Fig. 7. Schematic drawing of Nti molecular function. O-fucosecontaining glycans attached to the specific EGF repeat of Notch is the tetrasaccharide: Sia-2, 3-Gal-ß1, 4-GlcNac-ß1, 3-Fuc-1-O-Ser/Thr. First, O-fucose is attached to a serine or threonine within a consensus sequence of Notch EGF repeat by Nti. O-fucosylation is essential for binding between Notch and Delta. Thus, if there is a lack of O-fucosylation, activation of Notch does not occur (lower panel). In the cells that do not express Fng, O-fucose on Notch does not elongate further (middle panel). However, Notch modified by O-fucose is competent to bind to the Delta and Serrate. Next, N-acetylglucosamine is added to the O-fucose residue by Fng, then O-fucose glycans are elongated by ß1, 4-galactosyltransferase and 2, 3-sialyltransferase (upper panel). Notch modified by these O-linked glycans has an enhanced activity to bind to Delta. Thus, in the cells expressing Fng and the other two endogenous glycosyltransferases, Notch become more potent to receive signal than neighboring cells that do not express Fng.

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