Cell fate choices dependent on Notch require appropriate glycan expression. (A) Notch mutations were originally identified based on aberrant wing morphology. Changes in cell fate generate wings that are notched at their margins (arrow). Wing notches arise from insufficient numbers of nonneural cells in the developing wing. In the embryo, loss of Notch signaling expands neural tissue at the expense of nonneural ectodermal cell fates. (B,C) Staining with a neuron-specific antibody reveals increased neural cell numbers in a Notch mutant (C) compared with wild-type (B). In comparison to wild-type (D), loss of the egghead or brainiac genes (E), which are essential for glycosphingolipid synthesis, results in neurogenic phenotypes similar to loss of Notch signaling. (B,C, Reprinted, with permission of the Company of Biologists, from Lai EC. 2004. Development 131: 965–973; D,E, reprinted, with permission of the Company of Biologists, from Goode S, et al. 1992. Development 116: 177–192.)