Seogang Hyun1, 3, Jung Hyun Lee1, 3, Hua Jin1, 3, JinWu Nam1, Bumjin Namkoong1, Gina Lee2, Jongkyeong Chung2 and V. Narry Kim1,*
1 School of Biological Sciences and National Creative Research Center, Seoul National University, Seoul, 151-742, Korea
2 Department of Biological Sciences and National Creative Research Center, Korea Advanced Institute of Science and Technology, Daejon, 305-701, Korea
3 These authors contributed equally to this work
How body size is determined is a long-standing question in biology, yet its regulatory mechanisms remain largely unknown. Here, we find that a conserved microRNA miR-8 and its target, USH, regulate body size in Drosophila. miR-8 null flies are smaller in size and defective in insulin signaling in fat body that is the fly counterpart of liver and adipose tissue. Fat body-specific expression and clonal analyses reveal that miR-8 activates PI3K, thereby promoting fat cell growth cell-autonomously and enhancing organismal growth non-cell-autonomously. Comparative analyses identify USH and its human homolog, FOG2, as the targets of fly miR-8 and human miR-200, respectively. USH/FOG2 inhibits PI3K activity, suppressing cell growth in both flies and humans. FOG2 directly binds to p85α, the regulatory subunit of PI3K, and interferes with the formation of a PI3K complex. Our study identifies two novel regulators of insulin signaling, miR-8/miR-200 and USH/FOG2, and suggests their roles in adolescent growth, aging, and cancer.