Independent transcription of miR-281 in the intron of ODA in Drosophila melanogaster.

MicroRNAs (miRNAs) have recently received much interest for their role in post-transcriptional regulation. However, the study of miRNA transcription lags behind that of gene cloning and functional analysis. The MiR-281 in Drosophila melanogaster is located in the first intron of isoform RA of the ornithine decarboxylase antizyme (ODA) gene. ODA has three isoforms because of alternative transcription start sites (TSSs). Expression profile analysis indicated that miR-281 is not co-expressed with any ODA isoform. We amplified the primary transcripts of miR-281 using the RACE technique. The pri-miRNA is 2149bp with a poly (A) tail and a canonical polyadenylation signal (AATAAA). Chromatin immunoprecipitation analysis confirmed the binding of hypophosphorylated Pol-II and the transcription factor Myc at the core miR-281 promoter region. The abundance of miR-281 does not correlate, either positively or negatively, with the expression of any ODA isoform, indicating that ODA has little influence on the transcription of miR-281.