Notch signalling is a cell signalling pathway whose role is, among many others, to control the cell differentiation process in equivalent precursor cells. This means it is crucial in embryonic development, to the point that it has been tested on mice that the removal of glycans in Notch proteins can result in embryonic death or malformations of vital organs like the heart.
Some of the specific modulators that control this process are glycosyltransferases located in the endoplasmic reticulum and the Golgi apparatus. The Notch proteins go through these organelles in their maturation process and can be subject to different types of glycosylation: N-linked glycosylation and O-linked glycosylation (more specifically: O-linked glucose and O-linked fucose).
All of the Notch proteins are modified by an O-fucose, because they share a common trait: O-fucosylation consensus sequences. One of the modulators that intervene in this process is the Fringe, a glycosyltransferase that modifies the O-fucose to activate or deactivate parts of the signalling, acting as a positive or negative regulator, respectively.