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Fig. 2 | Cell & Bioscience

Fig. 2

From: MicroRNAs: emerging driver of cancer perineural invasion

Fig. 2

Biogenesis of miRNAs. Canonical microRNA biogenesis, miRNAs formation starts with transcription, during which pri-miRNAs are generated by RNA Pol II and III. Microprocessor complex composed of Drosha and DGCR8 excises pri-miRNAs, and pre-miRNAs is produced in the nucleus. Then, the nuclear Exp5 forming complex with the Ran-GTP exports pre-miRNAs to the cytoplasm, where the pre-miRNA is cleaved by Dicer, generating a mature double-stranded miRNA duplex. Subsequently, the guide strand of the miRNA duplex is incorporated onto Ago protein complex, forming RISC to recognize and interact with the 3’-UTR of their targets. Conversely, the passenger strand is deemed non-functional and degraded once released. Drosha-independent miRNAs biogenesis, the Drosha-independent mirtron genes do not undergo Drosha cleavage but demand mRNA splicing and debranching forming a stem-loop structure analogous to the pre-miRNA synthesized in the canonical approach. The subsequent generation process of miRNAs is similar to canonical pathway. Dicer-independent miRNAs biogenesis, the Dicer-independent pathway is mainly involved in the generation of miR-451 family, which is processed by the microprocessor complex Drosha/DGCR8 in the nucleus. Then, a short pre-miRNA was generated and transported to the cytoplasm by Exp5. The pre-miR-451 is cleaved by Ago2 and trimmed by PARN engendering the mature miR-451, which integrated into Ago to constitute the functional core of RISC

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