ABSTRACT
The Notch genes encode single-pass transmembrane receptors that transduce the extracellular signals responsible for cell fate determination during several steps of metazoan development. The mechanism by which extracellular signals affect gene transcription and ultimately cell fate decisions is beginning to emerge for the Notch signalling pathway. One paradigm is that ligand binding to Notch triggers a Presenilin1-dependent proteolytic release of the Notch intracellular domain from the membrane, resulting in low amounts of Notch intracellular domain which form a nuclear complex with CBF1/Su(H)/Lag1 to activate transcription of downstream targets. Not all observations clearly support this processing model, and the most rigorous test of it is to block processing in vivo and then determine the ability of unprocessed Notch to signal. Here we report that the phenotypes associated with a single point mutation at the intramembranous processing site of Notch1, Val1,744-->Gly, resemble the null Notch1 phenotype. Our results show that efficient intramembranous processing of Notch1 is indispensable for embryonic viability and proper early embryonic development in vivo.
Subject(s)
Embryonic and Fetal Development/physiology , Membrane Proteins/physiology , Protein Processing, Post-Translational , Receptors, Cell Surface , Transcription Factors , Alleles , Animals , Cloning, Molecular , Embryo, Mammalian , Embryonic and Fetal Development/genetics , Fetal Death/genetics , Gene Targeting , Germ-Line Mutation , Homozygote , Immunoglobulins , In Situ Hybridization , Ligands , Membrane Proteins/genetics , Mice , Mice, Inbred C57BL , Phenotype , Point Mutation , Protein Processing, Post-Translational/genetics , Receptor, Notch1 , Receptors, Cytokine/biosynthesisABSTRACT
Delta and Notch are required for partitioning of vein and intervein cell fates within the provein during Drosophila metamorphosis. We find that partitioning of these fates is dependent on Delta-mediated signalling from 22 to 30 hours after puparium formation at 25 degrees C. Within the provein, Delta is expressed more highly in central provein cells (presumptive vein cells) and Notch is expressed more highly in lateral provein cells (presumptive intervein cells). Accumulation of Notch in presumptive intervein cells is dependent on Delta signalling activity in presumptive vein cells and constitutive Notch receptor activity represses Delta accumulation in presumptive vein cells. When Delta protein expression is elevated ectopically in presumptive intervein cells, complementary Delta and Notch expression patterns in provein cells are reversed, and vein loss occurs because central provein cells are unable to stably adopt the vein cell fate. Our findings imply that Delta-Notch signalling exerts feedback regulation on Delta and Notch expression during metamorphic wing vein development, and that the resultant asymmetries in Delta and Notch expression underlie the proper specification of vein and intervein cell fates within the provein.
Subject(s)
Drosophila/growth & development , Drosophila/genetics , Membrane Proteins/genetics , Wings, Animal/growth & development , Animals , Animals, Genetically Modified , Drosophila/metabolism , Drosophila Proteins , Feedback , Gene Expression Regulation, Developmental , Genes, Insect , Intracellular Signaling Peptides and Proteins , Membrane Proteins/metabolism , Metamorphosis, Biological , Phenotype , Pupa/genetics , Pupa/growth & development , Pupa/metabolism , Receptors, Notch , Signal Transduction , Wings, Animal/metabolismABSTRACT
We have examined expression of the neurogenic gene, Delta (Dl), and the regulatory relationships between the Delta-Notch signalling pathway and the proneural gene, achaete, during microchaeta development in Drosophila. Delta is expressed in all microchaeta proneural cells and microchaeta sensory organ precursors (SOPs) and is expressed dynamically in SOP progeny. We find that Delta expression in microchaeta proneural cells is detected prior to the onset of achaete expression and arises normally in the absence of achaete/scute function, indicating that initial Delta expression in the notum is not dependent on proneural gene function. Activation of the Delta-Notch pathway results in loss of Delta protein accumulation, suggesting that Delta expression is regulated, in part, by Delta-Notch signalling activity. We find that Delta signalling is required for correct delineation of early proneural gene expression in developing nota. Within microchaeta proneural stripes, we demonstrate that Delta-Notch signalling prohibits adoption of the SOP fate by repressing expression of proneural genes.
