Identification of components involved in Epsin ubiquitination



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Notch signaling is a major signaling pathway that occurs in many tissues at in nearly all stages of development. In Drosophila, Notch and its ligands, Delta and Serrate, physically interact as a part of activation of the signal. Notch activation requires the endocytic adaptor protein Epsin to facilitate the endocytosis of the ligand Delta. Our laboratory has discovered that Epsin activity is regulated by ubiquitination. Liquid facets, the gene coding for the Drosophila protein related to Epsin, was discovered to be an enhancer of the fat facets (faf) mutant eye phenotype. faf codes for a deubiquitinating enzyme. Epsin has been determined to be a key substrate of the activity of Faf in the eye. An F1 screen for dominant suppressors of the faf phenotype was performed to identify the E3 ubiquitin ligase whose substrate is Epsin. The E2 ubiquitin-conjugating enzyme UbcD1 was isolated as a strong suppressor of the faf mutant eye defect. UbcD1 has previously been identified as a strong suppressor of faf. An RNAi approach was used to study UbcD1’s role in Epsin ubiquitination further. The data that I obtained do not elucidate the UbcD1’s role in Epsin ubiquitination, but instead suggest an alternative role that should be considered.