Spatiotemporal patterns of expression of IGSF4 in developing mouse nervous system

Microarray analysis of gene expression in the cyclooxygenase knockout mice - a connection to autism spectrum disorder

The cellular and molecular events that take place during brain development play an important role in governing function of the mature brain. Lipid-signalling molecules such as prostaglandin E₂ (PGE₂ ) play an important role in healthy brain development. Abnormalities along the COX-PGE₂ signalling pathway due to genetic or environmental causes have been linked to autism spectrum disorder (ASD). This study aims to evaluate the effect of altered COX-PGE₂ signalling on development and function of the prenatal brain using male mice lacking cyclooxygenase-1 and cyclooxygenase-2 (COX-1^-/- and COX-2^-/- ) as potential model systems of ASD. Microarray analysis was used to determine global changes in gene expression during embryonic days 16 (E16) and 19 (E19). Gene Ontology: Biological Process (GO:BP) and Kyoto Encyclopedia of Genes and Genomes (KEGG) were implemented to identify affected developmental genes and cellular processes. We found that in both knockouts the brain at E16 had nearly twice as many differentially expressed genes, and affected biological pathways containing various ASD-associated genes important in neuronal function. Interestingly, using GeneMANIA and Cytoscape we also show that the ASD-risk genes identified in both COX-1^-/- and COX-2^-/- models belong to protein-interaction networks important for brain development despite of different cellular localization of these enzymes. Lastly, we identified eight genes that belong to the Wnt signalling pathways exclusively in the COX-2^-/- mice at E16. The level of PKA-phosphorylated β-catenin (S552), a major activator of the Wnt pathway, was increased in this model, suggesting crosstalk between the COX-2-PGE₂ and Wnt pathways during early brain development. Overall, these results provide further molecular insight into the contribution of the COX-PGE₂ pathways to ASD and demonstrate that COX-1^-/- and COX-2^-/- animals might be suitable new model systems for studying the disorders.

SynCAM, a novel putative tumor suppressor, suppresses growth and invasiveness of glioblastoma

SynCAM, also named by TSLC1, SgIGSF and IGSF4, was identified as a neural tissue-specific immunoglobulin-like cell-cell adhesion molecule. However, the role of SynCAM in tumorigenesis remains elusive. We aimed to clarify its epigenetic regulation and biological functions in glioblastoma. SynCAM was silenced in 72 % (5/7) glioblastoma cell lines. A significant downregulation was also detected in paired glioblastoma tumors compared with adjacent non-cancerous tissues. In contrast, SynCAM was readily expressed in various normal adult brain tissues. Ectopic expression of SynCAM in the silenced cancer cell line T98G significantly reduced colony formation and cell proliferation, induced cell cycle arrests and repressed cell invasive ability. Nude mice were subcutaneously injected into the flank with T98G cells and treated with normal saline, pcDNA3.1 (vector) or pcDNA3.1-SynCAM, respectively. Treatment with pcDNA3.1-SynCAM retarded growth in the xenografts, which contributed to a 58 % decrease in tumor volume compared to controls. In conclusion, our results suggest that SynCAM suppressions growth of glioblastoma and may serve as a novel functional tumor-suppressor gene.

IGSF4 is a novel TCR ζ-chain-interacting protein that enhances TCR-mediated signaling

Immunoglobulin superfamily member 4 (IGSF4) is a known ligand of CRTAM, a receptor expressed in activated NKT and CD8(+) T cells, but its function in T cell immunity has not been elucidated. In this study, we show that IGSF4 directly interacts with the T cell receptor (TCR) ζ-chain and enhances TCR signaling by enhancing ζ-chain phosphorylation. Ectopic overexpression of IGSF4 enhances TCR-mediated T cell activation. In contrast, IGSF4 knockdown shows a dramatic decrease in markers associated with T cell activation compared with those in control small interfering RNA. The transmembrane domain is essential for TCR ζ-chain association and clustering to the immunological synapse, and the ectodomain is associated with T cell interaction with antigen-presenting cells (APCs). IGSF4-deficient mice have impaired TCR-mediated thymocyte selection and maturation. Furthermore, these mice reveal attenuated effector T cell functions accompanied by defective TCR signaling. Collectively, the results indicate that IGSF4 plays a central role in T cell functioning by dual independent mechanisms, control of TCR signaling and control of T cell-APC interaction.

Cell cloning-based transcriptome analysis in Rett patients: relevance to the pathogenesis of Rett syndrome of new human MeCP2 target genes

More than 90% of Rett syndrome (RTT) patients have heterozygous mutations in the X-linked methyl-CpG binding protein 2 (MECP2) gene that encodes the methyl-CpG-binding protein 2, a transcriptional modulator. Because MECP2 is subjected to X chromosome inactivation (XCI), girls with RTT either express the wild-type or mutant allele in each individual cell. To test the consequences of MECP2 mutations resulting from a genome-wide transcriptional dysregulation and to identify its target genes in a system that circumvents the functional mosaicism resulting from XCI, we carried out gene expression profiling of clonal populations derived from fibroblast primary cultures expressing exclusively either the wild-type or the mutant MECP2 allele. Clonal cultures were obtained from skin biopsy of three RTT patients carrying either a non-sense or a frameshift MECP2 mutation. For each patient, gene expression profiles of wild-type and mutant clones were compared by oligonucleotide expression microarray analysis. Firstly, clustering analysis classified the RTT patients according to their genetic background and MECP2 mutation. Secondly, expression profiling by microarray analysis and quantitative RT-PCR indicated four up-regulated genes and five down-regulated genes significantly dysregulated in all our statistical analysis, including excellent potential candidate genes for the understanding of the pathophysiology of this neurodevelopmental disease. Thirdly, chromatin immunoprecipitation analysis confirmed MeCP2 binding to respective CpG islands in three out of four up-regulated candidate genes and sequencing of bisulphite-converted DNA indicated that MeCP2 preferentially binds to methylated-DNA sequences. Most importantly, the finding that at least two of these genes (BMCC1 and RNF182) were shown to be involved in cell survival and/or apoptosis may suggest that impaired MeCP2 function could alter the survival of neurons thus compromising brain function without inducing cell death.

Expression and adhesion profiles of SynCAM molecules indicate distinct neuronal functions

Cell-cell interactions through adhesion molecules play key roles in the development of the nervous system. Synaptic cell adhesion molecules (SynCAMs) comprise a group of four immunoglobulin (Ig) superfamily members that mediate adhesion and are prominently expressed in the brain. Although SynCAMs have been implicated in the differentiation of neurons, there has been no comprehensive analysis of their expression patterns. Here we examine the spatiotemporal expression patterns of SynCAMs by using reverse transcriptase-polymerase chain reaction, in situ hybridization, and immunohistological techniques. SynCAMs 1-4 are widely expressed throughout the developing and adult central nervous system. They are prominently expressed in neurons throughout the brain and are present in both excitatory and inhibitory neurons. Investigation of different brain regions in the developing and mature mouse brain indicates that each SynCAM exhibits a distinct spatiotemporal expression pattern. This is observed in all regions analyzed and is particularly notable in the cerebellum, where SynCAMs display highly distinct expression in cerebellar granule and Purkinje cells. These unique expression profiles are complemented by specific heterophilic adhesion patterns of SynCAM family members, as shown by cell overlay experiments. Three prominent interactions are observed, mediated by the extracellular domains of SynCAMs 1/2, 2/4, and 3/4. These expression and adhesion profiles of SynCAMs together with their previously reported functions in synapse organization indicate that SynCAM proteins contribute importantly to the synaptic circuitry of the central nervous system.

Six cadm/SynCAM genes are expressed in the nervous system of developing zebrafish

The Cadm (cell adhesion molecule) family of cell adhesion molecules (also known as IGSF4, SynCAM, Necl and TSLC) has been implicated in a multitude of physiological and pathological processes, such as spermatogenesis, synapse formation and lung cancer. The precise mechanisms by which these adhesion molecules mediate these diverse functions remain unknown. To investigate mechanisms of action of these molecules during development, we have identified zebrafish orthologs of Cadm family members and have examined their expression patterns during development and in the adult. Zebrafish possess six cadm genes. Sequence comparisons and phylogenetic analysis suggest that four of the zebrafish cadm genes represent duplicates of two tetrapod Cadm genes, whereas the other two cadm genes are single orthologs of tetrapod Cadm genes. All six zebrafish cadms are expressed throughout the nervous system both during development and in the adult. The spatial and temporal patterns of expression suggest multiple roles for Cadms during nervous system development.

Nectin-like molecule 1 is a glycoprotein with a single N-glycosylation site at N290KS which influences its adhesion activity

Nectin-like molecule 1 (NECL1)/CADM3/IGSF4B/TSLL1/SynCAM3, from now on referred to as NECL1, is a neural tissue-specific immunoglobulin-like cell-cell adhesion molecule which has Ca(2+)-independent homo- or heterophilic cell-cell adhesion activity and plays an important role in the formation of synapses, axon bundles and myelinated axons. Here we first detected the expression of NECL1 in human fetal and adult brains, and mouse brains at different developmental stages. The results indicated that two bands with molecular weights of about 62 kDa and 48 kDa were found in human fetal brain, while only one band with a molecular weight of about 48 kDa was found in human adult brain; two bands with molecular weights of about 62 kDa and 48 kDa whose expression level gradually increased were also found from mouse E16 to P14, while only one band with a molecular weight of about 48 kDa was found from P14. Bioinformatics analysis showed there were two putative N-glycosylation sites within human NECL1 at positions N25LS and N290KS and within mouse Necl1 at positions N23LS and N288KS, respectively. There was no O-glycosylation site in either human NECL1 or mouse Necl1. Based on the results of N-Glycosidase F treatment with human fetal brain tissue and lysates from transient transfection with human wild-type or glycosylation site mutant NECL1 in 293ET cells, we demonstrated that human NECL1 is an N-linked glycoprotein with a single glycosylation site at position N290KS. Cell aggregation assay further showed there was an increased adhesion activity after the glycosylation site mutation of NECL1 molecule.

The adhesion molecule Necl-3/SynCAM-2 localizes to myelinated axons, binds to oligodendrocytes and promotes cell adhesion

Background

Cell adhesion molecules are plasma membrane proteins specialized in cell-cell recognition and adhesion. Two related adhesion molecules, Necl-1 and Necl-2/SynCAM, were recently described and shown to fulfill important functions in the central nervous system. The purpose of the work was to investigate the distribution, and the properties of Necl-3/SynCAM-2, a previously uncharacterized member of the Necl family with which it shares a conserved modular organization and extensive sequence homology.

Results

We show that Necl-3/SynCAM-2 is a plasma membrane protein that accumulates in several tissues, including those of the central and peripheral nervous system. There, Necl-3/SynCAM-2 is expressed in ependymal cells and in myelinated axons, and sits at the interface between the axon shaft and the myelin sheath. Several independent assays demonstrate that Necl-3/SynCAM-2 functionally and selectively interacts with oligodendrocytes. We finally prove that Necl-3/SynCAM-2 is a bona fide adhesion molecule that engages in homo- and heterophilic interactions with the other Necl family members, leading to cell aggregation.

Conclusion

Collectively, our manuscripts and the works on Necl-1 and SynCAM/Necl-2 reveal a complex set of interactions engaged in by the Necl proteins in the nervous system. Our work also support the notion that the family of Necl proteins fulfils key adhesion and recognition functions in the nervous system, in particular between different cell types.

A central role for Necl4 (SynCAM4) in Schwann cell-axon interaction and myelination

Myelination in the peripheral nervous system requires close contact between Schwann cells and the axon, but the underlying molecular basis remains largely unknown. Here we show that cell adhesion molecules (CAMs) of the nectin-like (Necl, also known as SynCAM or Cadm) family mediate Schwann cell-axon interaction during myelination. Necl4 is the main Necl expressed by myelinating Schwann cells and is located along the internodes in direct apposition to Necl1, which is localized on axons. Necl4 serves as the glial binding partner for axonal Necl1, and the interaction between these two CAMs mediates Schwann cell adhesion. The disruption of the interaction between Necl1 and Necl4 by their soluble extracellular domains, or the expression of a dominant-negative Necl4 in Schwann cells, inhibits myelination. These results suggest that Necl proteins are important for mediating axon-glia contact during myelination in peripheral nerves.