Project description:The in vitro high-throughput human pri-miRNA processing assays were conducted to check whether mismatches and wobble base pairs in the upper stem of pri-miRNAs affects the DROSHA cleavage.
Project description:MicroRNAs (miRNAs) are small RNAs that regulate gene expression. miRNAs are produced from primary miRNAs (pri-miRNAs), the cleavage of which is catalyzed by the Microprocessor complex. Microprocessor therefore plays a key role in determining the efficiency and precision of miRNA production, and thus the function of the final miRNA product. In this study, we utilized high-throughput sequencing-integrated enzymology with purified Microprocessor proteins and randomized pri-miRNA sequences to investigate the catalytic mechanism of Microprocessor. We identified multiple mismatches and wobble base pairs in the upper stem of pri-miRNAs, which determine the efficiency and accuracy of pri-miRNA processing. The existence of these RNA elements helps to explain the alternative cleavage mechanism of Microprocessor, which occurs for some human pri-miRNAs. We also showed that these RNA elements are targets of RNA-editing or single nucleotide polymorphisms (SNPs) for regulating miRNA biogenesis. These findings considerably improve our understanding of pri-miRNA processing mechanisms, and provide a foundation for interpreting differential miRNA expression by several mechanisms, such as RNA modifications and SNPs.
Project description:To investigate the precise processing mechanism of pri-miRNA, we prepared 38,880 pri-miRNA variants which contain unique barcode sequences (Fang and Bartel, Mol Cell, 60: 131) and performed high-throughput processing experiments.
Project description:We asked whether the human drosha protein, an RNase III homolog known to process microRNAs (miRNAs), might also be a small nuclear RNA (snRNA) 3' processing factor. Using retroviral siRNA silencing constructs, we stably knocked down drosha protein to nearly undetectable levels. Knockdown cells exhibited reduced growth rates and viability compared to controls, but no accumulation of unprocessed U2 snRNA precursors. In fungi, RNase III homologs process rRNA precursors and certain mRNAs. Although rRNA processing appears to be normal in the drosha knockdown cells, expression microarray analysis revealed misregulation of several mRNAs involved in cell growth and proliferation. Curiously, drosha knockdown appeared to downregulate the predicted mRNA targets of several miRNAs Keywords: siRNA knockdown
Project description:DROSHA serves as a gatekeeper of the microRNA (miRNA) pathway by processing primary transcripts (pri-miRNAs). While the functions of structured domains of DROSHA have been well-documented, the contribution of N-terminal proline-rich disordered domain (PRD) remains elusive. Here we show that the PRD promotes the processing of miRNA hairpins located within introns. We identified a DROSHA isoform (p140) lacking the PRD, which is produced by proteolytic cleavage. Small RNA sequencing revealed that p140 is significantly impaired in the maturation of intronic miRNAs. Consistently, our minigene constructs demonstrated that PRD enhances the processing of intronic hairpins, but not those in exons. Splice site mutations did not affect the PRD’s enhancing effect on intronic constructs, suggesting that the PRD acts independently of splicing reaction by interacting with sequences residing within introns. The N-terminal regions from zebrafish and Xenopus DROSHA can replace the human counterpart, indicating functional conservation despite poor sequence alignment. Moreover, we found that rapidly evolving intronic miRNAs are generally more dependent on PRD than conserved ones, suggesting a role of PRD in miRNA evolution. Our study reveals a new layer of miRNA regulation mediated by a low-complexity disordered domain that senses the genomic contexts of miRNA loci.
Project description:We asked whether the human drosha protein, an RNase III homolog known to process microRNAs (miRNAs), might also be a small nuclear RNA (snRNA) 3' processing factor. Using retroviral siRNA silencing constructs, we stably knocked down drosha protein to nearly undetectable levels. Knockdown cells exhibited reduced growth rates and viability compared to controls, but no accumulation of unprocessed U2 snRNA precursors. In fungi, RNase III homologs process rRNA precursors and certain mRNAs. Although rRNA processing appears to be normal in the drosha knockdown cells, expression microarray analysis revealed misregulation of several mRNAs involved in cell growth and proliferation. Curiously, drosha knockdown appeared to downregulate the predicted mRNA targets of several miRNAs Experiment Overall Design: The experimental goal was to evaluate gene expression changes induced by siRNA knockdown of drosha. Four samples of HeLa cells were transfected with retroviral siRNA expression vectors: two replicates of an anti-GFP siRNA vector (siGFP) and two different anti-drosha siRNA vectors (sidroshaB and sidroshaC). Cells were selected with puromycin 24 hours after transfection and harvested 72 hours after transfection. Trizol-harvested RNA was processed with standard Affymetrix protocols and hybridized to U133Plus2.0 GeneChips. Signals were scaled to an arbitrary global mean value of 800.
Project description:MIR15A and MIR16-1, located in chromosomal band 13q14, are tumor suppressor miRNAs often deleted and downregulated in chronic lymphocytic leukemia (CLL). This downregulation is not only due to loss of 13q, as it occurs also in 13q+/+ CLL patients. We found that a subgroup of CLL patients has a dysregulation of miR-15 /-16 processing intermediates due to defective processing by Drosha. These patients have reduced levels of miR-15a, miR-16 and miR-15b (another member of the miR-15 family), but not of most other miRNAs. Thus, we show that modulation of miRNA maturation leads to specific downregulation of a family of tumor suppressor miRNAs in leukemic cells. 11 normal processing CLL sample; 12 processing defective CLL patients
Project description:MicroRNAs (miRNAs) are a class of small noncoding RNAs about 22-nucleotide (nt) in length that collectively regulate more than 60% of coding genes. Aberrant miRNA expression is associated with numerous diseases, including cancer. miRNA biogenesis is licensed by the ribonuclease (RNase) III enzyme Drosha, the regulation of which is critical in determining miRNA levels. We and others have previously revealed that alternative splicing regulates the subcellular localization of Drosha. To further investigate the alternative splicing landscape of Drosha transcripts, we performed PacBio sequencing in different human cell lines. We identified two novel isoforms resulting from partial intron-retention in the region encoding the Drosha catalytic domain. One isoform (AS27a) generates a truncated protein that is unstable in cells. The other (AS32a) produces a full-length Drosha with a 14 amino acid insertion in the RIIID domain. By taking advantage of Drosha knockout cells in combination with a previously established reporter assay, we demonstrated that Drosha-AS32a lacks cleavage activity. Furthermore, neither Drosha-27a nor Drosha-32a were able to rescue miRNA expression in the Drosha knockout cells. Interestingly, both isoforms were abundantly detected in a wide range of cancer cell lines (up to 15% of all Drosha isoforms). Analysis of the RNA-seq data from over 1000 breast cancer patient samples revealed that the AS32a is relatively more abundant in tumors than in normal tissue, suggesting that AS32a may play a role in cancer development.