Cross-talk of anosmin-1, the protein implicated in X-linked Kallmann's syndrome, with heparan sulphate and urokinase-type plasminogen activator

Feedback Regulation of Signaling Pathways for Precise Pre-Placodal Ectoderm Formation in Vertebrate Embryos

Intracellular signaling pathways are essential to establish embryonic patterning, including embryonic axis formation. Ectodermal patterning is also governed by a series of morphogens. Four ectodermal regions are thought to be controlled by morphogen gradients, but some perturbations are expected to occur during dynamic morphogenetic movement. Therefore, a mechanism to define areas precisely and reproducibly in embryos, including feedback regulation of signaling pathways, is necessary. In this review, we outline ectoderm pattern formation and signaling pathways involved in the establishment of the pre-placodal ectoderm (PPE). We also provide an example of feedback regulation of signaling pathways for robust formation of the PPE, showing the importance of this regulation.

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.

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.

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.

Novel application of luciferase assay for the in vitro functional assessment of KAL1 variants in three females with septo-optic dysplasia (SOD)

KAL1 is implicated in 5% of Kallmann syndrome cases, a disorder which genotypically overlaps with septo-optic dysplasia (SOD). To date, a reporter-based assay to assess the functional consequences of KAL1 mutations is lacking. We aimed to develop a luciferase assay for novel application to functional assessment of rare KAL1 mutations detected in a screen of 422 patients with SOD. Quantitative analysis was performed using L6-myoblasts stably expressing FGFR1, transfected with a luciferase-reporter vector containing elements of the FGF-responsive osteocalcin promoter. The two variants assayed [p.K185N, p.P291T], were detected in three females with SOD (presenting with optic nerve hypoplasia, midline and pituitary defects). Our novel assay revealed significant decreases in transcriptional activity [p.K185N: 21% (p < 0.01); p.P291T: 40% (p < 0.001)]. Our luciferase-reporter assay, developed for assessment of KAL1 mutations, determined that two variants in females with hypopituitarism/SOD are loss-of-function; demonstrating that this assay is suitable for quantitative assessment of mutations in this gene.

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.

Decreased expression of Kallmann syndrome 1 sequence gene (KAL1) contributes to oral squamous cell carcinoma progression and significantly correlates with poorly differentiated grade

BACKGROUND

Kallmann syndrome 1 sequence gene (KAL1) protein is an extracellular matrix associated protein which plays vital roles in neurons development and cell migration. However, its biological functions and clinical implications have yet not been revealed in oral carcinogenesis. The objective of the study was to evaluate the role of KAL1 in oral cancer and determine clinical significance of KAL1 in oral squamous cell carcinomas (OSCCs).

METHODS

The expression pattern of KAL1 was examined in a testing cohort including OSCCs (n = 42) and paired adjacent tissues (PATs) (n = 14) by real-time PCR. The result was further validated in a validating cohort of OSCCs (n = 32). Correlation between clinicopathological parameters and KAL1 mRNA levels was analyzed by Kruskal-Wallis test. In vitro, the effects of KAL1 ablation through siRNA-mediated knockdown on the proliferation of OSCC cells were determined by CCK-8, BrdU, and colonies formation assays, respectively. In addition, cell cycle distribution was further evaluated by cytometry.

RESULTS

We observed that remarkably decreased expression of KAL1 mRNA in two independent cohorts (P = 0.0002 and P = 0.033, respectively). Furthermore, downregulated KAL1 mRNA was significantly associated with worse pathological grade (P = 0.013 and P = 0.035, respectively). Upon KAL1 silencing, the proliferation and colonies formation potentials of OSCC cells were notably promoted by accelerating G1 to M phase transition.

CONCLUSION

These data indicated that KAL1 plays a potential suppressive role on OSCC initiation and progression, and KAL1 gene may serve as an adjuvant biomarker for the identification of pathological grade.

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.

Syndecan promotes axon regeneration by stabilizing growth cone migration

Growth cones facilitate the repair of nervous system damage by providing the driving force for axon regeneration. Using single-neuron laser axotomy and in vivo time-lapse imaging, we show that syndecan, a heparan sulfate (HS) proteoglycan, is required for growth cone function during axon regeneration in C. elegans. In the absence of syndecan, regenerating growth cones form but are unstable and collapse, decreasing the effective growth rate and impeding regrowth to target cells. We provide evidence that syndecan has two distinct functions during axon regeneration: (1) a canonical function in axon guidance that requires expression outside the nervous system and depends on HS chains and (2) an intrinsic function in growth cone stabilization that is mediated by the syndecan core protein, independently of HS. Thus, syndecan is a regulator of a critical choke point in nervous system repair.

Anosmin-1 contributes to brain tumor malignancy through integrin signal pathways

Anosmin-1, encoded by the KAL1 gene, is an extracellular matrix (ECM)-associated protein which plays essential roles in the establishment of olfactory and GNRH neurons during early brain development. Loss-of-function mutations of KAL1 results in Kallmann syndrome with delayed puberty and anosmia. There is, however, little comprehension of its role in the developed brain. As reactivation of developmental signal pathways often takes part in tumorigenesis, we investigated if anosmin-1-mediated cellular mechanisms associated with brain tumors. Our meta-analysis of gene expression profiles of patients' samples and public microarray datasets indicated that KAL1 mRNA was significantly upregulated in high-grade primary brain tumors compared with the normal brain and low-grade tumors. The tumor-promoting capacity of anosmin-1 was demonstrated in the glioblastoma cell lines, where anosmin-1 enhanced cell motility and proliferation. Notably, anosmin-1 formed a part of active β1 integrin complex, inducing downstream signaling pathways. ShRNA-mediated knockdown of anosmin-1 attenuated motility and growth of tumor cells and induced apoptosis. Anosmin-1 may also enhance the invasion of tumor cells within the ECM by modulating cell adhesion and activating extracellular proteases. In a mouse xenograft model, anosmin-1-expressing tumors grew faster, indicating the role of anosmin-1 in tumor microenvironment in vivo. Combined, these data suggest that anosmin-1 can facilitate tumor cell proliferation, migration, invasion, and survival. Therefore, although the normal function of anosmin-1 is required in the proper development of GNRH neurons, overexpression of anosmin-1 in the developed brain may be an underlying mechanism for some brain tumors.

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.

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.

GnRH neuronal migration and olfactory bulb neurite outgrowth are dependent on FGF receptor 1 signaling, specifically via the PI3K p110α isoform in chick embryo

Fibroblast growth factor (FGF) signaling is essential for both olfactory bulb (OB) morphogenesis and the specification, migration, and maturation of the GnRH-secreting neurons. Disruption of FGF signaling contributes to Kallmann syndrome characterized by both anosmia and sexual immaturity. However, several unanswered questions remain as to which specific FGF receptor (FGFR)-1 signaling pathways are necessary for OB and GnRH neuronal development. Here, using pharmacological phosphatidylinositol 3-kinase (PI3K) isoform-specific inhibitors, we demonstrate a central role for the PI3K p110α isoform as a downstream effector of FGFR1 signaling for both GnRH neuronal migration and OB development. We show that signaling via the PI3K p110α isoform is required for GnRH neuronal migration in explant cultures of embryonic day (E) 4 chick olfactory placodes. We also show that in ovo administration of LY294002, a global PI3K inhibitor as well as an inhibitor to the PI3K p110α isoform into the olfactory placode of E3 chick embryo impairs GnRH neuronal migration toward the forebrain. In contrast, in ovo PI3K inhibitor treatment produced no obvious defects on primary olfactory sensory neuron axonal targeting and bundle formation. We also demonstrate that anosmin-1 and FGF2 induced neuronal migration of immortalized human embryonic GnRH neuroblast cells (FNC-B4-hTERT) is mediated by modulating FGFR1 signaling via the PI3K p110α isoform, specifically through phosphorylation of the PI3K downstream effectors, Akt and glycogen synthase kinase-3β. Finally, we show that neurite outgrowth and elongation of OB neurons in E10 chick OB explants are also dependent on the PI3K p110α isoform downstream of FGFR1. This study provides mechanistic insight into the etiology of Kallmann syndrome.

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.

Human epididymis protein-4 (HE-4): a novel cross-class protease inhibitor

Epididymal proteins represent the factors necessary for maturation of sperm and play a crucial role in sperm maturation. HE-4, an epididymal protein, is a member of whey acidic protein four-disulfide core (WFDC) family with no known function. A WFDC protein has a conserved WFDC domain of 50 amino acids with eight conserved cystine residue. HE-4 is a 124 amino acid long polypeptide with two WFDC domains. Here, we show that HE-4 is secreted in the human seminal fluid as a disulfide-bonded homo-trimer and is a cross-class protease inhibitor inhibits some of the serine, aspartyl and cysteine proteases tested using hemoglobin as a substrate. Using SPR we have also observed that HE-4 shows a significant binding with all these proteases. Disulfide linkages are essential for this activity. Moreover, HE-4 is N-glycosylated and highly stable on a wide range of pH and temperature. Taken together this suggests that HE-4 is a cross-class protease inhibitor which might confer protection against microbial virulence factors of proteolytic nature.

Expression of recombinant Atlantic salmon serum C-type lectin in Drosophila melanogaster Schneider 2 cells

The Atlantic salmon (Salmo salar) serum lectin (SSL) is a soluble C-type lectin that binds bacteria, including salmon pathogens. This lectin is a cysteine-rich oligomeric protein. Consequently, a Drosophila melanogaster expression system was evaluated for use in expressing SSL. A cDNA encoding SSL was cloned into a vector designed to express it as a fusion protein with a hexahistidine tag, under the control of the Drosophila methallothionein promoter. The resulting construct was stably transfected into Drosophila S2 cells. After CdCl2 induction, transfected S2 cells secreted recombinant SSL into the cell culture medium. A cell line derived from stably transformed polyclonal cell populations expressing SSL was used for large-scale expression of SSL. Recombinant SSL was purified from the culture medium using a two-step purification scheme involving affinity binding to yeast cells and metal-affinity chromatography. Although yields of SSL were very low, correct folding and functionality of the recombinant SSL purified in this manner was demonstrated by its ability to bind to Aeromonas salmonicida. Therefore, Drosophila S2 cells may be an ideal system for the production of SSL if yields can be increased.

New understandings of the genetic basis of isolated idiopathic central hypogonadism

Idiopathic hypogonadotropic hypogonadism is a rare disease that is characterized by delayed/absent puberty and/or infertility due to an insufficient stimulation of an otherwise normal pituitary-gonadal axis by gonadotrophin-releasing hormone (GnRH) action. Because reduced or normal luteinizing hormone (LH)/follicle-stimulating hormone (FSH) levels may be observed in the affected patients, the term idiopathic central hypogonadism (ICH) appears to be more appropriate. This disease should be distinguished from central hypogonadism that is combined with other pituitary deficiencies. Isolated ICH has a complex pathogenesis and is fivefold more prevalent in males. ICH frequently appears in a sporadic form, but several familial cases have also been reported. This finding, in conjunction with the description of numerous pathogenetic gene variants and the generation of several knockout models, supports the existence of a strong genetic component. ICH may be associated with several morphogenetic abnormalities, which include osmic defects that, with ICH, constitute the cardinal manifestations of Kallmann syndrome (KS). KS accounts for approximately 40% of the total ICH cases and has been generally considered to be a distinct subgroup. However, the description of several pedigrees, which include relatives who are affected either with isolated osmic defects, KS, or normo-osmic ICH (nICH), justifies the emerging idea that ICH is a complex genetic disease that is characterized by variable expressivity and penetrance. In this context, either multiple gene variants or environmental factors and epigenetic modifications may contribute to the variable disease manifestations. We review the genetic mechanisms that are presently known to be involved in ICH pathogenesis and provide a clinical overview of the 227 cases that have been collected by the collaborating centres of the Italian ICH Network.

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.

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.

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

Anosmin-1, defective in Kallmann's syndrome, participates in the adhesion, migration and differentiation of different cell types in the CNS. Although not fully understood, the mechanisms of action of Anosmin-1 involve the interaction with different proteins, being the interaction with fibroblast growth factor receptor 1 (FGFR1) and the modulation of its signalling the best studied to date. Using glutathione-S-transferase pull-down assays we demonstrate that the FnIII.3 (Fibronectin-like type III) domain and the combination whey acidic protein-FnIII.1, but not each of them individually, interact with FGFR1. The interaction of the whey acidic protein-FnIII.1 domains is substantially reduced when the cysteine-rich region is present, suggesting a likely regulatory role for this domain. The introduction in FnIII.3 of any of the two missense mutations found in Kallmann's syndrome patients, E514K and F517L, abolished the interaction with FGFR1, what suggests an important role for these residues in the interaction. Interestingly, the chemoattraction of Anosmin-1 on rat neuronal precursors (NPs) via FGFR1 is retained by the N-terminal region of Anosmin-1 but not by FnIII.3 alone, and is lost in proteins carrying either one of the missense mutations, probably because of a highly reduced binding capacity to FGFR1. We also describe homophilic interaction Anosmin-1/Anosmin-1 via the FnIII repeats 1 and 4, and the interaction of FnIII.1 and FnIII.3 with Fibronectin and of FnIII.3 with Laminin.

Frequent gene conversion events between the X and Y homologous chromosomal regions in primates

Background

Mammalian sex-chromosomes originated from a pair of autosomes. A step-wise cessation of recombination is necessary for the proper maintenance of sex-determination and, consequently, generates a four strata structure on the X chromosome. Each stratum shows a specific per-site nucleotide sequence difference (p-distance) between the X and Y chromosomes, depending on the time of recombination arrest. Stratum 4 covers the distal half of the human X chromosome short arm and the p-distance of the stratum is ~10%, on average. However, a 100-kb region, which includes KALX and VCX, in the middle of stratum 4 shows a significantly lower p-distance (1-5%), suggesting frequent sequence exchanges or gene conversions between the X and Y chromosomes in humans. To examine the evolutionary mechanism for this low p-distance region, sequences of a corresponding region including KALX/Y from seven species of non-human primates were analyzed.

Results

Phylogenetic analysis of this low p-distance region in humans and non-human primate species revealed that gene conversion like events have taken place at least ten times after the divergence of New World monkeys and Catarrhini (i.e., Old World monkeys and hominoids). A KALY-converted KALX allele in white-handed gibbons also suggests a possible recent gene conversion between the X and Y chromosomes. In these primate sequences, the proximal boundary of this low p-distance region is located in a LINE element shared between the X and Y chromosomes, suggesting the involvement of this element in frequent gene conversions. Together with a palindrome on the Y chromosome, a segmental palindrome structure on the X chromosome at the distal boundary near VCX, in humans and chimpanzees, may mediate frequent sequence exchanges between X and Y chromosomes.

Conclusion

Gene conversion events between the X and Y homologous regions have been suggested, mainly in humans. Here, we found frequent gene conversions in the evolutionary course of primates. An insertion of a LINE element at the proximal end of the region may be a cause for these frequent conversions. This gene conversion in humans may also be one of the genetic causes of Kallmann syndrome.

Novel insights in FGFR1 regulation: lessons from Kallmann syndrome

Disrupted fibroblast growth factor receptor (FGFR)1 signalling has been shown to cause Kallmann syndrome (KS), a human genetic disorder characterised by olfactory bulb dysgenesis and hypogonadotrophic hypogonadism. Loss-of-function mutations in the KS gene KAL-2/FGFR1 account for roughly 10% of KS cases, leading to the autosomal dominant form of the disease. Anosmin-1, the KAL-1 gene product underlying X-linked KS, modulates FGFR1 signalling via regulation of FGF2/FGFR1/heparin signalling complex assembly and activity. This review covers recent advances in the potential interactions of KS-associated molecules within the FGFR1 signalling complex, and demonstrates a novel mechanism of pre-signalling modulation that mechanistically links an autosomal dominant and sex-linked mode of inheritance of this disease, highlighting the central role of FGFR1 signalling in KS.

Human GnRH deficiency: a unique disease model to unravel the ontogeny of GnRH neurons

Evolutionary survival of a species is largely a function of its reproductive fitness. In mammals, a sparsely populated and widely dispersed network of hypothalamic neurons, the gonadotropin-releasing hormone (GnRH) neurons, serve as the pilot light of reproduction via coordinated secretion of GnRH. Since it first description, human GnRH deficiency has been recognized both clinically and genetically as a heterogeneous disease. A spectrum of different reproductive phenotypes comprised of congenital GnRH deficiency with anosmia (Kallmann syndrome), congenital GnRH deficiency with normal olfaction (normosmic idiopathic hypogonadotropic hypogonadism), and adult-onset hypogonadotropic hypogonadism has been described. In the last two decades, several genes and pathways which govern GnRH ontogeny have been discovered by studying humans with GnRH deficiency. More importantly, detailed study of these patients has highlighted the emerging theme of oligogenicity and genotypic synergism, and also expanded the phenotypic diversity with the documentation of reversal of GnRH deficiency later in adulthood in some patients. The underlying genetic defect has also helped understand the associated nonreproductive phenotypes seen in some of these patients. These insights now provide practicing clinicians with targeted genetic diagnostic strategies and also impact on clinical management.

Anosmin-1a is required for fasciculation and terminal targeting of olfactory sensory neuron axons in the zebrafish olfactory system

The KAL-1 gene underlies the X-linked form of Kallmann syndrome (KS), a neurological disorder that impairs the development of the olfactory and GnRH systems. KAL-1 encodes anosmin-1, a cell matrix protein that shows cell adhesion, neurite outgrowth, and axon-guidance and -branching activities. We used zebrafish embryos as model to better understand the role of this protein during olfactory system (OS) development. First, we detected the protein in olfactory sensory neurons from 22 h post-fertilization (hpf) onward, i.e. prior their pioneer axons reached presumptive olfactory bulbs (OBs). We found that anosmin-1a depletion impaired the fasciculation of olfactory axons and their terminal targeting within OBs. Last, we showed that kal1a inactivation induced a severe decrease in the number of GABAergic and dopaminergic OB neurons. Though the phenotypes induced following anosmin-1a depletion in zebrafish embryos did not match precisely the defects observed in KS patients, our results provide the first demonstration of a direct requirement for anosmin-1 in OS development in vertebrates and stress the role of OB innervation on OB neuron differentiation.

Novel mechanisms of fibroblast growth factor receptor 1 regulation by extracellular matrix protein anosmin-1

Activation of fibroblast growth factor (FGF) signaling is initiated by a multiprotein complex formation between FGF, FGF receptor (FGFR), and heparan sulfate proteoglycan on the cell membrane. Cross-talk with other factors could affect this complex assembly and modulate the biological response of cells to FGF. We have previously demonstrated that anosmin-1, a glycosylated extracellular matrix protein, interacts with the FGFR1 signaling complex and enhances its activity in an IIIc isoform-specific and HS-dependent manner. The molecular mechanism of anosmin-1 action on FGFR1 signaling, however, remains unknown. Here, we show that anosmin-1 directly binds to FGFR1 with high affinity. This interaction involves domains in the N terminus of anosmin-1 (cysteine-rich region, whey acidic protein-like domain and the first fibronectin type III domain) and the D2-D3 extracellular domains of FGFR1. In contrast, anosmin-1 binds to FGFR2IIIc with much lower affinity and displays negligible binding to FGFR3IIIc. We also show that FGFR1-bound anosmin-1, although capable of binding to FGF2 alone, cannot bind to a FGF2.heparin complex, thus preventing FGFR1.FGF2.heparin complex formation. By contrast, heparin-bound anosmin-1 binds to pre-formed FGF2.FGFR1 complex, generating an anosmin-1.FGFR1.FGF2.heparin complex. Furthermore, a functional interaction between anosmin-1 and the FGFR1 signaling complex is demonstrated by immunofluorescence co-localization and Transwell migration assays where anosmin-1 was shown to induce opposing effects during chemotaxis of human neuronal cells. Our study provides molecular and cellular evidence for a modulatory action of anosmin-1 on FGFR1 signaling, whereby binding of anosmin-1 to FGFR1 and heparin can play a dual role in assembly and activity of the ternary FGFR1.FGF2.heparin complex.

A novel role for anosmin-1 in the adhesion and migration of oligodendrocyte precursors

At embryonic stages of development, oligodendrocyte precursors (OPCs) generated in the preoptic area colonize the entire optic nerve (ON). Different factors controlling migration of ON OPCs have been identified, including secreted growth factors, morphogens and guidance cues, as well as cell adhesion molecules. We have shown previously that the soluble form of the extracellular matrix (ECM) protein anosmin-1, impairs OPC migration induced by FGF-2. In the present work, we show that anosmin-1 is expressed by both migrating OPCs and axons of the retinal ganglion cells in the embryonic ON. In vitro, we observe that OPC migration is strongly impaired by contact with anosmin-1 when used as a substrate and, in contrast to previous results, this effect is independent of FGF-2/FGFR1 signaling. We also show that OPCs preferentially adhere to anosmin-1 when compared with other ECM molecules used as substrates, and that when the endogenous anosmin-1 expressed by OPCs is blocked, OPC adhesion to all the different substrates (including anosmin-1), is significantly reduced. This novel effect of anosmin-1 on cell adhesion is also independent of FGF-2/FGFR1. We finally demonstrate that the blockade of the endogenous anosmin-1 expressed by OPCs impairs their migration. Our data suggest that the endogenous anosmin-1 expressed by OPCs is necessary for the correct adhesion of these cells to the different components of the ECM (including anosmin-1 itself), contributing to the migration of these cells.

Diversity in fibroblast growth factor receptor 1 regulation: learning from the investigation of Kallmann syndrome

The unravelling of the genetic basis of the hypogonadotrophic hypogonadal disorders, including Kallmann syndrome (KS), has led to renewed interest into the developmental biology of gonadotrophin-releasing hormone (GnRH) neurones and, more generally, into the molecular mechanisms of reproduction. KS is characterised by the association of GnRH deficiency with diminished olfaction. Until recently, only two KS-associated genes were known: KAL1 and KAL2. KAL1 encodes the cell membrane and extracellular matrix-associated secreted protein anosmin-1 which is implicated in the X-linked form of KS. Anosmin-1 shows high affinity binding to heparan sulphate (HS) and its function remains the focus of ongoing investigation, although a role in axonal guidance and neuronal migration, which are processes essential for normal GnRH ontogeny and olfactory bulb histogenesis, has been suggested. KAL2, identified as the fibroblast growth factor receptor 1 (FGFR1) gene, has now been recognised to be the underlying genetic defect for an autosomal dominant form of KS. The diverse signalling pathways initiated upon FGFR activation can elicit pleiotropic cellular responses depending on the cellular context. Signalling through FGFR requires HS for receptor dimerisation and ligand binding. Current evidence supports a HS-dependent interaction between anosmin-1 and FGFR1, where anosmin-1 serves as a co-ligand activator enhancing the signal activity, the finer details of whose mechanism remain the subject of intense investigation. Recently, mutations in the genes encoding prokineticin 2 (PK2) and prokineticin receptor 2 (PKR2) were reported in a cohort of KS patients, further reinforcing the view of KS as a multigenic trait involving divergent pathways. Here, we review the historical and current understandings of KS and discuss the latest findings from the molecular and cellular studies of the KS-associated proteins, and describe the evidence that suggests convergence of several of these pathways during normal GnRH and olfactory neuronal ontogeny.

KAL1 mutations are not a common cause of idiopathic hypogonadotrophic hypogonadism in humans

Hypogonadotrophic hypogonadism results in the absence of puberty and if left untreated leads to infertility. Mutations in KAL1 are known to account for some of the cases of Kallmann syndrome. The aim of this study was to determine the prevalence of KAL1 mutations in a large number of patients with idiopathic hypogonadotrophic hypogonadism (IHH). One hundred and thirty eight patients (109 males and 29 females) with IHH were studied for mutations in KAL1. DNA from these patients was subjected to denaturing gradient gel electrophoresis or single strand conformation polymorphism to identify mutations. Sequencing was performed to confirm mutations detected. Four mutations were found in 109 males (3.7%). All four mutations were in anosmic/hyposmic men making the prevalence 4/63 (6.3%) in this group of patients. No mutations were found in the 29 female patients. KAL1 mutations are an uncommon cause of Kallmann syndrome.

Genetic insights into human isolated gonadotropin deficiency

The identification of naturally occurring genetic mutations has provided unique insight into the current knowledge of the human hypothalamic-pituitary-gonadal axis. In the past decade, several monogenic causes have been reported in patients with isolated gonadotropin deficiency. Kallmann Syndrome is a clinically and genetically heterogeneous disorder, characterized by isolated hypogonadotropic hypogonadism and anosmia or hyposmia. To date, loss-of-function mutations in the genes encoding anosmin-1 (KAL1) and fibroblast growth factor receptor 1 (FGFR1) have been described in the X-linked and autosomal dominant forms of this syndrome, respectively. More recently, several heterozygous, homozygous or compound heterozygous mutations in the G protein-coupled prokineticin receptor-2 (PROKR2) and one of its ligands, prokineticin-2 (PROK2) were described in Kallmann syndrome. In addition, complex genetic transmission (digenic inheritance) was recently demonstrated in this condition. Regarding isolated hypogonadotropic hypogonadism without olfactory abnormalities, loss-of-function mutations in the Gonadotropin-releasing hormone (GnRH) receptor (GnRH-R) or the G-protein coupled receptor 54 (GPR54) genes, both encoding transmembrane receptors, have been described, as well as FGFR1 mutations. Finally, mutations of the beta sub-units of LH and FSH have been described in patients with selective gonadotropin deficiency. We review the role of these distinct genetic factors in human isolated hypogonadotropic hypogonadism.

Molecular pathogenesis of Kallmann's syndrome

Hypogonadotrophic hypogonadism (HH) is characterized by delayed or absent pubertal development secondary to gonadotrophin deficiency. HH can result from mutations of the gonadotrophin-releasing hormone receptor 1, the gonadotrophin beta-subunits, or various transcription factors involved in pituitary gland development. HH occurs in DAX1 mutations when associated with adrenal insufficiency (adrenal hypoplasia congenita), and is also linked with obesity in patients with mutations of leptin and its receptor, as well as mutations in prohormone convertase 1. Rarely, HH has resulted from kisspeptin receptor (GPR54) mutations, a gene implicated in the regulation of pubertal onset. When occurring with anosmia (a lack of sense of smell), HH is referred to as Kallmann's syndrome (KS). Two KS-related loci are currently known: KAL1, encoding anosmin-1, responsible for X-linked KS, and KAL2, encoding the fibroblast growth factor receptor 1 (FGFR1), mutated in autosomal dominant KS. Anosmin-1 is an extracellular glycoprotein with some unique structural characteristics; it interacts with both urokinase-type plasminogen activator and FGFR1. It has previously been shown that anosmin-1 enhances FGFR1 signalling in a heparan sulphate-dependent manner, and proposed that anosmin-1 fine-tunes FGFR1 signalling during olfactory and GnRH neuronal development. Here, we review the known normosmic causes of HH, and discuss novel developmental and molecular mechanisms underlying KS; finally, we introduce three novel genes (NELF, PKR2, and CHD7) that may be associated with some phenotypic features of KS.

Functional dissection of the Drosophila Kallmann's syndrome protein DmKal-1

BACKGROUND

Anosmin-1, the protein implicated in the X-linked Kallmann's syndrome, plays a role in axon outgrowth and branching but also in epithelial morphogenesis. The molecular mechanism of its action is, however, widely unknown. Anosmin-1 is an extracellular protein which contains a cysteine-rich region, a whey acidic protein (WAP) domain homologous to some serine protease inhibitors, and four fibronectin-like type III (FnIII) repeats. Drosophila melanogaster Kal-1 (DmKal-1) has the same protein structure with minor differences, the most important of which is the presence of only two FnIII repeats and a C-terminal region showing a low similarity with the third and the fourth human FnIII repeats. We present a structure-function analysis of the different DmKal-1 domains, including a predicted heparan-sulfate binding site.

RESULTS

This study was performed overexpressing wild type DmKal-1 and a series of deletion and point mutation proteins in two different tissues: the cephalopharyngeal skeleton of the embryo and the wing disc. The overexpression of DmKal-1 in the cephalopharyngeal skeleton induced dosage-sensitive structural defects, and we used these phenotypes to perform a structure-function dissection of the protein domains. The reproduction of two deletions found in Kallmann's Syndrome patients determined a complete loss of function, whereas point mutations induced only minor alterations in the activity of the protein. Overexpression of the mutant proteins in the wing disc reveals that the functional relevance of the different DmKal-1 domains is dependent on the extracellular context.

CONCLUSION

We suggest that the role played by the various protein domains differs in different extracellular contexts. This might explain why the same mutation analyzed in different tissues or in different cell culture lines often gives opposite phenotypes. These analyses also suggest that the FnIII repeats have a main and specific role, while the WAP domain might have only a modulator role, strictly connected to that of the fibronectins.

C. elegans Kallmann syndrome protein KAL-1 interacts with syndecan and glypican to regulate neuronal cell migrations

The anosmin-1 protein family regulates cell migration, axon guidance, and branching, by mechanisms that are not well understood. We show that the C. elegans anosmin-1 ortholog KAL-1 promotes migrations of ventral neuroblasts prior to epidermal enclosure. KAL-1 does not modulate FGF signaling in neuroblast migration and acts in parallel to other neuroblast migration pathways. Defects in heparan sulfate (HS) synthesis or in specific HS modifications disrupt neuroblast migrations and affect the KAL-1 pathway. KAL-1 binds the cell surface HS proteoglycans syndecan/SDN-1 and glypican/GPN-1. This interaction is mediated via HS side chains and requires specific HS modifications. SDN-1 and GPN-1 are expressed in ventral neuroblasts and have redundant roles in KAL-1-dependent neuroblast migrations. Our findings suggest that KAL-1 interacts with multiple HSPGs to promote cell migration.

Mechanisms of Disease: insights into X-linked and autosomal-dominant Kallmann syndrome

Kallmann syndrome (KS) is a disorder characterized by hypogonadotropic hypogonadism and anosmia. Although KS is genetically heterogeneous, only two causal genes have been identified to date. These include an X-linked gene that encodes anosmin 1 and an autosomal gene that encodes fibroblast growth factor receptor 1. Mutations in these two genes result in disorders that often include, but are not limited to, severe defects in olfactory and reproductive functions. In this respect, KS can be regarded as a 'human model' for understanding critical factors that regulate olfactory and reproductive development. Here we give an overview of the disorders that stem from mutations in these two genes, with special emphasis on the cellular mechanisms underlying olfactory and reproductive anomalies. Other, less well-known aspects of KS, such as the convergence of symptoms in patients with different genetic forms of KS and the unpredictable manifestation of KS symptoms, are also discussed.

Isolated gonadotropic deficiency with and without anosmia: a developmental defect or a neuroendocrine regulation abnormality of the gonadotropic axis

Hypogonadotropic hypogonadism has been described in several human genetic diseases. Congenital isolated hypogonadotropic hypogonadism is classified into two categories: one that is associated with anosmia (Kallmann syndrome) and one that is apparently isolated. Mutations and deletions of the KAL1 gene, which encodes for a protein involved in cell adhesion, have been observed in many cases of the X-linked form of Kallmann syndrome. Recently, loss-of-function mutations of fibroblast growth factor receptor-1 (FGFR1) were associated with an autosomal dominant form of Kallmann syndrome. Genotype-phenotype correlations confirm the large spectrum of the phenotype due to FGFR1 mutations. Cases of isolated hypogonadotropic hypogonadism were considered to be idiopathic until the description of mutations of the gonadotropin releasing hormone receptor, luteinizing hormone and follicle stimulating hormone genes. However, defects in these genes only account for a small percentage of familial cases, which suggests that other proteins may be involved in regulation of the gonadotropic axis. We recently described GPR54 as one of these proteins by genome mapping in a very informative family. In vivo studies and genotype-phenotype correlations indicate that gonadotropic axis regulation by GPR54 occurs mainly at the level of the hypothalamus.

Patterns of polymorphism and divergence in stress-related yeast proteins

Yeast genomes contain variable number tandem repeats (VNTRs) within coding regions of DNA. A significant number of these genes are involved in cell rescue, defence and virulence and are regulated by genetic elements associated with stress. Alleles that encode variable length, single amino acid tracts, are mainly associated with transcription and proteins localized within the nucleus. Alleles that encode proteins containing oligopeptide repeats or minisatellites are over-represented in cell wall and extracellular space locations. Functional analysis of the latter group reveals that these proteins are involved in biogenesis of cellular components and in interaction with the cellular environment, especially in relation to stress resistance, heat shock response, temperature perception and adhesion. A significantly high number of these proteins have regions rich in threonine and/or serine that contain repeated sequences, variable in length within yeast species. DNA sequences encoding serine- and/or threonine-rich regions give rise to polymorphic alleles and therefore may confer a selective advantage to cells. We propose that these regions are the focus of mutational and recombination events that, when coupled with directed selection, may contribute to genetic variation within stress-related genes.

Extended and Flexible Domain Solution Structure of the Extracellular Matrix Protein Anosmin-1 by X-ray Scattering, Analytical Ultracentrifugation and Constrained Modelling

Kallmann's syndrome corresponds to a loss of sense of smell and hypogonadotrophic hypogonadism. Defects in anosmin-1 result in the X-linked inherited form of Kallmann's syndrome. Anosmin-1 is an extracellular matrix protein comprised of an N-terminal, cysteine-rich (Cys-box) domain and a whey acidic protein-like (WAP) domain, followed by four fibronectin type III (FnIII) domains. The solution structures of recombinant proteins containing the first three domains (PIWF1) and all six domains (PIWF4) were determined by X-ray scattering and analytical ultracentrifugation. Guinier analyses showed that PIWF1 and PIWF4 have different radii of gyration (R(G)) values of 3.1 nm and 6.7 nm, respectively, but similar cross-sectional radii of gyration (R(XS)) values of 1.5 nm and 1.9 nm, respectively. Distance distribution functions showed that the maximum lengths of PIWF1 and PIWF4 were 11 nm and 23 nm, respectively. Analytical ultracentrifugation gave sedimentation coefficients of 2.52 S and 3.55 S for PIWF1 and PIWF4, respectively. The interpretation of the scattering data by constrained modelling requires homology models for all six domains in anosmin-1. While models were already available for the WAP and FnIII domains, searches suggested the Cys-box domain may resemble the cysteine-rich region of the insulin-like growth factor receptor. Automated constrained molecular modelling based on joining the anosmin-1 domains with structurally randomised linkers resulted in 10,000 models for anosmin-1. A trial-and-error search showed that about 0.1-1.4% of these models fitted the X-ray data. The best models showed that the three domains and six domains in PIWF1 and PIWF4, respectively, were extended. The inter-domain linkers in anosmin-1 could not all be extended at the same time, and there was evidence for inter-domain flexibility. Models with folded-back domain arrangements do not fit the data. These solution structures account for the known biological function of anosmin-1, in particular its ability to interact with its three macromolecular ligands.

Anosmin-1 modulates fibroblast growth factor receptor 1 signaling in human gonadotropin-releasing hormone olfactory neuroblasts through a heparan sulfate-dependent mechanism

Defects of either anosmin-1 or fibroblast growth factor receptor 1 (FGFR1) are known to underlie hereditary Kallmann's syndrome (KS), a human disorder of olfactory and gonadotropin-releasing hormone (GnRH) neuronal ontogeny. Here, we report a functional interaction between anosmin-1 and the FGFR1-FGF2-heparan sulfate complex, leading to amplified responses in the FGFR1 signaling pathway. In human embryonic GnRH olfactory neuroblasts, wild-type anosmin-1, but not proteins with loss-of-function KS mutations, induces neurite outgrowth and cytoskeletal rearrangements through FGFR1-dependent mechanisms involving p42/44 and p38 mitogen-activated protein kinases and Cdc42/Rac1 activation. Furthermore, anosmin-1 enhances FGF2 signaling specifically through FGFR1 IIIc in heterologous BaF3 lymphoid cells in a heparan sulfate-dependent manner. Our study provides compelling evidence for anosmin-1 as an isoform-specific co-ligand modulator of FGFR signaling that amplifies and specifies FGFR1 signaling responses during human nervous system development and defines a mechanism underlying the link between autosomal and X-linked KS.

Survey of the year 2004 commercial optical biosensor literature

The year 2004 represents a milestone for the biosensor research community: in this year, over 1000 articles were published describing experiments performed using commercially available systems. The 1038 papers we found represent an approximately 10% increase over the past year and demonstrate that the implementation of biosensors continues to expand at a healthy pace. We evaluated the data presented in each paper and compiled a 'top 10' list. These 10 articles, which we recommend every biosensor user reads, describe well-performed kinetic, equilibrium and qualitative/screening studies, provide comparisons between binding parameters obtained from different biosensor users, as well as from biosensor- and solution-based interaction analyses, and summarize the cutting-edge applications of the technology. We also re-iterate some of the experimental pitfalls that lead to sub-optimal data and over-interpreted results. We are hopeful that the biosensor community, by applying the hints we outline, will obtain data on a par with that presented in the 10 spotlighted articles. This will ensure that the scientific community at large can be confident in the data we report from optical biosensors.