MicroRNA-dependent regulation of metamorphosis and identification of microRNAs in the red flour beetle, Tribolium castaneum

To date, although some microRNAs (miRNAs) have been discovered in the holometabolism insect Tribolium castaneum, large numbers of miRNAs still require investigation. Knocking down Dicer-1 (Dcr-1) and Argonaute-1 (Ago-1) in late larvae impaired miRNA synthesis, affected the juvenile hormone pathway by up-regulating Methoprene-tolerant (Met) and Krüppel-homolog1 (Kr-h1) transcript levels, and resulted in a series of defects in T. castaneum development and metamorphosis. Thus, high-throughput Illumina/Solexa sequencing was performed with a mixed sample of eight key developmental stages of T. castaneum. In total, 1154 unique miRNAs were discovered containing 274 conserved miRNAs belong to 68 miRNA families, 108 known candidate miRNAs and 772 novel miRNAs. Genome locus analysis showed that miRNA clusters are more abundant in T. castaneum than other species. The results indicated that RNAi of Dcr-1 and Ago-1 in T. castaneum resulted in miRNA-induced metamorphosis defects. Furthermore, large numbers of novel miRNAs were discovered in T. castaneum and localized to T. castaneum genome loci.