miR-124 controls Drosophila behavior and is required for neural development.

MicroRNA-124 (miR-124) is an evolutionarily conserved, small, noncoding RNA molecule that participates in the central nervous system (CNS) developmental control of gene expression. In the current study, we found that Drosophila embryos lacking the mir-124 gene did not exhibit detectable defects in axon growth or CNS development. On the other hand, adult mutants showed severe problems in locomotion, flight, and female fertility. Furthermore, the deficits that we observed in the adult stage could be marginally rescued with elav-GAL4 driven expression of miR-124, making elav-GAL4 an excellently simulated driver to induce entopic over-expression of miR-124. Further developmental assessment in the third instar larval neuromuscular junction (NMJ) and dendritic arborization (DA) neurons was performed with miR-124 knock outs, flies over-expressing miR-124, and rescue models. Typically, the absence and over-abundance of a molecular signal exerts opposite effects on development or phenotype. However, we determined that both miR-124 knock-outs and over-expressing flies displayed reduced NMJ 6/7 bouton number and branch length. Similarly, reduced ddaE branching numbers were observed between the two mutant lines. As to ddaF, we found that branching number was not influenced by mir-124 knock out, but was statistically reduced by miR-124 over-expression. While we were not able to determine any causal relationship between behavioral defects and dysplasia of NMJs or DA neurons, there were some accompanying relationships among behavioral phenotypes, NMJ abnormalities, and ddaE/ddaF dendritic branching which were all controlled by miR-124.