* Why Is N-Glycolylneuraminic Acid Rare in the Vertebrate Brain?
- The sialic acids N-acetylneuraminic acid (Neu5Ac) and N-glycolylneuraminic acid (Neu5Gc) differ by a single oxygen atom and are widely found at the terminal position of glycans on vertebrate cell surfaces. In animals capable of synthesizing Neu5Gc, most tissues and cell types express both sialic acids, in proportions that vary between species. However, it has long been noted that Neu5Gc is consistently expressed at trace to absent levels in the brains of all vertebrates studied to date. Although several reports have claimed to find low levels of Neu5Gc-containing glycans in neural tissue, no study definitively excludes the possibility of contamination with glycans from non-neural cell types. This distribution of a molecule - prominently but variably expressed in extraneural tissues but very low or absent in the brain - is, to our knowledge, unique. The evolutionarily conserved brain-specific suppression of Neu5Gc may indicate that its presence is toxic to this organ; however, no studies to date have directly addressed this very interesting question. Here we provide a historical background to this issue and discuss potential mechanisms causing the suppression of Neu5Gc expression in brain tissue, as well as mechanisms by which Neu5Gc may exert the presumed toxicity. Finally, we discuss future approaches towards understanding the mechanisms and implications of this unusual finding.
=>密室, 細胞, 電池, 独房・細胞, 監房, 組織, 独房
Overview of noun cell
The noun cell has 7 senses (first 3 from tagged texts)
1. (71) cell -- (any small compartment; "the cells of a honeycomb")
2. (44) cell -- ((biology) the basic structural and functional unit of all organisms; they may exist
as independent units of life (as in monads) or may form colonies or tissues as in higher plants and
animals)
3. (1) cell, electric cell -- (a device that delivers an electric current as the result of a
chemical reaction)
4. cell, cadre -- (a small unit serving as part of or as the nucleus of a larger political movement)
5. cellular telephone, cellular phone, cellphone, cell, mobile phone -- (a hand-held mobile
radiotelephone for use in an area divided into small sections, each with its own short-range
transmitter/receiver)
6. cell, cubicle -- (small room in which a monk or nun lives)
7. cell, jail cell, prison cell -- (a room where a prisoner is kept)
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