A Genetic Screen for Localized mRNAs and Investigation of a Selected Positive Hit in Drosophila Class IV da Neurons

Abstract

mRNA localization is important for polarized cells in that it spatially restricts gene expression and allows for rapid response to local stimuli through on-site regulation of translation. This phenomenon is well-characterized in a variety of organisms and cell types, but its role during neuronal dendritic development is not yet fully understood. Further research into this area could have implications for a variety of neurodevelopmental and psychiatric disorders associated with dendritic abnormalities, such as autism and schizophrenia. Here, we conducted a screen to identify mRNA transcripts that localize to the processes of class IV dendritic arborization (da) neurons in Drosophila melanogaster third instar larvae. These are sensory neurons with highly elaborated dendritic arbors reminiscent of some types of cortical neurons in mammals. The screen was conducted by randomly tagging endogenous mRNA transcripts in vivo with MS2 RNA stem-loops, which bind MS2 coat protein-red fluorescent protein (MCP-RFP fusion protein) to enable subsequent visualization of transcript localization by fluorescence confocal microscopy. Twenty-seven percent of the lines screened exhibited mRNA localization to axons and dendrites. Two of these genes were identified via TAIL-PCR as Sir2 and Mrp4. The role of Sir2 in class IV da neurons was investigated by targeted knockdown and overexpression. The author found that Sir2 overexpression results in a more forceful response to noxious stimuli and in defective foraging locomotion relative to control. Ultimately, these data lay the groundwork for future studies examining the role of mRNA localization in the regulation of gene function in neurons.