MiR-9a targets Serpent to control fat body growth in Drosophila

During metamorphosis, the fat body serves as a central integrator of diverse hormonal and nutritional signals, orchestrating systemic developmental processes. In addition to protein-coding genes, microRNAs (miRNAs), a class of non-coding RNAs, have been implicated in the control of tissue growth. However, the miRNA regulatory network governing fat body growth during metamorphosis remains incompletely characterized. In this study, we show that the miR-9 family (miR-9a, miR-9b, and miR-9c) is highly expressed during the pre-metamorphic stage, where it suppresses fat body growth, and thereby modulates systemic growth during metamorphosis. Mechanistically, miR-9a directly targets the mRNA of GATA transcription factor Serpent (Srp). miR-9a-mediated repression of Srp attenuates global translation in fat body cells and ultimately leads to a developmental impairment. The ability of the miR-9 family to regulate fat body growth could have implications for understanding the functions of miR-9 in metamorphosis.