Genetic screen to test microRNA function in peripheral glia morphology

Glial cells perform many functions in the nervous system, including maintaining the blood-brain/nerve barriers and structurally supporting axons. While their functions are well-characterized, the complex molecular mechanisms important for their development are less known. Here, we investigated whether microRNA-mediated post-transcriptional regulation is involved during glial development, ensheathment and blood-nerve-barrier formation in Drosophila . In this study, we systematically knocked down 120 different microRNAs by competitive inhibition using microRNA-sponges and analyzed peripheral glial morphology. Knockdown of miRNA-125 in the blood-nerve barrier-forming glia (subperineurial glia) resulted in the most penetrant morphological defects. Since microRNA-125 is co-transcribed with miRNAs-let7 and −100 in a genetic cluster, our further verification for subperineurial glia function included miRNA-125 plus all other members of this cluster. However, the loss of each individual gene and the entire cluster did not lead to any morphological defects in the subperineurial glia. To test the efficiency of the microRNA sponge approach in subperineurial glia, we expressed a sponge targeting a microRNA established to be vital for blood-brain barrier formation (microRNA-285) and found no defects in brain lobes and peripheral nerves. Given that a scrambled-sponge control also generated morphological defects, this suggests that using miRNA sponge lines may not be an effective approach to study miRNA function in Drosophila peripheral glia.