Non-cell autonomous <i>miR-9a</i> modulates female receptivity by constraining sensory neuron growth in <i>Drosophila melanogaster</i>

Female Drosophila melanogaster undergo a dynamic transition in sexual behavior, shifting from high receptivity to active rejection of courting males. While this post-mating switch is well characterized, the molecular mechanisms governing this plasticity remain incompletely understood. Here, we identify the conserved microRNA, miR-9a, as a critical regulator of this process. We show that miR-9a mutant females exhibit a premature rejection phenotype, mimicking the behavior of mated females, which is correlated with an aberrant overgrowth of adult body wall sensory neurons. We demonstrate that this neuronal phenotype is governed by a dual regulatory system. First, in a non-cell autonomous mechanism, miR-9a expression in the epidermis is required to constrain sensory neuron dendrite growth, indicating that an epithelial-derived signal patterns the underlying neuron. Second, miR-9a interacts genetically with the transcription factor senseless (sens) and the novel RNA-binding protein bruno2 (bru2). Reducing the dosage of either sens or bru2 rescues both the neuronal and behavioral defects of miR-9a mutants. Our findings reveal an integrated, inter-tissue signaling axis where epithelial miR-9a orchestrates a non-cell autonomous cue that modulates a cell-intrinsic network to ensure the precise development of sensory neurons, thereby calibrating behavioral responses critical for reproductive success.