Figure 1.

Presenilin-dependent activity of Notch in the embryonic central nervous system. Neuroblasts marked by the expression of Hb protein are shown in wild-type (A, C, and E) and PS⁻ (B, D, and F) embryos that ubiquitously express either N⁺ (A and B), N^ECN (C and D), or N^intra (E and F) under Gal4/UAS control. (A) Ubiquitous expression of N⁺ in otherwise wild-type embryos has little or no effect on neuroblast segregation. (C and E) In contrast, ubiquitous expression of either N^ECN or N^intra suppresses neuroblast segregations, indicating constitutive transducing activity. In PS⁻ embryos, most or all ventral ectodermal cells segregate as neuroblasts, even when N⁺ or N^ECN are ubiquitously expressed (B and D), indicating that the transducing activity of these transmembrane forms requires Presenilin. In contrast, neuroblast segregation is suppressed in PS⁻ embryos expressing N^intra (F), indicating that this form of Notch bypasses the requirement for Presenilin. All embryos are shown in ventral aspect just after completion of germ-band elongation (anterior to the left). The structure of the Notch proteins are shown schematically: EGF, epidermal growth factor motifs; LNR, LIN-12/Notch repeat motifs; TM, transmembrane domain; CDC10, CDC10/SWI6 motifs.