Use of the Neural Cell Adhesion Molecule VASE Exon by Neurons Is Associated with a Specific Down‐Regulation of Neural Cell Adhesion Molecule‐Dependent Neurite Outgrowth in the Developing Cerebellum and Hippocampus

Abstract

The development of the CNS is associated with an increasing use of the 30-bp variable alternative, spliced exon (VASE) in neural cell adhesion molecule (NCAM). We have assessed the relative usage of VASE by reverse transcriptase-linked polymerase chain reaction in the developing cerebellum and hippocampus at times when neurons isolated from these tissues can respond to substrate-associated NCAM by increased axonal growth and also at later developmental stages, when they are no longer responsive to substrate-associated NCAM. Neurons isolated from the developing cerebellum at postnatal day 6 respond to NCAM with increased neurite growth. NCAM transcripts from these cells were found to have negligible levels of VASE usage. In contrast, neurons that are isolated at later stages of development (postnatal days 8, 10, and 11) and do not respond to NCAM were found to synthesise a much higher proportion of NCAM transcripts containing VASE. In the hippocampus, embryonic day 18 neurons, which are responsive to NCAM, express low levels of VASE, whereas postnatal days 4 and 5 neurons, which are not responsive to NCAM, have a greater proportion of transcripts containing VASE. Thus, the level of NCAM VASE exon usage by neurons appears to be a good indicator of the ability of these cells to respond to non-VASE-containing NCAM (expressed in a cellular substratum) by increased neurite outgrowth.

VASE-encoded peptide modifies NCAM- and L1-mediated neurite outgrowth

“…Our data support the view that a developmental switch from NCAM without VASE to NCAM with VASE (Small and Akeson, 1990;Walsh et al, 1992) leads to different receptor systems at the neuronal cell surface and, thus, different signaling mechanisms all funneling into neurite outgrowth. By these mechanisms a fine tuning and variation of neurite outgrowth and stability of neuronal interactions appears conceivable.…”

“…NCAM and L1 can act by homophilic (Hoffman and Edelman, 1983;Lemmon et al, 1989), heterophilic (Pollerberg et al, 1987;Werz and Schachner, 1988;Grumet, 1992) and assisted homophilic binding, interacting with each other in the surface membrane of one cell (cis-interaction) via an oligomannosidic glycan (Horstkorte et al, 1993) and binding to L1 at an opposing cell surface (trans-interaction; Kadmon et al, 1990a,b). NCAM contains in its fourth Ig-like domain (Ig4) the binding site for the L1-associated oligomannosidic glycans (Horstkorte et al, 1993) and 10 amino acids derived from a variable alternatively spliced exon (VASE or , Santoni et al, 1989;Small et al, 1988) which is rarely expressed at early postnatal stages but becomes up-regulated at later stages in cerebellar and hippocampal neurons (Small and Akeson, 1990;Walsh et al, 1992). Fibroblasts transfected with NCAM with VASE and used as substrate show reduced neurite outgrowth-promoting activity for cerebellar neurons and PC12 cells Liu et al, 1993).…”

Spatial versus consumptive competition at polyneuronally innervated neuromuscular junctions

“…There are presently thought to be about 200 molecular forms of N-CAM, based on alternative splicing and/or variable glycosylation. Some of these isoforms promote and others inhibit neurite growth (Small & Akeson, 1990;Saffell, Walsh & Doherty, 1991;Walsh, Furness, Moore, Ashton & Doherty, 1992;Zorn & Krieg, 1992). Different isoforms of N-CAM are expressed in neonatal muscles, compared with mature or ageing muscles (Andersson, Olsen, Zhernosekov, Gaardsvoll, Krog, Linnemann & Bock, 1993).…”

Retinoic acid‐induced changes in polysialyltransferase mRNA expression and NCAM polysialylation in human neuroblastoma cells

“…Likewise, the increasing use of other NCAM splice variants may prevent the efficient polysialylation of NCAM 140 and 180 in RA-differentiated SH-SY5Y cells. Various studies on brain development and tissue differentiation have indicated the coincidence of decreasing PSA expression and the increasing use of the alternatively spliced VASE exon in the fourth Ig-like domain of NCAM (Small and Akeson, 1990;Walsh et al, 1992;Oka et al, 1995). This inverse relationship raised the possibility that enhanced VASE expression may be a negative regulator of NCAM polysialylation in the RAdifferentiated SH-SY5Y cells.…”

“…The coincidence of decreasing PSA expression and increasing use of the alternatively spliced VASE exon in the fourth Ig-like domain of NCAM (Small and Akeson, 1990;Walsh et al, 1992;Oka et al, 1995) prompted the possibility that enhanced VASE expression may be a negative regulator of NCAM polysialylation. However, one of these studies demonstrated that chicken NCAM containing VASE was only slightly less polysialylated than NCAM without VASE, indicating that VASE does not play a dominant role in the down-regulation of NCAM polysialylation (Oka et al, 1995).…”