The full-length transcripts and promoter analysis of intergenic microRNAs in Drosophila melanogaster.

MicroRNA (miRNA) transcription is still not well understood until now. To increase the miRNA abundance, we stimulated miRNA transcription with CuSO(4) and knocked down Drosha enzyme using dsRNA in Drosophila S2 cells. The full length transcripts of bantam, miR-276a and miR-277, the 5'-end of miR-8, the 3'-end of miR-2b and miR-10 were obtained. We also conducted a series of miRNA promoter analysis to prove the reliability of RACE results. Luciferase-reporter assays proved that both bantam and miR-276a promoters successfully drove the expressions of downstream luciferase genes. The promoter activities were impaired by introducing one or multiple mutations at predicted transcription factor binding sites. Chromatin immunoprecipitation analysis confirmed that hypophosphorylated RNA polymerase II and transcription factor c-Myc physically bind at miRNA promoter. RNA interference of transcription factors Mad and Prd led to down-expression of bantam, miR-277 and miR-2b but not miR-276a, whereas RNAi of Dorsal had the opposite effect.