Research Projects

Drosophila Malpighian tubules (MTs) are also known as fly kidneys, due to their functional and developmental similarities to mammalian kidneys. These tubules evade ecdysone-induced programmed cell death during metamorphosis and are carried over in the adult, in spite of the expression of active caspases. We show that Caspase- 3 homolog, Drice, in Drosophila is essential for precise architecture of the MTs. Caspase-3 absence in results in formation of fluid filled cysts and increased uric acid deposition and, which resemble human polycystic kidney phenotype. Drice, being a caspase, executes program cell death, nonetheless has been associated with non-lethal cellular functions, albeit requiring sub-lethal levels of caspase activity, not enough to trigger apoptosis. In this project, we will understand the non-apoptotic role of caspases in MTs development. The polycystic phenotype of MTs in Drice mutants closely resembles human polycystic kidney disease (PKD) caused by mutation in Pkd1, known as Autosomal Dominant Polycystic Kidney Disease. In mouse models, it has been shown that Rho GTPase signalling in association with Hippo signalling effector YAP, and its target c-Myc promotes proliferation and kidney dilation. Downregulation of Rho in Pkd1 mutant kidney cells suppress cystogenesis. These observations are corroborated in our recent report on Drosophila showing Rho GTPase to be an important regulator of Drice-mediated morphogenesis of Malpighian tubules (Ojha and Tapadia, 2021). Ongoing work has now identified that downregulation of YAP homolog in Drosophila, Yorkie, also rescues the polycystic phenotype (unpublished data). Based on these observations, we hypothesise that cross-talk between RhoA, hippo and c-Myc could be important for proper development of MTs and that Drice could be an important regulator in orchestrating these events. We will understand the regulatory layers that lead to caspase activation for non-lethal function, without triggering apoptosis and if Drice is mediating crosstalk between Rho, hippo and c-Myc. Identifying substrates of Drice and comparing it with salivary glands, which are histolysed, will help in elucidating rationale for non-lethal activity of caspases. Genetic interaction studies will help in establishing how network of signalling pathways are coupled for kidney development, and provide a comprehensive tool to study kidney diseases. Polycystic kidney disease is characterized by excess of fluid secretion and uric acid deposition, which are strong predictors of biochemical and metabolic abnormality. Thus the role of these factors in uric deposition and fluid generation will be studied. The results obtained can allow us to superimpose fly kidney development and function to mammalian kidneys, and will help in generating a reliable model to study kidney diseases. We will draw parallels to tumour cells escaping apoptosis, and if Drice substrates have a role in the invasive property of tumour cells.