Program in Neuroscience

About

MicroRNAs are a recently discovered class of small RNAs that regulate the expression of target genes. Some microRNAs have been highly conserved across millions of years of animal evolution, suggesting that their regulation of particular target genes plays an essential role in animal development and/or function. Yet, for many of these conserved microRNAs, their relevant gene targets as well as their developmental function are not known. We use the fruitfly Drosophila melanogaster to identify the molecular and cellular roles that evolutionarily conserved microRNAs play in the formation and function of complex organisms.

Our current interest is the function of a single gene, let-7-Complex, which encodes three different and highly conserved microRNAs (mir-100, let-7 and miR-125). Flies in which the let-7-Complex gene has been disrupted proceed through development and emerge as normal looking adults. However, these animals are defective in many adult behaviors (flight, locomotion, fertility, egg-laying, etc). We have found that a let-7-Complex transcriptional reporter is expressed throughout the nervous system during metamorphosis (see Figure 1). Therefore, we hypothesize that let-7-Complex microRNAs function in the profound remodeling of the nervous system that occurs during the larval to adult transition. We are taking the following steps to further characterize the function of the let-7-Complex gene.

1. Analyze let-7-Complex mutant phenotypes. We are currently applying developmental neurobiology approaches to identify the particular neurons in which let-7-Complex microRNAs are expressed as well as characterize the cellular defects caused by their removal. We ultimately hope to connect particular let-7-Complex neuronal circuits to the behaviors affected but their removal.

2. Characterize let-7-Complex target genes. Using an assay (see Figure 2) that we developed, we identified three target genes that let-7-Complex microRNAs regulate. We are currently studying where, when and why these three target genes need to be regulated by let-7-Complex microRNAs.

3. Identify genes that regulate let-7-Complex expression and activity. In the eye assay presented in Figure 2, eye color provides a very clear indicator of let-7-Complex activity. This assay can therefore be used to identify genes that regulate let-7-Complex, which can range from transcription factors that specifically activate let-7-Complexexpression to microRNA co-factors that regulate microRNA function more generally. We are conducting large-scale genetic screens to identify such genes.