Project description:Background: The expression of microRNAs (miRNAs) is primarily regulated during their transcription. However, the transcriptional regulation of miRNA genes has not been studied extensively owing to the lack of sufficient information about the promoters and transcription start sites of most miRNAs. Results: In this study, we identified the transcription start sites of human primary miRNAs (pri-miRNAs) using DROSHA knockout cells. DROSHA knockout resulted in increased accumulation of pri-miRNAs and facilitated the precise mapping of their 5′ end nucleotides using the rapid amplification of cDNA ends (RACE) technique. By analyzing the promoter region encompassing the transcription start sites of miRNAs, we found that the unrelated miRNAs in their sequences have many common elements in their promoters for binding the same transcription factors. Moreover, by analyzing intronic miRNAs, we also obtained comprehensive evidence that miRNA-harboring introns are spliced more slowly than other introns. Conclusions: The precisely mapped transcription start sites of pri-miRNAs, and the list of transcription factors for pri-miRNAs regulation, will be valuable resources for future studies to understand the regulatory network of miRNAs.
Project description:MicroRNAs (miRNA) are short non-coding RNAs widely implicated in development, gene regulation, and disease progression. Most miRNAs utilize the RNase III enzymes Drosha and Dicer for biogenesis in animals. One notable exception is the RNA polymerase II transcription start sites (TSS) miRNAs whose biogenesis requires Dicer but not Drosha. The functional importance of the TSS-miRNA biogenesis pathway has remained uncertain due to their unelucidated targetomes. To better understand the function of TSS-miRNAs, we applied a modified Crosslinking, Ligation, and Sequencing of Hybrids on Argonaute (Ago-qCLASH) to identify the targets for TSS-miRNAs in HCT116 colorectal cancer cells with or without Drosha knockout (KO). We observed that miR-320a hybrids dominate in TSS-miRNA hybrids identified by Ago-qCLASH. Targets for miR-320a are enriched in the eIF2 signaling pathway, a downstream component of the unfolded protein response. Consistently, in miR-320a mimic- and inhibitor- transfected cells, differentially expressed genes are enriched in the eIF2 signaling pathway. Within the Ago-qCLASH data, we identified the endoplasmic reticulum (ER) chaperone Calnexin as a direct miR-320a target, thus connecting miR-320a to the unfolded protein response. During ER stress, but not amino acid deprivation, miR-320a up-regulates ATF4, a critical transcription factor for resolving ER stress. Our study helps to elucidate the targetome of the TSS-miRNAs in colorectal cancer cells and establishes miR-320a as a regulator of unfolded protein response.
Project description:Mapping of active transcription start sites using PRO-cap in whole-embryo at 3-4h and 6-8h AEL. Two biological replicates were performed at each time point.