miRNome analyses reveal K box miRNAs function in mediating class specific dendrite morphogenesis. Srividya Chandramouli Iyer¹, Myurajan Rubaharan¹, Ramakrishna Meduri¹, Shruthi Sivakumar¹, Francis Aguisanda¹, Suhas Gondi¹, Atit Patel¹, Eswar P R Iyer¹, Diane Bortolamiol-Becet², Eric C. Lai², Daniel N. Cox¹. 1) School of Systems Biology, Krasnow Inst. Adv. Study, George Mason University, Fairfax, VA; 2) Sloan-Kettering Institute, Dept. Developmental Biology, New York, NY.

   While microRNAs (miRNAs) have recently emerged as critical post-transcriptional modulators of gene expression in neuronal development, very little is known regarding the roles of miRNA-mediated regulation in the specification of cell-type specific dendritic complexity. The dendritic arborization (da) sensory neurons of the Drosophila PNS offer an excellent model system for elucidating the molecular mechanisms governing class specific dendrite morphogenesis and for exploring miRNA-mediated control of this process. To facilitate functional analyses of miRNA regulation in da neurons, we have conducted whole-genome miRNA expression profiling as well as mRNA expression profiling of three distinct classes of da neurons, thereby generating a comprehensive molecular gene expression signature within these individual subclasses of da neurons. To further validate the role of the significantly expressed miRNAs in directing dendritic architecture, we conducted a genome-wide UAS-miRNA phenotypic screen using live-image confocal microscopy to directly assess the effect of over/mis-expression of individual and clustered miRNAs on neurons of varying dendritic complexity. Through this approach, we have identified numerous miRNAs with previously unknown functions in dendritic development, including the K box family of miRNAs. Both gain-of-function and loss-of-function analyses, via miRNA sponge transgenes, reveal that K box miRNAs repress the expression of genes required to restrict dendritic branching complexity in da neuron subclasses. Moreover, we have implemented an integrative bioinformatic analysis approach involving inverse correlation between miRNA and mRNA expression profiling data in combination with existing target prediction algorithms to identify putative target of miRNAs in regulating da neuron dendritic development.