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First published online 19 November 2003
doi: 10.1242/dev.00883

Development 130, 6411-6421 (2003)
Published by The Company of Biologists 2003
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An O-fucose site in the ligand binding domain inhibits Notch activation

Liang Lei, Aiguo Xu, Vladislav M. Panin* and Kenneth D. Irvine{dagger}

Howard Hughes Medical Institute, Waksman Institute and Department of Molecular Biology and Biochemistry, Rutgers The State University of New Jersey, Piscataway, NJ 08854, USA

{dagger} Author for correspondence (e-mail: irvine{at}waksman.rutgers.edu)

Accepted 25 September 2003

Two glycosyltransferases that transfer sugars to EGF domains, OFUT1 and Fringe, regulate Notch signaling. However, sites of O-fucosylation on Notch that influence Notch activation have not been previously identified. Moreover, the influences of OFUT1 and Fringe on Notch activation can be positive or negative, depending on their levels of expression and on whether Delta or Serrate is signaling to Notch. Here, we describe the consequences of eliminating individual, highly conserved sites of O-fucose attachment to Notch. Our results indicate that glycosylation of an EGF domain proposed to be essential for ligand binding, EGF12, is crucial to the inhibition of Serrate-to-Notch signaling by Fringe. Expression of an EGF12 mutant of Notch (N-EGF12f) allows Notch activation by Serrate even in the presence of Fringe. By contrast, elimination of three other highly conserved sites of O-fucosylation does not have detectable effects. Binding assays with a soluble Notch extracellular domain fusion protein and ligand-expressing cells indicate that the NEGF12f mutation can influence Notch activation by preventing Fringe from blocking Notch-Serrate binding. The N-EGF12f mutant can substitute for endogenous Notch during embryonic neurogenesis, but not at the dorsoventral boundary of the wing. Thus, inhibition of Notch-Serrate binding by O-fucosylation of EGF12 might be needed in certain contexts to allow efficient Notch signaling.

Key words: fringe, Notch, Fucose, Glycosylation, O-fucosyltransferase, Drosophila






© The Company of Biologists Ltd 2003