Poster abstracts

Poster number 59 submitted by Nathen Zavada

Elucidating the roles of divergent Notch ligands and fringe glycosylation in vertebrate segmentation

Nathen Zavada (Molecular Genetics), Dustin Servello (Molecular Genetics )

Abstract:
Somitogenesis is the developmental process where the precursors to the vertebrate axial skeleton are produced. This process is timed by the segmentation clock, an oscillatory gene network in the presomitic mesoderm (PSM). Synchronized, oscillatory gene expression in the PSM requires regulated Notch pathway activity. In the PSM, NOTCH1 is activated by the Delta-like 1 (DLL1) ligand presented on the membrane of an adjacent cell (trans-activation), triggering release of the Notch Intracellular Domain (NICD) which activates downstream genes. In mammals, Notch signaling in the clock is affected by a divergent ligand, Delta-like 3 (DLL3), (which cannot activate NOTCH1 in trans) and by Lunatic fringe (LFNG), a glycosyltransferase that modifies EGF repeat domains in receptors and ligands. We recently found that DLL3 promotes signal-sending activity by cells that co-express DLL1 and NOTCH1, a novel function for DLL3. This activity is attenuated by LFNG, supporting a model where periodic glycosylation of NOTCH1 and the ligands coordinates oscillatory Notch activity in the PSM. In our ongoing work, we find that avian DLL3 plays a similar role in somitogenesis despite extensive structural divergence, providing an evolutionary tool to help identify crucial protein domains. Moving forward, we seek a mechanistic understanding of the roles of DLL3 and LFNG in oscillatory Notch activity in the PSM. We are actively working to identify protein domains in the receptor and ligands that are necessary for protein interactions in cis that influence signal-sending and signal receiving activities at the cellular level. Completion of this work will identify protein domains in the ligands and receptor that mediate protein:protein interactions in cis, and will determine how glycosylation by LFNG modulates those interactions, providing insight into a novel mechanism to regulate Notch pathway activity.

Keywords: Vertebrate segementation, Notch signaling, Protein structure-function