A mammalian homolog of unc-53 is regulated by all-trans retinoic acid in neuroblastoma cells and embryos

Mutated neuron navigator 3 as a candidate gene for a rare neurodevelopmental disorder

BACKGROUND

Neuron navigator 3 (NAV3) is characterized as one of the neuron navigator family (NAV1, NAV2, NAV3) proteins predominantly expressed in the nervous system. The NAV3-encoded protein comprises a conserved AAA and coiled-coil domains characteristic of ATPases, which are associated with different cellular activities.

METHODS

We describe a Saudi proband presenting a complex recessive neurodevelopmental disorder (NDD). Whole exome sequencing (WES) followed by Sanger sequencing, 3D protein modeling and RT-qPCR was performed.

RESULTS

WES revealed a bi-allelic frameshift variant (c.2604_2605delAG; p.Val870SerfsTer12) in exon 12 of the NAV3 gene. Furthermore, RT-qPCR revealed a significant decrease in the NAV3 mRNA expression in the patient sample, and 3D protein modeling revealed disruption of the overall secondary structure.

CONCLUSION

For the time, we associate a bi-allelic variant in the NAV3 gene causing NDD in humans.

Neuron navigators: A novel frontier with physiological and pathological implications

Neuron navigators are microtubule plus-end tracking proteins containing basic and serine rich regions which are encoded by neuron navigator genes (NAVs). Neuron navigator proteins are essential for neurite outgrowth, neuronal migration, and overall neurodevelopment along with some other functions as well. The navigator proteins are substantially expressed in the developing brain and have been reported to be differentially expressed in various tissues at different ages. Over the years, the research has found neuron navigators to be implicated in a spectrum of pathological conditions such as developmental anomalies, neurodegenerative disorders, neuropathic pain, anxiety, cancers, and certain inflammatory conditions. The existing knowledge about neuron navigators remains sparse owing to their differential functions, undiscovered modulators, and unknown molecular mechanisms. Investigating the possible role of neuron navigators in various physiological processes and pathological conditions pose as a novel field that requires extensive research and might provide novel mechanistic insights and understanding of these aspects.

Loss of Neuron Navigator 2 Impairs Brain and Cerebellar Development

Cerebellar hypoplasia and dysplasia encompass a group of clinically and genetically heterogeneous disorders frequently associated with neurodevelopmental impairment. The Neuron Navigator 2 (NAV2) gene (MIM: 607,026) encodes a member of the Neuron Navigator protein family, widely expressed within the central nervous system (CNS), and particularly abundant in the developing cerebellum. Evidence across different species supports a pivotal function of NAV2 in cytoskeletal dynamics and neurite outgrowth. Specifically, deficiency of Nav2 in mice leads to cerebellar hypoplasia with abnormal foliation due to impaired axonal outgrowth. However, little is known about the involvement of the NAV2 gene in human disease phenotypes. In this study, we identified a female affected with neurodevelopmental impairment and a complex brain and cardiac malformations in which clinical exome sequencing led to the identification of NAV2 biallelic truncating variants. Through protein expression analysis and cell migration assay in patient-derived fibroblasts, we provide evidence linking NAV2 deficiency to cellular migration deficits. In model organisms, the overall CNS histopathology of the Nav2 hypomorphic mouse revealed developmental anomalies including cerebellar hypoplasia and dysplasia, corpus callosum hypo-dysgenesis, and agenesis of the olfactory bulbs. Lastly, we show that the NAV2 ortholog in Drosophila, sickie (sick) is widely expressed in the fly brain, and sick mutants are mostly lethal with surviving escapers showing neurobehavioral phenotypes. In summary, our results unveil a novel human neurodevelopmental disorder due to genetic loss of NAV2, highlighting a critical conserved role of the NAV2 gene in brain and cerebellar development across species.

The Neuron Navigators: Structure, function, and evolutionary history

Neuron navigators (Navigators) are cytoskeletal-associated proteins important for neuron migration, neurite growth, and axon guidance, but they also function more widely in other tissues. Recent studies have revealed novel cellular functions of Navigators such as macropinocytosis, and have implicated Navigators in human disorders of axon growth. Navigators are present in most or all bilaterian animals: vertebrates have three Navigators (NAV1-3), Drosophila has one (Sickie), and Caenorhabditis elegans has one (Unc-53). Structurally, Navigators have conserved N- and C-terminal regions each containing specific domains. The N-terminal region contains a calponin homology (CH) domain and one or more SxIP motifs, thought to interact with the actin cytoskeleton and mediate localization to microtubule plus-end binding proteins, respectively. The C-terminal region contains two coiled-coil domains, followed by a AAA+ family nucleoside triphosphatase domain of unknown activity. The Navigators appear to have evolved by fusion of N- and C-terminal region homologs present in simpler organisms. Overall, Navigators participate in the cytoskeletal response to extracellular cues via microtubules and actin filaments, in conjunction with membrane trafficking. We propose that uptake of fluid-phase cues and nutrients and/or downregulation of cell surface receptors could represent general mechanisms that explain Navigator functions. Future studies developing new models, such as conditional knockout mice or human cerebral organoids may reveal new insights into Navigator function. Importantly, further biochemical studies are needed to define the activities of the Navigator AAA+ domain, and to study potential interactions among different Navigators and their binding partners.

Sequential events during the quiescence to proliferation transition establish patterns of follicle cell differentiation in the Drosophila ovary

Stem cells cycle between periods of quiescence and proliferation to promote tissue health. In Drosophila ovaries, quiescence to proliferation transitions of follicle stem cells (FSCs) are exquisitely feeding-dependent. Here, we demonstrate feeding-dependent induction of follicle cell differentiation markers, eyes absent (Eya) and castor (Cas) in FSCs, a patterning process that does not depend on proliferation induction. Instead, FSCs extend micron-scale cytoplasmic projections that dictate Eya-Cas patterning. We identify still life and sickie as necessary and sufficient for FSC projection growth and Eya-Cas induction. Our results suggest that sequential, interdependent events establish long-term differentiation patterns in follicle cell precursors, independently of FSC proliferation induction.

Using coding and non-coding rare variants to target candidate genes in patients with severe tinnitus

Tinnitus is the phantom percept of an internal non-verbal set of noises and tones. It is reported by 15% of the population and it is usually associated with hearing and/or brain disorders. The role of structural variants (SVs) in coding and non-coding regions has not been investigated in patients with severe tinnitus. In this study, we performed whole-genome sequencing in 97 unrelated Swedish individuals with chronic tinnitus (TIGER cohort). Rare single nucleotide variants (SNV), large structural variants (LSV), and copy number variations (CNV) were retrieved to perform a gene enrichment analysis in TIGER and in a subgroup of patients with severe tinnitus (SEVTIN, n = 34), according to the tinnitus handicap inventory (THI) scores. An independent exome sequencing dataset of 147 Swedish tinnitus patients was used as a replication cohort (JAGUAR cohort) and population-specific datasets from Sweden (SweGen) and Non-Finish Europeans (NFE) from gnomAD were used as control groups. SEVTIN patients showed a higher prevalence of hyperacusis, hearing loss, and anxiety when they were compared to individuals in the TIGER cohort. We found an enrichment of rare missense variants in 6 and 8 high-constraint genes in SEVTIN and TIGER cohorts, respectively. Of note, an enrichment of missense variants was found in the CACNA1E gene in both SEVTIN and TIGER. We replicated the burden of missense variants in 9 high-constrained genes in the JAGUAR cohort, including the gene NAV2, when data were compared with NFE. Moreover, LSVs in constrained regions overlapping CACNA1E, NAV2, and TMEM132D genes were observed in TIGER and SEVTIN.

Convergent copy number increase of genes associated with freshwater colonization in fishes

Copy number variation (CNV) can cause phenotypic changes. However, in contrast to amino acid substitutions and cis-regulatory changes, little is known about the functional categories of genes in which CNV is important for adaptation to novel environments. It is also unclear whether the same genes repeatedly change the copy numbers for adapting to similar environments. Here, we investigate CNV associated with freshwater colonization in fishes, which was observed multiple times across different lineages. Using 48 ray-finned fishes across diverse orders, we identified 23 genes whose copy number increases were associated with freshwater colonization. These genes showed enrichment for peptide receptor activity, hexosyltransferase activity and unsaturated fatty acid metabolism. We further revealed that three of the genes showed copy number increases in freshwater populations compared to marine ancestral populations of the stickleback genus Gasterosteus. These results indicate that copy number increases of genes involved in fatty acid metabolism (FADS2), immune function (PSMB8a) and thyroid hormone metabolism (UGT2) may be important for freshwater colonization at both the inter-order macroevolutionary scale and at the intra-genus microevolutionary scale. Further analysis across diverse taxa will help to understand the role of CNV in the adaptation to novel environments. This article is part of the theme issue 'Genetic basis of adaptation and speciation: from loci to causative mutations'.

Growth cone macropinocytosis of neurotrophin receptor and neuritogenesis are regulated by neuron navigator 1

Neuron navigator 1 (Nav1) is a cytoskeleton-associated protein expressed during brain development that is necessary for proper neuritogenesis, but the underlying mechanisms are poorly understood. Here we show that Nav1 is present in elongating axon tracts during mouse brain embryogenesis. We found that depletion of Nav1 in cultured neurons disrupts growth cone morphology and neurotrophin-stimulated neuritogenesis. In addition to regulating both F-actin and microtubule properties, Nav1 promotes actin-rich membrane ruffles in the growth cone and promotes macropinocytosis at those membrane ruffles, including internalization of the TrkB receptor for the neurotrophin brain-derived neurotropic factor (BDNF). Growth cone macropinocytosis is important for downstream signaling, neurite targeting, and membrane recycling, implicating Nav1 in one or more of these processes. Depletion of Nav1 also induces transient membrane blebbing via disruption of signaling in the Rho GTPase signaling pathway, supporting the novel role of Nav1 in dynamic actin-based membrane regulation at the cell periphery. These data demonstrate that Nav1 works at the interface of microtubules, actin, and plasma membrane to organize the cell periphery and promote uptake of growth and guidance cues to facilitate neural morphogenesis during development.

Alternative splicing modulation by G-quadruplexes

Alternative splicing is central to metazoan gene regulation, but the regulatory mechanisms are incompletely understood. Here, we show that G-quadruplex (G4) motifs are enriched ~3-fold near splice junctions. The importance of G4s in RNA is emphasised by a higher enrichment for the non-template strand. RNA-seq data from mouse and human neurons reveals an enrichment of G4s at exons that were skipped following depolarisation induced by potassium chloride. We validate the formation of stable RNA G4s for three candidate splice sites by circular dichroism spectroscopy, UV-melting and fluorescence measurements. Moreover, we find that sQTLs are enriched at G4s, and a minigene experiment provides further support for their role in promoting exon inclusion. Analysis of >1,800 high-throughput experiments reveals multiple RNA binding proteins associated with G4s. Finally, exploration of G4 motifs across eleven species shows strong enrichment at splice sites in mammals and birds, suggesting an evolutionary conserved splice regulatory mechanism.

Here the authors shows that G-quadruplexes, non-canonical DNA/RNA structures, can have a direct impact on alternative splicing and that binding of splicing regulators is affected by their presence.

Quantitative dissection of multilocus pathogenic variation in an Egyptian infant with severe neurodevelopmental disorder resulting from multiple molecular diagnoses

Genomic sequencing and clinical genomics have demonstrated that substantial subsets of atypical and/or severe disease presentations result from multilocus pathogenic variation (MPV) causing blended phenotypes. In an infant with a severe neurodevelopmental disorder, four distinct molecular diagnoses were found by exome sequencing (ES). The blended phenotype that includes brain malformation, dysmorphism, and hypotonia was dissected using the Human Phenotype Ontology (HPO). ES revealed variants in CAPN3 (c.259C > G:p.L87V), MUSK (c.1781C > T:p.A594V), NAV2 (c.1996G > A:p.G666R), and ZC4H2 (c.595A > C:p.N199H). CAPN3, MUSK, and ZC4H2 are established disease genes linked to limb-girdle muscular dystrophy (OMIM# 253600), congenital myasthenia (OMIM# 616325), and Wieacker-Wolff syndrome (WWS; OMIM# 314580), respectively. NAV2 is a retinoic-acid responsive novel disease gene candidate with biological roles in neurite outgrowth and cerebellar dysgenesis in mouse models. Using semantic similarity, we show that no gene identified by ES individually explains the proband phenotype, but rather the totality of the clinically observed disease is explained by the combination of disease-contributing effects of the identified genes. These data reveal that multilocus pathogenic variation can result in a blended phenotype with each gene affecting a different part of the nervous system and nervous system-muscle connection. We provide evidence from this n = 1 study that in patients with MPV and complex blended phenotypes resulting from multiple molecular diagnoses, quantitative HPO analysis can allow for dissection of phenotypic contribution of both established disease genes and novel disease gene candidates not yet proven to cause human disease.

The +TIP Navigator-1 is an actin-microtubule crosslinker that regulates axonal growth cone motility

Microtubule (MT) plus-end tracking proteins (+TIPs) are central players in the coordination between the MT and actin cytoskeletons in growth cones (GCs) during axon guidance. The +TIP Navigator-1 (NAV1) is expressed in the developing nervous system, yet its neuronal functions remain poorly elucidated. Here, we report that NAV1 controls the dynamics and motility of the axonal GCs of cortical neurons in an EB1-dependent manner and is required for axon turning toward a gradient of netrin-1. NAV1 accumulates in F-actin-rich domains of GCs and binds actin filaments in vitro. NAV1 can also bind MTs independently of EB1 in vitro and crosslinks nonpolymerizing MT plus ends to actin filaments in axonal GCs, preventing MT depolymerization in F-actin-rich areas. Together, our findings pinpoint NAV1 as a key player in the actin-MT crosstalk that promotes MT persistence at the GC periphery and regulates GC steering. Additionally, we present data assigning to NAV1 an important role in the radial migration of cortical projection neurons in vivo.

Expression pattern of Nav2 in the murine CNS with development

Neuron navigator 2 (NAV2, RAINB1, POMFIL2, HELAD1, unc53H2) is essential for nervous system development. In the present study the spatial distribution of Nav2 transcript in mouse CNS during embryonic, postnatal and adult life is examined. Because multiple NAV2 proteins are predicted based on alternate promoter usage and RNA splicing, in situ hybridization was performed using probes designed to the 5' and 3' ends of the Nav2 transcript, and PCR products using primer sets spanning the length of the mRNA were also examined by real time PCR (qPCR). These studies support full-length Nav2 transcript as the predominant form in the wild-type mouse CNS. The developing cortex, hippocampus, thalamus, olfactory bulb, and granule cells (GC) within the cerebellum show the highest expression, with a similar staining pattern using either the 5'Nav2 or 3'Nav2 probe. Nav2 is expressed in GC precursors migrating over the cerebellar primordium as well as in the postmitotic premigratory cells of the external granule cell layer (EGL). It is expressed in the cornu ammonis (CA) and dentate gyrus (DG) throughout hippocampal development. In situ hybridization was combined with immunohistochemistry for Ki67, CTIP2 and Nissl staining to follow Nav2 transcript location during cortical development, where it is observed in neuroepithelial cells exiting the germinal compartments, as well as later in the cortical plate (CP) and developing cortical layers. The highest levels of Nav2 in all brain regions studied are observed in late gestation and early postnatal life which coincides with times when neurons are migrating and differentiating. A hypomorphic mouse that lacks the full-length transcript but expresses shorter transcript shows little staining in the CNS with either probe set except at the base of the cerebellum, where a shorter Nav2 transcript is detected. Using dual fluorescent probe in situ hybridization studies, these cells are identified as oligodendrocytes and are detected using both Olig1 and the 3'Nav2 probe. The identification of full-length Nav2 as the primary transcript in numerous brain regions suggests NAV2 could play a role in CNS development beyond that of its well-established role in the cerebellum.

Human Cerebral Organoids and Fetal Brain Tissue Share Proteomic Similarities

The limited access to functional human brain tissue has led to the development of stem cell-based alternative models. The differentiation of human pluripotent stem cells into cerebral organoids with self-organized architecture has created novel opportunities to study the early stages of the human cerebral formation. Here we applied state-of-the-art label-free shotgun proteomics to compare the proteome of stem cell-derived cerebral organoids to the human fetal brain. We identified 3,073 proteins associated with different developmental stages, from neural progenitors to neurons, astrocytes, or oligodendrocytes. The major protein groups are associated with neurogenesis, axon guidance, synaptogenesis, and cortical brain development. Glial cell proteins related to cell growth and maintenance, energy metabolism, cell communication, and signaling were also described. Our data support the variety of cells and neural network functional pathways observed within cell-derived cerebral organoids, confirming their usefulness as an alternative model. The characterization of brain organoid proteome is key to explore, in a dish, atypical and disrupted processes during brain development or neurodevelopmental, neurodegenerative, and neuropsychiatric diseases.

Genomic and non-genomic pathways are both crucial for peak induction of neurite outgrowth by retinoids

Retinoic acid (RA) is the active metabolite of vitamin A and essential for many physiological processes, particularly the induction of cell differentiation. In addition to regulating genomic transcriptional activity via RA receptors (RARs) and retinoid X receptors (RXRs), non-genomic mechanisms of RA have been described, including the regulation of ERK1/2 kinase phosphorylation, but are poorly characterised. In this study, we test the hypothesis that genomic and non-genomic mechanisms of RA are regulated independently with respect to the involvement of ligand-dependent RA receptors. A panel of 28 retinoids (compounds with vitamin A-like activity) showed a marked disparity in genomic (gene expression) versus non-genomic (ERK1/2 phosphorylation) assays. These results demonstrate that the capacity of a compound to activate gene transcription does not necessarily correlate with its ability to regulate a non-genomic activity such as ERK 1/2 phosphorylation. Furthermore, a neurite outgrowth assay indicated that retinoids that could only induce either genomic, or non-genomic activities, were not strong promoters of neurite outgrowth, and that activities with respect to both transcriptional regulation and ERK1/2 phosphorylation produced maximum neurite outgrowth. These results suggest that the development of effective retinoids for clinical use will depend on the selection of compounds which have maximal activity in non-genomic as well as genomic assays.

Association Between Titin Loss-of-Function Variants and Early-Onset Atrial Fibrillation

Importance

Atrial fibrillation (AF) is the most common arrhythmia affecting 1% of the population. Young individuals with AF have a strong genetic association with the disease, but the mechanisms remain incompletely understood.

Objective

To perform large-scale whole-genome sequencing to identify genetic variants related to AF.

Design, Setting, and Participants

The National Heart, Lung, and Blood Institute's Trans-Omics for Precision Medicine Program includes longitudinal and cohort studies that underwent high-depth whole-genome sequencing between 2014 and 2017 in 18 526 individuals from the United States, Mexico, Puerto Rico, Costa Rica, Barbados, and Samoa. This case-control study included 2781 patients with early-onset AF from 9 studies and identified 4959 controls of European ancestry from the remaining participants. Results were replicated in the UK Biobank (346 546 participants) and the MyCode Study (42 782 participants).

Exposures

Loss-of-function (LOF) variants in genes at AF loci and common genetic variation across the whole genome.

Main Outcomes and Measures

Early-onset AF (defined as AF onset in persons <66 years of age). Due to multiple testing, the significance threshold for the rare variant analysis was P = 4.55 × 10-3.

Results

Among 2781 participants with early-onset AF (the case group), 72.1% were men, and the mean (SD) age of AF onset was 48.7 (10.2) years. Participants underwent whole-genome sequencing at a mean depth of 37.8 fold and mean genome coverage of 99.1%. At least 1 LOF variant in TTN, the gene encoding the sarcomeric protein titin, was present in 2.1% of case participants compared with 1.1% in control participants (odds ratio [OR], 1.76 [95% CI, 1.04-2.97]). The proportion of individuals with early-onset AF who carried a LOF variant in TTN increased with an earlier age of AF onset (P value for trend, 4.92 × 10-4), and 6.5% of individuals with AF onset prior to age 30 carried a TTN LOF variant (OR, 5.94 [95% CI, 2.64-13.35]; P = 1.65 × 10-5). The association between TTN LOF variants and AF was replicated in an independent study of 1582 patients with early-onset AF (cases) and 41 200 control participants (OR, 2.16 [95% CI, 1.19-3.92]; P = .01).

Conclusions and Relevance

In a case-control study, there was a statistically significant association between an LOF variant in the TTN gene and early-onset AF, with the variant present in a small percentage of participants with early-onset AF (the case group). Further research is necessary to understand whether this is a causal relationship.

Family-based association analysis of NAV2 gene with the risk and age at onset of Alzheimer's disease

The neuron navigator 2 (NAV2) gene is highly expressed in brain and involved in the nervous system development and may play a role in Alzheimer's disease (AD). We aimed to investigate the associations of 317 single-nucleotide polymorphisms (SNPs) in the NAV2 gene with the risk and age at onset (AAO) of AD using a family-based sample (1266 AD cases and 1279 healthy relatives). Association with the risk of AD was assessed using family-based association test -generalized estimating equations (FBAT- GEE) statistics while the association with AAO as a quantitative trait was evaluated using the FBAT-Wilcoxon statistic. Single marker analysis showed that 20 SNPs were significantly associated with the risk of AD (top SNP rs7112354 with p=8.46×10-4) and 11 SNPs were associated with AAO (top SNP rs1354269 with p=2.87×10-3). Interestingly, two SNPs rs17614100 and rs12364788 were associated with both the risk (p=1.7×10-2 and 2.71×10-2; respectively) and AAO (p=1.85×10-3 and 6.06×10-3; respectively). Haplotype analyses further supported the results of single marker analyses. In addition, functional analysis showed that NAV2 mRNA had significant expression across ten human brain regions examined and significantly correlated with APOE expression in four of ten regions. The present study is the first study providing evidence of several genetic variants within the NAV2 gene influencing the risk and AAO of AD.

Neuron navigator 2 overexpression indicates poor prognosis of colorectal cancer and promotes invasion through the SSH1L/cofilin-1 pathway

Background

Neuron navigator 2 (NAV2) encodes a member of the neuron navigator gene family, which plays a role in tumorigenesis and cell migration. However, the prognostic value of NAV2 expression in colorectal cancer (CRC) patients and the potential pathway through which NAV2 promotes migration and invasion in CRC cell lines is poorly understood.

Methods

The expression level of NAV2 was detected in CRC tissues from two different CRC cohorts by immunohistochemistry, qRT-PCR and Western blotting; the correlation between NAV2 expression and clinicopathological characters was analyzed, and the prognostic value of NAV2 expression was analyzed using a Cox regression model. CRC cell lines with NAV2 knocked out were used to validate the function and potential pathway used by NAV2 to promote CRC cell migration and invasion.

Results

The results showed that NAV2 was overexpressed in CRC tissues, and it was closely correlated with depth of invasion, and lymph and distant metastasis. Multivariate analysis indicated that high NAV2 expression was a poor prognostic indicator of recurrence-free survival and overall survival in CRC patients. Furthermore, Cox regression analysis revealed that high NAV2 expression integrated with high tumor budding grade was a powerful independent predictive factor of CRC clinical outcome. In vitro and in vivo assays demonstrated that knockdown of NAV2 led to reduced migration and invasion of cancer cells, and the process involved the regulation of F-actin polymerization through the SSH1L/cofilin-1 pathway.

Conclusion

Based on these findings, NAV2 could serve as both a prognostic biomarker and a potential therapeutic target for patients with NAV2-positive CRC.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-015-0237-3) contains supplementary material, which is available to authorized users.

TIPsy tour guides: how microtubule plus-end tracking proteins (+TIPs) facilitate axon guidance

The growth cone is a dynamic cytoskeletal vehicle, which drives the end of a developing axon. It serves to interpret and navigate through the complex landscape and guidance cues of the early nervous system. The growth cone’s distinctive cytoskeletal organization offers a fascinating platform to study how extracellular cues can be translated into mechanical outgrowth and turning behaviors. While many studies of cell motility highlight the importance of actin networks in signaling, adhesion, and propulsion, both seminal and emerging works in the field have highlighted a unique and necessary role for microtubules (MTs) in growth cone navigation. Here, we focus on the role of singular pioneer MTs, which extend into the growth cone periphery and are regulated by a diverse family of microtubule plus-end tracking proteins (+TIPs). These +TIPs accumulate at the dynamic ends of MTs, where they are well-positioned to encounter and respond to key signaling events downstream of guidance receptors, catalyzing immediate changes in microtubule stability and actin cross-talk, that facilitate both axonal outgrowth and turning events.

PLR-1, a putative E3 ubiquitin ligase, controls cell polarity and axonal extensions in C. elegans

During embryonic development neurons differentiate and extend axons and dendrites that have to reach their appropriate targets. In Caenorhabditis elegans the AVG neuron is the first neuron to extend an axon during the establishment of the ventral nerve cord, the major longitudinal axon tract in the animal. In genetic screens we isolated alleles of plr-1, which caused polarity reversals of the AVG neuron as well as outgrowth and navigation defects of the AVG axon. In addition plr-1 mutants show outgrowth defects in several other classes of neurons as well as the posterior excretory canals. plr-1 is predicted to encode a transmembrane E3 ubiquitin ligase and is widely expressed in the animal including the AVG neuron and the excretory cell. plr-1 has recently been shown to negatively regulate Wnt signalling by removing Wnt receptors from the cell surface. We observed that mutations in a gene reducing Wnt signalling as well as mutations in unc-53/NAV2 and unc-73/Trio suppress the AVG polarity defects in plr-1 mutants, but not the defects seen in other cells. This places plr-1 in a Wnt regulation pathway, but also suggests that plr-1 has Wnt independent functions and interacts with unc-53 and unc-73 to control cell polarity.

14-3-3ε and NAV2 interact to regulate neurite outgrowth and axon elongation

Neuron navigator 2 (NAV2) is required for all-trans retinoic acid (atRA) to induce neurite outgrowth in human neuroblastoma cells. Further, ectopic overexpression of full-length human NAV2 rescues an axonal elongation defect in the Caenorhabditis elegans unc-53 (NAV2 ortholog) mutant. Using a region of NAV2 that independently associates with the cytoskeleton as bait in a yeast-two-hybrid screen, 14-3-3ε was identified as a novel NAV2 interacting partner. Amino acids 761-960 of NAV2 are sufficient to confer a positive interaction with 14-3-3ε as evidenced by a two-hybrid screen and co-immunoprecipitation assay. Knockdown of 14-3-3ε leads to a decrease in atRA-mediated neurite outgrowth, similar to the elongation defects observed when NAV2 is depleted or mutated. Likewise, posterior lateral microtubule (PLM) defects in C. elegans fed unc-53 RNAi are similar to those fed ftt-2 (14-3-3 homolog) RNAi. The discovery of an interaction between NAV2 and 14-3-3ε could provide insight into the mechanism by which NAV2 participates in promoting cell migration and neuronal elongation.

Admixture mapping identifies a locus on 6q25 associated with breast cancer risk in US Latinas

Among US Latinas and Mexican women, those with higher European ancestry have increased risk of breast cancer. We combined an admixture mapping and genome-wide association mapping approach to search for genomic regions that may explain this observation. Latina women with breast cancer (n= 1497) and Latina controls (n= 1272) were genotyped using Affymetrix and Illumina arrays. We inferred locus-specific genetic ancestry and compared the ancestry between cases and controls. We also performed single nucleotide polymorphism (SNP) association analyses in regions of interest. Correction for multiple-hypothesis testing was conducted using permutations (P(corrected)). We identified one region where genetic ancestry was significantly associated with breast cancer risk: 6q25 [odds ratio (OR) per Indigenous American chromosome 0.75, 95% confidence interval (CI): 0.65-0.85, P= 1.1 × 10(-5), P(corrected)= 0.02]. A second region on 11p15 showed a trend towards association (OR per Indigenous American chromosome 0.77, 95% CI: 0.68-0.87, P= 4.3 × 10(-5), P(corrected)= 0.08). In both regions, breast cancer risk decreased with higher Indigenous American ancestry in concordance with observations made on global ancestry. The peak of the 6q25 signal includes the estrogen receptor 1 (ESR1) gene and 5' region, a locus previously implicated in breast cancer. Genome-wide association analysis found that a multi-SNP model explained the admixture signal in both regions. Our results confirm that the association between genetic ancestry and breast cancer risk in US Latinas is partly due to genetic differences between populations of European and Indigenous Americans origin. Fine-mapping within the 6q25 and possibly the 11p15 loci will lead to the discovery of the biologically functional variant/s behind this association.

Distinct cell guidance pathways controlled by the Rac and Rho GEF domains of UNC-73/TRIO in Caenorhabditis elegans

The cytoskeleton regulator UNC-53/NAV2 is required for both the anterior and posterior outgrowth of several neurons as well as that of the excretory cell while the kinesin-like motor VAB-8 is essential for most posteriorly directed migrations in Caenorhabditis elegans. Null mutations in either unc-53 or vab-8 result in reduced posterior excretory canal outgrowth, while double null mutants display an enhanced canal extension defect, suggesting the genes act in separate pathways to control this posteriorly directed outgrowth. Genetic analysis of putative interactors of UNC-53 or VAB-8, and cell-specific rescue experiments suggest that VAB-8, SAX-3/ROBO, SLT-1/Slit, and EVA-1 are functioning together in the outgrowth of the excretory canals, while UNC-53 appears to function in a parallel pathway with UNC-71/ADAM. The known VAB-8 interactor, the Rac/Rho GEF UNC-73/TRIO operates in both pathways, as isoform specific alleles exhibit enhancement of the phenotype in double-mutant combination with either unc-53 or vab-8. On the basis of these results, we propose a bipartite model for UNC-73/TRIO activity in excretory canal extension: a cell autonomous function that is mediated by the Rho-specific GEF domain of the UNC-73E isoform in conjunction with UNC-53 and UNC-71 and a cell nonautonomous function that is mediated by the Rac-specific GEF domain of the UNC-73B isoform, through partnering with VAB-8 and the receptors SAX-3 and EVA-1.

Nuclear GRP75 binds retinoic acid receptors to promote neuronal differentiation of neuroblastoma

Retinoic acid (RA) has been approved for the differentiation therapy of neuroblastoma (NB). Previous work revealed a correlation between glucose-regulated protein 75 (GRP75) and the RA-elicited neuronal differentiation of NB cells. The present study further demonstrated that GRP75 translocates into the nucleus and physically interacts with retinoid receptors (RARα and RXRα) to augment RA-elicited neuronal differentiation. GRP75 was required for RARα/RXRα-mediated transcriptional regulation and was shown to reduce the proteasome-mediated degradation of RARα/RXRαin a RA-dependent manner. More intriguingly, the level of GRP75/RARα/RXRα tripartite complexes was tightly associated with the RA-induced suppression of tumor growth in animals and the histological grade of differentiation in human NB tumors. The formation of GRP75/RARα/RXRα complexes was intimately correlated with a normal MYCN copy number of NB tumors, possibly implicating a favorable prognosis of NB tumors. The present findings reveal a novel function of nucleus-localized GRP75 in actively promoting neuronal differentiation, delineating the mode of action for the differentiation therapy of NB by RA.

The all-trans retinoic acid (atRA)-regulated gene Calmin (Clmn) regulates cell cycle exit and neurite outgrowth in murine neuroblastoma (Neuro2a) cells

The vitamin A metabolite all-trans retinoic acid (atRA) functions in nervous system development and regulates cell proliferation and differentiation. Neuroblastoma cells (SH-SY5Y and Neuro2a or N2A) exposed to atRA undergo growth inhibition and neuronal differentiation, both of which are preceded by an increase in Clmn mRNA. Treatment of N2A cells with atRA produces a reduction in phosphohistone 3 immunostaining and BrdU incorporation, both indicators of a reduction in cell proliferation. These effects are nearly eliminated in atRA-treated shClmn knockdown cells. Loss of Clmn in the mouse N2A cell line also results in a significant reduction of atRA-mediated neurite outgrowth, a response that can be rescued by reintroduction of the Clmn sequence. In contrast, ectopic overexpression of Clmn produces an increase in the cyclin dependent kinase inhibitor, p21(Cip1), a decrease in cyclin D1 protein and an increase in hypophosphorylated Rb, showing that Clmn participates in G(1)/S arrest. Clmn overexpression alone is sufficient to inhibit N2A cell proliferation, whereas both Clmn and atRA must be present to induce neurite outgrowth. This study shows that the atRA-responsive gene Clmn promotes exit from the cell cycle, a requisite event for neuronal differentiation.

Nav2 hypomorphic mutant mice are ataxic and exhibit abnormalities in cerebellar development

Development of the cerebellum involves a coordinated program of neuronal process outgrowth and migration resulting in a foliated structure that plays a key role in motor function. Neuron navigator 2 (Nav2) is a cytoskeletal-interacting protein that functions in neurite outgrowth and axonal elongation. Herein we show that hypomorphic mutant mice lacking the full-length Nav2 transcript exhibit ataxia and defects in cerebellar development. At embryonic day (E)17.5, the mutant cerebellum is reduced in size and exhibits defects in vermal foliation. Reduction in cell proliferation at early times (E12.5 and E14.5) may contribute to this size reduction. The full-length Nav2 transcript is expressed in the premigratory zone of the external granule layer (EGL). Granule cells in the germinal zone of the EGL appear to proliferate normally, however, due to the reduction in cerebellar circumference there are fewer total BrdU-labeled granule cells in the mutants, and these fail to migrate normally toward the interior of the cerebellum. In Nav2 hypomorphs, fewer granule cells migrate out of cerebellar EGL explants and neurite outgrowth from both explants and isolated external granule cell cultures is reduced. This suggests that the formation of parallel axon fibers and neuronal migration is disrupted in Nav2 mutants. This work supports an essential role for full-length Nav2 in cerebellar development, including axonal elongation and migration of the EGL neurons.

Vitamin A in reproduction and development

The requirement for vitamin A in reproduction was first recognized in the early 1900's, and its importance in the eyes of developing embryos was realized shortly after. A greater understanding of the large number of developmental processes that require vitamin A emerged first from nutritional deficiency studies in rat embryos, and later from genetic studies in mice. It is now generally believed that all-trans retinoic acid (RA) is the form of vitamin A that supports both male and female reproduction as well as embryonic development. This conclusion is based on the ability to reverse most reproductive and developmental blocks found in vitamin A deficiency induced either by nutritional or genetic means with RA, and the ability to recapitulate the majority of embryonic defects in retinoic acid receptor compound null mutants. The activity of the catabolic CYP26 enzymes in determining what tissues have access to RA has emerged as a key regulatory mechanism, and helps to explain why exogenous RA can rescue many vitamin A deficiency defects. In severely vitamin A-deficient (VAD) female rats, reproduction fails prior to implantation, whereas in VAD pregnant rats given small amounts of carotene or supported on limiting quantities of RA early in organogenesis, embryos form but show a collection of defects called the vitamin A deficiency syndrome or late vitamin A deficiency. Vitamin A is also essential for the maintenance of the male genital tract and spermatogenesis. Recent studies show that vitamin A participates in a signaling mechanism to initiate meiosis in the female gonad during embryogenesis, and in the male gonad postnatally. Both nutritional and genetic approaches are being used to elucidate the vitamin A-dependent pathways upon which these processes depend.

Lack of change in markers of presynaptic terminal abundance alongside subtle reductions in markers of presynaptic terminal plasticity in prefrontal cortex of schizophrenia patients

BACKGROUND

Reduced synaptic connectivity in frontal cortex may contribute to schizophrenia symptoms. While altered messenger RNA (mRNA) and protein expression of various synaptic genes have been found, discrepancies between studies mean a generalizable synaptic pathology has not been identified.

METHODS

We determined if mRNAs encoding presynaptic proteins enriched in inhibitory (vesicular gamma-aminobutyric acid transporter [VGAT] and complexin 1) and/or excitatory (vesicular glutamate transporter 1 [VGluT1] and complexin 2) terminals are altered in the dorsolateral prefrontal cortex of subjects with schizophrenia (n = 37 patients, n = 37 control subjects). We also measured mRNA expression of markers associated with synaptic plasticity/neurite outgrowth (growth associated protein 43 [GAP43] and neuronal navigators [NAVs] 1 and 2) and mRNAs of other synaptic-associated proteins previously implicated in schizophrenia: dysbindin and vesicle-associated membrane protein 1 (VAMP1) mRNAs using quantitative polymerase chain reaction.

RESULTS

No significant changes in complexin 1, VGAT, complexin 2, VGluT1, dysbindin, NAV2, or VAMP1 mRNA expression were found; however, expression of mRNAs associated with plasticity/cytoskeletal modification (GAP43 and NAV1) was reduced in schizophrenia. Although dysbindin mRNA did not differ in schizophrenia compared with control subjects, dysbindin mRNA positively correlated with GAP43 and NAV1 in schizophrenia but not in control subjects, suggesting low levels of dysbindin may be linked to reduced plasticity in the disease state. No relationships between three dysbindin genetic polymorphisms previously associated with dysbindin mRNA levels were found.

CONCLUSIONS

A reduction in the plasticity of synaptic terminals supports the hypothesis that their reduced modifiability may contribute to neuropathology and working memory deficits in schizophrenia.

Tissue type-specific expression of the dsRNA-binding protein 76 and genome-wide elucidation of its target mRNAs

Background

RNA-binding proteins accompany all steps in the life of mRNAs and provide dynamic gene regulatory functions for rapid adjustment to changing extra- or intracellular conditions. The association of RNA-binding proteins with their targets is regulated through changing subcellular distribution, post-translational modification or association with other proteins.

Methodology

We demonstrate that the dsRNA binding protein 76 (DRBP76), synonymous with nuclear factor 90, displays inherently distinct tissue type-specific subcellular distribution in the normal human central nervous system and in malignant brain tumors of glial origin. Altered subcellular localization and isoform distribution in malignant glioma indicate that tumor-specific changes in DRBP76-related gene products and their regulatory functions may contribute to the formation and/or maintenance of these tumors. To identify endogenous mRNA targets of DRBP76, we performed RNA-immunoprecipitation and genome-wide microarray analyses in HEK293 cells, and identified specific classes of transcripts encoding critical functions in cellular metabolism.

Significance

Our data suggest that physiologic DRBP76 expression, isoform distribution and subcellular localization are profoundly altered upon malignant transformation. Thus, the functional role of DRBP76 in co- or post-transcriptional gene regulation may contribute to the neoplastic phenotype.

Genomic alterations of chromosome region 11p as predictive marker by array comparative genomic hybridization in lung adenocarcinoma patients

Array comparative genomic hybridization (aCGH) provides a method to quantitatively measure the changes of DNA copy number with an extremely high resolution and to map them directly onto the complete linear genome sequences. In this study, we used aCGH to compare genomic alterations in fresh-frozen lung cancer tissues of 21 adenocarcinomas (AdCCs) (11 early relapse and 10 nonrelapse) and identified genomic alterations that showed significant by different frequency between early relapse and nonrelapse AdCCs. Twelve clones were identified by the false discovery rate (FDR) test, and Kaplan-Meier analyses were selected as predictive markers. The significant gain clones were found in 11p (11p15.4, 11p15.1, and 11p13). When the cutoff value was 2, study of the association between candidate clones and relapse prediction revealed that early relapse and nonrelapse groups were most effectively separated. To further validate the gain of chromosome 11p region that was identified by array CGH, fluorescence in situ hybridization (FISH) was performed. To further confirm the results of aCGH, copy number changes of cancer-related candidate genes in AdCC patients were compared by real-time quantitative polymerase chain reaction. Array CGH and real-time quantitative polymerase chain reaction data were found to correspond to delineated DNA copy number changes. Genomic alterations of chromosome 11p region in AdCC patients were observed with aCGH, and a relapsable marker was identified in the nonrelapse group. This marker could be useful in stratifying patient groups according to likelihood of relapse for adjuvant treatment after surgical resection.

Nav2 is necessary for cranial nerve development and blood pressure regulation

BACKGROUND

All-trans retinoic acid (atRA) is required for nervous system development, including the developing hindbrain region. Neuron navigator 2 (Nav2) was first identified as an atRA-responsive gene in human neuroblastoma cells (retinoic acid-induced in neuroblastoma 1, Rainb1), and is required for atRA-mediated neurite outgrowth. In this paper, we explore the importance of Nav2 in nervous system development and function in vivo.

RESULTS

Nav2 hypomorphic homozygous mutants show decreased survival starting at birth. Nav2 mutant embryos show an overall reduction in nerve fiber density, as well as specific defects in cranial nerves IX (glossopharyngeal) and X (vagus). Nav2 hypomorphic mutant adult mice also display a blunted baroreceptor response compared to wild-type controls.

CONCLUSIONS

Nav2 functions in mammalian nervous system development, and is required for normal cranial nerve development and blood pressure regulation in the adult.

Navigating the cell: UNC-53 and the navigators, a family of cytoskeletal regulators with multiple roles in cell migration, outgrowth and trafficking

Changes in cell shape are associated with a variety of processes including cell migration, axon outgrowth, cell division and vesicle trafficking. C. elegans UNC-53 and its vertebrate homologs, the Navigators, are required for the migration of cells and the outgrowth of neuronal processes. The identification of novel molecular interactions and live imaging studies have revealed that UNC-53/NAVs are signal transducers associated with actin filaments, microtubules and intermediate filaments. In addition to modulating cytoskeletal dynamics at the leading edge of migrating or outgrowing cells, both UNC-53 and the navigators are expressed in adult cells, conspicuously those with specialized roles in endocytosis or secretion. Collectively, these results suggest that UNC-53/NAVs may be a central regulator of cytoskeletal dynamics, responsible for integrating signaling cues to multiple components of the cytoskeleton to coordinate rearrangement during cell outgrowth or trafficking.

Identification of AhR-regulated genes involved in PAH-induced immunotoxicity using a highly-sensitive DNA chip, 3D-Gene Human Immunity and Metabolic Syndrome 9k

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental contaminants with various toxic effects including immune suppression. However, the molecular mechanism of their toxicity has not been fully clarified. The purpose of this study was to identify novel aryl hydrocarbon receptor (AhR)-regulated genes involved in PAH-induced immunotoxicity using a highly-sensitive DNA chip, 3D-Gene(TM) Human Immunity & Metabolic Syndrome 9k. Leucine-rich repeat-containing protein 25, glucosaminyl (N-acetyl) transferase 3 (GCNT3), thyroxine-binding globulin, aldehyde dehydrogenase 8A1, diacylglycerol O-acyltransferase homolog 2 (DGAT2), haptoglobin, neuron navigator 2 isoform 1, hemopexin and bile acid receptor were found to be up- or down-regulated by PAHs via AhR. Among these genes, GCTN3 and DGAT2 were responsible for immune responses. Therefore, disruption of the expression of these genes via AhR may be one of the causes of the immunotoxicity of PAHs.

The cell migration molecule UNC-53/NAV2 is linked to the ARP2/3 complex by ABI-1

The shape changes that are required to position a cell to migrate or grow out in a particular direction involve a coordinated reorganization of the actin cytoskeleton. Although it is known that the ARP2/3 complex nucleates actin filament assembly, exactly how the information from guidance cues is integrated to elicit ARP2/3-mediated remodeling during outgrowth remains vague. Previous studies have shown that C. elegans UNC-53 and its vertebrate homolog NAV (Neuronal Navigators) are required for the migration of cells and neuronal processes. We have identified ABI-1 as a novel molecular partner of UNC-53/NAV2 and have found that a restricted calponin homology (CH) domain of UNC-53 is sufficient to bind ABI-1. ABI-1 and UNC-53 have an overlapping expression pattern, and display similar cell migration phenotypes in the excretory cell, and in mechanosensory and motoneurons. Migration defects were also observed after RNAi of proteins known to function with abi-1 in actin dynamics, including nck-1, wve-1 and arx-2. We propose that UNC-53/NAV2, through its CH domain, acts as a scaffold that links ABI-1 to the ARP2/3 complex to regulate actin cytoskeleton remodeling.

The atRA-responsive gene neuron navigator 2 functions in neurite outgrowth and axonal elongation

Neuron navigator 2 (Nav2) was first identified as an all-trans retinoic acid (atRA)-responsive gene in human neuroblastoma cells (retinoic acid-induced in neuroblastoma 1, RAINB1) that extend neurites after exposure to atRA. It is structurally related to the Caenorhabditis elegans unc-53 gene that is required for cell migration and axonal outgrowth. To gain insight into NAV2 function, the full-length human protein was expressed in C. elegans unc-53 mutants under the control of a mechanosensory neuron promoter. Transgene expression of NAV2 rescued the defects in unc-53 mutant mechanosensory neuron elongation, indicating that Nav2 is an ortholog of unc-53. Using a loss-of-function approach, we also show that Nav2 induction is essential for atRA to induce neurite outgrowth in SH-SY5Y cells. The NAV2 protein is located both in the cell body and along the length of the growing neurites of SH-SY5Y cells in a pattern that closely mimics that of neurofilament and microtubule proteins. Transfection of Nav2 deletion constructs in Cos-1 cells reveals a region of the protein (aa 837-1065) that directs localization with the microtubule cytoskeleton. Collectively, this work supports a role for NAV2 in neurite outgrowth and axonal elongation and suggests this protein may act by facilitating interactions between microtubules and other proteins such as neurofilaments that are key players in the formation and stability of growing neurites.

atRA Regulation of NEDD9, a gene involved in neurite outgrowth and cell adhesion

We previously identified NEDD9 (RAINB2/HEF1/Cas-L) as a new downstream target of all-trans retinoic acid (atRA) and its receptors in the human neuroblastoma cell line, SH-SY5Y [R.A. Merrill, A.W.-M. See, M.L. Wertheim, M. Clagett-Dame, Dev. Dyn. 231 (2004) 564-575; R.A. Merrill, J.M. Ahrens, M.E. Kaiser, K.S. Federhart, V.Y. Poon, M. Clagett-Dame, Biol. Chem. 385 (2004) 605-614]. We now provide functional evidence that NEDD9 is directly regulated by atRA through a complex retinoic acid response element (RARE) located in the NEDD9 proximal promoter and consisting of four conserved half-sites separated by 1, 5, and 1 intervening base pairs. We show that a region of the human NEDD9 promoter from -1670 to +15 is sufficient to confer atRA-responsiveness and that a complex RARE located from -475 to -445 is necessary for this effect. While mutation of any one half-site does not eliminate complex formation in electrophoretic mobility shift assays (EMSA); these same mutations, when tested in transient transfection assays, markedly decrease atRA-responsiveness. Finally, chromatin immunoprecipitation (ChIP) assays demonstrate that RAR and RXR are bound to the RARE in cells.

Profilin 1 obtained by proteomic analysis in all-trans retinoic acid-treated hepatocarcinoma cell lines is involved in inhibition of cell proliferation and migration

Previous studies have shown that all-trans retinoic acid (ATRA) suppresses growth of hepatocarcinoma cell in vitro. To understand the underlying mechanisms, we investigated the protein expression profiles by 2-DE in hepatocarcinoma cell line SMMC-7721 treated with ATRA. Our results reveal that six proteins were differently expressed in response to ATRA. Using MS and database searching, they were identified as profilin 1, phosphoglycerate kinase 1, RuvB-like 1, alpha-enolase, pyridoxal kinase and F-actin capping protein. We selected the up-regulated protein, profilin 1 (PFN1), for further studies. The PFN1 expression was increased in response to ATRA in a dose- and time-dependent manner. The PFN1 expression was reduced dramatically in four hepatoma cell lines compared to L02 cell line of non-tumor origin. The PFN1 expression was also examined in 4 cases of primary hepatocarcinoma tissues by Western blot and 30 cases by tissues microarray. It was found that the protein level of PFN1 was lower in hepatocarcinoma tissues compared to that in the adjacent tissues. Similar to ATRA, overexpression of PFN1 led to inhibition of cell proliferation and migration. Furthermore, RNAi-based PFN1 knockdown could rescue the inhibitory effect of ATRA on cell proliferation and migration. In conclusion, ATRA inhibited cell proliferation and migration through up-regulation of PFN1.

Role of all-trans retinoic acid in neurite outgrowth and axonal elongation

The vitamin A metabolite, all-trans retinoic acid (atRA) plays essential roles in nervous system development, including neuronal patterning, survival, and neurite outgrowth. Our understanding of how the vitamin A acid functions in neurite outgrowth comes largely from cultured embryonic neurons and model neuronal cell systems including human neuroblastoma cells. Specifically, atRA has been shown to increase neurite outgrowth from embryonic DRG, sympathetic, spinal cord, and olfactory receptor neurons, as well as dissociated cerebra and retina explants. A role for atRA in axonal elongation is also supported by a limited number of studies in vivo, in which a deficiency in retinoid signaling produced either by dietary or genetic means has been shown to alter neurite outgrowth from the spinal cord and hindbrain regions. Human neuroblastoma cells also show enhanced numbers of neurites and longer processes in response to atRA. The mechanism whereby retinoids regulate neurite outgrowth includes, but is not limited to, the regulation of the transcription of neurotrophin receptors. More recent evidence supports a role for atRA in regulating components of other signaling pathways or candidate neurite-regulating factors. Some of these effects, such as that on neuron navigator 2 (NAV2), may be direct, whereas others may be secondary to other atRA-induced changes in the cell. This review focuses on what is currently known about neurite initiation and growth, with emphasis on the manner in which atRA may influence these events.

Synthesis and preliminary chemotherapeutic evaluation of the fully C-linked glucuronide of N-(4-hydroxyphenyl)retinamide

All-trans retinoic acid analogues such as N-(4-hydroxyphenyl)retinamide (4-HPR) are effective chemopreventive and chemotherapeutic agents but their utility has been hampered by dose-limiting side effects. The glucuronide derivatives of 4-HPR, the oxygen-linked 4-HPROG and the carbon-linked 4-HPRCG, have been found to be more effective agents. The synthetic route to the fully C-linked analogue of 4-HPROG (4-HBRCG), which employs Suzuki coupling and Umpolung chemistries as key methodologies, is shown. The results of this study show 4-HBRCG to be an effective chemotherapeutic agent in a rat mammary tumor model while being devoid of classical retinoid toxicities.

New therapeutic target for CNS injury? The role of retinoic acid signaling after nerve lesions

Experiments with sciatic nerve lesions and spinal cord contusion injury demonstrate that the retinoic acid (RA) signaling cascade is activated by these traumatic events. In both cases the RA-synthesizing enzyme is RALDH-2. In the PNS, lesions cause RA-induced gene transcription, intracellular translocation of retinoid receptors, and increased transcription of CRBP-I, CRABP-II, and retinoid receptors. The activation of RARbeta appears to be responsible for neurotrophic and neuritogenic effects of RA on dorsal root ganglia and embryonic spinal cord. While the physiological role of RA in the injured nervous system is still under investigation three domains of functions are suggested: (1) neuroprotection and support of axonal growth, (2) modulation of the inflammatory reaction by microglia/macrophages, and (3) regulation of glial differentiation. Few studies have been performed to support nerve regeneration with RA signals in vivo, but a large number of experiments with neuronal and glial cell cultures and spinal cord explants point to beneficial effects of RA, so that future therapeutic approaches will likely focus on the activation of RA signaling.

Primary Cutaneous T-Cell Lymphomas Show a Deletion or Translocation AffectingNAV3, the HumanUNC-53Homologue

Multicolor fluorescent in situ hybridization (FISH) was used to identify acquired chromosomal aberrations in 12 patients with mycosis fungoides or Sézary syndrome, the most common forms of primary cutaneous T-cell lymphoma (CTCL). The most frequently affected chromosome was 12, which showed clonal deletions or translocations with a break point in 12q21 or 12q22 in five of seven consecutive Sézary syndrome patients and a clonal monosomy in the sixth patient. The break point of a balanced translocation t(12;18)(q21;q21.2), mapped in the minimal common region of two deletions, fine mapped to 12q2. By locus-specific FISH, the translocation disrupted one gene, NAV3 (POMFIL1), a human homologue of unc-53 in Caenorhabditis elegans. A missense mutation in the remaining NAV3 allele was found in one of six cases with a deletion or translocation. With locus-specific FISH, NAV3 deletions were found in the skin lesions of four of eight (50%) patients with early mycosis fungoides (stages IA-IIA) and in the skin or lymph node of 11 of 13 (85%) patients with advanced mycosis fungoides or Sézary syndrome. Preliminary functional studies with lentiviral small interfering RNA-based NAV3 silencing in Jurkat cells and in primary lymphocytes showed enhanced interleukin 2 expression (but not CD25 expression). Thus, NAV3 may contribute to the growth, differentiation, and apoptosis of CTCL cells as well as to the skewing from Th1-type to Th2-type phenotype during disease progression. NAV3, a novel putative haploinsufficient tumor suppressor gene, is disrupted in most cases of the commonest types of CTCL and may thus provide a new diagnostic tool.

Mouse neuron navigator 1, a novel microtubule-associated protein involved in neuronal migration

The development of the nervous system (NS) requires the coordinated migration of multiple waves of neurons and subsequent processes of neurite maturation, both involving selective guidance mechanisms. In Caenorhabditis elegans, unc-53 codes for a new multidomain protein involved in the directional migration of a subset of cells. We describe here the first functional characterization of the mouse homologue, mouse Neuron navigator 1 (mNAV1), whose expression is largely restricted to the NS during development. EGFP-mNAV1 associates with microtubules (MTs) plus ends present in the growth cone through a new microtubule-binding (MTB) domain. Moreover, its overexpression in transfected cells leads to MT bundling. The abolition of mNAV1 causes loss of directionality in the leading processes of pontine-migrating cells, providing evidence for a role of mNAV1 in mediating Netrin-1-induced directional migration.

LL5beta: a regulator of postsynaptic differentiation identified in a screen for synaptically enriched transcripts at the neuromuscular junction

In both neurons and muscle fibers, specific mRNAs are concentrated beneath and locally translated at synaptic sites. At the skeletal neuromuscular junction, all synaptic RNAs identified to date encode synaptic components. Using microarrays, we compared RNAs in synapse-rich and -free regions of muscles, thereby identifying transcripts that are enriched near synapses and that encode soluble membrane and nuclear proteins. One gene product, LL5β, binds to both phosphoinositides and a cytoskeletal protein, filamin, one form of which is concentrated at synaptic sites. LL5β is itself associated with the cytoplasmic face of the postsynaptic membrane; its highest levels border regions of highest acetylcholine receptor (AChR) density, which suggests a role in “corraling” AChRs. Consistent with this idea, perturbing LL5β expression in myotubes inhibits AChR aggregation. Thus, a strategy designed to identify novel synaptic components led to identification of a protein required for assembly of the postsynaptic apparatus.

Crk-associated substrate (Cas) family member, NEDD9, is regulated in human neuroblastoma cells and in the embryonic hindbrain by all-trans retinoic acid

The vitamin A metabolite, all-trans retinoic acid (atRA), plays an essential role in vertebrate embryogenesis, including development of the nervous system. In the human neuroblastoma cell line, SH-SY5Y, atRA rapidly induces (within 4 hr) the expression of the Crk-associated substrate (Cas) family member, neural precursor cell-expressed, developmentally down-regulated gene 9 (NEDD9) also called the human enhancer of filamentation (HEF1). NEDD9 is expressed in the developing hindbrain (5-somite stage) in the presumptive rhombomeres 2, 3, and 5 before the onset of overt segmentation. Exposure of rat embryos to excess atRA at times ranging from E9.25 to E12 leads to altered NEDD9 expression in the developing hindbrain within 6 hr. NEDD9 expression is also perturbed in vitamin A-deficient embryos. A putative retinoic acid response element in the 5' region of the NEDD9 promoter binds specifically to a RXR/RAR heterodimer and forms a higher molecular weight complex upon addition of a retinoic acid receptor-specific antibody. Regulation of NEDD9 may be an important means whereby atRA promotes cell spreading and neurite outgrowth in SH-SY5Y human neuroblastoma cells, and NEDD9 represents a new downstream target of atRA and its receptors in the developing hindbrain.

All-trans retinoic acid-responsive genes identified in the human SH-SY5Y neuroblastoma cell line and their regulated expression in the nervous system of early embryos

The vitamin A metabolite, all-trans retinoic acid (atRA), is required for embryonic development. atRA binds to the nuclear retinoic acid receptors and regulates the transcription of specific target genes. In order to identify atRA-induced genes that play a role in neural development, a subtractive library was created from SH-SY5Y neuroblastoma cells, a human cell line that exhibits changes in cell adhesion and neurite outgrowth after exposure to the vitamin A acid. We report here the identification of 14 genes that are rapidly induced by atRA (retinoic acid induced in neuroblastoma or RAINB), eight of which were previously not known to be atRA responsive (BTBD11, calmin, cyclin M2, ephrin B2, HOXD10, NEDD9, RAINB6 and tenascin R). mRNA regulation by atRA was confirmed in SH-SY5Y cells by Northern blotting, and gene regulation was studied in additional human cell lines using the quantitative polymerase chain reaction. The majority of the atRA-responsive clones revealed in this screen are highly expressed in the nervous system of developing rat embryos. Further, the expression of several of these genes is perturbed in developing rat embryos exposed to excess atRA or conversely, deprived of sufficient retinoid during early development. We propose that a subset of these genes lie downstream of atRA and its receptors in the regulation of neurite outgrowth and cell adhesion in both neural and non-neural tissues within the developing embryo.

Sensory deficits in mice hypomorphic for a mammalian homologue of unc-53

The migration of cells and the extension of cellular processes along pathways to their defined destinations are crucial in the development of higher organisms. Caenorhabditis elegans unc-53 plays an important role in cell migration and the outgrowth of cellular processes such as axons. To gain further insight into the biological function of unc53H2, a recently identified mammalian homologue of unc-53, we have generated mice carrying a mutation of unc53H2 and provide evidence that unc53H2 is involved in neuronal development and, more specifically, the development of different sensory systems. The unc53H2 hypomorphic mouse showed a general impaired acuity of several sensory systems (olfactory, auditory, visual and pain sensation) which in case of the visual system was corroborated by the morphological observation of hypoplasia of the optic nerve. We hypothesize that in analogy with its C. elegans homologue, unc53H2 may play a role in the processes of cellular outgrowth and migration.

unc-53 controls longitudinal migration in C. elegans

Cell migration and outgrowth are thought to be based on analogous mechanisms that require repeated cycles of process extension, reading and integration of multiple directional signals, followed by stabilisation in a preferred direction, and renewed extension. We have characterised a C. elegans gene, unc-53, that appears to act cell autonomously in the migration and outgrowth of muscles, axons and excretory canals. Abrogation of unc-53 function disrupts anteroposterior outgrowth in those cells that normally express the gene. Conversely, overexpression of unc-53 in bodywall muscles leads to exaggerated outgrowth. UNC-53 is a novel protein conserved in vertebrates that contains putative SH3- and actin-binding sites. unc-53 interacts genetically with sem-5 and we demonstrated a direct interaction in vitro between UNC-53 and the SH2-SH3 adaptor protein SEM-5/GRB2. Thus, unc-53 is involved in longitudinal navigation and might act by linking extracellular guidance cues to the intracellular cytoskeleton.