Elucidating The Role of Rumi and O-Glucosylation In The Drosophila Eye

<p>Rumi is a protein <em>O-</em>glucosyltransferase that adds the sugar <em>O-</em>glucose onto the serine in the target sequence C-S-X-S-(P/A)-C found within properly folded EGF repeats. It was first discovered to modify the <em>Drosophila </em>Notch extracellular domain and to be required for Notch signaling in a temperature dependent manner, but other targets of Rumi remained unknown. Several other proteins in the <em>Drosophila </em>proteome harbor multiple consensus sequence highly predictive of <em>O-</em>glucose, including the transmembrane protein Crumbs and the secreted protein Eyes shut (Eys). Both of these proteins are required for proper eye development and mutations in their human homologs cause a blindness disorder named retinitis pigmentosa. Therefore, we sought to determine whether Rumi plays a role in photoreceptor development. We found that <em>rumi^–/–</em> animals have defects in photoreceptor spacing in which many neighboring rhabdomeres are attached. This phenotype cannot be explained by the loss of <em>O-</em>glucose on Notch or Crumbs. However, <em>eys </em>genetically interacts with <em>rumi</em>, and in <em>rumi^–/–</em> animals at the start of rhabdomere separation, Eys accumulates intracellularly and decreased levels of Eys reach the extracellular space. Overexpressing a mutant Eys transgene which contains no intact <em>O-</em>glucosylation sites also results in intracellular accumulation of Eys, suggesting that loss of <em>O-</em>glucose from Eys is the cause. Additionally, both the intracellular accumulation and the rhabdomere attachment defect grow more severe at higher temperatures, and Eys degrades at higher temperatures in <em>rumi^–/–</em>. In addition, removing one copy of the chaperone <em>Hsc70-3 </em>enhances the <em>rumi^–/–</em> phenotype. Together, these data suggest that loss of <em>O-</em>glucose from Eys causes a defect in its proper folding, which leads to decreased Eys reaching the extracellular space and therefore a failure in full separation of the rhabdomeres.</p>

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Dissertation (PhD)

Year dc:date.available

2015

Author dc:creator

• Haltom, Amanda

Contributors dc:contributor

• Hamed Jafar-Nejad
• William Mattox
• Michael Galko

• Rumi
• glycosylation
• O-glucosylation
• photoreceptor
• Eyes shut
• Eys
• Developmental Biology
• Genetics
• Medicine and Health Sciences

Repository record dc:identifier

https://digitalcommons.library.tmc.edu/utgsbs_dissertations/551

OAI identifier oai:identifier

oai:digitalcommons.library.tmc.edu:utgsbs_dissertations-1590