The neural cell adhesion molecule, N-CAM, appears on early embryonic cells and is important in the formation of cell collectives and their boundaries at sites of morphogenesis. Later in development it is found on various differentiated tissues and is a major CAM mediating adhesion among neurons and between neurons and muscle. To provide a molecular basis for understanding N-CAM function, the complete amino acid sequences of the three major polypeptides of N-CAM and most of the noncoding sequences of their messenger RNA's were determined from the analysis of complementary DNA clones and were verified by amino acid sequences of selected CNBr fragments and proteolytic fragments. The extracellular region of each N-CAM polypeptide includes five contiguous segments that are homologous in sequence to each other and to members of the immunoglobulin superfamily, suggesting that interactions among immunoglobulin-like domains form the basis for N-CAM homophilic binding. Although different in their membrane-associated and cytoplasmic domains, the amino acid sequences of the three polypeptides appear to be identical throughout this extracellular region (682 amino acids) where the binding site is located. Variations in N-CAM activity thus do not occur by changes in the amino acid sequence that alter the specificity of binding. Instead, regulation is achieved by cell surface modulation events that alter N-CAM affinity, prevalence, mobility, and distribution on the surface. A major mechanism for modulation is alternative RNA splicing resulting in N-CAM's with different cytoplasmic domains that differentially interact with the cell membrane. Such regulatory mechanisms may link N-CAM binding function with other primary cellular processes during the embryonic development of pattern.

http://science.sciencemag.org/content/sci/236/4803/799.full.pdf

Neural cell adhesion molecule: structure, immunoglobulin-like domains, cell surface modulation, and alternative RNA splicing.

We studied the risk of the development of acute myeloid leukemia (AML) during initial remission in 733 consecutive children with acute lymphoid leukemia (ALL) who were treated with intensive chemotherapy. This complication was identified according to standard morphologic and cytochemical criteria in 13 patients 1.2 to 6 years (median, 3.0) after the diagnosis of ALL. At three years of follow-up, the cumulative risk of secondary AML during the first bone marrow remission was 1.6 percent (95 percent confidence limits, 0.7 and 3.5 percent); at six years, it was 4.7 percent (2 and 10 percent). The development of secondary AML was much more likely among patients with a T-cell than a non-T-cell immunophenotype (cumulative risk, 19.1 percent [6 and 47 percent] at six years). Sequential cytogenetic studies in 10 patients revealed entirely different karyotypes in 9, suggesting the induction of a second neoplasm. In eight of these patients, the blast cells had abnormalities of the 11 q23 chromosomal region...

Secondary acute myeloid leukemia in children treated for acute lymphoid leukemia.

The voltage-sensitive sodium channel confers electrical excitability on neurons, a fundamental property required for higher processes including cognition. The ion-conducting α-subunit of the channel is regulated by two known auxiliary subunits, β1 and β2. We have identified rat and human forms of an additional subunit, β3. It is most closely related to β1 and is the product of a separate gene localized to human chromosome 11q23.3. When expressed in Xenopus oocytes, β3 inactivates sodium channel opening more slowly than β1 does. Structural modeling has identified an amino acid residue in the putative α-subunit binding site of β3 that may play a role in this difference. The expression of β3 within the central nervous system differs significantly from β1. Our results strongly suggest that β3 performs a distinct neurophysiological function.

https://www.pnas.org/content/pnas/97/5/2308.full.pdf

β3: An additional auxiliary subunit of the voltage-sensitive sodium channel that modulates channel gating with distinct kinetics

Human muscle neural cell adhesion molecule (N-CAM): Identification of a muscle-specific sequence in the extracellular domain

The neural cell adhesion molecule, NCAM, is involved in multiple cis- and trans-homophilic interactions (NCAM binding to NCAM) thereby facilitating cell-cell adhesion through the formation of zipper-like NCAM-complexes. NCAM is also involved in heterophilic interactions with a number of proteins and extracellular matrix molecules. Some of these heterophilic interactions are mutually exclusive, and some interfere with or are dependent on homophilic NCAM interactions. Furthermore, both homo- and heterophilic interactions are modulated by posttranslational modifications of NCAM. Heterophilic NCAM-interactions initiate several intracellular signal transduction pathways ultimately leading to biological responses involving cellular differentiation, proliferation, migration and survival. Both homo- and heterophilic NCAM-interactions can be mimicked by synthetic peptides, which can induce NCAM-like signalling, and in vitro and in vivo studies suggest that such NCAM mimetics may be used for the treatment of neurodegenerative disorders.

Zippers make signals: NCAM-mediated molecular interactions and signal transduction.

cDNA clones containing sequences coding for the murine neural cell adhesion molecule (N-CAM) were used in Southern hybridizations on human genomic DNA and demonstrated approximately 90% homology between human and murine NCAM genes. In situ hybridization with one of these clones was performed on human metaphase chromosomes and allowed the localization of the human NCAM gene to band q23 of chromosome 11. The genes for two other cell surface molecules believed to be involved in cell-cell interactions, Thy-1 and the delta chain of the T3-T cell receptor complex, have recently been localized to the same region of chromosome 11 in man. Moreover, this region of the human chromosome 11 appears to be syntenic to a region of murine chromosome 9 that also contains the staggerer locus: staggerer mice show abnormal neurological features which may be related to abnormalities in the conversion of the embryonic to the adult forms of the N-CAM molecule.

/pdf/localization-of-the-human-ncam-gene-to-band-q23-of-1uv0hdefdp.pdf

Localization of the human NCAM gene to band q23 of chromosome 11: the third gene coding for a cell interaction molecule mapped to the distal portion of the long arm of chromosome 11.

M J Santoni

Papers

Localization of the human NCAM gene to band q23 of chromosome 11: the third gene coding for a cell interaction molecule mapped to the distal portion of the long arm of chromosome 11.