For more than a century, Drosophila melanogaster (fruit flies) have been an invaluable and versatile tool to further our understanding of cell signaling and survival mechanisms. To this day, they continue to shed light on the endogenous pathways that cancer cells can hijack in order to proliferate, metastasize, and recur following remission. The molecular conservation of these pathways invites parallels between the germline stem cells in D. melanogaster and the cancer stem-like cells in human carcinoma. In the same way that a tumor can relapse following a period of dormancy, Drosophila germline stem cells are capable of repopulating their niche after insult from Ionizing Radiation (IR). Utilizing this powerful model, we have conducted a small molecule drug screen of 512 compounds that we have narrowed down to eight candidate drugs that appear to increase cell death in Drosophila germline stem cells. Having already characterized the wild type Drosophila germline stem cell response to IR-induced DNA damage, we  probed how drug treatment and gene knockdown affected the germline stem cells' ability to recover from insult. Previous work in the Ruohola-Baker Lab has demonstrated the critical importance of the mechanistic target of rapamycin (mTOR) and the Tie receptor pathways in regulating regeneration after insult in the Drosophila germline. The Tuberous Sclerosis Complex (TSC), a heterodimer comprised of Tsc1 and Tsc2, is a known negative regulator of mTOR. Additionally, the Tie receptor is central to anti-apoptotic signal transduction in the Drosophila ovary. We have screened four candidate drugs to see if they effectively increase stem cell death in Tsc1-knockdown and Tie-null flies, in order to ascertain whether our drugs affect stem cell survival mechanisms through mTOR and/or Tie signaling. Our findings may shed light onto how to mitigate the quiescent threat of tumor relapse.

It is not fully known what controls signal preference in branched signal transduction pathways. One hypothesis is that the configuration and orientation of receptors determines signal preference. We are investigating this hypothesis in the context of the Tie2 receptor pathway which has downstream signaling involved in cell survival via Akt, migration via Dok-R, and sprouting via FAK, among other branches. We are using computer designed protein tools, short-armed claw trimers and nanocages, conjugated to F domains of the canonical Tie2 ligand angiopoietin 1 in our investigation. We have shown that short-armed claw trimers with three conjugated F domains do not yield increased phosphorylation of Akt, suggesting that more than three receptors must cluster together for signal activation. The nanocages are multivalent, for they have multiple F domains conjugated to them. We have different valency nanocages with different percentages of F domain conjugation. We are using these different valency nanocages to investigate which valency is optimal for receptor activation. We have shown that higher valency nanocages yield increased phosphorylation of Akt. We predict that higher valency nanocages cluster more Tie2 receptors together in a specific conformation. Thus, we show a positive correlation between Tie2 clustering and the phosphorylation of Akt due to Tie2 activation. Now we will investigate combination conjugations of F domain and integrin binders to the nanocages as well as other branches of the Tie2 pathway: Dok-R corresponding to wound healing ability and FAK corresponding to tube formation ability. This work has potential to help generate therapeutic compounds for wound healing.

Cancer stem cells are thought to play a role in relapses and metastasis in numerous cancers. The inability of traditional cancer therapies, such as chemotherapy, to eradicate these cancer stem cells prompted a search for small molecules that induced apoptosis in cancer stem cells. Drosophila germline stem cells can be used as a model system to emulate cancer stem cells. Upon irradiation, Drosophila germline stem cells are able to survive apoptosis through a molecular signal released by the apoptotic daughter cells via the TIE receptor. We have conducted an in vivo drug screen of 512 compounds in Drosophila melanogaster to find drugs that would disrupt this protective mechanism and induce apoptosis. In particular, Camptothecin, NSC 125197, and NSC 127458 were effective in killing germline stem cells. To test the effect of the small molecules we fed female flies the compound for 3 days, dissected and fixed the ovaries and stained for an apoptosis marker, activated caspase, and the GSC marker, adducin. We quantified the effect of the drug by analyzing the number of germline stem cells and caspase signaling on a confocal microscope. Through this system we aim to find potentially new, and more powerful anti-cancer drugs that can affect cancer stem cells. Future directions include attempting to understand the mechanism of action of these apoptotic compounds in hopes that they might be useful in the fight against cancer stem cells.

Understanding how extracellular environments facilitate the differentiation of stem cells holds much promise for the field of regenerative medicine. Non-muscle myosin II (NMII) plays an important role in cell morphology and also generates forces that alfter biochemical signalling. It has been shown that the activity of NMII controls mechanoreceptors and integrins facilitating stem cell fate. More specifically, mechanotransduction of transcriptional coactivators YAP/TAZ facilitate differentiation of mesenchymal stem cells (MSCs). YAP and TAZ are responsible for upregulating genes associated with stem cell differentiation. Under external stresses mesenchymal stem cells differentiate into osteocytes whereas softer extracellular conditions favor the differentiation into adipocytes through mechanotransduction of YAP and TAZ.To further explore the role of physical forces determining the fate of stem cells, we used a computationally designed self-assembling homo-polymer called 2E01, generated by the Institute for Protein Design (IPD). Mechanical stress and the physical activity of NMII can be mimicked by controlled expression of the length of the E01 protein fiber. We introduced the 2E01 gene under a doxycycline-inducible promoter into the AAVS1 "safe harbor" locus of the induced pluripotent stem cells (iPSC). Expression of the E01 fiber in iPSCs lead to changes in colony morphology and subsequent differentiation of those cells, suggesting that changing the morphology of cells can change their fate. I want to see if I can use the 2E01 fiber as a tool to accelerate differentiation from IPSCs to neuronal cells and cardiomyocytes. In addition, we expressed 2E01 in mesenchymal stem cells, a cell type currently used in lab, and observed the activity of YAP and TAZ as an indicator of differentiation. Utilization of the 2E01 fiber could be benefical to the field of regenerative medicine as a directed agent of physical manipulation towards desired stem cell fate.