ABSTRACT
The Notch receptor mediates cell interactions controlling the developmental fate of a broad spectrum of undifferentiated cells. By modulating Notch signaling in specific precursor cells during Drosophila imaginal disc development, we demonstrate that Notch activity can influence cell proliferation. The activation of the Notch receptor in the wing disc induces the expression of the wing margin patterning genes vestigial and wingless, and strong mitotic activity. However, the effect of Notch signaling on cell proliferation is not the simple consequence of the upregulation of either vestigial or wingless. Vestigial and Wingless, on the contrary, display synergistic effects with Notch signaling, resulting in the stimulation of cell proliferation in imaginal discs.
Subject(s)
Cell Communication , Drosophila Proteins , Drosophila/embryology , Membrane Proteins/metabolism , Receptors, Cell Surface/metabolism , Wings, Animal/embryology , Animals , Membrane Proteins/genetics , Mitosis , Models, Biological , Morphogenesis/genetics , Nuclear Proteins/metabolism , Proto-Oncogene Proteins/metabolism , Receptors, Notch , Suppression, Genetic , Wings, Animal/cytology , Wnt1 ProteinABSTRACT
The Notch (N) pathway defines an evolutionarily conserved cell signaling mechanism that governs cell fate choices through local cell interactions. The ankyrin repeat region of the Notch receptor is essential for signaling and has been implicated in the interactions between Notch and two intracellular elements of the pathway: Deltex (Dx) and Suppressor of Hairless (Su(H)). Here we examine directly the function of the Notch cdc10/ankyrin repeats (ANK repeats) by transgenic and biochemical analysis. We present evidence implicating the ANK repeats in the regulation of Notch signaling through homotypic interactions. In vivo expression of the Notch ANK repeats reveals a cell non-autonomous effect and elicits mutant phenotypes that indicate the existence of novel downstream events in Notch signaling. These signaling activities are independent of the known effector Su(H) and suggest the existence of yet unidentified Notch pathway components.
Subject(s)
Drosophila Proteins , Membrane Proteins/genetics , Membrane Proteins/metabolism , Receptor Protein-Tyrosine Kinases , Repressor Proteins/metabolism , Signal Transduction , Animals , Ankyrins/genetics , Ankyrins/metabolism , Binding Sites , Drosophila/genetics , Eye/growth & development , Eye/metabolism , Eye Proteins/genetics , Eye Proteins/metabolism , Insect Proteins/genetics , Insect Proteins/metabolism , Membrane Glycoproteins/genetics , Membrane Glycoproteins/metabolism , Mutation , Phenotype , Receptors, Notch , Recombinant Proteins/genetics , Recombinant Proteins/metabolism , Repetitive Sequences, Nucleic Acid , Repressor Proteins/geneticsABSTRACT
The Notch signaling pathway is known to regulate cell fate decisions in a variety of organisms from worms to humans. Although several components of the pathway have been characterized, the actual mechanism and molecular results of signaling remain elusive. We have examined the role of the Notch signaling pathway in the transcriptional regulation of two Drosophila Enhancer of split [E(spl)] genes, whose gene products have been shown to be downstream players in the pathway. Using a reporter assay system in Drosophila tissue culture cells, we have observed a significant induction of E(spl) m gamma and m delta expression after cotransfection with activated Notch. Characterization of the 5' regulatory regions of these two genes led to the identification of a number of target sites for the Suppressor of Hairless [Su(H)] protein, a transcription factor activated by Notch signaling. We show that Notch-inducible expression of E(spl) m gamma and m delta both in cultured cells and in vivo is dependent on functional Su(H). Although overexpression of Su(H) augments the level of induction of the reporter genes by activated Notch, Su(H) alone is insufficient to produce high levels of transcriptional activation. Despite the synergy observed between activated Notch and Su(H), the former affects neither the nuclear localization nor the DNA binding activity of the latter.
