The conserved microRNA miR-8-3p coordinates the expression of V-ATPase subunits to regulate ecdysone biosynthesis for Drosophila metamorphosis

The steroid hormone ecdysone is the central regulator of insect metamorphosis, during which a growing, immature larva is remodeled, through pupal stages, to a reproductive adult. However, the underlying mechanisms of ecdysone-mediated metamorphosis remain to be fully elucidated. Here, we identified metamorphosis-associated microRNAs (miRNAs) and their potential targets by cross-linking immunoprecipitation coupled with deep sequencing of endogenous Argonaute 1 protein in Drosophila. Interestingly, miR-8-3p targeted five Vha genes encoding distinct subunits of vacuolar H⁺-ATPase (V-ATPase), which has a vital role in the organellar acidification. The expression of ecdysone-responsive miR-8-3p is normally downregulated during Drosophila metamorphosis, but temporary overexpression of miR-8-3p in the whole body at the end of larval development led to defects in metamorphosis and survival, hallmarks of aberrant ecdysone signaling. In addition, miR-8-3p was expressed in the prothoracic gland (PG), which produces and releases ecdysone in response to prothoracicotropic hormone (PTTH). Notably, overexpression of miR-8-3p or knockdown of its Vha targets in the PG resulted in larger than normal, ecdysone-deficient larvae that failed to develop into the pupal stage but could be rescued by ecdysone feeding. Moreover, these animals showed defective PTTH signaling with a concomitant decrease in the expression of ecdysone biosynthetic genes. We also demonstrated that the regulatory network between the conserved miR-8-3p/miR-200 family and V-ATPase was functional in human cells. Consequently, our data indicate that the coordinated regulation of V-ATPase subunits by miR-8-3p is involved in Drosophila metamorphosis by controlling the ecdysone biosynthesis.