ELIZA

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501283 occurrences (No.27 in the rank) during 5 years in the PubMed. [cache]

306) 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.

--- ABSTRACT ---

PMID:23471785 DOI:10.1007/128_2013_419

2015 Topics in current chemistry

* 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.

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(2)40 null	(9)4 are	(16)3 while	(23)2 induced
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(5)34 and	(12)4 on	(19)2 compared
(6)6 was	(13)3 did	(20)2 decreased
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--- WordNet output for levels --- Overview of noun level The noun level has 8 senses (first 6 from tagged texts) 1. (69) degree, grade, level -- (a position on a scale of intensity or amount or quality; "a moderate grade of intelligence"; "a high level of care is required"; "it is all a matter of degree") 2. (22) grade, level, tier -- (a relative position or degree of value in a graded group; "lumber of the highest grade") 3. (15) degree, level, stage, point -- (a specific identifiable position in a continuum or series or especially in a process; "a remarkable degree of frankness"; "at what stage are the social sciences?") 4. (5) level -- (height above ground; "the water reached ankle level"; "the pictures were at the same level") 5. (1) level, spirit level -- (indicator that establishes the horizontal when a bubble is centered in a tube of liquid) 6. (1) horizontal surface, level -- (a flat surface at right angles to a plumb line; "park the car on the level") 7. level, layer, stratum -- (an abstract place usually conceived as having depth; "a good actor communicates on several levels"; "a simile has at least two layers of meaning"; "the mind functions on many strata simultaneously") 8. floor, level, storey, story -- (a structure consisting of a room or set of rooms at a single position along a vertical scale; "what level is the office on?") Overview of verb level The verb level has 6 senses (first 3 from tagged texts) 1. (4) level -- (aim at; "level criticism or charges at somebody") 2. (1) level, raze, rase, dismantle, tear down, take down, pull down -- (tear down so as to make flat with the ground; "The building was levelled") 3. (1) flush, level, even out, even -- (make level or straight; "level the ground") 4. charge, level, point -- (direct into a position for use; "point a gun"; "He charged his weapon at me") 5. level -- (talk frankly with; lay it on the line; "I have to level with you") 6. level, level off -- (become level or even; "The ground levelled off") --- WordNet end ---