observed the presence of a high level of trkB mRNA in primary brain cultures devoid of neuronal cells and highly enriched in glial fibrillary acidic protein-positive astroglial cells prepared from newborn rat cerebral hemispheres, cerebral cortex, hippocampus, and striatum. In primary astroglial cultures, the more abundant trkB transcripts code for the truncated receptor without tyrosine kinase activity; probes specific for the full-length trkB mRNA did not detect any signal in northern blot analysis. By the sensitive ribonuclease protection assay, we could show the presence of trkC mRNA in cultured astrocytes, whereas no trkA mRNA was detected. We confirmed the presence of relatively high levels of nerve growth factor and neurotrophin-3 mRNA, and very low basal level of brain-derived neurotrophic factor mRNA. Moreover, we demonstrated that another member of the neurotrophin family, neurotrophin-4, is also expressed in cultured astroglial cells. In view of the fact that many functional receptors for conventional neurotransmitters or neuropeptides present on astroglial cells may act via the adenylate cyclase system, we studied also the effect of agents able to increase the intracellular cyclic AMP concentration. A sharp increase in the trkB mRNA level was observed after treatment of primary astroglial cultures with dibutyryl cyclic AMP, 8-bromo-cyclic AMP, or the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine. On the contrary, trkC mRNA levels were unaffected by treatment with cyclic AMP-elevating agents. All the neurotrophin mRNAs examined, except neutrophin-4, were increased by 3-isobutyl-1-methylxanthine treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

No enteric neurons or glia develop in the gut below the rostral foregut in mice lacking glial cell line-derived neurotrophic factor (GDNF) or Ret. We analyzed the nature and age dependence of the effects of GDNF and, for comparison, those of NT-3, on the in vitro development of the precursors of enteric neurons and glia. Positive and negative immunoselection with antibodies to p75(NTR) were used to isolate crest-derived and crest-depleted populations of cells from the fetal rat bowel at E12, 14, and 16. Cells were typed immunocytochemically. GDNF stimulated the proliferation of nestin-expressing precursor cells isolated at E12, but not at E14-16. GDNF promoted the development of peripherin-expressing neurons (E12 >> E14-16) and expression of TrkC. GDNF inhibited expression of S-100-expressing glia at E14-16. NT-3 did not affect cells isolated at E12, never stimulated precursors to proliferate, and promoted glial as well as neuronal development at E14-16. GFRalpha-1 was expressed both by crest- and non-crest-derived cells, although only crest-derived cells anchored GFRalpha-1 and GFRalpha-2 (GFRalpha-1 >> GFRalpha-2). GDNF increased the number of neurons anchoring GFRalpha-1. GFRalpha-1 is immunocytochemically detectable in neurons of the E13 intestine and persists in adult neurons of both plexuses. We suggest that GDNF stimulates the proliferation of an early (E12) NT-3-insensitive precursor common to enteric neurons and glia; by E14, this common precursor is replaced by specified NT-3-responsive neuronal and glial progenitors. GDNF exerts a neurotrophic, but not a mitogenic, effect on the neuronal progenitor. The glial progenitor is not maintained by GDNF.

NEUROTROPHIN-3 (NT3) or TrkC null mutant mice were examined for the presence of muscle spindles. Muscles of mastication, but not limbs, contained spindles in newborn and adolescent mutants. The intramuscular distribution and morphological properties of spindles in mutant masticatory muscles were indistinguishable from those of wild-type spindles. Intrafusal fibers of NT3- or trkC-deficient spindles expressed the slow-tonic isoform of myosin heavy chains, characteristic of wild-type spindles. Sensory nerve endings were observed in spindles of mutants by electron microscopy. Thus, NT3 or trkC, which is expressed in wild-type spindles, may serve functions other than those related to spindle assembly. Presumably, proprioceptive neurons innervating jaw muscles are dependent on factors other than NT3 for survival and maintenance. (C) 1998 Rapid Science Ltd.