Biomedical subjects

D Linnemann

Publications and source records attributed to D Linnemann.

26 records · Page 2Linked to original sources

PubMed1988

Developmental study of the cell adhesion molecule L1.

Cell adhesion molecules are involved in several morphogenetic events during development. A spatiotemporal regulation of the expression of the neural cell adhesion molecule NCAM has previously been demonstrated. In this study, we describe developmental changes in the rat brain in the expression of another neural cell adhesion molecule, L1. The amount of L1 varies with age showing a peak value in early post-natal life. L1 is synthesized as a polypeptide with a relative molecular weight (Mr) of 200,000 in explant cultures of rat forebrain from embryonic day 17 to post-natal day 15, but L1 synthesis decreases relative to total protein synthesis during the same period. L1 sulphation does not appear to change developmentally whereas the degree of phosphorylation seems to decrease. At the plasma membrane L1 is present as three polypeptides with Mr 200,000, 140,000 and 80,000. The latter is phosphorylated like the 200,000 Mr polypeptide. Furthermore, L1 exists in a soluble form which consists of 170,000, 140,000 and 80,000 Mr polypeptides. During development a slight decrease in Mr of the 200,000 and 140,000 Mr polypeptides is observed, possibly due to changes in glycosylation. To conclude, L1 expression is temporally regulated and its function may thus, like NCAM, be developmentally modified by some of these changes.

Aging↗

PubMed1987

Characterization of soluble forms of NCAM.

Neural cell adhesion molecule (NCAM) has been described as a family of membrane glycoproteins. However, soluble NCAM immunoreactivity has long been recognized. We here show that soluble NCAM is composed of two quantitatively major polypeptides of Mr 180,000 and 115,000 and two minor components of Mr 160,000 and 145,000. Soluble NCAM was immunochemically identical to membrane NCAM, was polysialylated and carried the HNK-1 epitope. It only constituted 0.8% of total NCAM in newborn rat brain. Soluble NCAM appeared in neuronal cell culture medium 15-30 min after the start of synthesis preceding accumulation of membrane-associated NCAM on the cell surface. This indicates that soluble NCAM contains a secreted component.

Animals↗

PubMed1986

Developmental study of detergent solubility and polypeptide composition of the neural cell adhesion molecule.

The neural cell adhesion molecule (N-CAM), a glycoprotein synthesized by neurons, glial cells and muscle cells, is involved in cell-cell adhesion. In this report we describe developmental changes in the amount of N-CAM polypeptides in rat forebrain and in detergent solubility of N-CAM. The amount of N-CAM changed during development with a peak in early postnatal life. N-CAM was composed of the following polypeptides: HMr (molecular weight between 250,000 and 350,000 daltons), A (200,000 daltons), B (135,000 daltons) and C (115,000 daltons). In embryonic life N-CAM consisted of 10% HMr, 26% A, 53% B and 11% C. During development only the relative amount of polypeptide C increased significantly, from 11% at embryonic day 17 to 22% at postnatal day 4. Postnatally the polypeptide composition of N-CAM did not change. No Triton X-100 insoluble N-CAM was observed in early development, but at postnatal day 40 14% of N-CAM was Triton X-100 insoluble. This fraction was shown to consist of polypeptide C.

Aging↗

PubMed1986

Expression of the cell adhesion molecules N-CAM and L1 in B16 melanoma cells.

The cell adhesion molecules N-CAM and L1 are important for cell-cell recognition and cell migration and so may be involved in the metastatic process. We have studied the biosynthesis of N-CAM and L1 in the B16 melanoma cell lines B16-F1 and B16-F10 which differ in metastatic capacity. N-CAM was synthesised as two glycosylated polypeptides with Mr of 150,000 and 210,000; L1 was synthesised as one polypeptide with Mr of 215,000. In fetal neurons N-CAM is synthesised as a 135,000 and a 200,000 Mr polypeptide and L1 as a 200,000 Mr polypeptide. Thus, the Mr of N-CAM and L1 in tumour cells appeared to be 10,000-15,000 higher than in the normal cells. L1 was phosphorylated in the tumour cells as in neurons. The tumour cells also phosphorylated the 210,000 Mr N-CAM polypeptide, whereas no phosphorylation of the 150,000 Mr polypeptide was observed. In neuronal cells both the corresponding polypeptides are phosphorylated and thus the biosynthesis of N-CAM in tumour cells seem to differ from that in neuronal cells with regard to phosphorylation. No differences in biosynthesis of N-CAM or L1 were apparent between the two tumour cell lines, B16-F1 and B16-F10.

Antigens, Surface↗

PubMed1985

Biosynthesis of the neural cell adhesion molecule: characterization of polypeptide C.

The biosynthesis of the neural cell adhesion molecule (N-CAM) was studied in primary cultures of rat cerebral glial cells, cerebellar granule neurons, and skeletal muscle cells. The three cell types produced different N-CAM polypeptide patterns. Glial cells synthesized a 135,000 Mr polypeptide B and a 115,000 Mr polypeptide C, whereas neurons expressed a 200,000 Mr polypeptide A as well as polypeptide B. Skeletal muscle cells produced polypeptide B. The polypeptides synthesized by the three cell types were immunochemically identical. The membrane association of polypeptide C was investigated with methods that distinguish peripheral and integral membrane proteins. Polypeptide C was found to be a peripheral membrane protein, whereas polypeptides A and B were integral membrane proteins with cytoplasmic domains of approximately 50,000 and approximately 25,000 Mr, respectively. The affinity of the membrane binding of polypeptide C increased during postnatal development. The posttranslational modifications of polypeptide C were investigated in glial cell cultures, and it was found to be N-linked glycosylated and sulfated.

Age Factors↗

PubMed1985

A developmental study of the biosynthesis of the neural cell adhesion molecule.

The neural cell adhesion molecule (N-CAM) is a glycoprotein found in neurons, glial cells and muscle cells. In this report we describe developmental changes in biosynthesis of N-CAM polypeptides in rat forebrain explant cultures. N-CAM was synthesized as the following polypeptides: HMr (Mr between 250,000 and 350,000), A (200,000 Mr), B (135,000 Mr) and C (115,000 Mr). The biosynthetic pattern of N-CAM polypeptides changed during development: the biosynthesis of HMr and C increased relative to A and B. N-CAM biosynthesis decreased 100-fold from embryonic day 17 to postnatal day 25; N-CAM turnover decreased 350-fold during the same period. N-CAM polysialylation and sulfatation decreased markedly with age, whereas phosphorylation seemed to be constant during development. Only polypeptides A and B were phosphorylated, whereas A, B and C were sulfated. A was more sulfated and phosphorylated than B. It is concluded that the above described modulations of N-CAM may be of importance in the developmental regulation of cell-cell adhesion.

Age Factors↗

PubMed1984

Biosynthesis of the D2-cell adhesion molecule: post-translational modifications, intracellular transport, and developmental changes.

Posttranslational modifications and intracellular transport of the D2-cell adhesion molecule (D2-CAM) were examined in cultured fetal rat neuronal cells. Developmental changes in biosynthesis were studied in rat forebrain explant cultures. Two D2-CAM polypeptides with Mr of 187,000-210,000 (A) and 131,000-158,000 (B) were synthesized using radiolabeled precursors in cultured neurons. A and B were found to contain only N-linked complex oligosaccharides, and both polypeptides appeared to be polysialated as determined by [14C]mannosamine incorporation and precipitation with anti-polysialic acid antibody. The two polypeptides were sulfated in the trans-Golgi compartment and phosphorylated at the plasma membrane. D2-CAM underwent rapid intracellular transport, appearing at the cell surface within 35 min of synthesis. A and B were shown to be integral membrane proteins as seen by radioiodination by photoactivation employing a hydrophobic labeling reagent. In rat forebrain explant cultures, D2-CAM was synthesized as four polypeptides: A (195,000 Mr), B (137,000 Mr), C (115,000 Mr), and a group of polypeptides in the high molecular weight region (HMr) between 250,000 and 350,000. Peptide maps of the four polypeptides yielded similar patterns. Biosynthesis of C and HMr increased with age, relative to A and B. A and B were sulfated in embryonic brain, however, sulfation was not noticeable at postnatal ages. Phosphorylation, on the other hand, of A and B was observed at all ages examined. We suggest that D2-CAM function may be modified during development by changes in the relative synthesis of the different polypeptides, as well as by changes in their glycosylation and sulfation.

Animals↗

PubMedDate not supplied

Regional changes in expression of NCAM, GFAP, and S100 in aging rat brain.

In aging brain degenerative processes occur. However, the aging brain still have regenerative capacity although diminished compared to young rats. The neural cell adhesion molecule (NCAM) may be involved in neuroplasticity during regenerative events. In this study, the polypeptide composition and amount of NCAM was determined in regions of brain from young, mature and old rats. During adult life, the amount of NCAM decreased in several brain regions whereas in aged rats, NCAM was enhanced in all brain regions examined. The amount of the glial fibrillary acidic protein (GFAP) increased during aging in all brain regions reflecting general gliosis in the aged rat brain. The amount of the neuro- and gliotrophic protein S100 increased from young adult to mature age in all brain regions investigated followed by a decrease during old age. Aged rats were tested in a Morris water maze and a group of rats (20%) with learning impairment was defined. However, no differences in amount of NCAM, GFAP, or S100 were observed between aged rats with and without spatial learning impairment.

Aging↗