Tissue maintenance requires a balance between cell production and cell death. The former is dependent on the activity of stem cells, which in turn are dependent on both extrinsic signals produced by surrounding somatic tissue and intrinsic signals to control their behaviour. Additionally, stem cell activity may be regulated by systemic factors, demonstrating the complexity of stem cell regulation. The ovary of Drosophila melanogaster is a useful model for understanding tissue function as production of a viable egg requires the coordination of two different stem cell populations, the germline stem cells and follicle stem cells. In a screen designed to identify genes which regulate early oogenesis in the Drosophila ovary, we identified the four candidate genes which are described in the three papers found in this thesis. The first paper demonstrates that two RNA associated proteins, Ataxin 2 binding protein 1 and Gemin3, are essential for germline stem cell and follicle cell production in a Sex lethal dependent manner. The second shows that Glucuronyl transferase I, which is important for regulating the synthesis of key components of the extracellular matrix known as proteoglycans, is able to regulate the activity of several different signalling pathways. Finally, the third paper suggests that Defective proboscis extension response 9, a brain expressed gene involved in the behavioural response to alcohol, is important for regulating both follicle cells and germline stem cells at a systemic level. Taken together, these papers highlight the importance of intrinsic, extrinsic and systemic signalling in regulating stem cell function during Drosophila oogenesis.

Doctor of Philosophy / Biochemistry and Molecular Biophysics Interdepartmental Program / Erika R. Geisbrecht / Maintenance of muscle tissue during development is greatly dependent upon the extracellular matrix (ECM) to stabilize, sense, and compensate for changes in the local environment. Muscle has a particularly high demand for a dynamic ECM to allow for contraction and to transmit forces necessary for generating movement. Inefficient contraction and/or detachment can lead to muscle tissue damage and the release of damage-associated molecular patterns (DAMPs), which overactivate immune responses and drive the progression of muscle diseases. Our lab uses the Drosophila muscle attachment site (MAS) as a model to characterize novel genes and mechanisms involved in muscle maintenance. Initially, we were focused on characterizing a novel ECM protein, Fondue (Fon), which had previously been shown as a critical mediator of ECM stability in the hemolymph clot. Mutations in fon and the knockdown of fon through RNAi causes body wall muscles to detach and also creates large gaps between muscle hemisegments. TEM analysis of fon mutant MASs revealed a loss of ECM integrity and important support features including disruption of cuticle and tendon architectures, a lack of muscle-tendon interdigitation, and a loss of electron-dense matrix accumulation. More interestingly, a sensitized background screen revealed a subset of coagulation proteins, fon, Tiggrin, and Lsp1γ, that were necessary for stabilizing muscle attachment sites. Further investigation into gene expression profiles of mutants experiencing hypercontraction-induced muscle tissue stress indicated a clear trend of innate immune activation, suggesting a broader connection between muscle development and innate immunity. In fon mutants with muscle detachment, we also observe abnormal melanin accumulation as melanotic tumors or along the larval MASs, activation of Toll signaling in the fat body, and constitutive expression of the antimicrobial peptide (AMP), drosomycin. In a fon-sensitized background assay, we identified genetic interactions between fon and Toll pathway members, including the NFκB inhibitor/IκB, cactus. At the local level, fon-mediated muscle detachment and muscle hypercontraction mutants, Mhc[superscript]S1 and Brkd[superscript]J29, cause JAK/STAT activation within muscle tissue. We propose a model where muscle tissue stress caused by disruptions to muscle homeostasis progresses muscle disease through overactivation of the innate immune system. Understanding the mechanisms by which these two biological processes are intertwined will advance our knowledge of how tissue stresses can be sensed and elicit multi-tissue responses.

Nuclear receptors constitute a large family of transcription factors that are powerful regulators of animal tissue metabolism, homeostasis, tissue maintenance and development. They are particularly attractive for their ability to respond to the binding of hormones, metabolites, xenobiotics and artificially prepared molecules and transmit the interaction with these small lipophylic molecules to specific regulatory potential. In search for nuclear receptors that are likely to be critical for neural tissues in invertebrates and conserved during the evolution of animals, we have identified a close homologue of vertebrate TLX in a planarian Schmidtea mediterranea. Planaria represent very promising biological model systems for studies on tissue maintenance and regeneration. Planaria are able to resorb their tissues and use them as sources of energy during fasting and they re-build their bodies from neoblasts when food is plentiful. Our search in Schmidtea mediterranea's publicly accessible genome sequencing data indicated that planarian genome contains at least one gene with a high degree of similarity to vertebrate TLX. We cloned full length CDS (coding DNA sequence of cDNA) and characterized the gene functionally. This showed that the planarian and vertebrate NR2E1 are highly similar...

Nuclear receptors constitute a large family of transcription factors that are powerful regulators of animal tissue metabolism, homeostasis, tissue maintenance and development. They are particularly attractive for their ability to respond to the binding of hormones, metabolites, xenobiotics and artificially prepared molecules and transmit the interaction with these small lipophylic molecules to specific regulatory potential. In search for nuclear receptors that are likely to be critical for neural tissues in invertebrates and conserved during the evolution of animals, we have identified a close homologue of vertebrate TLX in a planarian Schmidtea mediterranea. Planaria represent very promising biological model systems for studies on tissue maintenance and regeneration. Planaria are able to resorb their tissues and use them as sources of energy during fasting and they re-build their bodies from neoblasts when food is plentiful. Our search in Schmidtea mediterranea's publicly accessible genome sequencing data indicated that planarian genome contains at least one gene with a high degree of similarity to vertebrate TLX. We cloned full length CDS (coding DNA sequence of cDNA) and characterized the gene functionally. This showed that the planarian and vertebrate NR2E1 are highly similar...