Expression of the unique NCAM VASE exon is independently regulated in distinct tissues during development.

Abstract

Abstract. During development of the rat central nervous system, neural cell adhesion molecule (NCAM) mRNAs containing in the extracellular domain a 30-bp alternative exon, here named VASE, replace RNAs that lack this exon. The presence of this alternative exon between previously described exons 7 and 8 changes the predicted loop structure of the derived polypeptide from one resembling an immunoglobulin constant region domain to one resembling an immunoglobulin variable domain. This change could have significant effects on NCAM polypeptide function and cell-cell interaction. In this report we test multiple rat tissues for the presence of additional alternative exons at this position and also examine the regulation of splicing of the previously described exon. To sensitively examine alternative splicing, polymerase chain reactions (PCRs) with primers flanking the exon 7/exon 8 alternative splicing site were performed. Four categories of RNA samples were tested for new exons: whole brain from embryonic day 11 to adult, specific brain regions dissected from adult brain, clonal lines of neural cells in vitro, and muscle cells and tissues cultured in vitro and obtained by dissection. Within the limits of the PCR methodology, no evidence for any alternative exon other than the previously identified VASE was obtained. The regulation of expression of this exon was found to be complex and tissue specific. Expression of the 30-bp exon in the heart and nervous system was found to be regulated independently; a significant proportion of embryonic day 15 heart NCAM mRNAs contain VASE while only a very small amount of day 15 nervous system mRNAs contain VASE. Some adult central nervous system regions, notably the olfactory bulb and the peripheral nervous system structures adrenal gland and dorsal root ganglia, express NCAM which contains very little VASE. VASE is undetectable in NCAM PCR products from the olfactory epithelium. Other nervous system regions express significant quantities of NCAM both with and without VASE. Clonal cell lines in culture generally expressed very little VASE. These results indicate that a single alternative exon, VASE, is found in NCAM immunoglobulin-like loop 4 and that distinct tissues and nervous system regions regulate expression of VASE independently both during development and in adult animals. T HE primary strategy for developmental regulation of the expression of most individual gene products is at the level of abundance. Most genes give rise to a single polypeptide product whose abundance is controlled through mechanisms regulating transcriptional and translational events and polypeptide turnover. The evolution of multigene families has allowed a second strategy for regulation of gene expression: selective expression of single members of the family in different tissues or distinct times in development. A third strategy for selective polypeptide expression is via While this manuscript was under review we learned of an additional alternatively spliced exon between exons 7 and 8 of rat NCAM whi...

Mouse Neogenin, a DCC-like molecule, has four splice variants and is expressed widely in the adult mouse and during embryogenesis

“…Expression of the VASE exon, encoding 10 amino acids situated in the fourth Ig domain, is not observed in neurons early in development. In contrast, up to 50% of N-CAM transcripts in neurons of the central nervous system in the adult contain this exon (Small and Akeson, 1990). Inclusion of the VASE sequence leads to loss of N-CAM-dependent neurite outgrowth activity while the cell adhesion function of N-CAM is una ected (Sa ell et al, 1994).…”

PQBP1, a factor linked to intellectual disability, affects alternative splicing associated with neurite outgrowth

“…The VASE-excluding isoform of NCAM-140 (VASE À ) promotes neurite outgrowth, while the VASE-including isoform (VASE + ) inhibits neurite outgrowth (Doherty et al 1992). The embryonic brain mainly expresses VASE À with gradual ascendancy until final dominance of VASE + expression toward adulthood, except in regions such as the olfactory bulb, where reformation of synapses and turnover of neurons continue (Small and Akeson 1990). Thus, the AS of VASE in NCAM-140 is a critical switch for neuronal plasticity.…”

Characterization of Mouse ST8Sia II (STX) as a Neural Cell Adhesion Molecule-specific Polysialic Acid Synthase

“…It was recently demonstrated that PSA expression in ciliary ganglion neurons of chick embryo was regulated by PSA synthase level (23). However, it has been shown that the alterations in the extracellular polypeptide structure of NCAM caused by alternative splicing affected the polysialylation of NCAM (31)(32)(33). Therefore, the structural change of NCAM due to a variable alternative spliced exon and the structural changes of N-glycans also regulates the PSA expression level (30,33).…”

“…However, it has been shown that the alterations in the extracellular polypeptide structure of NCAM caused by alternative splicing affected the polysialylation of NCAM (31)(32)(33). Therefore, the structural change of NCAM due to a variable alternative spliced exon and the structural changes of N-glycans also regulates the PSA expression level (30,33). The detailed structural changes of NCAM and its N-glycans during neural development, and in several tissues such as kidney and muscle, are important for understanding regulation of the polysialylation of NCAM.…”