Precise temporal and spatial regulation of gene expression is essential to many aspects of nervous system development, function and plasticity. Although much has been learned about transcriptional machinery that regulates genome deployment important for a variety of behaviors, such mechanisms alone are not sufficient to provide all of the regulatory strategies needed, particularly within the dynamic and complex cellular architecture of neurons and the neural circuits that they compose. It has become evident in recent years that the nervous system also relies on post-transcriptional mechanisms that offer both spatial and temporal control that can equip neurons for executing rapid and local changes in protein expression. Among several classes of mechanism, non-coding RNAs have emerged as a rich potential source of regulatory mechanism in the central nervous system. In particular, microRNAs (miRs) provide sequence-specific control over target mRNA translation and stability that can tune the levels of downstream proteins quite precisely thus improving the stability and robustness of molecular networks. Although miRs were recently discovered, we have already learned a great deal about the core biosynthetic and processing pathways that produce them, and the protein complexes that pair them with target transcripts. Moreover, expression profiling with increasingly sensitive methods has shown us that miR expression in the nervous system, in specific neuronal populations, and in synaptic compartments, is highly complex and dynamic. Finally, miR loci have also surfaced in genome-wide association studies of several neurological and psychiatric disorders, such as autism and schizophrenia, suggesting that miR dysregulation may contribute to diseases with multi-factorial genetic mechanisms.
These and other recent observations suggest that many miRs play important roles in shaping the development, function and plasticity of neural circuits. However, comprehensive analysis of miR function within the intact nervous system has been very challenging, leaving open key questions such as: How complex is the miR regulatory landscape for neural circuits that mediate essential behaviors? Are these miRs acting mainly during neural development or are they reused to manage ongoing neural circuit activity and adaptation to stimuli? To what extent are miR mechanisms utilized in many parts of the brain, or do they regulate distinct sets of target genes in different cell types and/or developmental stages? In order to address these questions, we have assembled a team of accomplished investigators prepared to work in unison using multiple robust behavioral and cellular assays as part of an integrated program. Our team includes Drs. David Van Vactor (Harvard Medical School), Leslie Griffith (Brandeis University), Ronald Davis (Scripps Institute), and Dennis Wall (Stanford University), who will each assume responsibility for key components of this joint program. We will use Drosophila as a model organism that offers many sophisticated genetic tools complementary to the innovative tools we will develop. Drosophila has proven to be particularly effective for identification and dissection of cellular and molecular mechanisms underlying well conserved behaviors. This model is also accessible to a full range of techniques for determining the detailed cellular and physiological phenotypes of mutants in specific pathways, thus offering a system ideal for mapping out miR functions on a comprehensive scale followed by mechanistic dissection that will effectively leverage a wealth of tools and knowledge. Together, we will (i) build and apply new genetic tools, (ii) apply these tools to identify miRs required in multiple neural circuits, (iii) discover the mechanisms and regulatory strategies for miR function in each context, and then (iv) compare each model to distinguish general and specific strategies and examine their conservation. This will be the first analysis of its kind in the nervous system.