Subtle roles of microRNAs let-7, miR-100 and miR-125 on wing morphogenesis in hemimetabolan metamorphosis

In most insect species, the microRNA (miRNA) let-7 clusters with miR-100 and miR-125 in the same primary transcript. The three miRNAs are involved in developmental timing in the nematode Caenorhabditis elegans and in the fly Drosophila melanogaster. In the cockroach Blattella germanica, the expression of these miRNAs increases dramatically in the wing pads around the molting peak of 20-hydroxyecdysone (20E) of the last instar nymph. When let-7 and miR-100 were depleted with specific anti-miRNAs in this instar, the resulting adults showed wings reduced in size (when miR-100 was depleted) or with malformed vein patterning (when let-7 and miR-100 were depleted). Depletion of miR-125 induced no apparent effects. Interestingly, the wing phenotype obtained after depleting let-7 and miR-100 is similar to that resulting from silencing the expression of Broad-Complex (BR-C) transcription factors with RNA interference (hindwings with a short CuP vein, with the vein/inter-vein pattern disorganized in the anterior part and showing anomalous bifurcations of the A-veins in the posterior part).