Determinants in the LIN-12/Notch Intracellular Domain That Govern Its Activity and Stability During Caenorhabditis elegans Vulval Development

Upon ligand binding, the LIN-12/Notch intracellular domain is released from its transmembrane tether to function in a nuclear complex to activate transcription of target genes. During Caenorhabditis elegans vulval development, LIN-12/Notch is activated by ligand in two of six multipotential Vulval Precursor Cells (VPCs), specifying the "2o vulval fate" and descendants that contribute to the vulva. If LIN-12 is ectopically activated in other VPCs, they also adopt the 2o fate, dividing to produce extra vulval cells and resulting in a "Multivulva" phenotype. Here, we identify determinants in the LIN-12 intracellular domain that govern its activity and stability during C. elegans vulval development; we assayed activity of mutant forms based on their ability to cause a Multivulva phenotype and stability using a GFP tag to visualize their accumulation. Our analysis has revealed that, while the ubiquitin ligase SEL-10/Fbw7 promotes LIN-12(intra) downregulation in VPCs, there is a distinct mechanism for downregulation of LIN-12(intra) in VPC descendants. Our analysis also revealed that LIN-12(intra) must be in the nuclear complex to be regulated appropriately in VPCs and their descendants, and that the structure or conformation of the carboxy terminal region influences the stability as well. Although activity and stability are generally well-correlated, exceptions where they are uncoupled suggests that there may be roles for the carboxy terminal region and sel-10 that are independent of their roles in regulating LIN-12(intra) stability.