Figure 1 .

Photomicrographs showing wild-type and lin-12/Notch mutant phenotypes. (Left) Drosophila embryos. Neuroblasts are marked by anti-Hunchback staining, and insets show the results of staining with an antibody to the intracellular domain of Notch. (Top Left) A wild-type embryo showing the normal pattern of neuroblast segregation from the ventral ectoderm and Notch protein predominantly at the surface of ectodermal cells. (Middle Left) An embryo expressing Notch^intra protein ubiquitously under heat-shock control: all ventral ectodermal cells remain ectodermal, and Notch^intra protein accumulates predominantly in nuclei. (Bottom Left) A Notch⁻ embryo: all ventral ectodermal cells segregate as neuroblasts, the classic “neurogenic phenotype.” (Right) C. elegans hermaphrodite gonads. Green fluorescent protein marks the anchor cell (AC) in a wild-type hermaphrodite, two ACs in a lin-12(0) hermaphrodite, and the lack of an AC in a lin-12(d) hermaphrodite. Drosophila photomicrographs courtesy of Gary Struhl; C. elegans photomicrographs courtesy of Maria Sallee.