Molecular characterization of human neogenin, a DCC-related protein, and the mapping of its gene (NEO1) to chromosomal position 15q22.3-q23

Genomic analyses of claw disorders in Holstein cows: Genetic parameters, trait associations, and genome-wide associations considering interactions of SNP and heat stress

The aim of the present study was an in-depth genomic analysis to understand the genomic mechanisms of the 3 claw disorders dermatitis digitalis (DD), interdigital hyperplasia (HYP), and sole ulcer (SU). In this regard, we estimated genetic parameters based on genomic relationship matrices, performed genome-wide association studies, annotated potential candidate genes, and inferred genetic associations with breeding goal traits considering the most important chromosomal segments. As a further novelty of this study, we inferred possible SNP × heat stress interactions for claw disorders. The study consisted of 17,264 first-lactation Holstein Friesian cows kept in 50 large-scale contract herds. The disease prevalence was 15.96, 2.36, and 8.20% for DD, HYP, and SU, respectively. The remaining breeding goal traits consisted of type traits of the feet and leg composite, female fertility, health traits, and 305-d production traits. The final genotype data set included 44,474 SNPs from the 17,264 genotyped cows. Heritabilities for DD, HYP, and SU were estimated in linear and threshold models considering the genomic relationship matrix (G matrix). Genetic correlations with breeding goal traits based on G were estimated in a series of bivariate linear models, which were verified via SNP effect correlations for specific chromosome segments (i.e., segments harboring potential candidate genes for DD, HYP, and SU). Genome-wide association studies were performed for all traits in a case-control design by applying a single SNP linear mixed model. Furthermore, for DD, HYP, and SU, we modeled SNP × heat stress interactions in genome-wide association studies. Single nucleotide polymorphism-based heritabilities were 0.04 and 0.08 for DD, 0.03 and 0.10 for SU, and 0.03 and 0.23 for HYP from linear and threshold models, respectively. The genetic correlations between DD, HYP, and SU with conformation traits from the feet and leg composite were positive throughout, indicating the value of indirect selection on conformation traits to improve claw health. Genetic correlations between DD, SU, and HYP with other breeding goal traits indicated impaired female fertility, impaired udder health status, and productivity decline of diseased cows. Genetic correlations among DD, SU, and HYP were moderate to large, indicating that different claw disorders have similar genetic mechanisms. Nevertheless, we identified disease-specific potential candidate genes, and genetic associations based on the surrounding SNPs partly differed from the genetic correlations. Especially for candidate genes contributing to 2 traits simultaneously, correlations based on SNP effects from the respective chromosome segment were close to 1 or to -1. In this regard, we annotated the candidate genes KRT33A and KRT33B for HYP and DD, KIF27 for HYP and calving to first insemination, and MAN1A1 for SU and the production traits. For SNP × heat stress interactions, we identified significant SNPs on BTA 2, 4, 5, 7, 8, 9, 13, 22, 25, and 28, and we annotated the potential candidate genes FSIP2, CLCN1, ADGRV1, DOP1A, THBD, and RHOBTB1. Results indicate gene-specific mechanisms of the claw disorders only in specific environments.

Transsynaptic cerebellin 4-neogenin 1 signaling mediates LTP in the mouse dentate gyrus

SignificanceSynapses are controlled by transsynaptic adhesion complexes that mediate bidirectional signaling between pre- and postsynaptic compartments. Long-term potentiation (LTP) of synaptic transmission is thought to enable synaptic modifications during memory formation, but the signaling mechanisms involved remain poorly understood. We show that binding of cerebellin-4 (Cbln4), a secreted ligand of presynaptic neurexin adhesion molecules, to neogenin-1, a postsynaptic surface protein known as a developmental netrin receptor, is essential for normal LTP at entorhinal cortex→dentate gyrus synapses in mice. Cbln4 and neogenin-1 are dispensable for basal synaptic transmission and not involved in establishing synaptic connections as such. Our data identify a netrin receptor as a postsynaptic organizer of synaptic plasticity that collaborates specifically with the presynaptic neurexin-ligand Cbln4.

Expression of Neighbor of Punc E11 (NOPE) in early stage esophageal adenocarcinoma is associated with reduced survival

Current recommendations suggest neoadjuvant treatment in node-positive esophageal cancer or tumors staged T3 and upwards but some T2 N0 patients might benefit from neoadjuvant therapy. It is of clinical relevance to identify this subgroup. Loss of epithelial apicobasal polarity is a key factor in the development of invasive capabilities of carcinoma. The oncofetal stem/progenitor cell marker NOPE is expressed in adult depolarized murine hepatocytes and in murine/human hepatocellular carcinoma. We analyzed NOPE expression in 363 patients with esophageal adenocarcinoma using an RNA Scope Assay on a tissue microarray and correlated results with clinical data. Median follow-up was 57.7 months with a 5-year survival rate of 26.6%. NOPE was detectable in 32 patients (8.8%). In pT1/2 stages, NOPE expression was associated with a significantly reduced median OS of 6.3 months (95% CI 1.2–19.4 months), the median OS is not reached in the NOPE-negative group (calculated mean OS 117.1 months) (P = 0.012). In advanced tumor stages, a NOPE dependent survival difference was not detected. This is the first report of NOPE expression demonstrating a prognostic value in esophageal cancer. Early stage, NOPE positive patients are at a high risk of tumor progression and may benefit from neoadjuvant treatment analogous to advanced stage cancer.

Rgma-Induced Neo1 Proteolysis Promotes Neural Tube Morphogenesis

Neuroepithelial cell (NEC) elongation is one of several key cell behaviors that mediate the tissue-level morphogenetic movements that shape the neural tube (NT), the precursor of the brain and spinal cord. However, the upstream signals that promote NEC elongation have been difficult to tease apart from those regulating apico-basal polarity and hingepoint formation, due to their confounding interdependence. The Repulsive Guidance Molecule a (Rgma)/Neogenin 1 (Neo1) signaling pathway plays a conserved role in NT formation (neurulation) and is reported to regulate both NEC elongation and apico-basal polarity, through signal transduction events that have not been identified. We examine here the role of Rgma/Neo1 signaling in zebrafish (sex unknown), an organism that does not use hingepoints to shape its hindbrain, thereby enabling a direct assessment of the role of this pathway in NEC elongation. We confirm that Rgma/Neo1 signaling is required for microtubule-mediated NEC elongation, and demonstrate via cell transplantation that Neo1 functions cell autonomously to promote elongation. However, in contrast to previous findings, our data do not support a role for this pathway in establishing apical junctional complexes. Last, we provide evidence that Rgma promotes Neo1 glycosylation and intramembrane proteolysis, resulting in the production of a transient, nuclear intracellular fragment (NeoICD). Partial rescue of Neo1a and Rgma knockdown embryos by overexpressing neoICD suggests that this proteolytic cleavage is essential for neurulation. Based on these observations, we propose that RGMA-induced NEO1 proteolysis orchestrates NT morphogenesis by promoting NEC elongation independently of the establishment of apical junctional complexes.SIGNIFICANCE STATEMENT The neural tube, the CNS precursor, is shaped during neurulation. Neural tube defects occur frequently, yet underlying genetic risk factors are poorly understood. Neuroepithelial cell (NEC) elongation is essential for proper completion of neurulation. Thus, connecting NEC elongation with the molecular pathways that control this process is expected to reveal novel neural tube defect risk factors and increase our understanding of NT development. Effectors of cell elongation include microtubules and microtubule-associated proteins; however, upstream regulators remain controversial due to the confounding interdependence of cell elongation and establishment of apico-basal polarity. Here, we reveal that Rgma-Neo1 signaling controls NEC elongation independently of the establishment of apical junctional complexes and identify Rgma-induced Neo1 proteolytic cleavage as a key upstream signaling event.

Inhibition of neogenin fosters resolution of inflammation and tissue regeneration

The resolution of inflammation is an active process that is coordinated by endogenous mediators. Previous studies have demonstrated the immunomodulatory properties of the axonal guidance proteins in the initial phase of acute inflammation. We hypothesized that the neuronal guidance protein neogenin (Neo1) modulates mechanisms of inflammation resolution. In murine peritonitis, Neo1 deficiency (Neo1-/-) resulted in higher efficacies in reducing neutrophil migration into injury sites, increasing neutrophil apoptosis, actuating PMN phagocytosis, and increasing the endogenous biosynthesis of specialized proresolving mediators, such as lipoxin A4, maresin-1, and protectin DX. Neo1 expression was limited to Neo1-expressing Ly6Chi monocytes, and Neo1 deficiency induced monocyte polarization toward an antiinflammatory and proresolving phenotype. Signaling network analysis revealed that Neo1-/- monocytes mediate their immunomodulatory effects specifically by activating the PI3K/AKT pathway and suppressing the TGF-β pathway. In a cohort of 59 critically ill, intensive care unit (ICU) pediatric patients, we found a strong correlation between Neo1 blood plasma levels and abdominal compartment syndrome, Pediatric Risk of Mortality III (PRISM-III) score, and ICU length of stay and mortality. Together, these findings identify a crucial role for Neo1 in regulating tissue regeneration and resolution of inflammation, and determined Neo1 to be a predictor of morbidity and mortality in critically ill children affected by clinical inflammation.

Depolarized Hepatocytes Express the Stem/Progenitor Cell Marker Neighbor of Punc E11 After Bile Duct Ligation in Mice

There is a medical need of biomarkers for disease stratification in cholestatic liver diseases that come along with changes in hepatocyte polarity. Neighbor of Punc E11 (Nope) is an oncofetal marker that is lost after final differentiation and polarization of hepatocytes. We analyzed the expression pattern of Nope and connexin (Cx) 26 as markers of hepatocyte polarization during murine liver development as well as in adult liver with or without bile duct ligation (BDL) by quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR), western blotting (WB), and immunohistochemistry. Nope is highly expressed in fetal and postnatal liver but barely detectable thereafter. Cx26, however, is much higher expressed in adult than in fetal liver. Postnatally, Nope is directed to the sinusoidal membrane of early hepatocytes while Cx26 remains distributed over the whole membrane indicating limited polarization. In the adult liver, only Cx26 is detectable and restricted to the bile canalicular domain indicating fully polarized hepatocytes. After BDL, Nope is again >300-fold upregulated while Cx26 is reduced rapidly. By immunohistochemistry, Nope identifies a subset of hepatocytes with randomly distributed Cx26. In summary, Nope identifies depolarized adult hepatocytes after cholestatic liver injury resembling early postnatal hepatocytes. Therefore, Nope might be a valuable histochemical biomarker allowing stage-specific stratifications in cholestatic liver diseases.

Neogenin recruitment of the WAVE regulatory complex maintains adherens junction stability and tension

To maintain tissue integrity during epithelial morphogenesis, adherens junctions (AJs) must resist the mechanical stresses exerted by dynamic tissue movements. Junctional stability is dependent on actomyosin contractility within the actin ring. Here we describe a novel function for the axon guidance receptor, Neogenin, as a key component of the actin nucleation machinery governing junctional stability. Loss of Neogenin perturbs AJs and attenuates junctional tension. Neogenin promotes actin nucleation at AJs by recruiting the Wave regulatory complex (WRC) and Arp2/3. A direct interaction between the Neogenin WIRS domain and the WRC is crucial for the spatially restricted recruitment of the WRC to the junction. Thus, we provide the first example of a functional WIRS–WRC interaction in epithelia. We further show that Neogenin regulates cadherin recycling at the AJ. In summary, we identify Neogenin as a pivotal component of the AJ, where it influences both cadherin dynamics and junctional tension.

The stability of epithelial adherens junctions depends on tension generated by actomyosin contractility. Here Lee et al. describe a novel role for the axon guidance receptor Neogenin in maintaining junctional stability by recruiting actin nucleation machinery to adherens junctions.

Guidance for life, cell death, and colorectal neoplasia by netrin dependence receptors

This review is focusing on a critical mediator of embryonic and postnatal development with multiple implications in inflammation, neoplasia, and other pathological situations in brain and peripheral tissues. These morphogenetic guidance and dependence processes are involved in several malignancies targeting the epithelial and immune systems including the progression of human colorectal cancers. We consider the most important findings and their impact on basic, translational, and clinical cancer research. Expected information can bring new cues for innovative, efficient, and safe strategies of personalized medicine based on molecular markers, protagonists, signaling networks, and effectors inherent to the Netrin axis in pathophysiological states.

Identification and localization of netrin-4 and neogenin in human first trimester and term placenta

We describe here for the first time the characterization of family member of netrins, netrin-4 and its receptor neogenin, during the development of the placenta. By using western blots and RT-PCR, we demonstrated the presence of netrin-4 and its receptor neogenin protein as well as their transcripts. Using immunohistochemistry, we studied the distribution of netrin-4 and neogenin in both the first trimester and term placenta. We observed staining of netrin-4 in villous and extravillous cytotrophoblasts, syncytiotrophoblast, and endothelial cells whereas staining in stromal cells was faint. In decidua, we observed netrin-4 labelling in glandular epithelial cells, perivascular decidualized cells, and endothelial cells. However, neogenin was absent in villous and extravillous cytotrophoblasts and was expressed only on syncytiotrophoblast and placental stromal cells in the first trimester and at term placenta. The pattern of distribution suggests that a functional netrin-4-neogenin pathway might be restricted to syncytiotrophoblasts, mesenchymal cells, and villous endothelial cells. This pathway function might vary with its localization in the placenta. It is possibly involved in angiogenesis, morphogenesis, and differentiation.

RGMa inhibits neurite outgrowth of neuronal progenitors from murine enteric nervous system via the neogenin receptor in vitro

The enteric nervous system (ENS) in vertebrate embryos is formed by neural crest-derived cells. During development, these cells undergo extensive migration from the vagal and sacral regions to colonize the entire gut, where they differentiate into neurons and glial cells. Guidance molecules like netrins, semaphorins, slits, and ephrins are known to be involved in neuronal migration and axon guidance. In the CNS, the repulsive guidance molecule (RGMa) has been implicated in neuronal differentiation, migration, and apoptosis. Recently, we described the expression of the subtypes RGMa and RGMb and their receptor neogenin during murine gut development. In the present study, we investigated the influence of RGMa on neurosphere cultures derived from fetal ENS. In functional in vitro assays, RGMa strongly inhibited neurite outgrowth of differentiating progenitors via the receptor neogenin. The repulsive effect of RGMa on processes of differentiated enteric neural progenitors could be demonstrated by collapse assay. The influence of the RGM receptor on ENS was also analyzed in neogenin knockout mice. In the adult large intestine of mutants we observed disturbed ganglia formation in the myenteric plexus. Our data indicate that RGMa may be involved in differentiation processes of enteric neurons in the murine gut.

Crystal structure of a hemojuvelin-binding fragment of neogenin at 1.8Å

Neogenin is a type I transmembrane glycoprotein with a large ectodomain containing tandem immunoglobulin-like and fibronectin type III (FNIII) domains. Closely related to the tumor suppressor gene DCC, neogenin functions in critical biological processes through binding to various ligands, including netrin, repulsive guidance molecules, and the iron regulatory protein hemojuvelin. We previously reported that neogenin binds to hemojuvelin through its membrane-proximal fifth and sixth FNIII domains (FN5-6), with domain 6 (FN6) contributing the majority of critical binding interactions. Here we present the crystal structure of FN5-6, the hemojuvelin-binding fragment of human neogenin, at 1.8Å. The two FNIII domains are orientated nearly linearly, a domain arrangement most similar to that of a tandem FNIII-containing fragment within the cytoplasmic tail of the β4 integrin. By mapping surface-exposed residues that differ between neogenin FN5-6 and the comparable domains from DCC, which does not bind hemojuvelin, we identified a potential hemojuvelin-binding site on neogenin FN6. Neogenin FN5, which does not bind hemojuvelin in isolation, exhibits a highly electropositive surface, which may be involved in interactions with negatively-charged polysaccharides or phospholipids in the membrane bilayer. The neogenin FN5-6 structure can be used to facilitate a molecular understanding of neogenin's interaction with hemojuvelin to regulate iron homeostasis and with hemojuvelin-related repulsive guidance molecules to mediate axon guidance.

Effect of different concentrations of neogenin on proliferation, apoptosis and related proliferative factors in human trophoblasts

The underlying effect of different concentrations of neogenin on proliferation, apoptosis and the related proliferative factors in human trophoblasts was explored in order to understand the function of neogenin during placentation. TEV-1 cell line was cultured and the expression of netrin-1 was detected by using indirect cellular immunofluorescence. Exponentially growing TEV-1 cells were treated by different concentrations of neogenin (0, 1, 5, 10, 50 ng/mL) for 24 h. Cell viability was measured by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay. TEV-1 cell apoptosis was assessed by flow cytometry (FCM). The expression of netrin-1 mRNA and protein in TEV-1 cells was examined by using real-time PCR and Western blot, respectively. It was found that immunoreactivity for netrin-1 was observed in cytoplasm of the trophoblasts. Immediately after treatment with different concentrations of neogenin for 24 h, the netrin-1 expression began to increase. Real-time PCR revealed that the expression level of netrin-1 mRNA was 37.59+/-10.25 times higher than control group when TEV-1 cells were exposed to 50 ng/mL neogenin (P<0.01), and the same tendency was seen by using Western blot. MTT results showed that proliferation of TEV-1 cells was independent of neogenin. Meanwhile, apoptosis was significantly increased to (22.15+/-6.15)% at 50 ng/mL neogenin and (6.55+/-0.25)% without neogenin (P<0.01). It is suggested that neogenin regulates proliferation and apoptosis of TEV-1 cells. And it can enhance the ability of TEV-1 cells to express netrin-1 in a dose-dependent manner. Neogenin may play an important biological role in the normal human pregnancy and contribute to the physiological pregnancy process.

RGMb controls aggregation and migration of Neogenin-positive cells in vitro and in vivo

The proliferation, migration and differentiation of dentate gyrus stem and precursor cells have aroused keen interest. Neogenin and RGMb are expressed in non-overlapping compartments of the developing dentate gyrus. While Neogenin is expressed in migrating and proliferating dentate precursors, RGMb is localized in structures bordering the developing dentate, such as cornus ammonis cells and Cajal-Retzius cells in the marginal zone including the hippocampal fissure. Co-immunoprecipitation and binding assays indicate a strong physical interaction. In vitro and in vivo migration of dentate neuroepithelial cells is abolished by RGMb, and cell adhesion is reduced when cells expressing Neogenin comes into contact with cells expressing RGMb. Ectopic expression of RGMb in organotypic slice cultures and after in utero electroporation in the hippocampus modifies precursor cell migration. Our results imply that Neogenin-RGMb interaction might be involved in neuronal migration in the dentate gyrus.

Neogenin interacts with hemojuvelin through its two membrane-proximal fibronectin type III domains

Hemojuvelin is a recently identified iron-regulatory protein that plays an important role in affecting the expression of hepcidin, a key iron regulatory hormone. Although the underlying mechanism of this process is not clear, several hemojuvelin-binding proteins, including the cell surface receptor neogenin and bone morphogenetic protein (BMP) cytokines, have been identified. The ectodomain of neogenin is composed of four immunoglobulin-like (Ig) domains followed by six fibronectin type III-like (FNIII) domains. Here we report expression of soluble versions of hemojuvelin and neogenin for biochemical characterization of their interaction and the interaction of HJV with BMP-2. Hemojuvelin normally undergoes an autocatalytic cleavage, and as in vivo, recombinant hemojuvelin exists as a mixture of cleaved and uncleaved forms. Neogenin binds to cleaved and noncleaved hemojuvelin, as verified by its binding to an uncleaved mutant hemojuvelin. We localized the hemojuvelin binding site on neogenin to the membrane-proximal fifth and sixth FNIII domains and the juxtamembrane linker and showed that a fragment containing only this region binds 2-3 orders of magnitude more tightly than the entire neogenin ectodomain. Binding to the most membrane-proximal region of neogenin may play a role in regulating the levels of soluble and membrane-bound forms of hemojuvelin, which in turn would influence the amount of free BMP-2 available for binding to its receptors and triggering transcription of the hepcidin gene. Our finding that BMP-2 and neogenin bind simultaneously to hemojuvelin raises the possibility that neogenin is part of a multiprotein complex at the hepatocyte membrane involving BMP, its receptors, and hemojuvelin.

Stem cells, cell transplantation and liver repopulation

Liver transplantation is currently the only therapeutic option for patients with end-stage chronic liver disease and for severe acute liver failure. Because of limited donor availability, attention has been focused on the possibility to restore liver mass and function through cell transplantation. Stem cells are a promising source for liver repopulation after cell transplantation, but whether or not the adult mammalian liver contains hepatic stem cells is highly controversial. Part of the problem is that proliferation of mature adult hepatocytes is sufficient to regenerate the liver after two-thirds partial hepatectomy or acute toxic liver injury and participation of stem cells is not required. However, under conditions in which hepatocyte proliferation is blocked, undifferentiated epithelial cells in the periportal areas, called "oval cells", proliferate, differentiate into hepatocytes and restore liver mass. These cells are referred to as facultative liver stem cells, but they do not repopulate the normal liver after their transplantation. In contrast, epithelial cells isolated from the early fetal liver can effectively repopulate the normal liver, but they are already traversing the hepatic lineage and may not be true stem cells. Mesenchymal stem cells and embryonic stem cells can be induced to differentiate along the hepatic lineage in culture, but at present these cells are inefficient in repopulating the liver. This review will characterize these various cell types and compare the properties of these cells and the conditions under which they do or do not repopulate the liver following their transplantation.

New cell surface markers for murine fetal hepatic stem cells identified through high density complementary DNA microarrays

Isolation of hepatic stem cells from the adult liver (AL) has not yet been achieved due to the lack of specific cell surface markers. To identify new surface markers for hepatic stem cells, we analyzed differences in the gene expression profile of embryonic day (ED) 13.5 fetal liver stem/progenitor cells (FLSPC) versus AL by complementary DNA (cDNA) microarray technology. Using FLSPC purified to >90% by immunomagnetic selection for E-cadherin and high density (27k) mouse cDNA microarrays, we identified 474 genes that are more strongly expressed in FLSPC (FLSPC-up genes) and 818 genes that are more strongly expressed in AL (AL-up genes). The most highly overrepresented gene ontology (GO) categories for FLSPC-up genes are nucleus, cellular proliferation, and cell cycle control. AL-up genes are overrepresented for genes in metabolic pathways for specific hepatic functions. We identified 24 FLSPC-up gene surface markers and 69 AL-up gene surface markers. Western blot studies confirmed the expression of the FLSPC-up gene neighbor of Punc E11 (Nope) in fetal liver, but expression was not detectable in AL. Immunohistochemistry, confocal microscopy, and fluorescence-activated cell sorting (FACS) analysis of fetal liver demonstrated that Nope is specifically expressed on the surface of FLSPC within the fetal liver.

CONCLUSION

This is the first microarray study to analyze the specific gene expression profile of purified murine FLSPC. Our analysis identified 24 new/potential cell surface markers for murine fetal hepatic stem cells, of which Nope may be particularly useful in future studies to identify, characterize and isolate hepatic stem cells from the AL.

Neogenin-RGMa Signaling at the Growth Cone Is Bone Morphogenetic Protein-independent and Involves RhoA, ROCK, and PKC

The repulsive guidance molecule RGMa has been shown to induce outgrowth inhibition of neurites by interacting with the transmembrane receptor neogenin. Here we show that RGMa-induced growth cone collapse is mediated by activation of the small GTPase RhoA, its downstream effector Rho kinase and PKC. In contrast to DRG cultures from neogenin-/- mice, in which no RGMa-mediated growth cone collapse and activation of RhoA occurred, treatment of wild type DRG neurites with soluble RGMa led to a marked activation of RhoA within 3 min followed by collapse, but left Rac1 and Cdc42 unaffected. Furthermore, preincubation of DRG axons with the bone morphogenetic protein (BMP) antagonist noggin had no effect on RGMa-mediated growth cone collapse, implying that the role of RGM in axonal guidance is neogenin- and not BMP receptor-dependent. Pretreatment with 1) C3-transferase, a specific inhibitor of the Rho GTPase; 2) Y-27632, a specific inhibitor of Rho kinase; and 3) Gö6976, the general PKC inhibitor, strongly inhibited the collapse rate of PC12 neurites. Growth cone collapse induced by RGMa was abolished by the expression of dominant negative RhoA, but not by dominant negative Rac1. In contrast to RGMa, netrin-1 induced no growth cone retraction but instead reduced RGMa-mediated growth cone collapse. These results suggest that activation of RhoA, Rho kinase, and PKC are physiologically relevant and important elements of the RGMa-mediated neogenin signal transduction pathway involved in axonal guidance.

Expression studies of neogenin and its ligand hemojuvelin in mouse tissues

Juvenile hemochromatosis is a severe hereditary iron overload disease caused by mutations in the HJV (hemojuvelin) and HAMP (hepcidin) genes. Hepcidin is an important iron regulatory hormone, and hemojuvelin may regulate hepcidin synthesis via the multifunctional membrane receptor neogenin. We explored the expression of murine hemojuvelin and neogenin mRNAs and protein. Real-time RT-PCR analysis of 18 tissues from male and female mice was performed to examine the mRNA expression profiles. To further study protein expression and localization we used immunohistochemistry on several tissues from three mouse strains. Mouse Neo1 mRNA was detectable in the 18 tissues tested, the highest signals being evident in the ovary, uterus, and testis. Neogenin protein was observed in the brain, skeletal muscle, heart, liver, stomach, duodenum, ileum, colon, renal cortex, lung, testis, ovary, oviduct, and uterus. The spleen, thymus, and pancreas were negative for neogenin. The highest signals for Hjv mRNA were detectable in the skeletal muscle, heart, esophagus, and liver. The results indicate that Neo1 mRNA is widely expressed in both male and female mouse tissues with the highest signals detected in the reproductive system. Moreover, Hjv and Neo1 mRNAs are simultaneously expressed in skeletal muscle, heart, esophagus, and liver.

Adaptation of estrogen-regulated genes in long-term estradiol deprived MCF-7 breast cancer cells

First line treatment of hormone dependent breast cancer initially causes tumor regression but later results in adaptive changes and tumor re-growth. Responses to second line treatments occur but tumors again begin to progress after a period of 12???18??months. In depth understanding of the adaptive process would allow the identification of targets to abrogate the development of hormonal resistance and prolong the efficacy of endocrine therapy. We have developed a model system to examine adaptive changes in human MCF-7 breast cancer cells. Upon deprivation of estradiol for a prolonged period of time, a maneuver analogous to surgical oophorectomy in pre-menopausal women and use of aromatase inhibitors in post-menopausal patients, tumor cells adapt and become hypersensitive to estradiol. We reasoned that the expression pattern of multiple genes would change in response to estradiol deprivation and that cDNA microarrays would provide an efficient means of assessing these changes. Accordingly, we examined the transcriptional responses to estradiol in long-term estradiol deprived (LTED) MCF-7 cells with a cDNA microarray containing 1901 known genes and ESTs. To assess the changes induced by long-term estradiol deprivation, we compared the effects of estradiol administration in LTED cells with those in MCF-7 cells, which we had previously reported, and confirmed with real time PCR using the parental and LTED cells. Seven genes and one EST were induced by estradiol in LTED but not in wild type MCF-7 cells, whereas ten genes were down-regulated by estradiol only in LTED cells. The expression of seven genes increased concurrently and five decreased in response to estradiol in both cell types. From these observations, we generated testable hypotheses regarding several genes including DKFZP, RAP-1, ribosomal protein S6, and TM4SF1. Based upon the known functions of these genes and the patterns of observed changes, we postulate that divergent regulation of these genes may contribute to the different biologic responses to estrogen in these cell lines. These results provide targets for further mechanistic studies in our experimental system. Our findings indicate that long-term estradiol deprivation causes expression changes in multiple genes and emphasizes the complexity of the process of cellular adaptation.

Survival trees for analyzing clinical outcome in lung adenocarcinomas based on gene expression profiles: identification of neogenin and diacylglycerol kinase alpha expression as critical factors

We present survival trees as an exploratory tool for revealing new insights into gene expression profiles in combination with clinical patient data. Survival trees partition the patient data studied into groups with similar survival outcomes and identify characteristic genetic profiles within these groups. We demonstrate the application of survival trees in a study involving the expression profiles of 3,588 genes in 211 lung adenocarcinoma patients. The survival tree identified a group of early-stage cancer patients with relatively low survival rates and another group of advanced-stage patients with remarkably good survival outcome. For both groups, the tree identified characteristic expression profiles of genes that might play a role in cancerogenesis and disease progression, notably the genes for the netrin receptor neogenin and the Ras/Rho kinase modulator diacylglycerol kinase alpha.

Developmental shift in expression of netrin receptors in the rat spinal cord: predominance of UNC-5 homologues in adulthood

Netrins are a family of secreted proteins required for normal neural development. Netrin-1 is expressed at similar levels in the adult rat spinal cord and the embryonic CNS, suggesting that it contributes to adult CNS function. Here we show that the netrin receptors dcc, neogenin, unc5h1, unc5h2, and unc5h3 are also expressed in the adult rat spinal cord. Lower levels of DCC and neogenin were detected in the adult relative to the embryonic CNS. Conversely, the adult spinal cord contains increased levels of UNC-5 homologues in comparison with the embryo. Multiple mRNA transcripts detected by Northern blot analysis suggested that netrin receptors might be encoded by alternatively spliced mRNAs. We have identified a novel alternatively spliced mRNA encoding UNC5H1, UNC5H1(Delta)TSP1, which lacks the first of the two extracellular thrombospondin domains. This novel splice variant is the major transcript detected in the early embryonic CNS, although both splice variants are expressed in the adult. Previously identified alternatively spliced mRNAs encoding DCC and neogenin were also detected. Dcc, neogenin, unc5h1, unc5h2, and unc5h3 are expressed by subsets of neurons. Robust expression of unc5h2 was found in glia. These findings suggest that unc-5 homologues constitute a major mode of netrin-1 signal transduction in the adult spinal cord and may be involved in phenomena analogous to axon repulsion, such as inhibiting process extension and collateral sprouting.

Overexpression of DRG2 suppresses the growth of Jurkat T cells but does not induce apoptosis

Developmentally regulated GTP-binding protein (DRG) is a new subfamily within the superfamily of GTP-binding proteins. Its expression is regulated during embryonic development. To investigate the effect of the expression of DRG2 on cell growth, we constructed a human Jurkat-T-cell line that overexpresses DRG2. Overexpression of DRG2 suppressed the growth and the aggregation of Jurkat cells but did not induce apoptotic cell death. We used cDNA microarray analysis to examine the global changes in gene expression induced by an overexpression of DRG2. DNA array analyses identified genes that may suppress cell growth at a number of levels in multiple signaling cascades in Jurkat cells and also several prosurvival genes that may protect cells from apoptosis.

Where the rubber meets the road: netrin expression and function in developing and adult nervous systems

Netrins are a family of secreted proteins that direct the migration of cells and axonal growth cones during neural development. They are bifunctional cues, attracting some cell types and repelling others. Netrins function as either short- or long-range cues, in some circumstances acting close to the surface of the cells that produce them and in other cases at a distance. Two classes of receptors mediate the response to netrin-1, the deleted in colorectal cancer family and the UNC-5 homolog family. Although netrin function has been extensively studied in the embryonic nervous system, netrin-1 is expressed in the adult mammalian spinal cord at a level similar to that in the embryonic CNS. In the adult and embryonic CNS, the majority of netrin-1 protein is not freely soluble but is associated with membranes and extracellular matrix. This distribution is consistent with netrin-1 acting as a short-range cue. Here we present a model whereby netrin-1 in the embryonic neural epithelium could act as a membrane-associated long-range cue. Netrin-1 is expressed in the adult by multiple types of neurons and by myelinating glia: oligodendrocytes in the CNS and Schwann cells in the PNS. In the white matter of the adult CNS, netrin-1 protein is absent from compact myelin but enriched in periaxonal myelin at the interface between axons and oligodendrocytes. This distribution suggests that in the adult nervous system netrin-1 may function to mediate cell-cell interactions. Furthermore, netrin receptor expression persists in neurons following injury, raising the possibility that netrin-1 may influence axonal regeneration.

Cloning, expression, and alternative splicing of neogenin1 in zebrafish

Caenorhabditis elegans UNC-40, Drosophila Frazzled, and vertebrate Neogenin and DCC constitute a subgroup of the immunoglobulin superfamily (IgSF). They possess four immunoglobulin-like domains and six fibronectin-type III repeats at the extracellular region, a single transmembrane region, and a approximately 300 amino-acid intracellular region. UNC-40, Frazzled and DCC can function in axon guidance as the receptor of Netrin (Cell Mol. Life Sci. 56 (1999) 62; Curr. Opin. Cell Biol. 10 (1998) 609). Neogenin binds to Netrin-1 with the same affinity as DCC in vitro (Cell 87 (1996) 175), and is expressed by neurons as they project axons (J. Cell Biol. 127 (1994) 2009), suggesting that it is also a DCC-like Netrin receptor. A zebrafish homologue of DCC (zDCC) is reported recently (Mech. Dev. 109 (2001) 105), but so far there is no report of zebrafish Neogenin. To elucidate a possible neural function of vertebrate Neogenin, we cloned and characterized a zebrafish homologue of neogenin, zneo1, and identified four alternative splice sites within it. In the adult, despite broad tissue distribution, our reverse transcription polymerase chain reaction and Northern analyses demonstrated the dominant expression of zneo1 mRNA in brain. We detected zneo1 mRNA in the embryos from 10 hpf onward and revealed its spatiotemporally regulated expression pattern in both neuronal and non-neuronal tissues by in situ hybridization. Our data showed that during early brain development, zneo1 mRNA was not only present in the proliferative ventricular zones but also in the domains of several first postmitotic neuron clusters when they extended axons. Alternative splicing generates several isoforms of zneo1. Most of them are developmentally regulated, showing distinct distribution in brain and other tissues.

Interaction of Myc-associated zinc finger protein with DCC, the product of a tumor-suppressor gene, during the neural differentiation of P19 EC cells

Expression of the DCC (deleted in colorectal cancer) protein is strongly induced during the neural differentiation of mouse P19 embryonal carcinoma (EC) cells that occurs when these cells are treated with retinoic acid (RA). Myc-associated zinc finger protein (MAZ) is a DNA-binding protein that is widely expressed and functions in human, mouse and hamster cells as an activator, an initiator or a terminator of transcription. However, the biological functions of MAZ remain elusive. We report here that MAZ associates with the cytoplasmic domain of the DCC protein in vivo and in vitro. Yeast two-hybrid assays confirmed this association. An immunofluorescence study demonstrated that DCC protein is expressed at elevated levels in neuron-like P19 EC cells, in particular in axons, in which the MAZ protein is also expressed. We found that MAZ was translocated from the nucleus to the cytoplasm during the RA-induced terminal differentiation of P19 EC cells with resultant loss of the ability of MAZ to bind to the ME1a1 site of the c-myc promoter. Taken together, our observations imply that the DCC protein might play a critical role as a signaling molecule in the regulation of the transcriptional activity of MAZ during the neural differentiation of P19 EC cells.

09/15: Comparative genomics of a conserved chromosomal region associated with a complex human phenotype

Three genes that encode related immunoglobulin superfamily molecules have recently been mapped to human chromosome 15 in the region q22.3-q23 and to the syntenic region on mouse chromosome 9. These genes presumably derived from gene duplications, and they are highly similar to Deleted in Colorectal Cancer (DCC), which functions as an axon guidance molecule during development of the nervous system. To find out whether additional genes of this class were present in a chromosomal cluster, we produced a comparative physical map within the region of synteny between mouse chromosome 9 and human chromosome 15. This interval overlaps the critical region for the fourth genetic locus for Bardet-Biedl syndrome (BBS4) in humans. Bardet-Biedl syndrome (OMIM 600374) is characterized by poly/syn/brachydactyly, retinal degeneration, hypogonadism, mental retardation, obesity, diabetes, and kidney abnormalities. A detailed map of this locus will help to identify candidate genes for this disorder.

Down syndrome cell adhesion molecule DSCAM mediates homophilic intercellular adhesion

Down Syndrome (DS) caused by trisomy 21 is the most common birth defect associated with mental retardation. Recently, a novel gene named, DSCAM, has been identified in the DS critical region. DSCAM is predicted to be a transmembrane protein with a very high structural and sequence homology to Ig superfamily of cell adhesion molecules and is expressed in the developing nervous system with the highest level in fetal brain. Diverse glycoproteins of cell surfaces and extracellular matrices operationally termed as 'adhesion molecule' are important in the specification of cell interactions during development, maintenance and regeneration of the nervous system. To understand the cellular function of DSCAM protein, we transfected human DSCAM cDNA into mouse fibroblast L cells and analysed its expression. On Western blot analysis, antibodies raised against recombinant DSCAM-Ig3 recognized a 198 kDa protein band in the membrane fraction of DSCAM transfected L cells. Stable transformants expressing DSCAM showed uniform surface expression. DSCAM-expressing transfectants exhibited enhanced adhesive properties, aggregating with faster kinetics and forming aggregates in a homophilic manner. Divalent cations are not required for this cell aggregation. These results demonstrate that DSCAM is a cell adhesion molecule that can mediate cation-independent homophilic binding activity between DSCAM expressing cells.

Cloning and expression of nope, a new mouse gene of the immunoglobulin superfamily related to guidance receptors

The novel mouse gene Nope was identified due to its proximity to the Punc gene on chromosome 9. With a domain structure of four immunoglobulin domains, five fibronectin type III repeats, a single transmembrane domain, and a cytoplasmic domain, Nope encodes a new member of the immunoglobulin superfamily of cell surface proteins. It displays a high level of similarity to Punc, as well as to guidance receptors such as the Deleted in Colorectal Cancer protein and Neogenin. Nope is expressed during embryonic development in the notochord, in developing skeletal muscles, and later in the ventricular zone of the nervous system. In the adult brain, Nope can be detected in the hippocampus. Radiation hybrid mapping of Nope, Punc, and Neogenin placed all three genes in close vicinity on mouse chromosome 9.