Date of Award

2014

Degree Name

Biomedical Sciences

College

Joan C. Edwards School of Medicine

Type of Degree

Ph.D.

Document Type

Dissertation

First Advisor

Simon Collier

Second Advisor

Beverly Delidow

Third Advisor

Richard Egleton

Fourth Advisor

Todd Green

Fifth Advisor

Guo-Zhang Zhu

Abstract

A critical step in cellular signaling through transmembrane receptors is the down-regulation of activated receptors through the multivesicular body (MVB) pathway to the lysosome. MVB generation is mediated by the highly conserved ESCRT (0, I, II, and III) protein complexes. Though the ESCRT-III complex provides the core function of the ESCRT machinery, it is the least characterized of the ESCRT complexes. The Chmp1 protein is an ESCRT-III component and a putative tumor suppressor that has been linked to pancreatic and renal cancers in humans. However, published data on Chmp1 activity are conflicting and its role during tissue development is not well defined.

Drosophila melanogaster (the common fruit fly) provides a powerful model system for investigating the function of genes involved in human development and disease. In this study, knockdown and over-expression techniques were used to investigate the function of Chmp1 in Drosophila. RNAi was used to reduce Chmp1 expression, and transgenic fly lines that allow for expression of either wild-type or epitope tagged Chmp1 were used to investigate over-expression, as well as the subcellular localization of Chmp1.

Knockdown of Chmp1 expression using RNAi was lethal in the fly, suggesting that Chmp1 is an essential gene for Drosophila development. In the wing, loss of Chmp1 activity caused a cell fate change from intervein to vein, which was likely a result of de-regulation of the Drosophila Epidermal Growth Factor Receptor (DER) pathway. Genetic interactions between Chmp1 and regulators of DER signaling suggest that Chmp1 negatively regulates DER signaling. Furthermore, Chmp1 knockdown also decreased Blistered expression, which is repressed by DER signaling.

Over-expression of Chmp1 had mild phenotypic effects, suggesting that dosage of Chmp1 is not critical for cellular function. Some of the epitope tagged Chmp1 protein was detected at the late endosome in Drosophila embryonic epithelial cells. This is consistent with Chmp1 functioning as an ESCRT-III component during MVB formation. Therefore, Drosophila Chmp1 may negatively regulate DER signaling through its role in MVB formation as an ESCRT-III component.

Subject(s)

Pancreas - Tumors.

Tumor suppressor proteins.