Purification and characterization of an 82-kD membrane protein as a neurite outgrowth factor binding protein: possible involvement of NOF binding protein in axonal outgrowth in developing retina

Melanoma Cell Adhesion Molecule Plays a Pivotal Role in Proliferation, Migration, Tumor Immune Microenvironment, and Immunotherapy in Colorectal Cancer

INTRODUCTION

MCAM, alternatively referred to as CD146, is an integral membrane glycoprotein belonging to the immunoglobulin superfamily. However, its importance in the tumorigenesis of colorectal cancer is still partially understood. Therefore, this study was designed to investigate the significance of MCAM in colorectal cancer.

METHODS

MCAM expression was analyzed by TCGA and GEO databases. qRT-PCR and IHC analysis were conducted to validate MCAM expression in patient tissues. The tumor-inhibiting ability of MCAM was further assessed by CCK-8 assay, colony formation assay, and wound-healing assay. qRT-PCR and WB analysis were conducted to evaluate the expression of EMT markers and MMP2/9. qRT-PCR analysis was utilized to detect the polarization status of macrophages. Kaplan-Meier curve, univariate, and multivariate cox analyses were employed to verify the ability of MCAM in prognosis prediction. TIDE scores were used to assess the impact of MCAM on immunotherapy.

RESULTS

The expression of MCAM was significantly downregulated in CRC, and low MCAM expression revealed poor prognosis in CRC patients. Moreover, MCAM overexpression inhibited the proliferation, migration, and invasive ability of CRC cells. Additionally, MCAM overexpression suppressed N-cadherin and MMP2/9 expression. Furthermore, MCAM impacted M1 macrophage polarization. MCAM is an independent predictor of CRC patient prognosis through Cox regression analysis. Lastly, TIDE score analysis indicated that elevated expression of MCAM increased immunotherapy efficacy.

CONCLUSION

The findings of this research suggest that MCAM impacts M1 macrophage polarization and enhances immunotherapy efficacy, underscoring its potential as a therapeutic target for colorectal cancer.

CD146, a therapeutic target involved in cell plasticity

Since its identification as a marker for advanced melanoma in the 1980s, CD146 has been found to have multiple functions in both physiological and pathological processes, including embryonic development, tissue repair and regeneration, tumor progression, fibrosis disease, and inflammations. Subsequent research has revealed that CD146 is involved in various signaling pathways as a receptor or co-receptor in these processes. This correlation between CD146 and multiple diseases has sparked interest in its potential applications in diagnosis, prognosis, and targeted therapy. To better comprehend the versatile roles of CD146, we have summarized its research history and synthesized findings from numerous reports, proposing that cell plasticity serves as the underlying mechanism through which CD146 contributes to development, regeneration, and various diseases. Targeting CD146 would consequently halt cell state shifting during the onset and progression of these related diseases. Therefore, the development of therapy targeting CD146 holds significant practical value.

Dynamic alternations of three-dimensional chromatin architecture contribute to phenotypic characteristics of breast muscle in chicken

Breast muscle growth rate and intramuscular fat (IMF) content show apparent differences between fast-growing broilers and slow-growing indigenous chickens. However, the underlying genetic basis of these phenotypic characteristics remains elusive. In this study, we investigate the dynamic alterations of three-dimensional genome architecture and chromatin accessibility in breast muscle across four key developmental stages from embryo to starter chick in Arbor Acres (AA) broilers and Yufen (YF) indigenous chickens. The limited breed-specifically up-regulated genes (Bup-DEGs) are embedded in breed-specific A compartment, while a majority of the Bup-DEGs involving myogenesis and adipogenesis are regulated by the breed-specific TAD reprogramming. Chromatin loops allow distal accessible regions to interact with myogenic genes, and those loops share an extremely low similarity between chicken with different growth rate. Moreover, AA-specific loop interactions promote the expression of 40 Bup-DEGs, such as IGF1, which contributes to myofiber hypertrophy. YF-specific loop interactions or distal accessible regions lead to increased expression of 5 Bup-DEGs, including PIGO, PEMT, DHCR7, TMEM38B, and DHDH, which contribute to IMF deposition. These results help elucidate the regulation of breast muscle growth and IMF deposition in chickens.

CD146 increases stemness and aggressiveness in glioblastoma and activates YAP signaling

Glioblastoma (GBM), a highly malignant and lethal brain tumor, is characterized by diffuse invasion into the brain and chemo-radiotherapy resistance resulting in poor prognosis. In this study, we examined the involvement of the cell adhesion molecule CD146/MCAM in regulating GBM aggressiveness. Analyses of GBM transcript expression databases revealed correlations of elevated CD146 levels with higher glioma grades, IDH-wildtype and unmethylated MGMT phenotypes, poor response to chemo-radiotherapy and worse overall survival. In a panel of GBM stem cells (GSCs) variable expression levels of CD146 were detected, which strongly increased upon adherent growth. CD146 was linked with mesenchymal transition since expression increased in TGF-ß-treated U-87MG cells. Ectopic overexpression of CD146/GFP in GG16 cells enhanced the mesenchymal phenotype and resulted in increased cell invasion. Conversely, GSC23-CD146 knockouts had decreased mesenchymal marker expression and reduced cell invasion in transwell and GBM-cortical assembloid assays. Moreover, using GSC23 xenografted zebrafish, we found that CD146 depletion resulted in more compact delineated tumor formation and reduced tumor cell dissemination. Stem cell marker expression and neurosphere formation assays showed that CD146 increased the stem cell potential of GSCs. Furthermore, CD146 mediated radioresistance by stimulating cell survival signaling through suppression of p53 expression and activation of NF-κB. Interestingly, CD146 was also identified as an inducer of the oncogenic Yes-associated protein (YAP). In conclusion, CD146 carries out various pro-tumorigenic roles in GBM involving its cell surface receptor function, which include the stimulation of mesenchymal and invasive properties, stemness, and radiotherapy resistance, thus providing an interesting target for therapy.

CD146, from a melanoma cell adhesion molecule to a signaling receptor

CD146 was originally identified as a melanoma cell adhesion molecule (MCAM) and highly expressed in many tumors and endothelial cells. However, the evidence that CD146 acts as an adhesion molecule to mediate a homophilic adhesion through the direct interactions between CD146 and itself is still lacking. Recent evidence revealed that CD146 is not merely an adhesion molecule, but also a cellular surface receptor of miscellaneous ligands, including some growth factors and extracellular matrixes. Through the bidirectional interactions with its ligands, CD146 is actively involved in numerous physiological and pathological processes of cells. Overexpression of CD146 can be observed in most of malignancies and is implicated in nearly every step of the development and progression of cancers, especially vascular and lymphatic metastasis. Thus, immunotherapy against CD146 would provide a promising strategy to inhibit metastasis, which accounts for the majority of cancer-associated deaths. Therefore, to deepen the understanding of CD146, we review the reports describing the newly identified ligands of CD146 and discuss the implications of these findings in establishing novel strategies for cancer therapy.

Cell Adhesion Molecules and Ubiquitination-Functions and Significance

Cell adhesion molecules of the immunoglobulin (Ig) superfamily represent the biggest group of cell adhesion molecules. They have been analyzed since approximately 40 years ago and most of them have been shown to play a role in tumor progression and in the nervous system. All members of the Ig superfamily are intensively posttranslationally modified. However, many aspects of their cellular functions are not yet known. Since a few years ago it is known that some of the Ig superfamily members are modified by ubiquitin. Ubiquitination has classically been described as a proteasomal degradation signal but during the last years it became obvious that it can regulate many other processes including internalization of cell surface molecules and lysosomal sorting. The purpose of this review is to summarize the current knowledge about the ubiquitination of cell adhesion molecules of the Ig superfamily and to discuss its potential physiological roles in tumorigenesis and in the nervous system.

CD146, a multi-functional molecule beyond adhesion

CD146 is a cell adhesion molecule (CAM) that is primarily expressed at the intercellular junction of endothelial cells. CD146 was originally identified as a tumor marker for melanoma (MCAM) due to its existence only in melanoma but not in the corresponding normal counterpart. However CD146 is not just a CAM for the inter-cellular and cell-matrix adhesion. Recent evidence indicates that CD146 is actively involved in miscellaneous processes, such as development, signaling transduction, cell migration, mesenchymal stem cells differentiation, angiogenesis and immune response. CD146 has increasingly become an important molecule, especially identified as a novel bio-marker for angiogenesis and for cancer. Here we have reviewed the dynamic research of CD146, particularly newly identified functions and the underlying mechanisms of CD146.

Dual role of melanoma cell adhesion molecule (MCAM)/CD146 in lymphocyte endothelium interaction: MCAM/CD146 promotes rolling via microvilli induction in lymphocyte and is an endothelial adhesion receptor

The melanoma cell adhesion molecule (MCAM)/CD146 is expressed as two isoforms differing by their cytoplasmic domain (MCAM long (MCAM-l) and MCAM short (MCAM-s)). MCAM being expressed by endothelial cells and activated T cells, we analyzed its involvement in lymphocyte trafficking. The NK cell line NKL1 was transfected by MCAM isoforms and submitted to adhesion on both the endothelial cell monolayer and recombinant molecules under shear stress. MCAM-l transfection reduced rolling velocity and increased NKL1 adhesion on the endothelial cell monolayer and VCAM-1. Scanning electron microscopy revealed that MCAM-l induced microvilli formation and extension. In contrast, MCAM short or mock transfection had no effect on adhesion of NKL1 cells and microvilli formation. As shown by mutagenesis, serine 32 of the MCAM-l cytoplasmic tail, belonging to a putative protein kinase C phosphorylation site, was necessary for MCAM-l-actin cytoskeleton interaction and microvilli induction. Accordingly, chelerythrine chloride, a protein kinase C inhibitor, abolished MCAM-l-induced microvilli and rolling of MCAM-l-transfected NKL1 cells. Inhibition of adhesion under shear stress by anti-MCAM Abs suggested that both lymphoid MCAM-l and endothelial MCAM were also directly involved in lymphocyte endothelium interaction. MCAM-l-transfected NKL1 and activated CD4 T cells adhered to rMCAM under shear stress whereas anti-MCAM Ab treatment inhibited this process. Taken together, these data establish that MCAM is involved in the initial steps of lymphocyte endothelium interaction. By promoting the rolling on the inflammation marker VCAM-1 via microvilli induction and displaying adhesion receptor activity involving possible homophilic MCAM-l-MCAM-l interactions, MCAM might be involved in the recruitment of activated T cells to inflammation sites.

Expression and involvement of gicerin, a cell adhesion molecule, in the development of chick optic tectum

Gicerin is a cell adhesion molecule belonging to the immunoglobulin superfamily. It has both a homophilic binding activity and a heterophilic binding activity to neurite outgrowth factor (NOF) a molecule belonging to the laminin family. We have reported many studies on the heterophilic activity of gicerin and NOF, but the function of its homophilic binding activity in vivo had been unclear. In the retina, gicerin is expressed in retinal ganglion cells only when they extend neurites to the optic tectum. In this report we have found that gicerin is also transiently expressed in the optic tectum during this time. First, cell aggregation assays were used to show that gicerin expressed in the optic tectum displays homophilic binding activity. Then, explant cultures of embryonic day 6 chick optic tectum on gicerin-Fc chimeric protein-coated dishes and NOF-coated dishes were carried out. It was found that gicerin-gicerin homophilic interactions promoted cell migration, whereas heterophilic interactions with NOF induced neurite formation. Furthermore, when anti-gicerin antibodies were injected in order to examine the effect of gicerin protein in the formation of the tectal layer in ovo, cell migration was strongly inhibited. These data suggest that homophilic interaction of gicerin participates in the migration of neural cells during the layer formation and plays a crucial role in the organization of the optic tectum.

Involvement of gicerin in the extension of microvilli

Gicerin is a cell adhesion molecule belonging to the immunoglobulin superfamily. To study the functional differences between l- and s-gicerin, we first examined the distribution of endogenous gicerin in B16 cells and found that l-gicerin was densely localized in microvilli. To clarify the relationship between gicerin and the microvilli, we established independent stable cell lines expressing l- and s-gicerin in L cells and found that l-gicerin localized to the microvilli. Scanning electron microscopic analysis revealed that the microvilli of l-gicerin-transfected cells were longer than those of s-gicerin and control transfectants. This suggested that l-gicerin might participate in the elongation of the microvilli. When cells were double-stained with antibodies to gicerin and moesin, a microvilli-specific protein, the staining of l-gicerin corresponded to that of moesin in the elongated microvilli. Moesin was coprecipitated with glutathione S-transferase-fusion proteins of the l-gicerin cytoplasmic domain but not with the s-gicerin cytoplasmic domain. To determine the region involved in the extension of microvilli, we generated transfectants of two truncated forms of l-gicerin cytoplasmic domain, and we found that only the transfectants of the longer mutant had the longer microvilli, while the shorter mutant exhibited short microvilli. These results suggested that l-gicerin-specific amino acid residues, especially amino acids 16-39, within the cytoplasmic domain of l-gicerin might be involved in the extension of microvilli.

Expression and adhesive ability of gicerin, a cell adhesion molecule, in the pock lesions of chorioallantoic membranes infected with an avian poxvirus

The expression and adhesive activities of gicerin, a cell adhesion protein, in the pock lesions on chicken chorioallantoic membranes (CAM) infected with an avian poxvirus were studied. In normal CAMs, gicerin was found on the flattened epithelial cells, and neurite outgrowth factor (NOF) was in the basement membrane. However, in the pock lesions on infected CAMs, gicerin was overexpressed on the cell membranes of hyperplastic epithelial cells forming thick epithelial layers. Neurite outgrowth factor was also found mainly in the basement membrane, but occasionally showed aberrant expression among hyperplastic cells. In vitro analyses, using the dissociated cells from pock lesions, demonstrated that an anti-gicerin polyclonal antibody inhibit cell aggregation activity and cell adhesion to NOF. These results suggest that gicerin might promote the cell-cell and cell-extracellular matrix protein bindings of the hyperplastic epithelial cells by its homophilic and heterophilic adhesive activities, and contribute to pock formation on the infected CAMs.

Development of the visual system of the chick. II. Mechanisms of axonal guidance

The quest to understand axonal guidance mechanisms requires exact and multidisciplinary analyses of axon navigation. This review is the second part of an attempt to synthesise experimental data with theoretical models of the development of the topographic connection of the chick retina with the tectum. The first part included classic ideas from developmental biology and recent achievements on the molecular level in understanding cytodifferentiation and histogenesis [J. Mey, S. Thanos, Development of the visual system of the chick. (I) Cell differentiation and histogenesis, Brain Res. Rev. 32 (2000) 343-379]. The present part deals with the question of how millions of fibres exit from the eye, traverse over several millimetres and spread over the optic tectum to assemble a topographic map, whose precision accounts for the sensory performance of the visual system. The following topics gained special attention in this review. (i) A remarkable conceptual continuity between classic embryology and recent molecular biology has revealed that positional cellular specification precedes and determines the formation of the retinotectal map. (ii) Graded expression of asymmetric genes, transcriptional factors and receptors for signal transduction during early development seem to play a crucial role in determining the spatial identity of neurons within surface areas of retina and optic tectum. (iii) The chemoaffinity hypothesis constitutes the conceptual framework for development of the retinotopic organisation of the primary visual pathway. Studies of repulsive factors in vitro developed the original hypothesis from a theoretical postulate of chemoattraction to an empirically supported concept based on chemorepulsion. (iv) The independent but synchronous development of retina and optic tectum in topo-chronologically corresponding patterns ensures that ingrowing retinal axons encounter receptive target tissue at appropriate locations, and at the time when connections are due to be formed. (v) The growth cones of the retino-fugal axons seem to be guided both by local cues on glial endfeet and within the extracellular matrix. On the molecular level, the ephrins and their receptors have emerged as the most likely candidates for the material substrate of a topographic projection along the anterior-posterior axis of the optic tectum. Yet, since a number of alternative molecules have been proposed for the same function, it remains the challenge for the near future to define the proportional contribution of each one of the individual mechanisms proposed by matching theoretical predictions with the experimental evidence.

HEMCAM/CD146 downregulates cell surface expression of (β)1 integrins

HEMCAM/gicerin, an immunoglobulin superfamily protein, is involved in homophilic and heterophilic adhesion. It interacts with NOF (neurite outgrowth factor), a molecule of the laminin family. Alternative splicing leads to mRNAs coding for HEMCAM with a short (HEMCAM-s) or a long cytoplasmic tail (HEMCAM-l). To investigate the cellular function of these two variants, we stably transfected murine fibroblasts with either form of HEMCAM. Expression of each isoform of this protein in L cells delayed proliferation and modified their adhesion properties to purified extracellular matrix proteins. Expression of either HEMCAM-s or HEMCAM-l inhibited integrin-dependent adhesion and spreading of fibroblasts to laminin 1, showing that this phenomenon did not depend on the cytoplasmic region. By contrast, L-cell adhesion and spreading to fibronectin depended on the HEMCAM isoform expressed. Flow cytometry and immunoprecipitation studies revealed that the expression of HEMCAM downregulated expression of the laminin-binding integrins (α)3 (β)1, (α)6 (β)1 and (α)7 (β)1, and fibronectin receptor (α)5 (β)1 from the cell surface. Semi-quantitative PCR and northern blot experiments showed that the expression of (α)6 (β)1 integrin modified by HEMCAM occurred at a translation or maturation level. Thus, our data demonstrate that HEMCAM regulates fibroblast adhesion by controlling (β)1 integrin expression. http://www.biologists.com/JCS/movies/jcs1886.html

Expression of gicerin, a novel cell adhesion molecule, is upregulated in the astrocytes after hypoglossal nerve injury in rats

Gicerin is an integral membrane glycoprotein which mediates cell-cell and cell-extracellular matrix (ECM) interactions in the nervous system. We studied gicerin expression in the hypoglossal nucleus post transection using in situ hybridization and immunocytochemistry. We found that hypoglossal nerve injury resulted in a significant increase in gicerin expression. Its expression levels reached peak values in reactive astrocytes surrounding axotomized motoneurons of the ipsilateral hypoglossal nucleus 14 days after hypoglossal nerve injury. The results indicate that gicerin is up-regulated during nerve regeneration, suggesting that gicerin expressed in the reactive astrocytes might be involved in the processes of nerve regeneration.

Gicerin, a cell adhesion molecule, participates in the histogenesis of retina

Gicerin is a novel cell adhesion molecule that belongs to the immunoglobulin superfamily. Gicerin protein adheres to neurite outgrowth factor (NOF), an extracellular matrix protein in the laminin family, and also exhibits homophilic adhesion. Heterophilic adhesion of gicerin to NOF is thought to play an active role in neurite outgrowth of developing retinal cells in vitro. In this study, we examined the adhesion activity of gicerin during the retinal development of Japanese quail using an antibody directed against gicerin, to elucidate the biological importance of gicerin in retinal histogenesis. Immunohistochemical and Western blot analysis showed that gicerin was highly expressed in the developing retina but suppressed in the mature retina. The aggregation of neural retinal cells from 5-day embryonic quail retina was significantly inhibited when incubated with a polyclonal antibody to gicerin, suggesting that gicerin protein participates in the adhesion of neural retinal cells of the developing retina. Furthermore, histogenesis of retina both in the organ cultures and in ovo embryos was severely disrupted by incubation with a gicerin antibody. These findings provide evidence that gicerin plays an important role in retinal histogenesis.

Neuron-specific expression of a chicken gicerin cDNA in transient transgenic zebrafish

Gicerin, a novel cell adhesion molecule which belongs to the immunoglobulin superfamily, is expressed temporally and spatially in the developing chick brain and retina. The previous in vitro experiments using transfected cells showed that gicerin can function as a cell adhesion molecule which has both homophilic and heterophilic binding activities. For the in vivo analyses of gicerin in neural development, we tried to utilize a zebrafish system, a vertebrate suitable for studying early development. We generated transient transgenic animals by microinjecting DNA constructs into zebrafish embryos. Chicken gicerin, under control of the neurofilament gene promoter, was preferentially expressed in neuronal cells and gicerin-expressing neurons exhibited a fasciculation formation with neighboring gicerin-positive axons, which may be partly due to homophilic cell adhesion activity of gicerin. These experimental results suggest that this fast and efficient transgenic animal system is useful for studying the functional roles of neuron-specific genes during the development.

Expression and functional analysis of a novel isoform of gicerin, an immunoglobulin superfamily cell adhesion molecule

We have cloned a novel cDNA of gicerin, a cell adhesion molecule belonging to the immunoglobulin superfamily. Both gicerin isoforms share the same extracellular domain, which has five immunoglobulin-like loop structures and a transmembrane domain as s-gicerin, but differ in the cytoplasmic tail domain. As the newly identified form has a larger cytoplasmic domain than the previously reported form, we refer to them as l-gicerin and s-gicerin, respectively. l-gicerin is transcribed from a distinct mRNA containing an inserted sequence not found in s-gicerin mRNA which caused a frameshift for the coding region for a cytoplasmic domain. Previous studies demonstrated that gicerin showed a doublet band of 82 and 90 kDa in chicken gizzard smooth muscle. We report that the 82-kDa protein corresponds to s-gicerin and the 90-kDa protein to l-gicerin. We also found that the two gicerin isoforms are expressed differentially in the developing nervous system. Functional analysis of these gicerin isoforms in stable transfectants revealed that they had differ in their homophilic adhesion properties, as well as in heterophilic cell adhesion assayed with neurite outgrowth factor. In addition, these isoforms have neurite-promoting activity by their homophilic adhesion, but differ in their ability to promote neurite outgrowth.

Expression of gicerin in development, oncogenesis and regeneration of the chick kidney

Neurite outgrowth factor, which promotes neurite extension from neuronal cells, is an extracellular matrix glycoprotein belonging to the laminin family. Gicerin is a protein that binds neurite outgrowth factor. Its cDNA cloning has revealed that it is a novel cell adhesion molecule belonging to the immunoglobulin super-family. Functional analysis demonstrates that gicerin possesses homophilic binding activity as well as heterophilic binding activity with neurite outgrowth factor. We examined the role and expression of neurite outgrowth factor and gicerin in chick kidney during development. In the embryonic kidney, gicerin was found to be highly expressed both on ureteric bud cells and metanephrogenic mesenchymal cells, when the mesenchymal cells become condensed to be converted into polarized epithelial cells. In the adult kidney, the expression of gicerin was decreased and restricted to the glomerulus, proximal tubule and medullary loop. On the other hand, neurite outgrowth factor was constitutively expressed in the basement membranes of tubules and the matrices of glomeruli during development. As some molecules which are expressed during embryogenesis and suppressed after maturation are re-expressed in tumor cells or tissues during regeneration, we also examined the expression of gicerin in chicken Wilms' tumor and regenerating kidney in interstitial nephritis. Gicerin was remarkably upregulated in Wilms' tumor and re-expressed in collecting ducts recovering from interstitial nephritis. These findings suggest that gicerin could play a role not only in normal renal development but also in oncogenesis and regeneration.

Molecular cloning and functional expression of gicerin, a novel cell adhesion molecule that binds to neurite outgrowth factor

Gicerin is an integral membrane glycoprotein of about 82 kd that is transiently expressed in the developing CNS. Gicerin was first identified as a binding protein for neurite outgrowth factor (NOF), a member of the laminin family of extracellular matrix proteins. By isolating and sequencing a gicerin cDNA, we have found that this protein is a novel member of the immunoglobulin superfamily. The deduced protein (584 amino acids) consists of five immunoglobulin-like loop structures in an extracellular domain, a single transmembrane region, and a short cytoplasmic tail. Cells transfected stably with gicerin cDNA adhered to NOF and aggregated with each other, indicating that gicerin exhibits both heterophilic and homophilic adhesion activities.

Extracellular matrix proteins with neurite promoting activity and their receptors

Characteristic features of the nervous system converge into network formation during the development. The neurons recognize precisely their target cells and form synapses, and these steps are complex, but well organized spatially and temporally. The neurite promotion from the neurons is one of the most important events for synapse formation. It is well known that extracellular matrix proteins such as laminin and their receptors, and cell adhesion molecules such as NCAM participate in cell migration and synaptic formation. We have isolated a neurite outgrowth factor (NOF) which promotes neurite outgrowth from various neurons and belongs to laminin family, and also its receptor which is identified to be an immunoglobulin superfamily protein by cDNA cloning. This ligand-receptor system is a unique example that a receptor with immunoglobulin-like structure interacts with an extracellular matrix protein.

Involvement of a receptor for neurite outgrowth factor (NOFR) in cerebellar neurogenesis

A receptor for neurite outgrowth factor (82 kDa membrane protein, NOFR) was detected in the developing chick cerebellum by immuno- and ligand blots. In immunohistochemical study, NOFR was maximally expressed in the external granular layer of cerebellum at embryonic day 10-12 and gradually decreased until embryonic day 18. Neurite outgrowth and cell migration induced by NOF from cerebellar explants were completely suppressed by the addition of anti-NOFR IgG. These results suggest that NOFR plays an important role in the cerebellar neurogenesis.

Diversity of axonal growth-promoting receptors and regulation of their function

Growth-promoting receptors for substrate-bound molecules are usually found to belong to the integrin, immunoglobulin, or cadherin families of glycoproteins. New members of each of these families have been identified in the past year, and advances have been made in our understanding of their functional regulation.

Neuronal interactions with the extracellular matrix

The interactions of neurons with extracellular cues are important in directing the formation of precise neuronal networks during the development of the nervous system. This review will focus on recent progress towards the understanding of the molecular machinery involved in the interactions of neurons with the extracellular matrix.

The formation of axonal pathways in developing cranial nerves

The roles of a variety of molecules including cell adhesion molecules and growth factors in the development of cranial nerves have begun to be understood in detail. In the course of embryonic development, cranial nerves are differentiated in concordance with the development of the metameric facial structure called 'ectomeres'. Each ectomere parallels the segmentation of the hindbrain called the 'rhombomere', in which pairs of metameric units cooperate to generate the repeating sequence of cranial branchiomotor nerves. A number of genes, including homeobox genes, are expressed in a rhombomere-specific pattern. For the formation of the olfactory nerve, it is suggested that several carbohydrate residues play important roles in receptor-target specificity. In the optic nerve, a combination of multiple cell adhesion molecules contributes to neurite growth in a developmental stage-specific manner. The development of the trigeminal nerve is under the control of both cell adhesion molecules and several growth factors. There is evidence that some of the adhesion molecules are expressed in a modality-specific way. There are also several molecules, such as 11p15 or TAG1/SNAP which are expressed only in selected cranial nerves. The growth rate of neurites also varies according to the individual nerves. Thus each cranial nerve has its own intrinsic properties and their outgrowth is the outcome of these properties and their interactions with surrounding non-neuronal tissues.