A threshold effect of the major isoforms of NCAM on neurite outgrowth

Abstract

Interactions between recognition molecules on the surface of neuronal growth cones and guidance cues present in the local cellular environment are thought to account for the growth of neurites in the highly stereospecific manner that contributes to correct target cell innervation. In vitro assays have been used to identify candidate molecular components of this system, either directly by demonstrating their ability to promote neurite outgrowth, or indirectly by the ability of specific antibodies to inhibit neurite outgrowth. The role of the neural cell adhesion molecule (NCAM) in pathway finding is not fully understood. Some immunological studies support a positive role; others do not, and it has been reported that purified NCAM does not support neurite outgrowth. We have previously shown that an arbitrary biochemical index of neurite outgrowth, the relative level of immunoreactive neurofilament protein, is increased when human and rat dorsal root ganglion neurons are cultured on monolayers of cells expressing transfected human NCAM. But, the complexity of growth precluded a simple morphological analysis and we did not determine the 'dose-response' relationship between NCAM expression and neuronal response. Here, we report on the morphology of rat cerebellar neurons cultured on monolayers of 3T3 cells transfected with complementary DNAs encoding all of the main NCAM isoforms found in cells such as astrocytes, Schwann cells and skeletal muscle. The data indicate that both transmembrane and glycosyl-phosphatidylinositol linked NCAM isoforms are potent substrates for neurite extension. A critical threshold value of NCAM expression is required for increased neurite outgrowth. Above this threshold, small increases in NCAM induce substantial increases in neurite outgrowth.

Identification of an Amino Acid Sequence Motif in the Cytoplasmic Domain of the NCAM‐140 kDa Isoform Essential for Its Neuritogenic Activity

“…Ectopic expression of cytNCAM-140 inhibits NCAM-stimulated neurite outgrowth NCAM has been shown to stimulate neurite outgrowth in both neurons and PC12 cells (Doherty et al, 1990(Doherty et al, , 1991a. Thus, the latter cells are regarded as a convenient and reliable model for the study of NCAM-mediated neuritogenesis.…”

Functional Consequences of the Interactions among the Neural Cell Adhesion Molecule NCAM, the Receptor Tyrosine Kinase TrkB, and the Inwardly Rectifying K+ Channel KIR3.3

“…Homophilic interaction of NCAM in a trans-position promotes neurite outgrowth from hippocampal neurons (21). Artificially premature expression of Kir3.1/3.3 in neonatal hippocampal neurons, which at this developmental stage do not express Kir3.3 channels, inhibits NCAM-dependent neurite outgrowth, suggesting that Kir3.3 disturbs the interaction between TrkB and NCAM that is required for TrkB-dependent NCAM-mediated neurite outgrowth (accompanying article (37)).…”

“…shown that substrate-coated NCAM enhances neurite outgrowth of dissociated early postnatal hippocampal neurons in comparison with substrate-coated poly-L-lysine (21). Therefore, we next investigated whether NCAM-dependent neurite outgrowth is affected by the interaction between the intracellular domains of NCAM and Kir3.3.…”

A Novel Family of Cyclic Peptide Antagonists Suggests That N-cadherin Specificity Is Determined by Amino Acids That Flank the HAV Motif

“…In brief, 80,000 3T3 cells (control and transfected) were plated into individual chambers of an 8-chamber tissue culture slide coated with polylysine and fibronectin and cultured in Dulbecco's modified Eagle's medium, 10% FCS. After 24 h, when confluent monolayers had formed, the medium was removed, and 3000 cerebellar neurons isolated from postnatal day 2-3 rats were plated into each well in SATO media (30) supplemented with 2% FCS. All of the test peptides were added immediately before the neurons as a 2ϫ stock prepared in SATO/2% FCS.…”