Contributions of chaperone and glycosyltransferase activities of O-fucosyltransferase 1 to Notch signaling.

BACKGROUND:O-fucosyltransferase1 (OFUT1) is a conserved ER protein essential for Notch signaling. OFUT1 glycosylates EGF domains, which can then be further modified by the N-acetylglucosaminyltransferase Fringe. OFUT1 also possesses a chaperone activity that promotes the folding and secretion of Notch. Here, we investigate the respective contributions of these activities to Notch signaling in Drosophila. RESULTS:We show that expression of an isoform lacking fucosyltransferase activity, Ofut1R245A, rescues the requirement for Ofut1 in embryonic neurogenesis. Lack of requirement for O-fucosylation is further supported by the absence of embryonic phenotypes in Gmd mutants, which lack all forms of fucosylation. Requirements for O-fucose during imaginal development were evaluated by characterizing clones of cells expressing only Ofut1R245A. These clones phenocopy fringe mutant clones, indicating that the absence of O-fucose is functionally equivalent to the absence of elongated O-fucose. CONCLUSION:Our results establish that Notch does not need to be O-fucosylated for fringe-independent Notch signaling in Drosophila; the chaperone activity of OFUT1 is sufficient for the generation of functional Notch.

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