Knowledge Bank

The Notch pathway is a cellular communication pathway that is essential for development of many multicellular organisms. It is an evolutionarily conserved pathway in which cell fates can be influenced in a context-dependent manner based on the pattern of ligand and receptor presentation in neighboring cells. Notch has several roles in cell differentiation, apoptotic cell fates, and cell proliferation (reviewed in Hori et al., 2013). Malfunctions in this pathway can lead to congenital defects such as Alagille Syndrome and many types of cancer. Overactivation of Notch can result in conditions favorable to tumor formation and survival. Jagged1 is a ligand that binds to the Notch receptor, normally resulting in the upregulation of Notch target genes when interactions occur between two adjacent cells. Like other Notch ligands, Jagged1 can also bind to Notch receptors co-expressed in the same cell. This interaction is called cis-inhibition and it limits the ability of both the receptor and the ligand in that cell from interacting with adjacent cells, which will alter the context in which those adjacent cells develop and grow. Defects in the Jagged1 ligand are associated with a wide variety of deleterious phenotypes including acute myeloid leukemia, Alagille syndrome, and adrenocortical carcinoma (Andersson et al., 2011). We have hypothesized that the glycosylation of Notch ligands can influence interactions between receptor and ligand in cis. Recently, the EGF 4-6 region in Serrate, the Drosophila homolog of JAGGED1 (JAG1), has been shown to be required for cis-inhibitory interactions with Notch, but dispensable for trans-activation of Notch (Fleming et al., 2013). This offers a new approach to dissecting the function of Jagged1 in trans-activation from its function in cis-inhibition. This project involves two aims: first, the use of co-culture assays to determine if the EGF 4-6 region in Jagged1 is required for cis-inhibition, but not for trans-activation. Then, the use of click chemistry reactions followed by co-culture assays to determine if glycosylation of these EGF repeats can influence the ability of Jagged1 to cis-inhibit Notch signaling.