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Fig. 1 | Stem Cell Research & Therapy

Fig. 1

From: Therapeutic effects of mesenchymal stem cells-derived extracellular vesicles’ miRNAs on retinal regeneration: a review

Fig. 1

MiRNA synthesis pathway. Biogenesis of miRNA begins with transcription of a miRNA gene (Canonical pathway) or the intron region of a protein-coding gene (Mirtron pathway) mainly by RNA polymerase II, and sometimes by RNA polymerase III in the nucleus. Canonical pathway: The sequences from miRNA genes transcription self-anneal and make hairpin-like structures called primary miRNAs (pri-miRNAs). Pri-miRNAs are being cut by DGCR8/Drosha complex and become pre-miRNAs. Mirtron pathway: Pre-miRNAs which are the result of intron regions of protein-coding genes are not dependent on Drosha complex. They are divided by spliceosome from the primary transcript of mRNAs. Then, they will self-anneal and become pre-miRNAs directly. All Pre-miRNAs from both pathways leave the nucleus and enter the cytoplasm by Exportin-5. There, the pre-miRNAs are cleaved by the Dicer/TRBP complex, yielding an about 22 nucleotides long miRNA: miRNA* duplex molecule. Then, this molecule will be loaded into the Argonaute (Ago) part of RNA-induced silencing complex (RISC). After discarding one of the strands, the other one will remain in the RISC and binds to 3’ untranslated regions of target mRNAs. miRNAs binding to target mRNAs lead to their translational repression, deadenylation and cleavage

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