Core B Project Leader: Van Vactor, David L. Project Summary / Abstract This program will rely on an innovative and growing resource of transgenic tools for in vivo analysis of microRNA (miR) function and activity. We have produced a partial collection of transgenic miR-SPonge (miR- SP) strains that are designed expressly to address the challenge of defining the cellular and developmental specificity of miR function within complex neural circuits and tissues with many constituent cell types. Preliminary data show that these tools are effective, however, accumulated data also show that many new sponge strains are needed to make this resource more comprehensive. Recent availability of many miR deletion alleles and UAS-miR mimic strains provides an important complement to our miR-SP resource, however, many new and selective null mutations are needed for a thorough and specific analysis of miR functions identified in our unpublished screens. In addition, informatics and expression analysis identifies promising target gene candidates that may define underlying downstream mechanisms for miRs that we find required in multiple neural circuits, however, new sensor reagents will be required to validate these and study their regulation in vivo. Core B will make and quality control these three types of reagents before they are distributed to our collaborators and the community by Core A.