C‐CAM is a cell adhesion molecule of the immunoglobulin superfamily with homophilic binding properties. Here we used the polymerase chain reaction to isolate clones of C‐CAM from a rat liver cDNA library. Sequence analyses identified two major isoforms, C‐CAM1 and C‐CAM2, which differed in their 3′ ends. C‐CAM2 lacked a sequence of 53 nucleotides that was present in C‐CAM1. This causes a frame shift and new stop codons, which gives rise to cytoplasmic domains of different sizes in the two isoforms (10 versus 71 amino‐acid residues). In addition, all the clones had a different nucleotide and deduced amino‐acid sequence (variant b) in the most N‐terminal of the four immunoglobulin‐like domains, compared to a previously published C‐CAM sequence (variant a). Northern‐blot analyses with specific oligonucleotide probes demonstrated that two different rat stocks expressed either variant a or variant b. Northern‐blot analyses of rat liver and lung also showed that at least five different C‐CAM transcripts are produced. Two major mRNA size classes of 4.0 kb and 6.0 kb, and one minor class of 3.0 kb were found. Both the 4.0‐kb and 3.0‐kb messenger classes reacted with two different probes that could distinguish between C‐CAM1 and C‐CAM2, while the 6.0‐kb population only reacted with the probe selective for C‐CAM1. Taken together these data demonstrate the existence of four different protein‐coding sequences of rat liver C‐CAM (C‐CAM1 a and b, and C‐CAM2 a and b). We suggest that both allelic variation and alternative splicing may contribute to the isoform‐expression pattern of C‐CAM in rats.

Neural cell adhesion molecule (NCAM) is expressed by muscle and involved in muscle-neuron and muscle-muscle cell interactions. The expression in muscle is regulated during myogenesis and by the state of innervation. In aged muscle, both neurogenic and myogenic degenerative processes occur. We here report quantitative and qualitative changes in NCAM protein and mRNA forms during aging in normal rat skeletal muscle. Determination of the amount of NCAM by e.l.i.s.a. showed that the level decreased from perinatal to adult age, followed by a considerable increase in 24-month-old rat muscle. Thus NCAM concentration in aged muscle was sixfold higher than in young adult muscle. In contrast with previous reports, NCAM polypeptides of 200, 145, 125 and 120 kDa were observed by immunoblotting throughout postnatal development and aging, the relative proportions of the individual NCAM polypeptides remaining virtually unchanged at all ages examined. However, changes in the extent of sialylation of NCAM were demonstrated. Even though the relative amounts of the various NCAM polypeptides were unchanged during aging, distinct changes in NCAM mRNA classes were observed. Three NCAM mRNA classes of 6.7, 5.2 and 2.9 kb were present in perinatal and young adult skeletal muscle, whereas only the 5.2 and 2.9 kb mRNA classes could be demonstrated in aged muscle. This indicates that metabolism of the various NCAM polypeptides is individually regulated during aging. Alternative splicing of NCAM mRNA in skeletal muscle was studied by Northern blotting using DNA oligonucleotide probes specifically hybridizing to selected exons or exon combinations. Exon VASE, which has previously been shown to be present in both brain and heart NCAM mRNA, was virtually absent from skeletal muscle at all ages studied. In contrast, the majority of NCAM mRNA in postnatal skeletal muscle was shown to contain extra exons inserted between exons 12 and 13. Of the various possible exon combinations at this splice site, the combinations 12-a-AAG-13 and 12-a-b seemed to be prevalent in postnatal skeletal muscle. No significant change in the relative proportion of these two exon combinations occurred during aging. The observed upregulation of NCAM protein in aged muscle supports the assumption that an increasing proportion of muscle fibres are denervated in aged muscle. Selective upregulation of the 5.2 and 2.9 kb mRNA forms have previously been demonstrated in muscle cell lines and in primary cultures of muscle cells during formation of myotubes in vitro, and this switch in NCAM mRNA classes has been suggested to correlate with myogenesis.(ABSTRACT TRUNCATED AT 250 WORDS)

The neural cell adhesion molecule, NCAM, plays an important role in cell-cell adhesion. Therefore, we have studied NCAM expression in the glioma cell lines BT4C and BT4Cn. We demonstrate that the 2 cell lines differ in their metastatic ability; while BT4C cells have a very low capacity for producing experimental metastases, that of BT4Cn cells is high. In BT4C cells NCAM is synthesized as 4 polypeptides with Mr's of 190,000, 140,000, 115,000 and 97,000. The 140,000, 115,000 and 97,000 polypeptides are glycosylated and for the 140,000 and 115,000 polypeptides sulfatation is observed. Conversely, no NCAM protein synthesis is observed in BT4Cn cells, even though NCAM mRNA is expressed. Thus, development of an increased metastatic capacity is accompanied by the disappearance of NCAM protein expression in this model system. The functional importance of NCAM expression was studied by a cell-substratum binding assay in which the binding of BT4C and BT4Cn cells to NCAM immobilized to glass was assessed. We found that BT4C cells adhere specifically to NCAM, and that adhesion is inhibited by anti-NCAM Fab'-fragments, while no specific binding of BT4Cn cells to NCAM was observed. The BT4C and BT4Cn cell lines thus constitute an important new model system for the study of tumor invasion and metastasis and of the role of cell adhesion molecules in these processes.

Neural cell adhesion molecule; Northern blotting; Oligonucleotide A number of different isoforms of the neural cell adhesion molecule (NCAM) have been identified. The difference between these is due to alternative splicing of a single NCAM gene. In rat brain NCAM mRNAs with sizes of 7.4, 6.7, 5.2, 4.3 and 2.9 kb have been reported. We have synthesized six DNA oligonucleotides, that hybridize to different exons in the NCAM gene. Furthermore we have constructed three oligonucleotides, that exclusively hybridize to mRNAs lacking certain exons, by letting them consist of sequences adjacent to both sides of the splice sites. By means of these probes we have characterized the five NCAM mRNAs in rat brain.

Cadherins are cell-cell adhesion molecules belonging to the Ca(2+)-dependent cadherin superfamily. In the last few years the number of cadherins identified in the nervous system has increased considerably. Cadherins are integral membrane glycoproteins. They are structurally closely related and interspecies homologies are high. The function is mediated through a homophilic binding mechanism, and intracellular proteins, directly or indirectly connected to the cadherins and the cytoskeleton, are necessary for cadherin activity. Cadherins have been implicated in segregation and aggregation of tissues at early developmental stages and in growth and guidance of axons during nervous system development. These functions are modified by changes in type(s) and amount of cadherins expressed at different developmental stages. The regulatory elements guiding cadherin expression are currently being elucidated.