Fig. 3

The schematic representation reveals the biogenesis of microRNAs (miRNAs). The biogenesis of microRNAs (miRNAs) unfolds through five key stages: Transcription: miRNA precursors originate from autonomously transcribed genes, co-transcripts with other genes, or introns of host genes. RNA polymerase II transcribes most miRNAs, though some come from RNA polymerase III co-transcripts with adjacent repetitive elements. The initial transcript, known as primary microRNA (pri-miRNA), includes an imperfectly double-stranded region within a hairpin loop, with longer sequences extending from both the 5′ and 3′ ends. Cleavage by DROSHA: The DROSHA nuclease, in association with the RNA-binding protein DGCR8 (forming the Microprocessor complex), endoribonucleolytically cleaves the 5′ and 3′ ends of the pri-miRNA. This cleavage produces a short hairpin structure, about 60 to 70 nucleotides long, called pre-microRNA (pre-miRNA). Nuclear Export by Exportin-5: The pre-miRNA associates with Exportin-5, Ran, and GTP to be transported through the nuclear pore into the cytoplasm. Cleavage by DICER1: In the cytoplasm, the pre-miRNA is processed by the RISC loading complex, which includes DICER1, an Argonaute protein, and either TARBP2 or PRKRA. DICER1 cleaves the pre-miRNA, resulting in a double-stranded miRNA approximately 21 to 23 nucleotides in length, with protruding single-stranded 3′ ends of 2–3 nucleotides. Incorporation into RNA-Induced Silencing Complex (RISC) and Strand Selection: The double-stranded miRNA is incorporated into an Argonaute protein within the RISC loading complex. The passenger strand is removed and degraded, while the guide strand is retained, directing the Argonaute complex (RISC) to target mRNAs