Understanding Neuronal Functions of Drosophila Chaperones

Ancy VS and Sandeep Raut

(Collaborator: Chandan Sahi, Chaperone Science Lab)

Protein homeostasis (proteostasis) is essential for maintaining the functionality of the proteome in neuronal cells. The disruption of proteostasis leads to aberrantly folded proteins that typically lose their functions. The accumulation of misfolded and aggregated protein is also cytotoxic and has been implicated in the pathogenesis of many neurodegenerative diseases. Moreover, several recent studies have also shown altered synaptic signalling leading to aberrant synaptic development and function. In this broad context, a role for Chaperones (also called, heat shock proteins) in the regulation of synaptic plasticity and multiple aspects of synapse regulation is becoming an issue of considerable interest. The fact that many of the chaperones are expressed in neurons underlies its importance in maintaining neuronal homeostasis and function. In order to gain functional relevance in vivo, we have performed an RNAi-mediated small scale targeted genetic screen on all Drosophila chaperone proteins identified using bioinformatics analysis We have undertaken studies that would help us understand cellular and molecular mechanisms and pathways underlying synaptic development and functions mediated by some of the Chaperones identified in this screen.

Understanding Regulation of Synaptic Differentiation by BAR-domain Family Proteins

Bhagaban Mallik, Shikha Kushwaha, Athira Nataraj and Manish Kumar Dwivedi

Neuromorphogenesis involve dynamic changes in the neuronal membrane as well as structural changes in the underlying neuronal cytoskeleton. Several studies have implicated a role of Bin-Amphiphysin-Rvs (BAR) domain containing proteins with membrane deforming properties in shaping up neuronal morphology. In order to gain deeper insights specifically in the context of neuronal function and development, we carried out a small scale RNAi-mediated genetic screen of twenty five Drosophila BAR domain proteins. One of the proteins we identified in this screen is Islet Cell Autoantigen 69 KDa (dICA69). dICA69 alters Spectrin cytoskeleton and affects synaptic targeting/retention of iGluR clusters. Interestingly, the stoichiometry of endogenous ICA69 is essential for normal synaptic iGluR targeting/retention. Moreover, dPick1 and dRab2 phenocopy dICA69 mutation. Our studies suggest that Rab2, genetically functions upstream of ICA69 and regulates its endogenous levels.

Understanding Regulation of CME-dependent Synaptic Signaling

Bhagaban Mallik, Ancy VS and Manish Kumar Dwivedi

Defects in clathrin-mediated endocytic pathway (CME) leads to NMJ morphological defects in Drosophila. While the morphological defects tightly correlate with elevated phospho-MAD in motor neuron nuclei and at the presynapses, the underlying signalling mechanisms leading to these defects are not fully understood. We have identified E3-ubiquitin ligase dependent signalling getting deregulated in the CME pathway mutants. We are attempting to understand how E3-Ubiquitin system regulates canonical p-MAD and non canonical MAP Kinase signalling in Drosophila neurons.