miR-34 regulates larval growth and wing morphogenesis by directly modulating ecdysone signalling and cuticle protein in Bombyx mori.

microRNAs (miRNA) are small non-coding RNAs that modulate the myriad biological activities by targeting genes, and many studies showed that miRNAs played a pivotal role in insect development. Here, we find that Bm-miRNA (miR-34) controls larval growth and wing morphology by targeting BmE74 and BmCPG4. Overexpression of miR-34 in the whole body caused a smaller body size, partially displays deformed wings and venation defects in adults. Ablation of miR-34 by transgenic CRISPR/Cas9 technology resulted in a severe developmental delay during the larval stage. Moreover, we confirmed that miR-34 directly targeted BmE74 and BmCPG4 by using a dual luciferase reporter assay in HEK293T cells. Remarkably, loss-of-function of BmCPG4 caused wing defects, which was similar to the phenotype of miR-34 overexpression in animals. In addition, our analysis revealed that ecdysone strongly inhibited miR-34 expression in vivo. Taken together, our study identifies miR-34 as a modulator that regulates larval growth and wing morphogenesis by directly modulating ecdysone signalling and cuticle protein in Bombyx mori.