Title

Interaction of Hippo pathway and Dronc to regulate organ size in Drosophila melanogaster

Date of Award

2014

Degree Name

Ph.D. in Biology

Department

Department of Biology

Advisor/Chair

Advisor: Kango-Singh Madhuri

Abstract

Hippo pathway is an organ size regulating pathway that has implications in organogenesis, cell competition, compensatory proliferation and regeneration. Recent studies have identified the role of impaired Hippo pathway in cancer and Alzheimer's. Down-regulation of pathway causes over-proliferation by up-regulation of target gene expression that promotes proliferation and prevents apoptosis. On the contrary, pathway hyper-activation causes cell death by up-regulating a pro-apoptotic protein Hid and without affecting the expression of Diap-1, a target protein that prevents apoptosis. However, down-regulation of Hid fails to significantly rescue Hippo pathway mediated cell death. This suggested that Hippo pathway mediated cell death is complex and may involve some other protein that interacts with Hippo pathway. The aim of my work was to thus identify the gene that interacts with Hippo pathway to cause cell death. To atttain this goal we tested for genetic interaction between known cell death regulators and the Hippo pathway to determine if loss of these cell death regulators could modulate Hippo pathway mediated cell death phenotype. Our experiments led to the identification of the apical caspase Dronc as a strong modulator of Hippo mediated cell death. Using genetic and biochemical techniques we further confirmed that Dronc is required by the Hippo pathway to regulate cell death and in addition dronc is the first target gene that is negatively regulated by the Hippo pathway. Subsequent analysis of the Hippo -Dronc interaction identified the requirement of p53 in the regulation of dronc expression. Loss of function analysis of dronc mutant clones led to the identification that dronc mutants show ectopic proliferation. Further analysis of the intrinsic cell death components of the pathway (Reaper, Hid, Grim, Dronc, Dark and Drice) showed that caspases affects cyclin regulation for tissue homeostasis. A side project focused on placing Scribble, an apico-basal polarity determining protein in the Hippo pathway hierarchy. Scribble loss from cells has been shown to cause neoplasia. We identified Scribble acts downstream of Fat and upstream of Dachs to control growth by regulating Warts activity.

Keywords

Drosophila melanogaster Genetics, Genetic regulation, Cell death, Biology, Hippo Pathway, DRONC, Scribble, Drosophila melanogaster, Organ Size

Rights Statement

Copyright 2014, author

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