Neuronal cell adhesion molecule NCAM

NCAM is found in three different forms, which share a common extracellular region but differ in their transmembrane/cytoplasmic segments. One form (the ssd or small surface-domain polypeptide) is anchored to the membrane via a phos-phoinositide, analogously to Thy-1 [196]. The other two forms differ in the size of the intracytoplasmic domain as a result of differential splicing. The relative proportion of the three forms varies with the tissue and the age of the animal. 

In the extracellular region, the most membrane-proximal unit is linked to three complex carbohydrates containing polymers of sialic acid. The number of sialic acid units is known to modulate the homophilic binding and varies with the developmental stage. 

NCAM is phylogenetically conserved. However, whilst in vertebrates it is expressed throughout life, in flies and nematodes its expression is restricted to stages of nervous system morphogenesis. 

Myelin associated glycoprotein neuronal cytoplasmic protein 3 (MAG/Ncp 3) 

MAG is one of a set of cell-surface glycoproteins expressed by myelin-forming cells which have been hypothesized to mediate the apposition of the myelin sheath to the axon. Two forms of MAG are known which, similarly to NCAM, differ in the intracytoplasmic domain as a result of alternative splicing. The carboxy-terminal 318 amino acids of MAG are identical to the partial sequence so far obtained of a protein that has been designated as rat neuronal cytoplasmic protein 3 [184], However, the latter was previously believed to be a neuropeptide precursor and to be expressed in specific groups of neurons rather than in glial cells. The reason for this discrepancy is unclear. 

---

In reproductive biology, sialic acid polymers are receiving more and more attention. Polysialic acid with a(2-8)-linkages was found to be expressed on mouse embryos before and after implantation and the neuronal cell adhesion molecule (NCAM), which bears a polysialic acid chain, seems to be involved in cellular interactions in the early mammalian embryo [101,1076]. A similar function is attributed to polysialic acid observed during a short period of the larval stage of Drosophila melanogaster [1077]. It has to be noted that this is the first report on the occurrence of sialic acid in insects. 

Cell membrane-associated proteins such as neuronal cell adhesion molecule (NCAM, CD56) and leu-7 (CD57) have raised interest as neuroendocrine cell... 

Conversely, a new line of inquiry examined glutamatergic activity, not as a blocker of neurotransmission but as an agonist of AMPA type receptors. A new class of compounds, called ampakines, act as long-term boosters of the learning process, Aniracetam [206] is considered as the major product in this series. It improves performance in all classical behavioural tests in animal models. The question which has to be answered is whether these compounds simply have symptomatic effects on memory processes or whether they have complementary properties such as inhibition of cell death [207], Furthermore, certain compounds currently classed as ampakines such as oxiracetam and piracetam have not been shown to be effective in Alzheimer s disease. Others, such as nefiracetam (12) are in the animal experimentation stage and appear to be promising because of their impact on the neuronal cell adhesion molecules (NCAM) [208] and their effect on synapse plasticity. 

PSA-NCAM, polysialic acid-neuronal cell adhesion molecule... 

NCAM, neuronal cell adhesion molecules (such as H-CAM, G-CAM, VCAM-1)... 

Adhesion molecules. The downregulation of the polysialylated neuronal cell adhesion molecule (PSA-NCAM) from the axonal surface (Charles et al 2000) is a necessary prerequisite to render the axon permissive to myelination (Charles et al., 2002 Coman et al., 2005). LI, another adhesion molecule expressed at the axonal surface, promotes myelination (Coman et al., 2005). 

Dityatev A, Dityateva G, Schachner M (2(KX)) Synaptic strength as a function of post- versus presynaptic expression of the neural cell adhesion molecule NCAM. Neuron 26 207-217... 

AC VIII, adenylyl cyclase type VIII BDNF, brain-derived neurotrophic factor CamKII, calcium-calmodulin kinase II GIRK2, G protein-activated inward rectifying potassium 2 MAOA, monoamine oxidase A n.d., not determined NCAM, neural cell adhesion molecule nNOS, neuronal nitric oxide synthase Petl, ETS domain transcription factor tPA, serine protease tissue-plasminogen activator (tPA). t/ > Increase/decrease in anxiety-related behavior. No effect. 

Kiss JZ, Wang C, Olive S, Rougon G, Lang J, Baetens D, Harry D, Pralong WF (1994) Activity-dependent mobilization of the adhesion molecule polysialic NCAM to the cell surface of neurons and endocrine cells. EMBO J 13 5284—5292... 

---