Biochemical dissection of Anosmin-1 interaction with FGFR1 and components of the extracellular matrix

Extracellular matrix protein anosmin-1 overexpression alters dopaminergic phenotype in the CNS and the PNS with no pathogenic consequences in a MPTP model of Parkinson's disease

The development and survival of dopaminergic neurons are influenced by the fibroblast growth factor (FGF) pathway. Anosmin-1 (A1) is an extracellular matrix protein that acts as a major regulator of this signaling pathway, controlling FGF diffusion, and receptor interaction and shuttling. In particular, previous work showed that A1 overexpression results in more dopaminergic neurons in the olfactory bulb. Prompted by those intriguing results, in this study, we investigated the effects of A1 overexpression on different populations of catecholaminergic neurons in the central (CNS) and the peripheral nervous systems (PNS). We found that A1 overexpression increases the number of dopaminergic substantia nigra pars compacta (SNpc) neurons and alters the striosome/matrix organization of the striatum. Interestingly, these numerical and morphological changes in the nigrostriatal pathway of A1-mice did not confer an altered susceptibility to experimental MPTP-parkinsonism with respect to wild-type controls. Moreover, the study of the effects of A1 overexpression was extended to different dopaminergic tissues associated with the PNS, detecting a significant reduction in the number of dopaminergic chemosensitive carotid body glomus cells in A1-mice. Overall, our work shows that A1 regulates the development and survival of dopaminergic neurons in different nuclei of the mammalian nervous system.

Mutation spectrum of Kallmann syndrome: identification of five novel mutations across ANOS1 and FGFR1

BACKGROUND

Kallmann syndrome (KS) is a common type of idiopathic hypogonadotropic hypogonadism. To date, more than 30 genes including ANOS1 and FGFR1 have been identified in different genetic models of KS without affirmatory genotype-phenotype correlation, and novel mutations have been found.

METHODS

A total of 35 unrelated patients with clinical features of disorder of sex development were recruited. Custom-panel sequencing or whole-exome sequencing was performed to detect the pathogenic mutations. Sanger sequencing was performed to verify single-nucleotide variants. Copy number variation-sequencing (CNV-seq) was performed to determine CNVs. The pathogenicity of the identified variant was predicted in silico. mRNA transcript analysis and minigene reporter assay were performed to test the effect of the mutation on splicing.

RESULTS

ANOS1 gene c.709 T > A and c.711 G > T were evaluated as pathogenic by several commonly used software, and c.1063-2 A > T was verified by transcriptional splicing assay. The c.1063-2 A > T mutation activated a cryptic splice acceptor site downstream of the original splice acceptor site and resulted in an aberrant splicing of the 24-basepair at the 5' end of exon 8, yielding a new transcript with c.1063-1086 deletion. FRFR1 gene c.1835delA was assessed as pathogenic according to the ACMG guideline. The CNV of del(8)(p12p11.22)chr8:g.36140000_38460000del was judged as pathogenic according to the ACMG & ClinGen technical standards.

CONCLUSIONS

Herein, we identified three novel ANOS1 mutations and two novel FGFR1 variations in Chinese KS families. In silico prediction and functional experiment evaluated the pathogenesis of ANOS1 mutations. FRFR1 c.1835delA mutation and del(8)(p12p11.22)chr8:g.36140000_38460000del were assessed as pathogenic variations. Therefore, our study expands the spectrum of mutations associated with KS and provides diagnostic evidence for patients who carry the same mutation in the future.

Anosmin 1 N-terminal domains modulate prokineticin receptor 2 activation by prokineticin 2

The X-linked form of Kallmann syndrome (KS), characterized by hypogonadotropic hypogonadism and anosmia, is due to mutations in the ANOS1 gene that encodes for the extracellular matrix (ECM) protein anosmin 1. Prokineticins (PKs) exert their biological functions through the activation of the G protein-coupled receptors (GPCRs) prokineticin receptor 1 and 2 (PKR1, 2), and mutations in the PK2 and PKR2 genes are involved in the pathogenesis of KS. We have previously shown interaction between PKR2 and anosmin 1 in vitro. In the current report we present evidence of the modulation of PK2/PKR2 activity by anosmin 1, since this protein is able to enhance the activation of the ERK1/2 (extracellular signal-regulated kinase 1/2) pathway elicited by PK2 through PKR2. We also show that the N-terminal region of anosmin 1, capable of binding to the PK2-binding domain of PKR2, seems to be responsible for this effect. The whey acidic protein domain (WAP) is necessary for this modulatory activity, although data from GST pull-down (glutathione-S-transferase) and analysis of the N267K mutation in the fibronectin type III domain 1 (FnIII.1) suggest the cysteine-rich (CR) and the FnIII.1 domains could assist the WAP domain both in the binding to PKR2 and in the modulation of the activation of the receptor by PK2. Our data support the idea of a modulatory role of anosmin 1 in the biological effects controlled by the PK2/PKR2 system.

Anosmin-1-Like Effect of UMODL1/Olfactorin on the Chemomigration of Mouse GnRH Neurons and Zebrafish Olfactory Axons Development

The impairment of development/migration of hypothalamic gonadotropin-releasing hormone (GnRH) neurons is the main cause of Kallmann's syndrome (KS), an inherited disorder characterized by hypogonadism, anosmia, and other developmental defects. Olfactorin is an extracellular matrix protein encoded by the UMODL1 (uromodulin-like 1) gene expressed in the mouse olfactory region along the migratory route of GnRH neurons. It shares a combination of WAP and FNIII repeats, expressed in complementary domains, with anosmin-1, the product of the ANOS1 gene, identified as the causative of KS. In the present study, we have investigated the effects of olfactorin in vitro and in vivo models. The results show that olfactorin exerts an anosmin-1-like strong chemoattractant effect on mouse-immortalized GnRH neurons (GN11 cells) through the activation of the FGFR and MAPK pathways. In silico analysis of olfactorin and anosmin-1 reveals a satisfactory similarity at the N-terminal region for the overall arrangement of corresponding WAP and FNIII domains and marked similarities between WAP domains’ binding modes of interaction with the resolved FGFR1–FGF2 complex. Finally, in vivo experiments show that the down-modulation of the zebrafish z-umodl1 gene (orthologous of UMODL1) in both GnRH3:GFP and omp2k:gap-CFPrw034 transgenic zebrafish strains leads to a clear disorganization and altered fasciculation of the neurites of GnRH3:GFP neurons crossing at the anterior commissure and a significant increase in olfactory CFP + fibers with altered trajectory. Thus, our study shows olfactorin as an additional factor involved in the development of olfactory and GnRH systems and proposes UMODL1 as a gene worthy of diagnostic investigation in KS.

Simplification of the purification of heat stable recombinant low molecular weight proteins and peptides from GST-fusion products

The synthesis and purification of peptides of importance in the fields of research and medicine continue to be a challenging task. Chemical synthesis of oligopeptides, especially those greater than 25 amino acids, is cost prohibitive. On the other hand, several bottlenecks exist in the production of recombinant short peptides in heterologous expression hosts such as Escherichia coli (E. coli). In this study, a rapid, cost-effective, and reliable method for the production and single-step-purification of peptides and small proteins was developed. Five peptides and small proteins were overexpressed in E. coli as GST-fusion products in high yields. The recombinant peptides or proteins were successfully purified after enzymatic cleavage with selective heat-induced precipitation of the GST-affinity tag. Qualitative and quantitative analysis using SDS-PAGE and mass spectrometric methods suggest that the recombinant peptides/ proteins were purified to greater than 95% homogeneity. Results of biophysical experiments, including multi-dimensional NMR spectroscopy, show that the purified proteins/ peptides retain their native conformation. Isothermal titration calorimetry studies indicate no significant change in the binding affinity of the heat-treated purified product to their interacting partner(s) compared to the recombinant peptides purified by conventional chromatographic procedures without subjecting to heat treatment. In our opinion, the results reported render the purification of recombinant proteins/ peptides of biomedical relevance using our proposed method easy and reliable.

Of mice and men - and guinea pigs?

This year marks the twentieth anniversary of the publication of the first draft of the human genome and its broad availability to the scientific community. In parallel, the annotation of the mouse genome led to the identification and analysis of countless genes by means of genetic manipulation. Today, when comparing both genomes, it might surprise that some genes are still seeking their respective homologs in either species. In this review, we aim at raising awareness for the remarkable differences between the researcher's favorite rodents, i.e., mice and rats, when it comes to the generation of rodent research models regarding genes with a particular delicate localization, namely the pseudoautosomal region on both sex chromosomes. Many of these genes are of utmost clinical relevance in humans and still miss a rodent disease model giving their absence in mice and rats or low sequence similarity compared to humans. The abundance of rodents within mammals prompted us to investigate different branches of rodents leading us to the re-discovery of the guinea pig as a mammalian research model for a distinct group of genes.

Role of Fibroblast Growth Factors Receptors (FGFRs) in Brain Tumors, Focus on Astrocytoma and Glioblastoma

Despite pharmacological treatments and surgical practice options, the mortality rate of astrocytomas and glioblastomas remains high, thus representing a medical emergency for which it is necessary to find new therapeutic strategies. Fibroblast growth factors (FGFs) act through their associated receptors (FGFRs), a family of tyrosine kinase receptors consisting of four members (FGFR1-4), regulators of tissue development and repair. In particular, FGFRs play an important role in cell proliferation, survival, and migration, as well as angiogenesis, thus their gene alteration is certainly related to the development of the most common diseases, including cancer. FGFRs are subjected to multiple somatic aberrations such as chromosomal amplification of FGFR1; mutations and multiple dysregulations of FGFR2; and mutations, translocations, and significant amplifications of FGFR3 and FGFR4 that correlate to oncogenesis process. Therefore, the in-depth study of these receptor systems could help to understand the etiology of both astrocytoma and glioblastoma so as to achieve notable advances in more effective target therapies. Furthermore, the discovery of FGFR inhibitors revealed how these biological compounds improve the neoplastic condition by demonstrating efficacy and safety. On this basis, this review focuses on the role and involvement of FGFRs in brain tumors such as astrocytoma and glioblastoma.

Functional Heterogeneity of Mouse and Human Brain OPCs: Relevance for Preclinical Studies in Multiple Sclerosis

Besides giving rise to oligodendrocytes (the only myelin-forming cell in the Central Nervous System (CNS) in physiological conditions), Oligodendrocyte Precursor Cells (OPCs) are responsible for spontaneous remyelination after a demyelinating lesion. They are present along the mouse and human CNS, both during development and in adulthood, yet how OPC physiological behavior is modified throughout life is not fully understood. The activity of adult human OPCs is still particularly unexplored. Significantly, most of the molecules involved in OPC-mediated remyelination are also involved in their development, a phenomenon that may be clinically relevant. In the present article, we have compared the intrinsic properties of OPCs isolated from the cerebral cortex of neonatal, postnatal and adult mice, as well as those recovered from neurosurgical adult human cerebral cortex tissue. By analyzing intact OPCs for the first time with 1H High Resolution Magic Angle Spinning Nuclear Magnetic Resonance (1H HR-MAS NMR) spectroscopy, we show that these cells behave distinctly and that they have different metabolic patterns in function for their stage of maturity. Moreover, their response to Fibroblast Growth Gactor-2 (FGF-2) and anosmin-1 (two molecules that have known effects on OPC biology during development and that are overexpressed in individuals with Multiple Sclerosis (MS)) differs in relation to their developmental stage and in the function of the species. Our data reveal that the behavior of adult human and mouse OPCs differs in a very dynamic way that should be very relevant when testing drugs and for the proper design of effective pharmacological and/or cell therapies for MS.

Serum levels of ANOS1 serve as a diagnostic biomarker of gastric cancer: a prospective multicenter observational study

BACKGROUND

Development of high-performance serum biomarkers will likely improve treatment outcomes of patients with gastric cancer (GC). We previously identified the candidate serum markers, anosmin 1 (ANOS1), dihydropyrimidinase-like 3 (DPYSL3), and melanoma-associated antigen D2 (MAGE-D2) and evaluated their clinical significance through a single-center retrospective analysis. Here we conducted a prospective multicenter observational study aimed at validating the diagnostic performance of these potential markers.

METHODS

We analyzed serum levels before and after surgery of the three potential biomarkers in patients with GC and healthy volunteers. Quantification of serum and GC tissue levels was performed using an ELISA.

RESULTS

Area under the curve (AUC) values that discriminated patients with GC from healthy controls were - 0.7058, 0.6188, and 0.5031 for ANOS1, DPYSL3, and MAGED2, respectively. The sensitivity and specificity of the ANOS1 assay were 0.36 and 0.85, respectively. The AUC value of ANOS1 that discriminated patients with stage I GC from healthy controls was 0.7131. Serum ANOS1 levels were significantly elevated in patients with stage I GC compared with those of healthy controls (median 1179 ng/ml and 461 ng/ml, respectively, P < 0.0001) and decreased after resection of primary GC lesions (P < 0.0001). The combination of serum ANOS1 and DPYSL3 levels increased the AUC value that discriminated patients with GC from healthy controls. Serum levels of ANOS1 did not significantly correlate with those of carcinoembryonic antigen, carbohydrate antigen 19-9, or other markers of inflammation.

CONCLUSIONS

Serum levels of ANOS1 may serve as a useful diagnostic tool for managing GC.

Anosmin-1 activates vascular endothelial growth factor receptor and its related signaling pathway for olfactory bulb angiogenesis

Anosmin-1 is a secreted glycoprotein encoded by the ANOS1 gene, and its loss of function causes Kallmann syndrome (KS), which is characterized by anosmia and hypogonadism due to olfactory bulb (OB) dysfunction. However, the physiological function of anosmin-1 remains to be elucidated. In KS, disordered angiogenesis is observed in OB, resulting in its hypoplasia. In this study, we examined the involvement of anosmin-1 in angiogenic processes. Anosmin-1 was detected on the vessel-like structure in OB of chick embryos, and promoted the outgrowth of vascular sprouts as shown by assays of OB tissue culture. Cell migration, proliferation, and tube formation of endothelial cells were induced by treatment with anosmin-1 as well as vascular endothelial growth factor-A (VEGF-A), and further enhanced by treatment with both of them. We newly identified that anosmin-1 activated VEGF receptor-2 (VEGFR2) by binding directly to it, and its downstream signaling molecules, phospholipase Cγ1 (PLCγ1) and protein kinase C (PKC). These results suggest that anosmin-1 plays a key role in the angiogenesis of developing OB through the VEGFR2–PLCγ1–PKC axis by enhancing the VEGF function.

Fibroblast Growth Factor Receptor Functions in Glioblastoma

Glioblastoma is the most lethal brain cancer in adults, with no known cure. This cancer is characterized by a pronounced genetic heterogeneity, but aberrant activation of receptor tyrosine kinase signaling is among the most frequent molecular alterations in glioblastoma. Somatic mutations of fibroblast growth factor receptors (FGFRs) are rare in these cancers, but many studies have documented that signaling through FGFRs impacts glioblastoma progression and patient survival. Small-molecule inhibitors of FGFR tyrosine kinases are currently being trialed, underlining the therapeutic potential of blocking this signaling pathway. Nevertheless, a comprehensive overview of the state of the art of the literature on FGFRs in glioblastoma is lacking. Here, we review the evidence for the biological functions of FGFRs in glioblastoma, as well as pharmacological approaches to targeting these receptors.

Cross-Talk between Fibroblast Growth Factor Receptors and Other Cell Surface Proteins

Fibroblast growth factors (FGFs) and their receptors (FGFRs) constitute signaling circuits that transmit signals across the plasma membrane, regulating pivotal cellular processes like differentiation, migration, proliferation, and apoptosis. The malfunction of FGFs/FGFRs signaling axis is observed in numerous developmental and metabolic disorders, and in various tumors. The large diversity of FGFs/FGFRs functions is attributed to a great complexity in the regulation of FGFs/FGFRs-dependent signaling cascades. The function of FGFRs is modulated at several levels, including gene expression, alternative splicing, posttranslational modifications, and protein trafficking. One of the emerging ways to adjust FGFRs activity is through formation of complexes with other integral proteins of the cell membrane. These proteins may act as coreceptors, modulating binding of FGFs to FGFRs and defining specificity of elicited cellular response. FGFRs may interact with other cell surface receptors, like G-protein-coupled receptors (GPCRs) or receptor tyrosine kinases (RTKs). The cross-talk between various receptors modulates the strength and specificity of intracellular signaling and cell fate. At the cell surface FGFRs can assemble into large complexes involving various cell adhesion molecules (CAMs). The interplay between FGFRs and CAMs affects cell–cell interaction and motility and is especially important for development of the central nervous system. This review summarizes current stage of knowledge about the regulation of FGFRs by the plasma membrane-embedded partner proteins and highlights the importance of FGFRs-containing membrane complexes in pathological conditions, including cancer.

ANOS1: a unified nomenclature for Kallmann syndrome 1 gene (KAL1) and anosmin-1

It is accepted that confusion regarding the description of genetic variants occurs when researchers do not use standard nomenclature. The Human Genome Organization Gene Nomenclature Committee contacted a panel of consultants, all working on the KAL1 gene, to propose an update of the nomenclature of the gene, as there was a convention in the literature of using the ‘KAL1’ symbol, when referring to the gene, but using the name ‘anosmin-1’ when referring to the protein. The new name, ANOS1, reflects protein name and is more transferrable across species.

GnRH-(1-5) Inhibits TGF-β Signaling to Regulate the Migration of Immortalized Gonadotropin-Releasing Hormone Neurons

Gonadotropin-releasing hormone (GnRH) neurons originate outside the central nervous system (CNS) in the nasal placode where their migration to the basal forebrain is dependent on the integration of multiple signaling cues during development. The proper migration and establishment of the GnRH neuronal population within the CNS are critical for normal pubertal onset and reproductive function. The endopeptidase EP24.15 is expressed along the migratory path of GnRH neurons and cleaves the full-length GnRH to generate the metabolite GnRH-(1-5). Using the GN11 cell model, which is considered a pre-migratory GnRH neuronal cell line, we demonstrated that GnRH-(1-5) inhibits cellular migration in a wound closure assay by binding the orphan G protein-coupled receptor 173 (GPR173). In our current experiments, we sought to utilize an in vitro migration assay that better reflects the external environment that migrating GnRH neurons are exposed to during development. Therefore, we used a transwell assay where the inserts were coated with or without a matrigel, a gelatinous mixture containing extracellular matrix (ECM) proteins, to mimic the extracellular environment. Interestingly, GnRH-(1-5) inhibited the ability of GN11 cells to migrate only through ECM mimetic and was dependent on GPR173. Furthermore, we found that GN11 cells secrete TGF-β1, 2, and 3 but only TGF-β1 release and signaling were inhibited by GnRH-(1-5). To identify potential mechanisms involved in the proteolytic activation of TGF-β, we measured a panel of genes implicated in ECM remodeling. We found that GnRH-(1-5) consistently increased tissue inhibitors of metalloproteinase 1 expression, which is an inhibitor of proteinase activity, leading to a decrease in bioactive TGF-β and subsequent signaling. These results suggest that GnRH-(1-5) activating GPR173 may modulate the response of migrating GnRH neurons to external cues present in the ECM environment via an autocrine-dependent mechanism involving TGF-β.

Tissue-type plasminogen activator exerts EGF-like chemokinetic effects on oligodendrocytes in white matter (re)myelination

Background

The ability of oligodendrocyte progenitor cells (OPCs) to give raise to myelin forming cells during developmental myelination, normal adult physiology and post-lesion remyelination in white matter depends on factors which govern their proliferation, migration and differentiation. Tissue plasminogen activator (tPA) is a serine protease expressed in the central nervous system (CNS), where it regulates cell fate. In particular, tPA has been reported to protect oligodendrocytes from apoptosis and to facilitate the migration of neurons. Here, we investigated whether tPA can also participate in the migration of OPCs during CNS development and during remyelination after focal white matter lesion.

Methods

OPC migration was estimated by immunohistological analysis in spinal cord and corpus callosum during development in mice embryos (E13 to P0) and after white matter lesion induced by the stereotactic injection of lysolecithin in adult mice (1 to 21 days post injection). Migration was compared in these conditions between wild type and tPA knock-out animals. The action of tPA was further investigated in an in vitro chemokinesis assay.

Results

OPC migration along vessels is delayed in tPA knock-out mice during development and during remyelination. tPA enhances OPC migration via an effect dependent on the activation of epidermal growth factor receptor.

Conclusion

Endogenous tPA facilitates the migration of OPCs during development and during remyelination after white matter lesion by the virtue of its epidermal growth factor-like domain.

Electronic supplementary material

The online version of this article (doi:10.1186/s13024-017-0160-5) contains supplementary material, which is available to authorized users.

Point mutations in KAL1 and the mitochondrial gene MT-tRNA(cys) synergize to produce Kallmann syndrome phenotype

Kallmann syndrome (KS) is an inherited developmental disorder defined as the association of hypogonadotropic hypogonadism and anosmia or hyposmia. KS has been shown to be a genetically heterogeneous disease with different modes of inheritance. However, variants in any of the causative genes identified so far are only found in approximately one third of KS patients, thus indicating that other genes or pathways remain to be discovered. Here, we report a large Han Chinese family with inherited KS which harbors two novel variants, KAL1 c.146G>T (p.Cys49Phe) and mitochondrial tRNA(cys) (m.5800A>G). Although two variants can't exert obvious effects on the migration of GnRH neurons, they show the synergistic effect, which can account for the occurrence of the disorder in this family. Furthermore, the disturbance of the mitochondrial cysteinyl-tRNA pathway can significantly affect the migration of GnRH cells in vitro and in vivo by influencing the chemomigration function of anosmin-1. Our work highlights a new mode of inheritance underlay the genetic etiology of KS and provide valuable clues to understand the disease development.

Anosmin-1 over-expression regulates oligodendrocyte precursor cell proliferation, migration and myelin sheath thickness

During development of the central nervous system, anosmin-1 (A1) works as a chemotropic cue contributing to axonal outgrowth and collateralization, as well as modulating the migration of different cell types, fibroblast growth factor receptor 1 (FGFR1) being the main receptor involved in all these events. To further understand the role of A1 during development, we have analysed the over-expression of human A1 in a transgenic mouse line. Compared with control mice during development and in early adulthood, A1 over-expressing transgenic mice showed an enhanced oligodendrocyte precursor cell (OPC) proliferation and a higher number of OPCs in the subventricular zone and in the corpus callosum (CC). The migratory capacity of OPCs from the transgenic mice is increased in vitro due to a higher basal activation of ERK1/2 mediated through FGFR1 and they also produced more myelin basic protein (MBP). In vivo, the over-expression of A1 resulted in an elevated number of mature oligodendrocytes with higher levels of MBP mRNA and protein, as well as increased levels of activation of the ERK1/2 proteins, while electron microscopy revealed thicker myelin sheaths around the axons of the CC in adulthood. Also in the mature CC, the nodes of Ranvier were significantly longer and the conduction velocity of the nerve impulse in vivo was significantly increased in the CC of A1 over-expressing transgenic mice. Altogether, these data confirmed the involvement of A1 in oligodendrogliogenesis and its relevance for myelination.

Anosmin-1 over-expression increases adult neurogenesis in the subventricular zone and neuroblast migration to the olfactory bulb

New subventricular zone (SVZ)-derived neuroblasts that migrate via the rostral migratory stream are continuously added to the olfactory bulb (OB) of the adult rodent brain. Anosmin-1 (A1) is an extracellular matrix protein that binds to FGF receptor 1 (FGFR1) to exert its biological effects. When mutated as in Kallmann syndrome patients, A1 is associated with severe OB morphogenesis defects leading to anosmia and hypogonadotropic hypogonadism. Here, we show that A1 over-expression in adult mice strongly increases proliferation in the SVZ, mainly with symmetrical divisions, and produces substantial morphological changes in the normal SVZ architecture, where we also report the presence of FGFR1 in almost all SVZ cells. Interestingly, for the first time we show FGFR1 expression in the basal body of primary cilia in neural progenitor cells. Additionally, we have found that A1 over-expression also enhances neuroblast motility, mainly through FGFR1 activity. Together, these changes lead to a selective increase in several GABAergic interneuron populations in different OB layers. These specific alterations in the OB would be sufficient to disrupt the normal processing of sensory information and consequently alter olfactory memory. In summary, this work shows that FGFR1-mediated A1 activity plays a crucial role in the continuous remodelling of the adult OB.

ERK1/2 signaling is essential for the chemoattraction exerted by human FGF2 and human anosmin-1 on newborn rat and mouse OPCs via FGFR1

Signaling through fibroblast growth factor receptors (FGFRs) is essential for many cellular processes including proliferation and migration, as well as differentiation events such as myelination. Anosmin-1 is an extracellular matrix (ECM) glycoprotein that interacts with the fibroblast growth factor receptor 1 (FGFR1) to exert its biological actions through this receptor, although the intracellular pathways underlying anosmin-1 signaling remain largely unknown. This protein is defective in the X-linked form of Kallmann syndrome (KS) and has a prominent role in the migration of neuronal and oligodendroglial precursors. We have shown that anosmin-1 exerts a chemotactic effect via FGFR1 on neuronal precursors from the subventricular zone (SVZ) and the essential role of the ERK1/2 signaling. We report here the positive chemotactic effect of FGF2 and anosmin-1 on rat and mouse postnatal OPCs via FGFR1. The same effect was observed with the truncated N-terminal region of anosmin-1 (A1Nt). The introduction in anosmin-1 of the missense mutation F517L found in patients suffering from KS annulled the chemotactic activity; however, the mutant form carrying the disease-causing mutation E514K also found in KS patients, behaved as the wild-type protein. The chemoattraction exhibited by FGF2 and anosmin-1 on OPCs was blocked by the mitogen-activated protein kinase (MAPK) inhibitor U0126, suggesting that the activation of the ERK1/2 MAPK signaling pathway following interaction with the FGFR1 is necessary for FGF2 and anosmin-1 to exert their chemotactic effect. In fact, both proteins were able to induce the phosphorylation of the ERK1/2 kinases after the activation of the FGFR1 receptor.

The effect of glia-glia interactions on oligodendrocyte precursor cell biology during development and in demyelinating diseases

Oligodendrocyte precursor cells (OPCs) originate in specific areas of the developing central nervous system (CNS). Once generated, they migrate towards their destinations where they differentiate into mature oligodendrocytes. In the adult, 5-8% of all cells in the CNS are OPCs, cells that retain the capacity to proliferate, migrate, and differentiate into oligodendrocytes. Indeed, these endogenous OPCs react to damage in demyelinating diseases, like multiple sclerosis (MS), representing a key element in spontaneous remyelination. In the present work, we review the specific interactions between OPCs and other glial cells (astrocytes, microglia) during CNS development and in the pathological scenario of MS. We focus on: (i) the role of astrocytes in maintaining the homeostasis and spatial distribution of different secreted cues that determine OPC proliferation, migration, and differentiation during CNS development; (ii) the role of microglia and astrocytes in the redistribution of iron, which is crucial for myelin synthesis during CNS development and for myelin repair in MS; (iii) how microglia secrete different molecules, e.g., growth factors, that favor the recruitment of OPCs in acute phases of MS lesions; and (iv) how astrocytes modify the extracellular matrix in MS lesions, affecting the ability of OPCs to attempt spontaneous remyelination. Together, these issues demonstrate how both astroglia and microglia influence OPCs in physiological and pathological situations, reinforcing the concept that both development and neural repair are complex and global phenomena. Understanding the molecular and cellular mechanisms that control OPC survival, proliferation, migration, and differentiation during development, as well as in the mature CNS, may open new opportunities in the search for reparative therapies in demyelinating diseases like MS.

Regulation of oligodendrocyte precursor migration during development, in adulthood and in pathology

Oligodendrocytes are the myelin-forming cells in the central nervous system (CNS). These cells originate from oligodendrocyte precursor cells (OPCs) during development, and they migrate extensively from oligodendrogliogenic niches along the neural tube to colonise the entire CNS. Like many other such events, this migratory process is precisely regulated by a battery of positional and signalling cues that act via their corresponding receptors and that are expressed dynamically by OPCs. Here, we will review the cellular and molecular basis of this important event during embryonic and postnatal development, and we will discuss the relevance of the substantial number of OPCs existing in the adult CNS. Similarly, we will consider the behaviour of OPCs in normal and pathological conditions, especially in animal models of demyelination and of the demyelinating disease, multiple sclerosis. The spontaneous remyelination observed after damage in demyelinating pathologies has a limited effect. Understanding the cellular and molecular mechanisms underlying the biology of OPCs, particularly adult OPCs, should help in the design of neuroregenerative strategies to combat multiple sclerosis and other demyelinating diseases.

Invertebrate models of kallmann syndrome: molecular pathogenesis and new disease genes

Kallmann Syndrome is a heritable disorder characterized by congenital anosmia, hypogonadotropic hypogonadism and, less frequently, by other symptoms. The X-linked form of this syndrome is caused by mutations affecting the KAL1 gene that codes for the extracellular protein anosmin-1. Investigation of KAL1 function in mice has been hampered by the fact that the murine ortholog has not been identified. Thus studies performed in other animal models have contributed significantly to an understanding of the function of KAL1. In this review, the main results obtained using the two invertebrate models, the nematode worm Caenorhabditis elegans and the fruit fly Drosophila melanogaster, are illustrated and the contribution provided by them to the elucidation of the molecular pathogenesis of Kallmann Syndrome is discussed in detail. Structure-function dissection studies performed in these two animal models have shown how the different domains of anosmin-1 carry out specific functions, also suggesting a novel intramolecular regulation mechanism among the different domains of the protein. The model that emerges is one in which anosmin-1 plays different roles in different tissues, interacting with different components of the extracellular matrix. We also describe how the genetic approach in C. elegans has allowed the discovery of the genes involved in KAL1-heparan sulfate proteoglycans interactions and the identification of HS6ST1 as a new disease gene.

Olfactory system and demyelination

Within the central nervous system, the olfactory system represents one of the most exciting scenarios since it presents relevant examples of long-life sustained neurogenesis and continuous axonal outgrowth from the olfactory epithelium with the subsequent plasticity phenomena in the olfactory bulb. The olfactory nerve is composed of nonmyelinated axons with interesting ontogenetic interpretations. However, the centripetal projections from the olfactory bulb are myelinated axons which project to more caudal areas along the lateral olfactory tract. In consequence, demyelination has not been considered as a possible cause of the olfactory symptoms in those diseases in which this sense is impaired. One prototypical example of an olfactory disease is Kallmann syndrome, in which different mutations give rise to combined anosmia and hypogonadotropic hypogonadism, together with different satellite symptoms. Anosmin-1 is the extracellular matrix glycoprotein altered in the X-linked form of this disease, which participates in cell adhesion and migration, and axonal outgrowth in the olfactory system and in other regions of the central nervous system. Recently, we have described a new patho-physiological role of this protein in the absence of spontaneous remyelination in multiple sclerosis. In the present review, we hypothesize about how both main and satellite neurological symptoms of Kallmann syndrome may be explained by alterations in the myelination. We revisit the relationship between the olfactory system and myelin highlighting that minor histological changes should not be forgotten as putative causes of olfactory malfunction.

Mutual influences between the main olfactory and vomeronasal systems in development and evolution

The sense of smell plays a crucial role in the sensory world of animals. Two chemosensory systems have been traditionally thought to play-independent roles in mammalian olfaction. According to this, the main olfactory system (MOS) specializes in the detection of environmental odorants, while the vomeronasal system (VNS) senses pheromones and semiochemicals produced by individuals of the same or different species. Although both systems differ in their anatomy and function, recent evidence suggests they act synergistically in the perception of scents. These interactions include similar responses to some ligands, overlap of telencephalic connections and mutual influences in the regulation of olfactory-guided behavior. In the present work, we propose the idea that the relationships between systems observed at the organismic level result from a constant interaction during development and reflects a common history of ecological adaptations in evolution. We review the literature to illustrate examples of developmental and evolutionary processes that evidence these interactions and propose that future research integrating both systems may shed new light on the mechanisms of olfaction.

The cysteine-rich region and the whey acidic protein domain are essential for anosmin-1 biological functions

The protein anosmin-1, coded by the KAL1 gene responsible for the X-linked form of Kallmann syndrome (KS), exerts its biological effects mainly through the interaction with and signal modulation of fibroblast growth factor receptor 1 (FGFR1). We have previously shown the interaction of the third fibronectin-like type 3 (FnIII) domain and the N-terminal region of anosmin-1 with FGFR1. Here, we demonstrate that missense mutations reported in patients with KS, C172R and N267K did not alter or substantially reduce, respectively, the binding to FGFR1. These substitutions annulled the chemoattraction of the full-length protein over subventricular zone (SVZ) neuronal precursors (NPs), but they did not annul it in the N-terminal-truncated protein (A1Nt). We also show that although not essential for binding to FGFR1, the cysteine-rich (CR) region is necessary for anosmin-1 function and that FnIII.3 cannot substitute for FnIII.1 function. Truncated proteins recapitulating nonsense mutations found in KS patients did not show the chemotropic effect on SVZ NPs, suggesting that the presence behind FnIII.1 of any part of anosmin-1 produces an unstable protein incapable of action. We also identify the extracellular signal-regulated kinase 1/2 (ERK1/2) pathway as necessary for the chemotropic effect exerted by FGF2 and anosmin-1 on rat SVZ NPs.

Megalin mediates the influence of sonic hedgehog on oligodendrocyte precursor cell migration and proliferation during development

Oligodendrocyte precursor cells (OPCs) of the optic nerve are generated in the preoptic area, from where they migrate to colonize it entirely. Sonic hedgehog (Shh) induces the proliferation of these cells as well as influencing their migration, acting through its canonical receptor (Ptc-1). However, the multiligand receptor megalin (or LRP-2) is also involved in Shh-induced OPC proliferation and migration, and thus, we have evaluated the relevance of this interaction. During the stages at which Shh influences OPC development, we found megalin to be selectively expressed by optic nerve astrocytes, whereas Ptc-1 and Gli1 were found in OPCs. Indeed, this pattern of expression paralleled the rostral-caudal expression of the three Shh-related molecules during the time course of plp-dm20(+) -OPC colonization. The blockage of megalin partially abolished OPC chemoattraction and fully impaired Shh-induced proliferation. Using in vitro co-cultures of dissociated optic nerve cells, we demonstrated that Shh was internalized by astrocytes via megalin, and sufficient Shh was subsequently released to produce the biological effects on OPCs observed in the nerve. Together, these data indicate that at least part of the influence of Shh on OPCs is mediated by megalin during optic nerve development, and that astrocytes expressing megalin transiently capture Shh to present it to OPCs and/or to control the gradient of this molecule during development.

FGF-2 and Anosmin-1 are selectively expressed in different types of multiple sclerosis lesions

Multiple sclerosis is a demyelinating disease that affects ≈ 2,000,000 people worldwide. In the advanced stages of the disease, endogenous oligodendrocyte precursors cannot colonize the lesions or differentiate into myelinating oligodendrocytes. During development, both FGF-2 and Anosmin-1 participate in oligodendrocyte precursor cell migration, acting via the FGF receptor 1 (FGFR1). Hence, we performed a histopathological and molecular analysis of these developmental modulators in postmortem tissue blocks from multiple sclerosis patients. Accordingly, we demonstrate that the distribution of FGF-2 and Anosmin-1 varies between the different types of multiple sclerosis lesions: FGF-2 is expressed only within active lesions and in the periplaque of chronic lesions, whereas Anosmin-1 is upregulated within chronic lesions and is totally absent in active lesions. We show that the endogenous oligodendrocyte precursor cells recruited toward chronic-active lesions express FGFR1, possibly in response to the FGF-2 produced by microglial cells in the periplaque. Also in human tissue, FGF-2 is upregulated in perivascular astrocytes in regions of the normal-appearing gray matter, where the integrity of the blood-brain barrier is compromised. In culture, FGF-2 and Anosmin-1 influence adult mouse oligodendrocyte precursor cell migration in the same manner as at embryonic stages, providing an explanation for the histopathological observations: FGF-2 attracts/enhances its migration, which is hindered by Anosmin-1. We propose that FGF-2 and Anosmin-1 are markers for the histopathological type and the level of inflammation of multiple sclerosis lesions, and that they may serve as novel pharmacogenetic targets to design future therapies that favor effective remyelination and protect the blood-brain barrier.

X-linked GnRH deficiency: role of KAL-1 mutations in GnRH deficiency

The gene for X-linked Kallmann's syndrome (KAL-1, encoding anosmin-1) was cloned in 1991. Over a decade elapsed before autosomal forms of KS and most of other genetic forms of isolated hypogonadotrophic hypogonadism (IHH) became characterized, and the genetic diversity of these disorders fully appreciated. Although KAL-1 mutations appear to cause a more severe reproductive phenotype than other IHH genes, the biology of this multidomain extracellular matrix protein has only been partially characterized. Initial studies suggested a central role of anosmin-1, in GnRH neuron ontogeny - specifically in GnRH neuronal migration from the cribriform plate area into the brain - as well as in olfactory bulb development. Anosmin-1 is expressed extracellularly, with high affinity binding to cell membrane heparan sulphate proteoglycans. It is expressed in the outer layers of the developing olfactory bulb, the neuroretina, the cerebellum, spinal cord and developing kidney. Recent observations have demonstrated an anosmin-1 heparan sulphate dependent functional interaction with the product of the autosomal dominant KAL-2 (FGFR1: anosmin-2) gene, thereby modulating FGFR1 signalling. Although these genes are frequently co-expressed in developing tissues, this may not represent the sole mode of action of anosmin-1, and FGFR1 independent actions of the protein have also been identified. Structural and in vitro functional studies have shown that anosmin-1 may have complex biological actions. Anosmin-1 interactions with FGFR1 have however been best characterized and represent the dominant focus of this chapter.

The WFDC1 gene: role in wound response and tissue homoeostasis

The present evaluates the key features of the WFDC1 [WAP (whey acidic protein) four disulfide core 1] gene that encodes ps20 (20 kDa prostate stromal protein), a member of the WAP family. ps20 was first characterized as a growth inhibitory activity that was secreted by fetal urogenital sinus mesenchymal cells. Purified ps20 exhibited several activities that centre on cell adhesion, migration and proliferation. The WFDC1 gene was cloned, contained seven exons, and was mapped to chromosome 16q24, suggesting that it may function as a tumour suppressor; however, direct evidence of this has not emerged. In vivo, ps20 stimulated angiogenesis, although expression of WFDC1/ps20 was down-regulated in the reactive stroma tumour microenvironment in prostate cancer. WFDC1 expression is differential in other cancers and inflammatory conditions. Recent studies point to a role in viral infectivity. Although mechanisms of action are not fully understood, WFDC1/ps20 is emerging as a secreted matricellular protein that probably affects response to micro-organisms and tissue repair homoeostasis.

Kallmann syndrome 1 gene is expressed in the marsupial gonad

Kallmann syndrome is characterized by hypogonadotrophic hypogonadism and anosmia. The syndrome can be caused by mutations in several genes, but the X-linked form is caused by mutation in the Kallmann syndrome 1 (KAL1). KAL1 plays a critical role in gonadotropin-releasing hormone (GnRH) neuronal migration that is essential for the normal development of the hypothalamic-pituitary-gonadal axis. Interestingly, KAL1 appears to be missing from the rodent X, and no orthologue has been detected as yet. We investigated KAL1 during development and in adults of an Australian marsupial, the tammar wallaby, Macropus eugenii. Marsupial KAL1 maps to an autosome within a group of genes that was added as a block to the X chromosome in eutherian evolution. KAL1 expression was widespread in embryonic and adult tissues. In the adult testis, tammar KAL1 mRNA and protein were detected in the germ cells at specific stages of differentiation. In the adult testis, the protein encoded by KAL1, anosmin-1, was restricted to the round spermatids and elongated spermatids. In the adult ovary, anosmin-1 was not only detected in the oocytes but was also localized in the granulosa cells throughout folliculogenesis. This is the first examination of KAL1 mRNA and protein localization in adult mammalian gonads. The protein localization suggests that KAL1 participates in gametogenesis not only through the development of the hypothalamic-pituitary-gonadal axis by activation of GnRH neuronal migration, but also directly within the gonads themselves. Because KAL1 is autosomal in marsupials but is X-linked in eutherians, its conserved involvement in gametogenesis supports the hypothesis that reproduction-related genes were actively recruited to the eutherian X chromosome.