Molecular cloning of olfactomedin, an extracellular matrix protein specific to olfactory neuroepithelium

Myocilin misfolding and glaucoma: A 20-year update

Mutations in the gene MYOC account for approximately 5% of cases of primary open angle glaucoma (POAG). MYOC encodes for the protein myocilin, a multimeric secreted glycoprotein composed of N-terminal coiled-coil (CC) and leucine zipper (LZ) domains that are connected via a disordered linker to a 30 kDa olfactomedin (OLF) domain. More than 90% of glaucoma-causing mutations are localized to the OLF domain. While myocilin is expressed in numerous tissues, mutant myocilin is only associated with disease in the anterior segment of the eye, in the trabecular meshwork. The prevailing pathogenic mechanism involves a gain of toxic function whereby mutant myocilin aggregates intracellularly instead of being secreted, which causes cell stress and an early timeline for TM cell death, elevated intraocular pressure, and subsequent glaucoma-associated retinal degeneration. In this review, we focus on the work our lab has conducted over the past ∼15 years to enhance our molecular understanding of myocilin-associated glaucoma, which includes details of the molecular structure and the nature of the aggregates formed by mutant myocilin. We conclude by discussing open questions, such as predicting phenotype from genotype alone, the elusive native function of myocilin, and translational directions enabled by our work.

Systemic Genotype-Phenotype Analysis of MYOC Variants Based on Exome Sequencing and Literature Review

PURPOSE

This study aims to characterize disease-causing variants in the myocilin gene (MYOC), which is associated with autosomal dominant primary open-angle glaucoma (adPOAG).

DESIGN

Case-control study.

METHODS

MYOC variants were collected from in-house exome sequencing data of 7092 individuals. Genotype-phenotype analysis and bioinformatics evaluation were used to distinguish potential pathogenic variants for POAG from others. MYOC mutations in published works of literature were also systemically analyzed.

RESULTS

In total, 53 variants in MYOC were detected in the 7092 subjects, including 45 rare variants (MAF < 0.01) and 8 polymorphisms (MAF ≥ 0.01), or 48 missense variants and 5 truncation variants. There was no difference in the frequency of the 8 polymorphisms between subjects with and without POAG (P > 0.05). The total number of rare MYOC variants was significantly higher in POAG than that in in-house controls (P = 3.31E-14). The pathogenic/likely pathogenic variants (p.P254T, p.S341P, p.G367R, p.P370L, p.D378G, p.C433Y, and p.L486F) were exclusively present in 8 POAG but absent in in-house controls (P = 2.79E-10). Rare truncation MYOC variants were not enriched in POAG as compared with those in in-house controls (P = 0.28). Further analysis of previously reported MYOC variants suggested that pathogenic/likely pathogenic variants were enriched in the conserved olfactomedin domain. Truncation MYOC variants were scattered in the coding region, where only p.Q368∗ had relatively strong evidence to be causative for adPOAG, whereas most others are questionable.

CONCLUSIONS

Most MYOC variants contributing to adPOAG could be characterized as rare missense variants located in OLF-domain and predicted to be damaging through multiple tools. The effect of other variants, especially for truncation variants (except for p.Q368∗) need further clarification.

Olfactomedin-like 2 A and B (OLFML2A and OLFML2B) expression profile in primates (human and baboon)

Background

The olfactomedin-like domain (OLFML) is present in at least four families of proteins, including OLFML2A and OLFML2B, which are expressed in adult rat retina cells. However, no expression of their orthologous has ever been reported in human and baboon.

Objective

The aim of this study was to investigate the expression of OLFML2A and OLFML2B in ocular tissues of baboons (Papio hamadryas) and humans, as a key to elucidate OLFML function in eye physiology.

Methods

OLFML2A and OLFML2B cDNA detection in ocular tissues of these species was performed by RT-PCR. The amplicons were cloned and sequenced, phylogenetically analyzed and their proteins products were confirmed by immunofluorescence assays.

Results

OLFML2A and OLFML2B transcripts were found in human cornea, lens and retina and in baboon cornea, lens, iris and retina. The baboon OLFML2A and OLFML2B ORF sequences have 96% similarity with their human’s orthologous. OLFML2A and OLFML2B evolution fits the hypothesis of purifying selection. Phylogenetic analysis shows clear orthology in OLFML2A genes, while OLFML2B orthology is not clear.

Conclusions

Expression of OLFML2A and OLFML2B in human and baboon ocular tissues, including their high similarity, make the baboon a powerful model to deduce the physiological and/or metabolic function of these proteins in the eye.

Mutated olfactomedin 1 in the interphotoreceptor matrix of the mouse retina causes functional deficits and vulnerability to light damage

Olfactomedin 1 (OLFM1) is a secreted glycoprotein and member of the olfactomedin protein family, which is preferentially expressed in various areas throughout the central nervous system. To learn about the functional properties of OLFM1 in the eye, we investigated its localization in the mouse and pig eye. In addition, we analyzed the ocular phenotype of Olfm1 mutant mice in which 52 amino acids were deleted in the central part (M2 region) of OLFM1. OLFM1 was detected in cornea, sclera, retina, and optic nerve of both wild-type and Olfm1 mutant littermates. By immunohistochemistry and double labeling with the lectin peanut agglutinin, OLFM1 was found in the interphotoreceptor matrix (IPM) of mouse and pig retina where it was directly localized to the inner segments of photoreceptors. Western blotting confirmed the presence of the OLFM1 isoforms pancortin 1 (BMY) and pancortin 2 (BMZ) in the IPM. The retinal phenotype of Olfm1 mutant mice did not obviously differ from that of wild-type littermates. In addition, outer nuclear layer (ONL) and total retinal thickness were not different, and the same was true for the area of the optic nerve in cross sections. Functional changes were observed though by electroretinography, which showed significantly lower a- and b-wave amplitudes in Olfm1 mutant mice when compared to age-matched wild-type mice. When light damage experiments were performed as an experimental paradigm of photoreceptor apoptosis, significantly more TUNEL-positive cells were observed in Olfm1 mutant mice 30 h after light exposure. One week after light exposure, the ONL was significantly thinner in Olfm1 mutant mice than in wild-type littermates indicating increased photoreceptor loss. No differences were observed when rhodopsin turnover or ERK1/2 signaling was investigated. We conclude that OLFM1 is a newly identified IPM molecule that serves an important role for photoreceptor homeostasis, which is significantly compromised in the eyes of Olfm1 mutant mice.

Quantifying Preferences and Responsiveness of Marine Zooplankton to Changing Environmental Conditions using Microfluidics

Global environmental change significantly affects marine species composition. However, analyzing the impact of these changes on marine zooplankton communities was so far mostly limited to assessing lethal doses through mortality assays and hence did not allow a direct assessment of the preferred conditions, or preferendum. Here, we use a microfluidic device to characterize individual behavior of actively swimming zooplankton, and to quantitatively determine their ecological preferendum. For the annelid zooplankton model Platynereis dumerilii we observe a broader pH preferendum than for the copepod Euterpina acutifrons, and reveal previously unrecognized sub-populations with different pH preferenda. For Platynereis, the minimum concentration difference required to elicit a response (responsiveness) is ~1 μM for H⁺ and ~13.7 mM for NaCl. Furthermore, using laser ablations we show that olfactomedin-expressing sensory cells mediate chemical responsiveness in the Platynereis foregut. Taken together, our microfluidic approach allows precise assessment and functional understanding of environmental perception on planktonic behaviour.

The Olfactory Transcriptome and Progression of Sexual Maturation in Homing Chum Salmon Oncorhynchus keta

Reproductive homing migration of salmonids requires accurate interaction between the reception of external olfactory cues for navigation to the spawning grounds and the regulation of sexual maturation processes. This study aimed at providing insights into the hypothesized functional link between olfactory sensing of the spawning ground and final sexual maturation. We have therefore assessed the presence and expression levels of olfactory genes by RNA sequencing (RNAseq) of the olfactory rosettes in homing chum salmon Oncorhynchus keta Walbaum from the coastal sea to 75 km upstream the rivers at the pre-spawning ground. The progression of sexual maturation along the brain-pituitary-gonadal axis was assessed through determination of plasma steroid levels by time-resolved fluoroimmunoassays (TR-FIA), pituitary gonadotropin subunit expression and salmon gonadotropin-releasing hormone (sgnrh) expression in the brain by quantitative real-time PCR. RNAseq revealed the expression of 75 known and 27 unknown salmonid olfactory genes of which 13 genes were differentially expressed between fish from the pre-spawning area and from the coastal area, suggesting an important role of these genes in homing. A clear progression towards final maturation was characterised by higher plasma 17α,20β-dihydroxy-4-pregnen-3-one (DHP) levels, increased pituitary luteinizing hormone β subunit (lhβ) expression and sgnrh expression in the post brain, and lower plasma testosterone (T) and 17β-estradiol (E2) levels. Olfactomedins and ependymin are candidates among the differentially expressed genes that may connect olfactory reception to the expression of sgnrh to regulate final maturation.

Olfactomedin 1 Deficiency Leads to Defective Olfaction and Impaired Female Fertility

Olfactomedin 1 (OLFM1) is a glycoprotein highly expressed in the brain. Olfm1(-/-) female mice were previously reported to have reduced fertility. Previous microarray analysis revealed Olfm1 among the most highly upregulated genes in the uterine luminal epithelium upon embryo implantation, which was confirmed by in situ hybridization. We hypothesized that Olfm1 deficiency led to defective embryo implantation and thus impaired fertility. Indeed, Olfm1(-/-) females had defective embryo implantation. However, Olfm1(-/-) females rarely mated and those that mated rarely became pregnant. Ovarian histology indicated the absence of corpora lutea in Olfm1(-/-) females, indicating defective ovulation. Superovulation using equine chorionic gonadotropin-human chorionic gonadotropin rescued mating, ovulation, and pregnancy, and equine chorionic gonadotropin alone rescued ovulation in Olfm1(-/-) females. Olfm1(-/-) females had a 13% reduction of hypothalamic GnRH neurons but comparable basal serum LH levels and GnRH-induced LH levels compared with wild-type controls. These results indicated no obvious local defects in the female reproductive system and a functional hypothalamic-pituitary-gonadal axis. Olfm1(-/-) females were unresponsive to the effects of male bedding stimulation on pubertal development and estrous cycle. There were 41% fewer cFos-positive cells in the mitral cell layer of accessory olfactory bulb upon male urine stimulation for 90 minutes. OLFM1 was expressed in the main and accessory olfactory systems including main olfactory epithelium, vomeronasal organ, main olfactory bulb, and accessory olfactory bulb, with the highest expression detected in the axon bundles of olfactory sensory neurons. These data demonstrate that defective fertility in Olfm1(-/-) females is most likely a secondary effect of defective olfaction.

Olfactomedin-1 Has a V-shaped Disulfide-linked Tetrameric Structure

Olfactomedin-1 (Olfm1; also known as noelin and pancortin) is a member of the olfactomedin domain-containing superfamily and a highly expressed neuronal glycoprotein important for nervous system development. It binds a number of secreted proteins and cell surface-bound receptors to induce cell signaling processes. Using a combined approach of x-ray crystallography, solution scattering, analytical ultracentrifugation, and electron microscopy we determined that full-length Olfm1 forms disulfide-linked tetramers with a distinctive V-shaped architecture. The base of the “V” is formed by two disulfide-linked dimeric N-terminal domains. Each of the two V legs consists of a parallel dimeric disulfide-linked coiled coil with a C-terminal β-propeller dimer at the tips. This agrees with our crystal structure of a C-terminal coiled-coil segment and β-propeller combination (Olfm1^coil-Olf) that reveals a disulfide-linked dimeric arrangement with the β-propeller top faces in an outward exposed orientation. Similar to its family member myocilin, Olfm1 is stabilized by calcium. The dimer-of-dimers architecture suggests a role for Olfm1 in clustering receptors to regulate signaling and sheds light on the conformation of several other olfactomedin domain family members.

Structural basis for misfolding in myocilin-associated glaucoma

Olfactomedin (OLF) domain-containing proteins play roles in fundamental cellular processes and have been implicated in disorders ranging from glaucoma, cancers and inflammatory bowel disorder, to attention deficit disorder and childhood obesity. We solved crystal structures of the OLF domain of myocilin (myoc-OLF), the best studied such domain to date. Mutations in myoc-OLF are causative in the autosomal dominant inherited form of the prevalent ocular disorder glaucoma. The structures reveal a new addition to the small family of five-bladed β-propellers. Propellers are most well known for their ability to act as hubs for protein-protein interactions, a function that seems most likely for myoc-OLF, but they can also act as enzymes. A calcium ion, sodium ion and glycerol molecule were identified within a central hydrophilic cavity that is accessible via movements of surface loop residues. By mapping familial glaucoma-associated lesions onto the myoc-OLF structure, three regions sensitive to aggregation have been identified, with direct applicability to differentiating between neutral and disease-causing non-synonymous mutations documented in the human population worldwide. Evolutionary analysis mapped onto the myoc-OLF structure reveals conserved and divergent regions for possible overlapping and distinctive functional protein-protein or protein-ligand interactions across the broader OLF domain family. While deciphering the specific normal biological functions, ligands and binding partners for OLF domains will likely continue to be a challenging long-term experimental pursuit, atomic detail structural knowledge of myoc-OLF is a valuable guide for understanding the implications of glaucoma-associated mutations and will help focus future studies of this biomedically important domain family.

The olfactomedin domain from gliomedin is a β-propeller with unique structural properties

All members of the olfactomedin (OLF) family have a conserved extracellular OLF domain, for which a structure has not been available. We present here the crystal structure of the OLF domain from gliomedin. Gliomedin is a protein expressed by Schwann cells in peripheral nerves, important for the formation of the nodes of Ranvier. Gliomedin interacts with neuronal cell adhesion molecules, such as neurofascin, but the structural details of the interaction are not known. The structure of the OLF domain presents a five-bladed β-propeller fold with unusual geometric properties. The symmetry of the structure is not 5-fold, but rather reveals a twisted arrangement. The conserved top face of the gliomedin OLF domain is likely to be important for binding to neuronal ligands. Our results provide a structural basis for the functions of gliomedin in Schwann cells, enable the understanding of the role of the gliomedin OLF domain in autoimmune neuropathies, and unravel the locations of human disease-causing mutations in other OLF family members, including myocilin.

Olfactomedin proteins: central players in development and disease

Olfactomedin proteins are characterized by a conserved domain of \texorpdfstring~\textasciitilde250 amino acids corresponding to the olfactomedin archetype first discovered in olfactory neuroepithelium. They arose early in evolution and occur throughout the animal kingdom. In mice and humans olfactomedin proteins comprise a diverse array of glycoproteins, many of which are critical for early development and functional organization of the nervous system as well as hematopoiesis. Olfactomedin domains appear to facilitate protein-protein interactions, intercellular interactions, and cell adhesion. Several members of the family have been implicated in various common diseases, notably myocilin in glaucoma and OLFM4 in cancer. This review highlights this important, hitherto understudied family of proteins.

Protein-DNA force assay in a microfluidic format

The detailed study of protein-DNA interactions is a core effort to elucidate physiological processes, including gene regulation, DNA repair and the immune response. The molecular force assay (MFA) is an established method to study DNA-binding proteins. In particular, high-affinity binder dissociation is made possible by the application of force. Microfluidic lab-on-a-chip approaches have proven helpful for parallelization, small sample volumes, reproducibility, and low cost. We report the successful combination of these two principles, forming a microfluidic molecular force assay and representing a novel use for the established MITOMI chip design. We present, characterize, validate and apply this integrated method. An alternative confocal fluorescence microscopy readout and analysis method is introduced and validated. In a multiplexing application, EcoRI binding is detected and characterized. This method paves the way for quantitative on-chip force measurements. It is suited for integration with DNA micro-spotting and in vitro expression of transcription factors to form a high-throughput chip for detailed DNA-protein interaction studies.

A molecular mechanism for glaucoma: endoplasmic reticulum stress and the unfolded protein response

Primary open angle glaucoma (POAG) is a common late-onset neurodegenerative disease. Ocular hypertension represents a major risk factor, but POAG etiology remains poorly understood. Some cases of early-onset congenital glaucoma and adult POAG are linked to mutations in myocilin, a secreted protein of poorly defined function. Transgenic overexpression of myocilin in Drosophila and experiments in mice and human populations implicate the unfolded protein response (UPR) in the pathogenesis of glaucoma. We postulate that compromised ability of the UPR to eliminate misfolded mutant or damaged proteins, including myocilin, causes endoplasmic reticulum stress, resulting in functional impairment of trabecular meshwork cells that regulate intraocular pressure. This mechanism of POAG is reminiscent of other age-dependent neurodegenerative diseases that involve accumulation of protein aggregates.

Olfactomedin-4 is a glycoprotein secreted into mucus in active IBD

BACKGROUND

Olfactomedin-4 (OLFM4) is a glycoprotein characteristic of intestinal stem cells and apparently involved in mucosal defense of the stomach and colon. Here we studied its expression, regulation and function in IBD.

METHODS

The expression of OLFM4, mucins Muc1 and Muc2, the goblet cell differentiation factor Hath1 and the proinflammatory cytokine IL-8 was measured in inflamed or noninflamed colon in IBD patients and controls. OLFM4 protein was located by immunohistochemistry, quantified by Dot Blot and its binding capacity to defensins HBD1-3 was investigated. The influence of bacteria with or without the Notch blocker dibenzazepine (DBZ) and of several cytokines on OLFM4 expression was determined in LS174T cells.

RESULTS

OLFM4 mRNA and protein were significantly upregulated in inflamed CD (4.3 and 1.7-fold) and even more pronounced in UC (24.8 and 3.7-fold). OLFM4 expression was correlated to IL-8 but not to Hath1. In controls immunostaining was restricted to the lower crypts but in inflamed IBD it expanded up to the epithelial surface including the mucus. OLFM4 bound to HBD1-3 without profoundly inactivating these defensins. In LS174T-cells OLFM4 mRNA was significantly augmented after incubation with Escherichia coli K12, Escherichia coli Nissle and Bacteroides vulgatus. DBZ downregulated OLFM4 expression and blocked bacterial induction whereas IL-22 but not TNF-α was stimulatory.

CONCLUSIONS

OLFM4 is overexpressed in active IBD and secreted into mucus. The induction is triggered by bacteria through the Notch pathway and also by the cytokine IL-22. OLFM4 seems to be of functional relevance in IBD as a mucus component, possibly by binding defensins.

OLFM4 is associated with lymph node metastasis and poor prognosis in patients with gastric cancer

PURPOSE

The present study investigated the clinical significance of the relationship between olfactomedin 4 (OLFM4) expression and the clinicopathological features of patients with gastric cancer.

METHODS

Tumor tissue and adjacent normal tissue, lymph nodes, and peritoneal metastases were analyzed by the Affymetrix GeneChip(®) HG-U133A2.0 array. The expression of OLFM4 was detected by real-time quantitative RT-PCR in gastric tumor tissue and adjacent normal tissue. OLFM4 expression was analyzed by immunohistochemistry in 436 clinicopathologically characterized gastric cancer cases and in corresponding distant metastases from 61 patients.

RESULTS

A total of 434 genes and 169 expressed sequence tags were upregulated, including OLFM4. The expression of OLFM4 mRNA or protein differed significantly among gastric tumor tissue, matched normal gastric mucosa, and lymph node metastases. Further multivariate analysis suggested that lymph node metastases and distant metastases, TNM stage, and expression of OLFM4 were independent prognostic indicators for gastric cancer.

CONCLUSION

Gene expression profiles were useful for simultaneously analyzing the expression levels of thousands of genes. Reduced expression of OLFM4 in gastric cancer is associated significantly with lymph node and distant metastases and with poor prognosis. OLFM4 may prove to be an important molecular marker for predicting the carcinogenesis, development, progression, and metastasis of gastric cancer.

Keeping an eye on myocilin: a complex molecule associated with primary open-angle glaucoma susceptibility

MYOC encodes a secretary glycoprotein of 504 amino acids named myocilin. MYOC is the first gene to be linked to juvenile open-angle glaucoma (JOAG) and some forms of adult-onset primary open-angle glaucoma (POAG). The gene was identified as an up-regulated molecule in cultured trabecular meshwork (TM) cells after treatment with dexamethasone and was originally referred to as trabecular meshwork-inducible glucocorticoid response (TIGR). Elevated intraocular pressure (IOP), due to decreased aqueous outflow, is the strongest known risk factor for POAG. Increasing evidence showed that the modulation of the wild-type (wt) myocilin protein expression is not causative of glaucoma while some misfolded and self-assembly aggregates of mutated myocilin may be associated with POAG in related or unrelated populations. The etiology of the disease remains unclear. Consequently, a better understanding of the molecular mechanisms underlyingPOAG is required to obtain early diagnosis, avoid potential disease progression, and develop new therapeutic strategies. In the present study, we review and discuss the most relevant studies regarding structural characterizations, expressions, molecular interactions, putative functions of MYOC gene and/or its corresponding protein in POAG etiology.

Systematic characterization of protein-DNA interactions

Sequence-specific protein-DNA interactions (PDIs) are critical for regulating many cellular processes, including transcription, DNA replication, repair, and rearrangement. We review recent experimental advances in high-throughput technologies designed to characterize PDIs and discuss recent studies that use these tools, including ChIP-chip/seq, SELEX-based approaches, yeast one-hybrid, bacterial one-hybrid, protein binding microarray, and protein microarray. The results of these studies have challenged some long-standing concepts of PDI and provide valuable insights into the complex transcriptional regulatory networks.

Stem cell marker olfactomedin 4: critical appraisal of its characteristics and role in tumorigenesis

Olfactomedin 4 (OLFM4), a member of the olfactomedin domain-containing proteins, is a glycoprotein with molecular weight of approximately 64 kDa. The protein is a "robust marker" of Lgr5+ stem cells and has been localised to mitochondria, nuclei and cell membranes. The bulk of OLFM4 exists in a polymeric form which is held together by disulfide bonds and carbohydrate interactions. Earlier studies revealed that the protein binds to lectins and cadherins, and facilitates cell-cell adhesion. Recent data demonstrated that the protein possesses several hallmarks of carcinogenesis. OLFM4 has also been purported to be an inducible resistance factor to apoptotic stimuli such as radiation and anticancer drugs. Here, we review its synonyms and classification, gene structure, protein structure, intracellular and tissue distribution, adhesive and antiapoptotic; mitotic; migratory and cell cycle regulatory characteristics. We also critically evaluate recent advances in understanding of the transcriptional regulation of OLFM4 and its upstream signalling pathways with special emphasis on carcinogenesis and outline future perspectives in the field.

Proteomic analysis of mesenchymal stem-like cells derived from ovarian teratoma: potential role of glutathione S-transferase M2 in ovarian teratoma

Ovarian teratoma is a dermoid cyst in the ovary that contains mature tissues such as hair, teeth, bone, thyroid, etc. To understand the molecular mechanisms of ovarian teratoma growth, a comparative proteomic analysis was undertaken using mesenchymal stem cell-like cells (MSCLCs) isolated from normal human ovarian or teratoma tissues. Both normal ovarian and teratoma MSCLCs expressed stem cell markers OCT4 and NANOG, and were negatively staining with the senescence-associated (SA) β-galactosidase. Furthermore, teratoma MSCLCs had higher proliferation and colony formation rates, with more angiogenic property than that of normal MSCLCs. Proteomic study revealed that 17 proteins had the expression changes over eightfold in ovarian teratoma MSCLCs compared with normal control. Interestingly, among them, GSTM2 was strongly expressed in teratoma MSCLCs. Moreover, overexpressed GSTM2 in the teratoma was associated with downregulation of p38 MAPK and activation of AKT and survivin. Taken together, these findings suggest that that ovarian teratoma MSCLCs have a higher potency for proliferation and angiogenesis and GSTM2 appears to be involved in the regulation of other survival genes.

Functional role of proteolytic processing of recombinant myocilin in self-aggregation

PURPOSE

Recombinant myocilin expressed in cells in culture is endoproteolytically cleaved in the endoplasmic reticulum by calpain II, releasing an N-terminal and a C-terminal fragment. This proteolytic processing has been speculated to regulate the molecular interactions of myocilin. The main purpose of this study was to analyze the effect of the proteolytic cleavage on myocilin aggregation.

METHODS

cDNAs encoding human myocilin and the N- and C-terminal fragments were transiently expressed in HEK-293T cells. Covalent interactions of recombinant myocilin were analyzed by SDS-PAGE and Western immunoblot analysis in different dissociating conditions. Noncovalent interactions were studied by solid-phase binding assays, performed with Ni-chelating HPLC-purified recombinant proteins, and by Far-Western blot analysis.

RESULTS

Western blot analysis of recombinant myocilin aggregates under either increasing ionic strength or increasing concentration of reducing agent indicated that ionic interactions do not contribute to the stability of the molecular complexes linked by disulfide bridges. Disulfide myocilin homoaggregates decreased as the proteolytic processing increased. Solid-phase binding assays showed the existence of high-affinity (K(d) = 0.068 microM) noncovalent myocilin-myocilin interactions and that processed fragments bound to the full-length protein with significantly reduced affinity. Far-Western blot analysis confirmed noncovalent interactions between recombinant myocilin disulfide aggregates.

CONCLUSIONS

The proteolytic processing of recombinant myocilin decreases myocilin homoaggregates. These data provide the first evidence of a functional role for this processing in myocilin aggregation and suggest that disulfide complexes of myocilin could organize into a dynamic extracellular network sustained by noncovalent N-terminal interactions.

Myocilin is a modulator of Wnt signaling

It is well documented that mutations in the MYOCILIN gene may lead to juvenile- and adult-onset primary open-angle glaucoma. However, the functions of wild-type myocilin are still not well understood. To study the functions of human myocilin and its two proteolytic fragments, these proteins were expressed in HEK293 cells. Conditioned medium from myocilin-expressing cells, as well as purified myocilin, induced the formation of stress fibers in primary cultures of human trabecular meshwork or NIH 3T3 cells. Stress fiber-inducing activity of myocilin was blocked by antibodies against myocilin, as well as secreted inhibitors of Wnt signaling, secreted Frizzled-related protein 1 (sFRP1) or sFRP3, and beta-catenin small interfering RNA. Interaction of myocilin with sFRP1, sFRP3, and several Frizzled receptors was confirmed by immunoprecipitation experiments and by binding of myocilin to the surface of cells expressing cysteine-rich domains of different Frizzled and sFRPs. Treatment of NIH 3T3 cells with myocilin and its fragments induced intracellular redistribution of beta-catenin and its accumulation on the cellular membrane but did not induce nuclear accumulation of beta-catenin. Overexpression of myocilin in the eye angle tissues of transgenic mice stimulated accumulation of beta-catenin in these tissues. Myocilin and Wnt proteins may perform redundant functions in the mammalian eye, since myocilin modulates Wnt signaling by interacting with components of this signaling pathway.

Transgenic mice expressing the Tyr437His mutant of human myocilin protein develop glaucoma

PURPOSE

To developed a genetic mouse model of primary open-angle glaucoma induced by expression of mutated human myocilin in transgenic mice and to test whether expression of mutated human myocilin in the eye angle structures produces more significant damage to the eye than does mutated mouse myocilin.

METHODS

Recombineering in Escherichia coli was used to introduce the Tyr437His point mutation into a BAC carrying the full-length human MYOCILIN (MYOC) gene and long flanking regions. This BAC was used to produce transgenic mice. The expression of myocilin in the iridocorneal angle tissues and aqueous humor was studied by immunohistochemistry and Western blot analysis. Intraocular pressure was measured noninvasively with a fiber optic transducer. Retinal ganglion cells were retrograde labeled with fluorescent gold, and counted 5 days after labeling.

RESULTS

BAC transgenic mice expressed elevated levels of myocilin in tissues of the iridocorneal angle. Expression of mutated myocilin induced its intracellular accumulation and prevented secretion of both mutated and wild-type myocilin into the aqueous humor. Transgenic mice demonstrated a moderate elevation of intraocular pressure, which was more pronounced at night than in daytime. In the peripheral retina, transgenic mice lost 20% of the retinal ganglion cells and 55% of large retinal ganglion cells. Axonal degeneration was observed at the periphery of the optic nerve.

CONCLUSIONS

Expression of equivalent levels of mutated human or mouse myocilin in the eyes of transgenic mice produce comparable pathologic changes that are similar to those observed in patients with glaucoma.

Reduced hGC-1 protein expression is associated with malignant progression of colon carcinoma

PURPOSE

hGC-1 (human granulocyte colony-stimulating factor-stimulated clone 1) is a gastrointestinal protein that is a member of the olfactomedin glycoprotein family. Its biological function remains poorly understood. Aberrant expression of hGC-1 in some human carcinomas has been recently reported. The purpose of this study was to examine hGC-1 expression in colon carcinoma and explore the relationship between hGC-1 expression and the clinicopathologic features of patients with colon cancer.

EXPERIMENTAL DESIGN

The expression of hGC-1 in colon adenocarcinoma tissues was examined by dot-blot analysis, in situ hybridization, and immunohistochemistry. The association of hGC-1 expression pattern with patient differentiation grade, tumor stage, metastasis, and survival were examined. To further investigate the involvement of hGC-1 in colon cancer progression, human colon carcinoma (HT-29) cells overexpressing hGC-1 were established and cell proliferation, adhesion, and migration were studied.

RESULTS

Compared with normal colon mucosa, the up-regulation of hGC-1 was more frequently detected in more differentiated colon cancers, whereas down-regulation or no expression was associated with poorly differentiated colon cancers. Interestingly, hGC-1 down-regulation was also found in late tumor-node-metastasis stage, metastasis, and in patients with shorter survival. The morphology and cortical actin distribution of HT-29 cells were altered by hGC-1 overexpression. However, this did not change cell proliferation, but decreased cell adhesion and migration.

CONCLUSION

Our findings indicate that hGC-1 is involved in colon cancer adhesion and metastasis, and that hGC-1 may be a useful marker for tumor differentiation and progression of human colon carcinoma.

Structural features and functional domains of amassin-1, a cell-binding olfactomedin protein

Amassin-1 mediates a rapid cell adhesion that tightly adheres sea urchin coelomocytes (body cavity immunocytes) together. Three major structural regions exist in amassin-1: a short beta region, 3 coiled coils, and an olfactomedin domain. Amassin-1 contains 8 disulfide-bonded cysteines that, upon reduction, render it inactive. Truncated forms of recombinant amassin-1 were expressed and purified from Pichia pastoris and their disulfide bonding and biological activities investigated. Expressed alone, the olfactomedin domain contained 2 intramolecular disulfide bonds, existed in a monomeric state, and inhibited amassin-1-mediated clotting of coelomocytes by a calcium-dependent cell-binding activity. The N-terminal beta region, containing 3 cysteines, was not required for clotting activity. The coiled coils may dimerize amassin-1 in a parallel orientation through a homodimerizing disulfide bond. Neither amassin-1 fragments that were disulfide-linked as dimers or that were engineered to exist as dimers induced coelomocytes clotting. Clotting required higher multimeric states of amassin-1, possibly tetramers, which occurred through the N-terminal beta region and (or) the first segment of coiled coils.

Expression of hGC-1 is correlated with differentiation of gastric carcinoma

AIMS

The human G-CSF-stimulated clone-1 (hGC-1) gene encodes a 510-amino acid olfactomedin-related glycoprotein whose exact in vivo localization and function still remain elusive. The aim of this study was to demonstrate hGC-1 protein localization in the normal human gastrointestinal tract and to explore further a potential relationship between hGC-1 expression and gastric carcinoma.

METHODS AND RESULTS

A specific hGC-1 polyclonal antibody raised against purified hGC-1 protein was developed and characterized. Using immunohistochemistry, it was demonstrated that hGC-1 is expressed in the oesophagus, stomach, small intestine and colon. The expression pattern of hGC-1 protein in 173 cases of gastric carcinoma was investigated and a striking correlation was demonstrated between hGC-1 expression and histological type and differentiation of gastric carcinoma. Enhanced hGC-1 expression was more frequently seen in intestinal-type adenocarcinoma, whereas loss of expression tended to occur in the diffuse type. hGC-1 was highly expressed in well or moderately differentiated cancers and was remarkably reduced or lost in poorly differentiated or undifferentiated tumours.

CONCLUSIONS

These investigations have defined for the first time the expression pattern of hGC-1 in the normal human gastrointestinal tract and provide a novel and sensitive marker for the differentiation of gastric carcinoma.

Secreted gliomedin is a perinodal matrix component of peripheral nerves

The interaction between gliomedin and the axonodal cell adhesion molecules (CAMs) neurofascin and NrCAM induces the clustering of Na⁺ channels at the nodes of Ranvier. We define new interactions of gliomedin that are essential for its clustering activity. We show that gliomedin exists as both transmembrane and secreted forms that are generated by proteolytic cleavage of the protein, and that only the latter is detected at the nodes of Ranvier. The secreted extracellular domain of gliomedin binds to Schwann cells and is incorporated into the extracellular matrix (ECM) in a heparin-dependent manner, suggesting the involvement of heparan sulfate proteoglycans (HSPGs). Furthermore, we show that the N-terminal region of gliomedin serves as an oligomerization domain that mediates self-association of the molecule, which is required for its binding to neurofascin and NrCAM. Our results indicate that the deposition of gliomedin multimers at the nodal gap by binding to HSPGs facilitates the clustering of the axonodal CAMs and Na⁺ channels.

Cleavage and oligomerization of gliomedin, a transmembrane collagen required for node of ranvier formation

Gliomedin, which has been implicated as a major player in genesis of the nodes of Ranvier, contains two collagenous domains and an olfactomedin-like domain and belongs to the group of type II transmembrane collagens that includes collagens XIII and XVII and ectodysplasin A. One characteristic of this protein family is that constituent proteins can exist in both transmembrane and soluble forms. Recently, gliomedin expressed at the tips of Schwann cell microvilli was found to bind axonal adhesion molecules neurofascin and NrCAM in interactions essential for Na(+)-channel clustering at the nodes of Ranvier in myelinating peripheral nerves. Interestingly, exogenously added olfactomedin domain was found to have the same effect as intact gliomedin. Here we analyze the tissue form of gliomedin and demonstrate that the molecule not only exists as full-length gliomedin but also as a soluble form shed from the cell surface in a furin-dependent manner. In addition, gliomedin can be further proteolytically processed by bone morphogenetic protein 1/Tolloid-like enzymes, resulting in release of the olfactomedin domain from the collagen domains. Interestingly, the later cleavage induces formation of higher order, insoluble molecular aggregates that may play important roles in Na(+)-channel clustering.

The glycoprotein hGC-1 binds to cadherin and lectins

Human granulocyte colony stimulating factor stimulated clone-1 (hGC-1, also known as GW112, OLM4, and hOlfD) is an olfactomedin-related glycoprotein of unknown function. We performed a series of biochemical studies to characterize its function. Using hGC-1 purified from baculovirus Sf9 cells we demonstrated that hGC-1 is a secreted glycoprotein containing N-linked carbohydrate chains and forms disulfide-bonded multimers. It binds to cell surfaces and to the locutions ricinus communis agglutinin I, concanavalin A and wheat germ agglutinin. Purified hGC-1 enhanced NIH3T3 and 293T/17 cell spreading and attachment, as did hGC-1-enriched culture supernatants of 293T/17 cells transfected with an hGC-1 expression vector. Coimmunoprecipitation studies demonstrated that hGC-1 interacts with cadherin in 293T/17 cells. This interaction depends on the C-terminal olfactomedin domain, but does not require the five well-conserved cysteine residues. However, cysteine residues at 83, 85, 246 and 437 are essential for secretion, and cysteine 226 is critical for hGC-1 multimer formation. Our studies demonstrated that hGC-1, an extracellular matrix glycoprotein, facilitates cell adhesion. Its potential interaction with endogenous cell surface lectins and cadherin may mediate this function.

Expression, purification, crystallization and preliminary X-ray analysis of the olfactomedin domain from the sea urchin cell-adhesion protein amassin

A family of animal proteins is emerging which contain a conserved protein motif known as an olfactomedin (OLF) domain. Novel extracellular protein-protein interactions occur through this domain. The OLF-family member amassin, from the sea urchin Strongylocentrotus purpuratus, has previously been identified to mediate a rapid cell-adhesion event resulting in a large aggregation of coelomocytes, the circulating immune cells. In this work, heterologous expression and purification of the OLF domain from amassin was carried out and initial crystallization trials were performed. A native data set has been collected, extending to 2.7 A under preliminary cryoconditions, using an in-house generator. This work leads the way to the determination of the first structure of an OLF domain.

Noelins modulate the timing of neuronal differentiation during development

Noelins comprise a family of extracellular proteins with proposed roles in neural and neural crest development. Here, we show that a previously uncharacterized family member, Noelin-4, functions to maintain neural precursors in an undifferentiated state and biases ectoderm toward a neural fate. We show that Noelin-4 is induced by the neurogenic genes X-ngnr-1 and XNeuroD. Over-expression of Noelin-4 causes expansion of the neural plate at the expense of neural crest and epidermis. Although there is an apparent increase in the neural precursor pool, no increase was noted in differentiated neurons. Later, derivatives such as the neural tube and retina appear enlarged. We show biochemically that Noelin-4 protein is glycosylated and secreted and that it interacts with Noelin-1, an isoform previously found to promote differentiation in neuralized animal caps. Accordingly, the neural precursor expansion activity of Noelin-4 is reversed by co-expression of Noelin-1. Our finding that Noelin isoforms can bind to and antagonize one another suggests that interacting Noelin isoforms may play a role in regulating timing of differentiation.

Identification and characterization of photomedins: novel olfactomedin-domain-containing proteins with chondroitin sulphate-E-binding activity

We screened more than 60000 RIKEN mouse cDNAs for novel ECM (extracellular matrix) proteins by extensive computational screening followed by recombinant expression and immunohistochemical characterization. We identified two novel olfactomedin-family proteins characterized by the presence of tandem CXCXCX9C motifs in the N-terminal region, a coiled-coil domain and an olfactomedin domain in the C-terminal region. These proteins, named photomedin-1 and photomedin-2, were secreted as disulphide-bonded dimers (photomedin-1) or oligomers/multimers (photomedin-2) with O-linked carbohydrate chains, although photomedin-1 was proteolytically processed in the middle of the molecule after secretion. In the retina, photomedin-1 was selectively expressed in the outer segment of photoreceptor cells and photomedin-2 was expressed in all retinal neurons. Among a panel of ECM components, including glycosaminoglycans, photomedins preferentially bound to chondroitin sulphate-E and heparin. These results, together, indicate that photomedins are novel olfactomedin-domain-containing extracellular proteins capable of binding to proteoglycans containing these glycosaminoglycan chains.

Monitoring chemical and physical stress using sea urchin immune cells

Coelomocytes are the cells freely circulating in the body fluid contained in echinoderm coelom and constitute the defence system, which, in response to injuries, host invasion, and adverse conditions, is capable of chemotaxis, phagocytosis, and production of cytotoxic metabolites. Red and colourless amoebocytes, petaloid and philopodial phagocytes, and vibratile cells are the cell types that, in different proportions, constitute the mixed coelomocyte cell population found in sea urchins. Advances in cellular and molecular biology have made it possible to identify a number of specific proteins expressed in coelomocytes under resting conditions or when activated by experimentally induced stress. Only recently, coelomocytes have been used for pollution studies with the aim of introducing a new biosensor for detection of stress at both cellular and molecular levels, as sentinel of sea health. In this chapter, we briefly review the important features of these valuable cells and describe studies on their use in the laboratory and in the field for the assessment of chemical and physical pollution of the sea.

Elucidation of subfamily segregation and intramolecular coevolution of the olfactomedin-like proteins by comprehensive phylogenetic analysis and gene expression pattern assessment

The categorization of genes by structural distinctions relevant to biological characteristics is very important for understanding of gene functions and predicting functional implications of uncharacterized genes. It was absolutely necessary to deploy an effective and efficient strategy to deal with the complexity of the large olfactomedin-like (OLF) gene family sharing sequence similarity but playing diversified roles in many important biological processes, as the simple highest-hit homology analysis gave incomprehensive results and led to inappropriate annotation for some uncharacterized OLF members. In light of evolutionary information that may facilitate the classification of the OLF family and proper association of novel OLF genes with characterized homologs, we performed phylogenetic analysis on all 116 OLF proteins currently available, including two novel members cloned by our group. The OLF family segregated into seven subfamilies and members with similar domain compositions or functional properties all fell into relevant subfamilies. Furthermore, our Northern blot analysis and previous studies revealed that the typical human OLF members in each subfamily exhibited tissue-specific expression patterns, which in turn supported the segregation of the OLF subfamilies with functional divergence. Interestingly, the phylogenetic tree topology for the OLF domains alone was almost identical with that of the full-length tree representing the unique phylogenetic feature of full-length OLF proteins and their particular domain compositions. Moreover, each of the major functional domains of OLF proteins kept the same phylogenetic feature in defining similar topology of the tree. It indicates that the OLF domain and the various domains in flanking non-OLF regions have coevolved and are likely to be functionally interdependent. Expanded by a plausible gene duplication and domain couplings scenario, the OLF family comprises seven evolutionarily and functionally distinct subfamilies, in which each member shares similar structural and functional characteristics including the composition of coevolved and interdependent domains. The phylogenetically classified and preliminarily assessed subfamily framework may greatly facilitate the studying on the OLF proteins. Furthermore, it also demonstrated a feasible and reliable strategy to categorize novel genes and predict the functional implications of uncharacterized proteins based on the comprehensive phylogenetic classification of the subfamilies and their relevance to preliminary functional characteristics.

Gliomedin Mediates Schwann Cell-Axon Interaction and the Molecular Assembly of the Nodes of Ranvier

Accumulation of Na(+) channels at the nodes of Ranvier is a prerequisite for saltatory conduction. In peripheral nerves, clustering of these channels along the axolemma is regulated by myelinating Schwann cells through a yet unknown mechanism. We report the identification of gliomedin, a glial ligand for neurofascin and NrCAM, two axonal immunoglobulin cell adhesion molecules that are associated with Na+ channels at the nodes of Ranvier. Gliomedin is expressed by myelinating Schwann cells and accumulates at the edges of each myelin segment during development, where it aligns with the forming nodes. Eliminating the expression of gliomedin by RNAi, or the addition of a soluble extracellular domain of neurofascin to myelinating cultures, which caused the redistribution of gliomedin along the internodes, abolished node formation. Furthermore, a soluble gliomedin induced nodal-like clusters of Na+ channels in the absence of Schwann cells. We propose that gliomedin provides a glial cue for the formation of peripheral nodes of Ranvier.

Myocilin is expressed in the glomerulus of the kidney and induced in mesangioproliferative glomerulonephritis

BACKGROUND

Myocilin is a 55 to 57 kD secreted glycoprotein and member of the olfactomedin protein family. It is expressed in high amounts in the outflow tissues of the aqueous humor in the eye where it is supposed to contribute to outflow resistance. Myocilin is mutated in some forms of primary open angle glaucoma and affected patients show very high intraocular pressures because of an increase in resistance to aqueous humor outflow. To obtain information, if myocilin may play a comparable role in other tissues with transendothelial fluid flow, we investigated its expression in the rat kidney.

METHODS

The expression of myocilin in the normal rat kidney and its changes during mesangioproliferative glomerulonephritis were investigated by immunohistochemistry, one- and two-dimensional gel electrophoresis with Western blotting, and reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

Myocilin and its mRNA were detected in isolated glomeruli. Immunohistochemistry showed specific labeling of glomerular cells, while tubular and interstitial regions were essentially negative. Double staining with the podocyte-specific markers synaptopodin and ezrin indicated that myocilin-positive cells were predominately podocytes. During mesangioproliferative glomerulonephritis, an induction of myocilin immunoreactivity was observed. Labeling for myocilin was now observed in activated mesangial cells and areas of glomerular sclerosis. In parallel cell culture experiments, mRNA for myocilin was detected in cultured murine podocytes and rat mesangial cells.

CONCLUSION

Myocilin is expressed in podocytes of the kidney and induced in mesangial cells during experimental mesangioproliferative glomerulonephritis. The specific function of myocilin in the kidney is not clear, but in a parallel to functions of other olfactomedin proteins, it might have a role in cell-cell adhesion and/or signaling processes.

Expression and characterization of disulfide bond use of oligomerized A2-Pancortins: Extracellular matrix constituents in the developing brain

The region-specific characteristics of the extracellular matrix are crucial for diverse functions in the brain. Pancortins/neuron-specific olfactomedin-related glycoproteins are components of the extracellular matrix. They comprise four alternatively spliced variants, Pancortin-1 to -4, which share a common portion, the B part, in the middle of their structure, have two pairs of alternatively spliced 5' regions, A1 and A2, and 3' regions, C1 and C2. Here we demonstrate that in mice, Pancortin-3 (A2-B-C1) and Pancortin-4 (A2-B-C2), which we have grouped together the A2-Pancortins, were transcribed early during the development of the brain in a region specific manner and were expressed very stably in vivo. They are N-glycosylated and secreted. Furthermore, we examined their ontogenetical expression profiles in the developing thalamus using antiserum against the common B region, since transient expressions of their mRNAs were notable there. In the developing thalami, they lasted long in oligomerized form even after the transcription of their mRNAs decreased to an undetectable level. Further analyses revealed that cysteine residues that are located in the common B part are important for homo- and hetero-oligomer formation of A2-Pancortins. When we substituted cysteine residues 45 and 47 with serine residues in that common B part, oligomerization of the A2-Pancortins was highly disturbed.

Determinants of Endometrial Receptivity

Understanding the molecular changes that occur during the window of implantation is fundamental to our knowledge of human reproduction. Lately, the development of microarray technology has allowed this process to be studied from a global molecular perspective. In the last 2 years, researchers have focused their efforts on throwing light on the gene expression profile of the receptive endometrium. The genes hold the key to the development of the endometrium at any stage, and we have focused our work on the window of implantation. The four most recently published works in this field have revealed a long list of genes that are up- or downregulated at the time of implantation. Although these studies have been conducted using varying approaches, collectively these studies identify new candidate markers that can be used to accurately diagnose the receptive state of the endometrium. The next step is to perform functional analysis for confirming the importance of these genes. In this article, we gather together these recent findings to provide an overview of the current knowledge regarding the genetic functioning of human endometrial receptivity and related processes.

hOLF44, a secreted glycoprotein with distinct expression pattern, belongs to an uncharacterized olfactomedin-like subfamily newly identified by phylogenetic analysis

Secreted proteins are indispensable for the development and differentiation of multicellular organisms. Cloning and characterization of novel or hypothetical genes encoding these proteins are therefore inviting great incentives. Using bioinformatics tools and experimental approaches, we isolated and characterized a human secreted glycoprotein, hOLF44, which contains a highly conserved olfactomedin-like (OLF) domain in the C-terminal. However, phylogenetic analysis revealed that hOLF44 is not clustered into any of the OLF subfamilies containing characterized members, and obviously falls into a newly identified uncharacterized OLF subfamily. Western blot analysis showed that hOLF44 protein is robustly secreted from the transfected COS-7 cells. Expression levels of hOLF44 mRNA are abundant in placenta, moderate in liver and heart, whereas fairly weak in other tissues examined. Immunohistochemical study on human term placenta demonstrated that hOLF44 is mainly localized extracellularly surrounding the syncytiotrophoblastic cells and very rarely expressed in the maternal decidua layer. These results suggest that hOLF44 may have matrix-related function involved in human placental and embryonic development, or play a similar role in other physiological processes. The further functional characterization of hOLF44 may provide insights into a better understanding of the newly identified OLF subfamily.

A conserved postsynaptic transmembrane protein affecting neuromuscular signaling in Caenorhabditis elegans

For a motor unit to function, neurons and muscle cells need to adopt their correct cell fate, form appropriate cellular contacts, and assemble a specific repertoire of signaling proteins into presynaptic and postsynaptic structures. In the nematode Caenorhabditis elegans, a disruption of any of these steps causes uncoordinated locomotory behavior (unc phenotype). We report here the positional cloning of a new unc gene, unc-122, which we show by mosaic analysis and tissue-specific rescue experiments to act in muscle to affect locomotory behavior. unc-122 codes for a phylogenetically conserved type II transmembrane protein with collagen repeats and a cysteine-rich olfactomedin domain. Together with uncharacterized proteins in C. elegans, Drosophila, and vertebrates, UNC-122 defines a novel family of proteins that we term "Colmedins." UNC-122 protein is expressed exclusively in muscle and coelomocytes and localizes to the postsynaptic surface of GABAergic and cholinergic neuromuscular junctions (NMJs). Presynaptic and postsynaptic structures are present and properly aligned in unc-122 mutant animals, yet the animals display neurotransmission defects characterized by an altered sensitivity toward drugs that interfere with cholinergic signaling. Moreover, unc-122 mutant animals display anatomical defects in motor axons that are likely a secondary consequence of neurotransmission defects. Both the neuroanatomical and locomotory defects worsen progressively during the life of an animal, consistent with a role of unc-122 in acute signaling at the NMJ. On the basis of motifs in the UNC-122 protein sequence that are characteristic of extracellular matrix proteins, we propose that UNC-122 is involved in maintaining a structural microenvironment that allows efficient neuromuscular signaling.

pDP4, a novel glycoprotein secreted by mature granulocytes, is regulated by transcription factor PU.1

The transcription factor PU.1 (Spi-1) is a well-characterized regulator of myeloid and lymphoid development. However, its role in mature functional cells is poorly studied. Here we report the characterization of the novel murine gene pDP4 (PU.1 difference product 4), which is absent from fetal livers of PU.1-deficient mice. pDP4 is transcribed as a single 3.2-kb mRNA with a 1518-base pair open reading frame encoded by 5 exons on chromosome 14. pDP4 expression is strongest in small intestine and bone marrow, in which it is expressed predominately in mature neutrophils. Interestingly, however, pDP4 expression is markedly down-regulated in neutrophils of the peripheral blood and peritoneum. The pDP4 gene encodes a secreted 57-kDa glycoprotein with an olfactomedin-like C-terminus. PU.1 binds to a functional site within the pDP4 promoter, and pDP4 expression in myeloid cells is strictly dependent on PU.1 and the presence of this site. In conclusion, we have identified a novel PU.1-regulated extracellular glycoprotein of the olfactomedin-like family with a possible role in neutrophilic trafficking.

Secreted glycoprotein myocilin is a component of the myelin sheath in peripheral nerves

The structure of the myelin sheath in peripheral nerves requires the expression of a specific set of proteins. In the present study, we report that myocilin, a member of the olfactomedin protein family, is a component of the myelin sheath in peripheral nerves. Myocilin is a secreted glycoprotein that forms multimers and contains a leucine zipper and an olfactomedin domain. Mutations in myocilin are responsible for some forms of glaucoma, a neurodegenerative disease that is characterized by a continuous loss of optic nerve axons. Myocilin mRNA was detected by Northern blotting in RNA from the rat sciatic and ophthalmic nerves. By one- and two-dimensional gel electrophoresis of proteins from the rat and human sciatic nerves, myocilin was found to migrate at an isoelectric point (pI) of 5.2-5.3 and a molecular weight of 55-57 kDa. Immunohistochemistry showed immunoreactivity for myocilin in paranodal terminal loops of the nodes of Ranvier and outer mesaxons and basal/abaxonal regions of the myelin sheath. Double-labeling experiments with antibodies against myelin basic protein showed no overlapping, while overlapping immunoreactivity was observed with antibodies against myelin-associated glycoprotein. The expression of myocilin in the sciatic nerve became detectable at postnatal day (P) 15 and reached adult levels at P20. No or minor expression of myocilin mRNA was found in brain, spinal cord, and optic nerve. mRNA of myocilin was detected in schwannoma cells in situ, but at considerably lower levels than in myelinated nerves. Myocilin might significantly contribute to the structure of the myelin sheath in peripheral nerves.

Penetrance and phenotype of the Cys433Arg myocilin mutation in a family pedigree with primary open-angle glaucoma

PURPOSE

To evaluate the penetrance and the clinical characteristics of the Cys433Arg myocilin mutation in a family pedigree with primary open-angle glaucoma.

PATIENTS AND METHODS

Primary open-angle glaucoma was defined as untreated intraocular pressure (IOP) over 24 mmHg, with characteristic optic nerve and visual field glaucomatous damage. Patients with IOP <24 mm Hg who were currently being treated for primary open-angle glaucoma were included as affected individuals. Genomic DNA was collected from peripheral blood. PCR, single-strand conformation polymorphism, and sequencing analyses were performed to identify the presence of the Cys433Arg mutation in family members.

RESULTS

Of the 48 members of this family evaluated, 17 (35%) were found to harbor the Cys433Arg mutation, 9 (53%) of whom were glaucomatous. None of the 31 individuals without the mutation had glaucoma. Among the 9 patients with glaucoma, 5 had undergone surgical procedure to improve IOP control, including all patients older than 40 years of age. The mutation's penetrance was 0% in persons younger than 10 years (0/4), 40% in those 11 to 30 years (2/5), 75% in persons 30 to 40 years (3/4), and 100% in those older than 40 years (4/4).

CONCLUSION

The Cys433Arg mutation in this pedigree was associated with a phenotype characterized by early-onset open-angle glaucoma, which frequently requires surgical intervention and is associated with a high penetrance

Expression and characterization of the olfactomedin domain of human myocilin

The olfactomedin-domain has been first identified in olfactomedin, an extracellular matrix protein of the olfactory neuroepithelium. Members of this extracellular domain-family have since been shown to be present in several metazoan proteins, such as latrophilins, myocilins, and noelins, but their biological function is unknown. The olfactomedin-domain of myocilin is of considerable interest, since mutations affecting this domain are associated with primary open angle glaucoma. In order to define structural features of this domain-type we have expressed the olfactomedin-domain of human myocilin in Pichia pastoris. The olfactomedin-domain contains a single disulphide-bond connecting Cys-245 and Cys-433 residues; secondary structure predictions and circular dichroism studies indicate that it consists primarily of beta-strands. It is noteworthy that the majority of mutations associated with severe forms of glaucoma affect residues that reside in conserved secondary structural elements of the olfactomedin-domain or are otherwise critical for the integrity of this protein-fold.

Amassin, an olfactomedin protein, mediates the massive intercellular adhesion of sea urchin coelomocytes

Sea urchins have a fluid-filled body cavity, the coelom, containing four types of immunocytes called coelomocytes. Within minutes after coelomic fluid is removed from the body cavity, a massive cell-cell adhesion of coelomocytes occurs. This event is referred to as clotting. Clotting is thought to be a defense mechanism against loss of coelomic fluid if the body wall is punctured, and it may also function in the cellular encapsulation of foreign material and microbes. Here we show that this intercoelomocyte adhesion is mediated by amassin, a coelomic plasma protein with a relative molecular mass (Mr) of 75 kD. Amassin forms large disulfide-bonded aggregates that adhere coelomocytes to each other. One half of the amassin protein comprises an olfactomedin (OLF) domain. Structural predictions show that amassin and other OLF domain-containing vertebrate proteins share a common architecture. This suggests that other proteins of the OLF family may function in intercellular adhesion. These findings are the first to demonstrate a function for a protein of the OLF family.

Myocilin and glaucoma: facts and ideas

Mutations in the MYOC gene that encodes for myocilin are causative for some forms of juvenile and adult-onset primary open-angle glaucoma (POAG). Myocilin is a secreted 55-57kDa glycoprotein that forms dimers and multimers. Characteristic structural motifs include a myosin-like domain, a leucine zipper region and an olfactomedin domain. Most of the mutations that have been identified in patients with POAG are localized in the olfactomedin domain, which is highly conserved among species. In the eye, myocilin is expressed in high amounts in the trabecular meshwork (TM), sclera, ciliary body and iris, and at considerable lower amounts in retina and optic nerve head. Secreted myocilin is present in the aqueous humor. In the TM, myocilin is found within the cytoplasm of TM cells and in the juxtacanalicular region in association with fibrillar extracellular matrix components. Since patients with mutations in myocilin may have high intraocular pressures, the role of myocilin for aqueous humor outflow has been investigated and conflicting results have been obtained. Recombinant myocilin increases outflow resistance in perfused anterior segment organ cultures, while overexpression of myocilin after viral gene transfer appears to reduce outflow resistance. In TM cells, the expression of myocilin is induced upon treatment with dexamethasone at a time course similar to that observed in steroid-induced glaucoma. Other factors that induce myocilin expression are transforming growth factor-beta and mechanical stretch. Promoter elements that are important for the glucocorticoid induction have not been identified, but it has been shown that upstream stimulatory factor is critical for the basal promoter activity of MYOC. Mice with a targeted disruption of the myocilin gene do not express a phenotype, indicating that the glaucomatous phenotype in humans is not because of a loss-of-function effect. Experimental studies show that mutated myocilin is not secreted, but appears to accumulate in the cells. Such an accumulation might interfere with TM function and lead to impaired outflow resistance, but, so far, experimental evidence for such a scenario is lacking. In addition, the normal function(s) of myocilin is (are) still elusive.

Characterizing gene expression during lens formation in Xenopus laevis: evaluating the model for embryonic lens induction

Few directed searches have been undertaken to identify the genes involved in vertebrate lens formation. In the frog Xenopus, the larval cornea can undergo a process of transdifferentiation to form a new lens once the original lens is removed. Based on preliminary evidence, we have shown that this process shares many elements of a common molecular/genetic pathway to that involved in embryonic lens development. A subtracted cDNA library, enriched for genes expressed during cornea-lens transdifferentiation, was prepared. The similarities/identities of specific clones isolated from the subtracted cDNA library define an expression profile of cells undergoing cornea-lens transdifferentiation ("lens regeneration") and corneal wound healing (the latter representing a consequence of the surgery required to trigger transdifferentiation). Screens were undertaken to search for genes expressed during both transdifferentiation and embryonic lens development. Significantly, new genes were recovered that are also expressed during embryonic lens development. The expression of these genes, as well as others known to be expressed during embryonic development in Xenopus, can be correlated with different periods of embryonic lens induction and development, in an attempt to define these events in a molecular context. This information is considered in light of our current working model of embryonic lens induction, in which specific tissue properties and phases of induction have been previously defined in an experimental context. Expression data reveal the existence of further levels of complexity in this process and suggests that individual phases of lens induction and specific tissue properties are not strictly characterized or defined by expression of individual genes.

Dorsalization of the neural tube by Xenopus tiarin, a novel patterning factor secreted by the flanking nonneural head ectoderm

We have isolated a novel secreted dorsalizing factor of the neural tube, Xenopus Tiarin, which belongs to the olfactomedin-related family. Tiarin expression starts at the late gastrula stage in the nonneural ectoderm adjacent to the anterior neural plate. Overexpression of Tiarin in the embryo causes expansion of dorsal neural markers and suppression of ventral markers. In the eye-forming field, Tiarin overexpression induces the retinal markers and represses optic stalk markers. Tiarin directly dorsalizes neural tissues in the absence of mesodermal tissues and antagonizes the ventralizing activity of Sonic hedghog (Shh). Unlike BMP4, another dorsalizing factor, Tiarin does not display antineuralizing activity on the ectoderm or mesoderm-ventralizing activity. These findings show that Tiarin is a novel patterning signal candidate acting in the specification of the dorsal neural tube.

Identification and characterization of a novel member of olfactomedin-related protein family, hGC-1, expressed during myeloid lineage development

We have cloned a novel hematopoietic granulocyte colony-stimulating factor (G-CSF)-induced olfactomedin-related glycoprotein, termed hGC-1 (human G-CSF-stimulated clone-1). mRNA differential display was used in conjunction with a modified two-phase liquid culture system. Cultures were enriched for early precursors of erythroid, myeloid, and megakaryocytic lineages, which were isolated after induction with erythropoietin, G-CSF, and thrombopoietin, respectively. RNA from the enriched cells was subjected to differential display analysis to identify lineage-specific expressed genes. One clone specifically induced by G-CSF, hGC-1, was characterized. The 2861 bp cDNA clone of hGC-1 contained an open reading frame of 1530 nucleotides, translating into a protein of 510 amino acids with a signal peptide and six N-linked glycosylation motifs. The protein sequence of hGC-1 showed it to be a glycoprotein of the olfactomedin family, which includes olfactomedin, TIGR, Noelin-2 and latrophilin-1. Olfactomedin-like genes show characteristic tissue-restricted patterns of expression; the specific tissues expressing these genes differ among the family members. hGC-1 was strongly expressed in the prostate, small intestine, and colon, moderately expressed in the bone marrow and stomach, and not detectable in other tissues. In vitro translation and ex vivo expression showed hGC-1 to be an N-linked glycoprotein. The hGC-1 gene locus mapped to chromosome 13q14.3. Together, our findings indicate that hGC-1 is primarily expressed as an extracellular olfactomedin-related glycoprotein during normal myeloid-specific lineage differentiation, suggesting the possibility of a matrix-related function for hGC-1 in differentiation.