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

Ultrafiltration and Fluid Excretion in Echinoids Involves the Axial Organ with Elimination via the Intestine

Many animals display nephridial structures for the ultrafiltration of metabolic waste. However, a nephridial equivalent and an excretory system are not generally recognized for echinoderms. Podocytes are nephridial cells that function in ultrafiltration of body fluids. Limited ultrastructural analyses of echinoderms identify cells with podocyte morphology in the axial organ and in the left coelom of larval sea urchins. Echinoid internal anatomy suggests that the excretory system functions by ultrafiltration in the axial organ, as well as filtrate flow via the water vascular system for excretion through the madreporite; however, these reports are based on morphology. To verify podocytes in the axial organ, orthologues of podocyte-specific genes were evaluated in the sea urchin genome and RNAseq data sets. To verify excretion from the madreporite, fluorescein was used as a tracer for nephridial clearance, and was injected into the main body cavity of sea urchins. Results showed that genes encoding proteins that function in podocytes of vertebrates are expressed specifically in the axial organ of sea urchins, in agreement with orthologue expression in the nurse shark kidney. However, fluorescein clearance from the body cavity shows elimination from the anus rather than the madreporite. This leads to the hypothesis that fluorescein and metabolic waste clearance occur through ultrafiltration by podocytes in the axial organ, but that the filtrate flows into the haemal system and the haemal capillaries in the intestinal walls, from which fluid is transferred to the intestinal lumen for elimination through the anus. Future testing is proposed to evaluate fluorescein filtration from the blastocoel of larvae into the left coelom, and for excretion by small or juvenile echinoids that have undergone tissue clearance to visualize the route of fluorescein flow within the internal anatomy of cleared, intact sea urchins.

Morpho-functional characterisation of cœlomocytes in the aquacultivated sea cucumber Holothuria scabra: From cell diversity to transcriptomic immune response

Holothuria scabra is one of the most valuable species of sea cucumber owing to its exploitation as a seafood product. This study aims to describe the main molecular and cellular actors in the immunology of this species. First, a detailed description of the immune cells - the cœlomocytes - is provided, highlighting five main cell types including phagocytes, small round cells (SRCs), spherulocytes, fusiform cells, and crystal cells, with a further five subtypes identified using transmission electron microscopy. Cœlomocyte aggregates were also described morphologically, yielding two main types, one comprising three successive maturation stages. A comparison of the concentration and proportion of cell populations was carried out between the two main body fluids, namely the hydrovascular fluid of the Polian vesicle (HF) and the perivisceral fluid of the general cavity (PF), and no clear relation could be highlighted. Next, the cœlomocyte immune response was studied 24 h after lipopolysaccharide (LPS) injection in the two body fluids. Firstly, the fluctuation in cell populations was assessed, and despite a high inter-individual variability, it shows a decrease in the phagocyte proportion and an increase in the SRC proportion. Secondly, the differential gene expression of PF cœlomocytes was studied by de novo RNA-sequencing between LPS-injected and control-injected individuals: 945 genes were differentially expressed, including 673 up-regulated and 272 down-regulated in the LPS-injected individuals. Among these genes, 80 had a presumed function in immunity based on their annotation, covering a wide range of immune mechanisms. Overall, this study reveals a complex immune system at both molecular and cellular levels and constitutes a baseline reference on H. scabra immunity, which may be useful for the development of sustainable aquaculture and provides valuable data for comparative immunology.

Mouse Tissue-Resident Peritoneal Macrophages in Homeostasis, Repair, Infection, and Tumor Metastasis

Large peritoneal macrophages (LPMs) are long-lived, tissue-resident macrophages, formed during embryonic life, developmentally and functionally confined to the peritoneal cavity. LPMs provide the first line of defense against life-threatening pathologies of the peritoneal cavity, such as abdominal sepsis, peritoneal metastatic tumor growth, or peritoneal injuries caused by trauma, or abdominal surgery. Apart from their primary phagocytic function, reminiscent of primitive defense mechanisms sustained by coelomocytes in the coelomic cavity of invertebrates, LPMs fulfill an essential homeostatic function by achieving an efficient clearance of apoptotic, that is crucial for the maintenance of self-tolerance. Research performed over the last few years, in mice, has unveiled the mechanisms by which LPMs fulfill a crucial role in repairing peritoneal injuries and controlling microbial and parasitic infections, reflecting that the GATA6-driven LPM transcriptional program can be modulated by extracellular signals associated with pathological conditions. In contrast, recent experimental evidence supports that peritoneal tumors can subvert LPM metabolism and function, leading to the acquisition of a tumor-promoting potential. The remarkable functional plasticity of LPMs can be nevertheless exploited to revert tumor-induced LPM protumor potential, providing the basis for the development of novel immunotherapeutic approaches against peritoneal tumor metastasis based on macrophage reprogramming.

Gata6+ large peritoneal macrophages: an evolutionarily conserved sentinel and effector system for infection and injury

There are striking similarities between the sea urchin cavity macrophage-like phagocytes (coelomocytes) and mammalian cavity macrophages in not only their location, but also their behaviors. These cells are crucial for maintaining homeostasis within the cavity following a breach, filling the gap and functioning as a barrier between vital organs and the environment. In this review, we summarize the evolving literature regarding these Gata6⁺ large peritoneal macrophages (GLPMs), focusing on ontogeny, their responses to perturbations, including their rapid aggregation via coagulation, as well as scavenger receptor cysteine-rich domains and their potential roles in diseases, such as cancer. We challenge the 50-year old phenomenon of the 'macrophage disappearance reaction' (MDR) and propose the new term 'macrophage disturbance of homeostasis reaction' (MDHR), which may better describe this complex phenomenon.

Coelomocyte populations in the sea urchin, Strongylocentrotus purpuratus, undergo dynamic changes in response to immune challenge

The sea urchin, Strongylocentrotus purpuratus has seven described populations of distinct coelomocytes in the coelomic fluid that are defined by morphology, size, and for some types, by known functions. Of these subtypes, the large phagocytes are thought to be key to the sea urchin cellular innate immune response. The concentration of total coelomocytes in the coelomic fluid increases in response to pathogen challenge. However, there is no quantitative analysis of how the respective coelomocyte populations change over time in response to immune challenge. Accordingly, coelomocytes collected from immunoquiescent, healthy sea urchins were evaluated by flow cytometry for responses to injury and to challenge with either heat-killed Vibrio diazotrophicus, zymosan A, or artificial coelomic fluid, which served as the vehicle control. Responses to the initial injury of coelomic fluid collection or to injection of V. diazotrophicus show significant increases in the concentration of large phagocytes, small phagocytes, and red spherule cells after one day. Responses to zymosan A show decreases in the concentration of large phagocytes and increases in the concentration of small phagocytes. In contrast, responses to injections of vehicle result in decreased concentration of large phagocytes. When these changes in coelomocytes are evaluated based on proportions rather than concentration, the respective coelomocyte proportions are generally maintained in response to injection with V. diazotrophicus and vehicle. However, this is not observed in response to zymosan A and this lack of correspondence between proportions and concentrations may be an outcome of clearing these large particles by the large phagocytes. Variations in coelomocyte populations are also noted for individual sea urchins evaluated at different times for their responses to immune challenge compared to the vehicle. Together, these results demonstrate that the cell populations in sea urchin immune cell populations undergo dynamic changes in vivo in response to distinct immune stimuli and to injury and that these changes are driven by the responses of the large phagocyte populations.

Galactose-Binding C-Type Lectin Promotes Cellular Aggregation of Coelomocytes in Sea Cucumber

Echinoderms have a large coelomic cavity containing coelomocytes. When the coelomic fluid is removed from the cavity, the cells aggregate immediately. We found that a fraction or an extract of the intestine of the sea cucumber, Apostichopus japonicus, markedly accelerated cellular movement and aggregation on a glass slide, and this effect was clearly inhibited by galactose. We successfully purified the aggregation-promoting factor, a 16 kDa protein, from the intestine. TOF-MS analysis followed by de novo sequencing revealed that the protein is a C-type lectin. RNA-seq data and cDNA cloning demonstrated the factor to be a novel lectin, named AjGBCL, consisting of 158 aa residues in the mature form. Microscopic observation revealed that most of the aggregating cells moved toward aggregates and not to an intestinal fragment, suggesting that AjGBCL is not a chemoattractant but a cellular aggregation-inducing factor that may induce aggregates to release chemoattractant. We report, for the first time, an endogenous molecule that promotes coelomocyte aggregation in echinoderms.

Transcriptome analysis of growth variation in early juvenile stage sandfish Holothuria scabra

The sandfish Holothuria scabra is a high-value tropical sea cucumber species representing a major mariculture prospect across the Indo-Pacific. Advancements in culture technology, rearing, and processing present options for augmenting capture production, stock restoration, and sustainable livelihood activities from hatchery-produced sandfish. Further improvements in mariculture production may be gained from the application of genomic technologies to improve performance traits such as growth. In this study, we performed de novo transcriptome assembly and characterization of fast- and slow-growing juvenile H. scabra from three Philippine populations. Analyses revealed 66 unigenes that were consistently differentially regulated in fast-growing sandfish and found to be associated with immune response and metabolism. Further, we identified microsatellite and single nucleotide polymorphism markers potentially associated with fast growth. These findings provide insight on potential genomic determinants underlying growth regulation in early juvenile sandfish which will be useful for further functional studies.

Primordial GATA6 macrophages function as extravascular platelets in sterile injury

Most multicellular organisms have a major body cavity that harbors immune cells. In primordial species such as purple sea urchins, these cells perform phagocytic functions but are also crucial in repairing injuries. In mammals, the peritoneal cavity contains large numbers of resident GATA6⁺ macrophages, which may function similarly. However, it is unclear how cavity macrophages suspended in the fluid phase (peritoneal fluid) identify and migrate toward injuries. In this study, we used intravital microscopy to show that cavity macrophages in fluid rapidly form thrombus-like structures in response to injury by means of primordial scavenger receptor cysteine-rich domains. Aggregates of cavity macrophages physically sealed injuries and promoted rapid repair of focal lesions. In iatrogenic surgical situations, these cavity macrophages formed extensive aggregates that promoted the growth of intra-abdominal scar tissue known as peritoneal adhesions.

From Coelomocytes to Colored Aggregates: Cellular Components and Processes Involved in the Immune Response of the Holothuroid Cucumaria frondosa

AbstractWhile so-called brown bodies were first defined in the 1950s as colorful aggregates of cells in the general cavity of echinoderms and other marine benthic taxa, their distribution and role have not yet been fully clarified. This work characterized free coelomocytes and corresponding aggregates ("bodies") in the hydrovascular system and perivisceral coelom, as well as those attached on the membranes of the viscera, in the holothuroid Cucumaria frondosa. Responses to the presence of foreign particles were investigated, providing novel insights on the immune system. A total of eight coelomocyte cell types was detected, while aggregates were formed of three to six types of coelomocytes. Only red-colored aggregates were found in the hydrovascular system, whereas brown aggregates were confined to the perivisceral coelom. The encapsulation mechanism of foreign particles injected in the hydrovascular system was monitored. Particles were first gathered by phagocytes and vibratile, crystal, and morula cells into a whitish aggregate that was then covered by hemocytes, imparting a red color to the aggregates. After their transfer to the perivisceral coelom, aggregates became brown and were ultimately expelled through the anus. Finally, a range of stressors (i.e., harvesting method, presence of a predator, and physical injury) was found to increase the abundance of aggregates, thus highlighting the role of these bodies in the immune response of C. frondosa.

Autofluorescence mediated red spherulocyte sorting provides insights into the source of spinochromes in sea urchins

Red spherule cells (RSCs) are considered one of the prime immune cells of sea urchins, but their detailed biological role during immune responses is not well elucidated. Lack of pure populations accounts for one of the major challenges of studying these cells. In this study, we have demonstrated that live RSCs exhibit strong, multi-colour autofluorescence distinct from other coelomocytes, and with the help of fluorescence-activated cell sorting (FACS), a pure population of live RSCs was successfully separated from other coelomocytes in the green sea urchin, Strongylocentrotus droebachiensis. This newly developed RSCs isolation method has allowed profiling of the naphthoquinone content in these cells. With the use of ultra high-performance liquid chromatography, UV absorption spectra, and high-resolution tandem mass spectrometry, it was possible to identify sulphated derivatives of spinochrome C, D, E and spinochrome dimers, which suggests that the RSCs may play an important biological role in the biogenesis of naphthoquinone compounds and regulating their bioactivity.

Injury affects coelomic fluid proteome of the common starfish, Asterias rubens

Echinoderms, possessing outstanding regenerative capabilities, provide a unique model system for the study of response to injury. However, little is known about the proteomic composition of coelomic fluid, an important biofluid circulating throughout the animal's body and reflecting the overall biological status of the organism. In this study, we used LC-MALDI tandem mass spectrometry to characterize the proteome of the cell-free coelomic fluid of the starfish Asterias rubens and to follow the changes occurring in response to puncture wound and blood loss. In total, 91 proteins were identified, of which 61 were extracellular soluble and 16 were bound to the plasma membrane. The most represented functional terms were 'pattern recognition receptor activity' and 'peptidase inhibitor activity'. A series of candidate proteins involved in early response to injury was revealed. Ependymin, β-microseminoprotein, serum amyloid A and avidin-like proteins, which are known to be involved in intestinal regeneration in the sea cucumber, were also identified as injury-responsive proteins. Our results expand the list of proteins potentially involved in defense and regeneration in echinoderms and demonstrate dramatic effects of injury on the coelomic fluid proteome.

Bioinformatic exploration of OLFML2B overexpression in gastric cancer base on multiple analyzing tools

Background

Gastric cancer (GC) is one of the most commonly occuring gastrointestinal tumor types, and early diagnosis and operation have a notable effect on the prognosis of patients. Although certain markers, including HER2, VEGER-2, ERCC1 and Bcl-2, have been utilized in clinical practise to screen out new patients with GC, the results of using these markers remains poor. The role of olfactomedin-like 2B (OLFML2B) in GC, as a member of the olfactomedin domain-containing proteins family, is remain unclear.

Methods

In the present study, we assessed the expression of OLFML2B, including mRNA and protein level, by using The Cancer Genome Atlas (TCGA) database and 13 pairs of clinical samples between GC and NG tissues. The correlation between expression of OLFML2B and prognosis of GC was evaculated by the Kaplan-Meier plotter and OncoLnc online tools. In addition, mechanism analysis of OLFML2B in GC was explored thought bioinformatic tools, including cBioPortal and FunRich software.

Results

In our study, the mRNA expression of OLFML2B in GC both TCGA database and clinical samples was consistently revealed to be significantly higher compared with that in NG tissues (P < 0.0001 for TCGA database and P = 0.0034 for clinical samples), and high OLFML2B expression was found in 9 (69.23%) of 13 clinical GC by immunohistochemistry and was positively correlated with the depth of tumor invasion and clinical stage (TNM). In addition, the AUC for a ROC of 0.867 indicated a moderate diagnostic ability of OLFML2B for GC. Survival analysis from the Kaplan-Meier plotter (P = 2.6 × 10^− 6) and OncoLnc (P = 0.00276) revealed that the high expression of OLFML2B was associated with a short overall survival. Futhermore, 5% (24/478) alterations of OLFML2B were identified from cBioPortal, and among them, missense mutation (14/478) was the primary type. The results from FunRich revealed that OLFML2B participated in mediating multiple biological processes including cell growth and maintenance, regulation of the cell cycle, apoptosis and cell communication through multiple signaling pathways including the M/G1 transition pathway, post-translational protein modification and DNA replication pre-initiation.

Conclusions

Taken together, it could be deduced that OLFML2B may act as an oncogene in the development of GC and the overexpression of OLFML2B in GC may be used as a novel diagnostic and prognostic target for GC.

Sea urchin Paracentrotus lividus immune cells in culture: formulation of the appropriate harvesting and culture media and maintenance conditions

The sea urchin is an emergent model system for studying basic and translational immunology. Here we report a new method for the harvesting and maintenance of primary immune cells isolated from adult Paracentrotus lividus, a common Mediterranean sea urchin species. This optimised method uses coelomocyte culture medium, containing a high-affinity Ca²⁺ chelator, as the ideal harvesting and anti-clotting vehicle and short-term culture medium (≤48 h), and artificial seawater as the master medium that maintains cell survival and in vitro-ex vivo physiological homeostasis over 2 weeks. Gradually reducing the amount of anticoagulant solution in the medium and regularly replacing the medium led to improved culture viability. Access to a robust and straightforward in vitro-ex vivo system will expedite our understanding of deuterostome immunity as well as underscore the potential of sea urchin with respect to biomedicine and regulatory testing.

This article has an associated First Person interview with the first author of the paper.

Summary: Appropriate culture methods for sea urchin immune cells provide an invaluable and amenable model for answering immunological questions while limiting the use of mammalian organisms.

Methods for collection, handling, and analysis of sea urchin coelomocytes

Sea urchin coelomocytes can be collected in large numbers from adult sea urchins of the species, Strongylocentrotus purpuratus, which typically has 12-40mL of coelomic fluid. Coelomocytes are used for analysis of immune reactions and immune gene expression in addition to basic functions of cells, in particular for understanding structure and modifications of the cytoskeleton in phagocytes. The methods described here include coelomocyte isolation, blocking the clotting reaction, establishing and maintaining primary cultures, separation of different types of coelomocytes into fractions, processing live coelomocytes for light microscopy, fixation and staining for light and electron microscopy, analysis of coelomocyte populations by flow cytometry, and sorting single cells for more detailed follow-up analyses including transcriptomics or genomic characteristics. These methods are provided to make working with coelomocytes accessible to researchers who are unfamiliar with these cells and perhaps to aid others who have worked extensively with invertebrate cells.

Single-cell analysis of progenitor cell dynamics and lineage specification in the human fetal kidney

The mammalian kidney develops through reciprocal interactions between the ureteric bud and the metanephric mesenchyme to give rise to the entire collecting system and the nephrons. Most of our knowledge of the developmental regulators driving this process arises from the study of gene expression and functional genetics in mice and other animal models. In order to shed light on human kidney development, we have used single-cell transcriptomics to characterize gene expression in different cell populations, and to study individual cell dynamics and lineage trajectories during development. Single-cell transcriptome analyses of 6414 cells from five individual specimens identified 11 initial clusters of specific renal cell types as defined by their gene expression profile. Further subclustering identifies progenitors, and mature and intermediate stages of differentiation for several renal lineages. Other lineages identified include mesangium, stroma, endothelial and immune cells. Novel markers for these cell types were revealed in the analysis, as were components of key signaling pathways driving renal development in animal models. Altogether, we provide a comprehensive and dynamic gene expression profile of the developing human kidney at the single-cell level.

Summary: New markers for specific cell types in the developing human kidney are identified and computational approaches infer developmental trajectories and interrogate the complex network of signaling pathways and cellular transitions.

Gene expression across tissues, sex, and life stages in the sea urchin Tripneustes gratilla [Toxopneustidae, Odontophora, Camarodonta]

The pan-tropical sea urchin Tripneustes gratilla is an ecologically and economically important shallow water algal grazer. The aquaculture of T. gratilla has spurred growing interest in the population biology of the species, and by extension the generation of more molecular resources. To this purpose, de novo transcriptomes of T. gratilla were generated for two adults, a male and a female, as well as for a cohort of approximately 1000 plutei larvae. Gene expression profiles of three adult tissue samples were quantified and compared. These samples were of gonadal tissue, the neural ring, and pooled tube feet and pedicellariae. Levels of shared and different gene expression between sexes, as well as across functional categories of interest, including the immune system, toxins, genes involved in fertilization, and sensory genes are highlighted. Differences in expression of isoforms between the sexes and Sex determining Region Y-related High Mobility Group box groups is observed. Additionally an expansion of the tumor suppressor DMBT1 is observed in T. gratilla when compared to the annotated genome of the sea urchin Strongylocentrotus purpuratus. The draft transcriptome of T. gratilla is presented here in order to facilitate more genomic level analysis of emerging model sea urchin systems.

Differential count and time-course analysis of the cellular composition of coelomocyte aggregate of the Japanese sea cucumber Apostichopus japonicus

Echinoderms have many types of coelomocytes, which have been known to form aggregates immediately after they are removed from the coelom. To assess the roles that each type of coelomocyte plays in aggregate formation, cellular components of coelomocyte aggregates of the Japanese sea cucumber, Apostichopus japonicus, were investigated. The coelomocytes were tentatively classified into 12 types based on May-Grunwald/Giemsa staining. After the coelom was incubated for 30 min or 6 h, the aggregates were disaggregated completely with 200 mM EDTA. Differential counts of the dissociated cells indicated that the largest component of the aggregates was amoebocytes (67.8%) and the second-largest component of the aggregates incubated 30 min was a type of basophilic granulocyte. In the 6h-incubated aggregates, the fraction of amoebocytes decreased to 59.0%, while that of lymphoid cells significantly increased, which suggests that lymphoid cells participate in late-stage aggregation. After 24-h incubation, only a portion of the aggregated cells could be disaggregated with EDTA. After 48 h, most of the cells could not be detached from the aggregates. Microscopy of frozen sections of the aggregates after 6-h incubation revealed that amoebocytes constructed a mesh-like structure to which other types of cells adhered. After 48 h, the borders of the cells and the intracellular granules were not recognizable. In time-lapse microscopy, the aggregates were observed to move on a glass slide, which suggests that aggregates can "crawl" on the intraluminal surface of the coelom toward, for example, injured regions in the body of the sea cucumber.

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.

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.

Single sea urchin phagocytes express messages of a single sequence from the diverse Sp185/333 gene family in response to bacterial challenge

Immune systems in animals rely on fast and efficient responses to a wide variety of pathogens. The Sp185/333 gene family in the purple sea urchin, Strongylocentrotus purpuratus, consists of an estimated 50 (±10) members per genome that share a basic gene structure but show high sequence diversity, primarily due to the mosaic appearance of short blocks of sequence called elements. The genes show significantly elevated expression in three subpopulations of phagocytes responding to marine bacteria. The encoded Sp185/333 proteins are highly diverse and have central effector functions in the immune system. In this study we report the Sp185/333 gene expression in single sea urchin phagocytes. Sea urchins challenged with heat-killed marine bacteria resulted in a typical increase in coelomocyte concentration within 24 h, which included an increased proportion of phagocytes expressing Sp185/333 proteins. Phagocyte fractions enriched from coelomocytes were used in limiting dilutions to obtain samples of single cells that were evaluated for Sp185/333 gene expression by nested RT-PCR. Amplicon sequences showed identical or nearly identical Sp185/333 amplicon sequences in single phagocytes with matches to six known Sp185/333 element patterns, including both common and rare element patterns. This suggested that single phagocytes show restricted expression from the Sp185/333 gene family and infers a diverse, flexible, and efficient response to pathogens. This type of expression pattern from a family of immune response genes in single cells has not been identified previously in other invertebrates.

Expression analysis of immune related genes identified from the coelomocytes of sea cucumber (Apostichopus japonicus) in response to LPS challenge

The sea cucumber (Apostichopus japonicus) occupies a basal position during the evolution of deuterostomes and is also an important aquaculture species. In order to identify more immune effectors, transcriptome sequencing of A. japonicus coelomocytes in response to lipopolysaccharide (LPS) challenge was performed using the Illumina HiSeq™ 2000 platform. One hundred and seven differentially expressed genes were selected and divided into four functional categories including pathogen recognition (25 genes), reorganization of cytoskeleton (27 genes), inflammation (41 genes) and apoptosis (14 genes). They were analyzed to elucidate the mechanisms of host-pathogen interactions and downstream signaling transduction. Quantitative real-time polymerase chain reactions (qRT-PCRs) of 10 representative genes validated the accuracy and reliability of RNA sequencing results with the correlation coefficients from 0.88 to 0.98 and p-value <0.05. Expression analysis of immune-related genes after LPS challenge will be useful in understanding the immune response mechanisms of A. japonicus against pathogen invasion and developing strategies for resistant markers selection.

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.

Shotgun proteomics of coelomic fluid from the purple sea urchin, Strongylocentrotus purpuratus

The purple sea urchin has a complex immune system that is likely mediated by gene expression in coelomocytes (blood cells). A broad array of potential immune receptors and immune response proteins has been deduced from their gene models. Here we use shotgun mass spectrometry to describe 307 proteins with possible immune function in sea urchins including proteins involved in the complement pathway and numerous SRCRs. The relative abundance of dual oxidase 1, ceruloplasmin, ferritin and transferrin suggests the production of reactive oxygen species in coelomocytes and the sequestration of iron. Proteins such as selectin, cadherin, talin, galectin, amassin and the Von Willebrand factor may be involved in generating a strong clotting reaction. Cell signaling proteins include a guanine nucleotide binding protein, the Rho GDP dissociation factor, calcium storage molecules and a variety of lipoproteins. However, based on this dataset, the expression of TLRs, NLRs and fibrinogen domain containing proteins in coelomic fluid and coelomocytes could not be verified.

Aggregation of sea urchin phagocytes is augmented in vitro by lipopolysaccharide

Development of protocols and media for culturing immune cells from marine invertebrates has not kept pace with advancements in mammalian immune cell culture, the latter having been driven by the need to understand the causes of and develop therapies for human and animal diseases. However, expansion of the aquaculture industry and the diseases that threaten these systems creates the need to develop cell and tissue culture methods for marine invertebrates. Such methods will enable us to better understand the causes of disease outbreaks and to develop means to avoid and remedy epidemics. We report a method for the short-term culture of phagocytes from the purple sea urchin, Strongylocentrotus purpuratus, by modifying an approach previously used to culture cells from another sea urchin species. The viability of cultured phagocytes from the purple sea urchin decreases from 91.6% to 57% over six days and phagocyte morphology changes from single cells to aggregates leading to the formation of syncytia-like structures. This process is accelerated in the presence of lipopolysaccharide suggesting that phagocytes are capable of detecting this molecular pattern in culture conditions. Sea urchin immune response proteins, called Sp185/333, are expressed on the surface of a subset of phagocytes and have been associated with syncytia-like structures. We evaluated their expression in cultured phagocytes to determine their possible role in cell aggregation and in the formation of syncytia-like structures. Between 0 and 3 hr, syncytia-like structures were observed in cultures when only ∼10% of the cells were positive for Sp185/333 proteins. At 24 hr, ∼90% of the nuclei were Sp185/333-positive when all of the phagocytes had aggregated into syncytia-like structures. Consequently, we conclude that the Sp185/333 proteins do not have a major role in initiating the aggregation of cultured phagocytes, however the Sp185/333 proteins are associated with the clustered nuclei within the syncytia-like structures.

The glaucoma-associated olfactomedin domain of myocilin is a novel calcium binding protein

Myocilin is a protein found in the trabecular meshwork extracellular matrix tissue of the eye that plays a role in regulating intraocular pressure. Both wild-type and certain myocilin variants containing mutations in the olfactomedin (OLF) domain are linked to the optic neuropathy glaucoma. Because calcium ions are important biological cofactors that play numerous roles in extracellular matrix proteins, we examined the calcium binding properties of the myocilin OLF domain (myoc-OLF). Our study reveals an unprecedented high affinity calcium binding site within myoc-OLF. The calcium ion remains bound to wild-type OLF at neutral and acidic pH. A glaucoma-causing OLF variant, myoc-OLF(D380A), is calcium-depleted. Key differences in secondary and tertiary structure between myoc-OLF(D380A) and wild-type myoc-OLF, as well as limited access to chelators, indicate that the calcium binding site is largely buried in the interior of the protein. Analysis of six conserved aspartate or glutamate residues and an additional 18 disease-causing variants revealed two other candidate residues that may be involved in calcium coordination. Our finding expands our knowledge of calcium binding in extracellular matrix proteins; provides new clues into domain structure, function, and pathogenesis for myocilin; and offers insights into highly conserved, biomedically relevant OLF domains.

OLFML3 expression is decreased during prenatal muscle development and regulated by microRNA-155 in pigs

The Olfactomedin-like 3 (OLFML3) gene has matrix-related function involved in embryonic development. MicroRNA-155 (miR-155), 21- to 23-nucleotides (nt) noncoding RNA, regulated myogenesis by target mRNA. Our LongSAGE analysis suggested that OLFML3 gene was differently expressed during muscle development in pig. In this study, we cloned the porcine OLFML3 gene and detected its tissues distribution in adult Tongcheng pigs and dynamical expression in developmental skeletal muscle (12 prenatal and 10 postnatal stages) from Landrace (lean-type) and Tongcheng (obese-type) pigs. Subsequently, we analyzed the interaction between OLFML3 and miR-155. The OLFML3 was abundantly expressed in liver and pancreas, moderately in lung, small intestine and placenta, and weakly in other tissues and postnatal muscle. There were different dynamical expression patterns between Landrace and Tongcheng pigs during prenatal skeletal muscle development. The OLFML3 was down-regulated (33-50 days post coitus, dpc), subsequently up-regulated (50-70 dpc), and then down-regulated (70-100 dpc) in Landrace pigs, while in Tongcheng pigs, it was down-regulated (33-50 dpc), subsequently up-regulated (50-55 dpc) and then down-regulated (55-100 dpc). There was higher expression in Tongcheng than Landrace in prenatal muscle from 33 to 60 dpc, and opposite situation from 65 to 100 dpc. Dual luciferase assay and real time PCR documented that OLFML3 expression was regulated by miR-155 at mRNA level. Our research indicated that OLFML3 gene may affect prenatal skeletal muscle development and was regulated by miR-155. These finding will help understanding biological function and expression regulation of OLFML3 gene in mammal animals.

Enzyme-linked immunosorbent assay (ELISA) measurement of vitellogenin in plasma and liver histopathology in barfin plaice Liopsetta pinnifasciata from Amursky Bay, Sea of Japan

Vitellogenin (Vg) of the barfin plaice Liopsetta pinnifasciata was isolated and purified. In native polyacrylamide gel electrophoresis, Vg appeared as one band. After being subjected to sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE), Vg fraction produced several polypeptides with molecular masses of 180, 98, 70, 52, 41 and 37 kDa. MALDI-TOF mass spectrometry (MS) of the 180- and 98-kDa Vg polypeptides from the SDS-PAGE gel and de novo sequencing of their four peptide fragments based on MS/MS analysis confirmed that the purified proteins were vitellogenins, which shared high similarity with the Vgs of the barfin flounder Verasper moseri and Atlantic halibut Hippoglossus hippoglossus. The most part of the predicted sequences obtained from the L. pinnifasciata 180-kDa polypeptide has previously been found in the V. moseri vitellogenin type B, the sequences obtained from the 98-kDa polypeptide were found in V. moseri vitellogenin type A, so these findings allow us to propose that L. pinnifasciata has at least two different forms of Vg. Rabbit polyclonal antibodies against Vg were produced, and a quantitative enzyme-linked immunosorbent assay was developed. The concentration of Vg in barfin plaice from the moderately contaminated area of Amursky Bay in the Sea of Japan was detected based on the maturity stage of their gonads. In November 2008, the Vg concentration in the plasma of females with advanced oogenesis varied from 5.295 to 28.367 mg/ml (mean 16.38 ± 6.73 mg/ml, CV = 41.1%); in the plasma of males, the concentration ranged from non-detectable to 0.957 mg/ml (0.29 ± 0.42 mg/ml, CV = 127.9%). In October 2009, the Vg concentration in female plasma was lower than in November 2008 (2.21-13.87 mg/ml). High individual variability of plasma Vg was characteristic for maturing males (CV = 200.3%) and immature females (CV = 255.5%), and there was no significant difference between plasma Vg concentrations in males captured in November 2008 and October 2009 or in maturing males and immature females. Vacuolisation of hepatocytes was more typical for males with low plasma Vg concentrations and females with high plasma Vg concentrations. Necrosis and pyknosis of hepatocyte nuclei were more frequent in males with high Vg concentrations and in females with low plasma Vg concentrations.

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.

Olfactomedin 2: expression in the eye and interaction with other olfactomedin domain-containing proteins

PURPOSE

Olfactomedin 2 (OLFM2) belongs to the family of olfactomedin domain-containing proteins. Genetic data suggest its association with glaucoma in Japanese patients. However, its functions are still elusive. In this study, the properties of mammalian OLFM2 were investigated.

METHODS

Expression of the rat and mouse Olfm2 gene was studied by using real-time PCR and in situ hybridization. Substitutions were introduced into OLFM2 by mutagenesis in vitro. Intracellular localization of OLFM2 was studied by confocal microscopy after transient transfection in HEK293 cells. Interaction of OLFM2 with olfactomedin 1 (Olfm1), olfactomedin 3 (Olfm3), myocilin, and gliomedin was studied by using co-immunoprecipitation.

RESULTS

Two major human OLFM2 mRNAs encode secreted proteins with a length of 454 and 478 amino acids. OLFM2 is more closely related to OLFM1 and -3 than to any other family members. Olfm2 showed the most dynamic expression pattern compared with Olfm1 and -3 during mouse eye development and was expressed preferentially in the developing retinal ganglion cell layer. Among three OLFM2 substitutions tested (T86M, R144Q, and L420S), only L420S completely blocked secretion of the protein. OLFM2 interacted with Olfm1 and -3, but not with myocilin and gliomedin. Co-transfection of the L420S mutant with wild-type Olfm1 and -3 significantly inhibited secretion of Olfm1 and -3.

CONCLUSIONS

Highly conserved OLFM2 protein may play an important role in the course of retinal and eye development. Severe mutations in one of the closely related olfactomedin domain-containing proteins (Olfm1-3) may block the secretion and probably the activity of all three family members, leading to more pronounced diseases of the retina than the knockout of individual genes.

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.

Olfactomedin domain-containing proteins: possible mechanisms of action and functions in normal development and pathology

A family of olfactomedin domain-containing proteins consists of at least 13 members in mammals. Although the first protein belonging to this family, olfactomedin, was isolated and partially characterized from frog olfactory neuroepithelim almost 20 years ago, the functions of many family members remain elusive. Most of the olfactomedin domain-containing proteins, similar to frog olfactomedin, are secreted glycoproteins that demonstrate specific expression patterns. Other family members are membrane-bound proteins that may serve as receptors. More than half of the olfactomedin domain-containing genes are expressed in neural tissues. Data obtained over the last several years demonstrate that olfactomedin domain-containing proteins play important roles in neurogenesis, neural crest formation, dorsal ventral patterning, cell-cell adhesion, cell cycle regulation, and tumorigenesis and may serve as modulators of critical signaling pathways (Wnt, bone morphogenic protein). Mutations in two genes encoding myocilin and olfactomedin 2 were implicated in glaucoma, and a growing number of evidence indicate that other genes belonging to the family of olfactomedin domain-containing proteins may contribute to different human disorders including psychiatric disorders. In this review, we summarize recent advances in understanding the possible roles of these proteins with special emphasis on the proteins that are preferentially expressed and function in neural tissues.

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.

Myocilin promotes substrate adhesion, spreading and formation of focal contacts in podocytes and mesangial cells

Myocilin, a secreted glycoprotein of the olfactomedin family, is constitutively expressed in podocytes of the rat kidney and induced in mesangial cells during mesangioproliferative glomerulonephritis. As myocilin has been found to be associated with fibrillar components of the extracellular matrix, and adhesive properties have been shown for other members of the olfactomedin family, we hypothesized that myocilin might play a role in cell-matrix interactions in the glomerulus. To elucidate functional properties of myocilin, recombinant myocilin was expressed in 293 EBNA cells and purified by Ni-chelate and heparin chromatography. Culture plates were coated with myocilin, and primary rat mesangial cells and cells from an immortal murine podocyte cell line were seeded onto the plates in serum free conditions. Both cell types showed concentration-dependant attachment to myocilin, an effect that was statistically significant and could be blocked with specific antibodies. When compared to equal amounts of fibronectin or collagen 1, myocilin was less effective in promoting substrate adhesion. Synergistic effects in substrate adhesion were observed when myocilin was added to low concentrations of fibronectin. Twenty-five percent of cells that had attached to myocilin substrates showed spreading and expressed focal contacts which were labeled by vinculin/phalloidin staining. Comparable findings were observed when human or murine trabecular meshwork cells were seeded on myocilin substrates. Adhesive properties of myocilin required multimer formation, and were not observed when culture plates were coated with a C-terminal fragment of myocilin, containing the olfactomedin domain. We conclude that myocilin promotes substrate adhesion of podocytes and mesangial cells, and might contribute to cell-matrix adhesion of both cell types in vivo.

Zebrafish olfactomedin 1 regulates retinal axon elongation in vivo and is a modulator of Wnt signaling pathway

Olfactomedin 1 (Olfm1) is a secreted glycoprotein belonging to a family of olfactomedin domain-containing proteins. It is involved in the regulation of neural crest production in chicken and promotes neuronal differentiation in Xenopus. Here, we investigate the functions of Olfm1 in zebrafish eye development. Overexpression of full-length Olfm1, and especially its BMY form lacking the olfactomedin domain, increased the thickness of the optic nerve and produced a more extended projection field in the optic tectum compared with control embryos. In contrast, injection of olfm1-morpholino oligonucleotide (Olfm1-MO) reduced the eye size, inhibited optic nerve extension, and increased the number of apoptotic cells in the retinal ganglion cell and inner nuclear layers. Overexpression of full-length Olfm1 increased the lateral separation of the expression domains of eye-field markers, rx3 and six3. The Olfm1-MO had the opposite effect. These data suggest that zebrafish Olfm1 may play roles in the early eye determination, differentiation, optic nerve extension, and branching of the retinal ganglion cell axon terminals, with the N-terminal region of Olfm1 being critical for these effects. Injection of RNA encoding WIF-1, a secreted inhibitor of Wnt signaling, caused changes in the expression pattern of rx3 similar to those observed after Olfm1-MO injection. Simultaneous overexpression of WIF-1 and Olfm1 abolished the WIF-1 effect. Physical interaction of WIF-1 and Olfm1 was demonstrated by coimmunoprecipitation experiments. We concluded that Olfm1 serves as a modulator of Wnt signaling.

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.

Neuroserpin regulates N-cadherin-mediated cell adhesion independently of its activity as an inhibitor of tissue plasminogen activator

Neuroserpin is an inhibitor of tissue plasminogen activator (tPA) that is expressed in developing and adult nervous systems. Spatial and temporal analysis of neuroserpin expression suggests that it is involved in regulating the proteolytic balance associated with axonogenesis and synaptogenesis during development and synaptic plasticity in the adult. Here we demonstrate that altered expression of neuroserpin modulates the degree of cell-cell adhesion in pheochromocytoma PC12 cells independently of its role as an inhibitor of tPA. Levels of the homophilic cell-cell adhesion molecule N-cadherin are increased in neuroserpin-overexpressing cell lines. N-cadherin immunoreactivity was detected in a Triton X-100-insoluble fraction and localized to regions of cell contact, consistent with a role in enhancing cell surface adhesion. PC12 cell lines expressing neuroserpin mutants that lack tPA inhibitory activity also showed increased cell-cell adhesion and N-cadherin expression. Our results identify neuroserpin as a novel regulator of cell-cell adhesion and the synaptic adhesion molecule N-cadherin as a key effecter in this response. In nerve cells, neuroserpin may regulate the levels of N-cadherin available for construction, maintenance, and control of synapses and synaptic dynamics.

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.

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.

The Role of Disulfide Bonds and α-Helical Coiled-coils in the Biosynthesis of Type XIII Collagen and Other Collagenous Transmembrane Proteins

Type XIII collagen is a type II transmembrane protein with three collagenous (COL1-3) and four noncollagenous domains (NC1-4). The human alpha1(XIII) chain contains altogether eight cysteine residues. We introduced point mutations to six of the most N-terminal cysteine residues, and we show here that the two cysteines 117 and 119 at the end of the N-terminal noncollagenous domain (NC1) are responsible for linking the three alpha1(XIII) chains together by means of interchain disulfide bonds. In addition, the intracellular and transmembrane domains have an impact on trimer formation, whereas the cysteines in the transmembrane domain and the COL1, the NC2, and the C-terminal NC4 domains do not affect trimer formation. We also suggest that the first three noncollagenous domains (NC1-3) harbor repeating heptad sequences typical of alpha-helical coiled-coils, whereas the conserved NC4 lacks a coiled-coil probability. Prevention of the coiled-coil conformation in the NC3 domain is shown here to result in labile type XIII collagen molecules. Furthermore, a new subgroup of collagenous transmembrane proteins, the Rattus norvegicus, Drosophila melanogaster, and Caenorhabditis elegans colmedins, is enlarged to contain also Homo sapiens collomin, and Pan troglodytes, Mus musculus, Tetraodon nigroviridis, and Dano rerio proteins. We suggest that there is a structurally varied group of collagenous transmembrane proteins whose biosynthesis is characterized by a coiled-coil motif following the transmembrane domain, and that these trimerization domains appear to be associated with each of the collagenous domains. In the case of type XIII collagen, the trimeric molecule has disulfide bonds at the junction of the NC1 and COL1 domains, and the type XIII collagen-like molecules (collagen types XXIII and XXV) and the colmedins are similar in that they all have a pair of cysteines in the same location. Moreover, furin cleavage at the NC1 domain can be expected in most of the proteins.

Diversity of olfactomedin proteins in the sea urchin

Olfactomedin (OLF) domain proteins maintain extracellular protein-protein interactions in diverse phyla. Only one OLF family member, amassin-1, has been described from the sea urchin Strongylocentrotus purpuratus, a basal invertebrate deuterostome. Amassin-1 mediates intercellular adhesion of coelomocytes (immunocytes). Here we describe the protein structural features of four additional OLF proteins, the total for the genome being five. Phylogenetically, four of these proteins (the amassins) form a subgroup among previously identified OLF proteins. The fifth OLF protein is within the colmedin subfamily and contains a type II transmembrane domain, collagen repeats, and an OLF domain. Sea urchin OLF proteins represent an intermediate diversification between protostomes and vertebrates. Transcripts of all five OLF family members are in coelomocytes and adult radial nerve tissue. Transcripts for some OLF proteins increase during late larval stages. Transcript levels for amassin-1 increase 1,000,000-fold, coinciding with formation of the adult urchin rudiment within the larval body.

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.

Optimedin induces expression of N-cadherin and stimulates aggregation of NGF-stimulated PC12 cells

Optimedin, also known as olfactomedin 3, belongs to a family of olfactomedin domain-containing proteins. It is expressed in neural tissues and Pax6 is involved in the regulation of its promoter. To study possible effects of optimedin on the differentiation of neural cells, we produced stably transfected PC12 cell lines expressing optimedin under a tetracycline-inducible promoter. Cells expressing high levels of optimedin showed higher growth rates and stronger adhesion to the collagen extracellular matrix as compared with control PC12 cells. After stimulation with nerve growth factor (NGF), optimedin-expressing cells demonstrated elevated levels of N-cadherin, beta-catenin, alpha-catenin and occludin as compared with stimulated, control PC12 cells. Expression of optimedin induced Ca(2+)-dependent aggregation of NGF-stimulated PC12 cells and this aggregation was blocked by the expression of N-cadherin siRNA. Expression of optimedin also changed the organization of the actin cytoskeleton and inhibited neurite outgrowth in NGF-stimulated PC12 cells. We suggest that expression of optimedin stimulates the formation of adherent and tight junctions on the cell surface and this may play an important role in the differentiation of the brain and retina through the modulation of cytoskeleton organization, cell-cell adhesion and migration.

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.

Functional analysis of chick ONT1 reveals distinguishable activities among olfactomedin-related signaling factors

The Olfactomedin family is a relatively new class of extracellular proteins. Two family members have been shown to play roles in the early development of ectodermal tissues: Noelin enhances neural crest generation in chick and Tiarin promotes dorsal neural specification in Xenopus. In this study, we introduce a novel member of the Olfactomedin family, ONT1. In the early chick embryo, ONT1 expression first appears at Hensen's node and subsequently in the axial and paraxial mesoderm. When the neural tube closes, strong expression of ONT1 is transiently found in the roof plate region from the rostral midbrain to the hindbrain. Overexpression of ONT1 in these regions prolongs the generation of neural crest cells in a manner similar to that of Noelin. Interestingly, ONT1 and Noelin have opposing effects on the expression of the migrating neural crest marker HNK-1 in the chick: they, respectively, cause suppression and ectopic induction of this marker. Differential activities among Olfactomedin-related factors are further examined in Xenopus. Microinjection of ONT1 mRNA into the Xenopus embryo expands the expression domain of the neural crest marker FoxD3 at the neurula stage whereas overexpression of Tiarin or Noelin suppresses FoxD3. ONT1 exhibits no dorsalizing effects on the Xenopus neural tube, which contrasts with the strong dorsalizing activity seen for Tiarin. Thus, distinct Olfactomedin-related factors evoke qualitatively different phenotypes even in the same experimental systems, suggesting that Olfactomedin family uses multiple response systems to mediate its signals in embryogenesis.

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.