Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.4.99.6 (sialyltransferase)
 1,546 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Neural cell adhesion molecules (NCAMs) constitute a group of cell surface glycoproteins that control cell-cell interactions and play important morphoregulatory roles in the developing and regenerating nervous system. NCAMs exist in a variety of isoforms differing in the cytoplasmic domain and/or their content in sialic acid. The highly sialylated form (PSA-NCAM) is expressed by neurons, whereas it is believed that the less sialylated NCAM forms are synthesised by astrocytes. Moreover, little is known about the molecular sequence of the events that contribute to its expression at the cell surface. Here we report that during the proliferation of cortical astrocytes, at 4 days in primary culture, these cells expressed PSA-NCAM as well as NCAM 180. Then, during cell differentiation these isoforms progressively disappeared and the NCAM 140 became predominant. By immunofluorescence and immunocytochemistry studies we also show that PSA-NCAM and NCAM are first observed in small cytoplasmic spots or vesicles, located in or near the Golgi apparatus, as demonstrated by their co-localization with labelled wheat germ agglutinin (WGA) in this cell organelle. Thereafter, immunostained cytoplasmic NCAM gradually disappeared and became detectable at the cell surface of differentiating astrocytes. We also describe for the first time sialyltransferase activity in these cells and report that the levels of this activity correlated with the decrease in PSA-NCAM expression during the differentiation of astrocytes. These results will contribute to our understanding of the PSA and NCAM intracellular transport pathways and their expression at the cell surface. Moreover, the presence of PSA-NCAM in astrocytes suggests their possible role in nerve branching, fasciculation, and synaptic plasticity.
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PMID:Intracellular location, temporal expression, and polysialylation of neural cell adhesion molecule in astrocytes in primary culture. 981 22

Neural cell adhesion molecules (NCAMs) play critical roles during development of the nervous system. The aim of this study is to investigate the possible effect of ethanol exposure on the pattern of expression and sialylation of NCAM isoforms during postnatal rat brain development because alterations in NCAM content and distribution have been associated with defects in cell migration, synapse formation, and memory consolidation, and deficits in these processes have been observed after in utero alcohol exposure. The expression of NCAM isoforms in the developing cerebral cortex of pups from control and alcohol-fed mothers was assessed by western blotting, ribonuclease protection assay, and immunocytochemistry. The highly sialylated form of NCAM [polysialic acid (PSA)-NCAM] is mainly expressed during the neonatal period and then is down-regulated in parallel with the appearance of NCAM 180 and NCAM 140. Ethanol exposure increases PSA-NCAM levels during the neonatal period, delays the loss of PSA-NCAM, decreases the amount of NCAM 180 and NCAM 140 isoforms, and reduces sialyltransferase activity during postnatal brain development. Neuraminidase treatment of ethanol-exposed neonatal brains leads to more intense band degradation products, suggesting a higher content of NCAM polypeptides carrying PSA in these samples. However, NCAM mRNA levels are not changed by ethanol. Immunocytochemical analysis demonstrates that ethanol triggers an increase in PSA-NCAM immunolabeling in the cytoplasm of astroglial cells, accompanied by a decrease in immunogold particles over the plasma membrane. These findings indicate that ethanol exposure during brain development alters the pattern of NCAM expression and suggest that modification of NCAM could affect neuronal-glial interactions that might contribute to the brain defects observed after in utero alcohol exposure.
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PMID:Alcohol exposure alters the expression pattern of neural cell adhesion molecules during brain development. 1093 76

Neural cell adhesion molecule (NCAM) is associated with polysialic acid (PSA), and its function is highly dependent on the extent of polysialylation through the activity of two polysialyltransferases, sialyltransferase-X (STX) and polysialyltransferase (PST). PSA-NCAM plays an important role in synaptic plasticity in the hippocampus. The involvement of STX and PST during mnesic processes was assessed in the adult rat hippocampus. We investigated whether different levels in learning and memory using an olfactory associative task influenced STX and PST gene expression in the hippocampus using semiquantitative transcription-polymerase chain reaction. Then, NCAM polysialylation and cell proliferation were quantified in the dentate gyrus of a "Learning and Memory" group using immunohistochemistry. We found that only the expression level of PST mRNA increased with learning performance and returned to an initial level when learned associations were consolidated in long-term memory, while STX mRNA levels remained unchanged. This phenomenon was accompanied by an increase in PSA on NCAM but not by cell proliferation in the dentate gyrus. Our results suggest a different involvement for STX and PST in neural plasticity: while STX is probably involved in the proliferation of neural progenitor cells, PST could play a key role in synaptic plasticity of mature neural networks. The expression of the STX and PST genes could, therefore, be useful markers of neurobiological plasticity in the brain, allowing to follow chronological events in limbic and cortical structures related first to learning and memory processes (for PST) and, second, to adult neurogenesis processes (for STX).
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PMID:Dynamic expression of the polysialyltransferase in adult rat hippocampus performing an olfactory associative task. 2475 9