Fig. 1

Overview of microRNA (miRNA) biogenesis and functional mechanisms. The biogenesis of miRNAs begins with the transcription of primary miRNA transcripts by RNA polymerases II and III. These primary miRNAs are then processed in the nucleus by the ribonuclease Drosha into precursor miRNAs (pre-miRNAs) that possess a characteristic stem-loop structure. The pre-miRNAs are subsequently exported from the nucleus to the cytoplasm by exportin-5. Once in the cytoplasm, the enzyme Dicer cleaves the pre-miRNAs to produce double-stranded miRNAs. Helicase enzymes then unwind these double strands, leading to the degradation of the passenger strand. At the same time, the mature miRNA strand is incorporated into the Argonaute (AGO) protein within the RNA-induced silencing complex (RISC). Within RISC, miRNAs can regulate gene expression by binding to complementary sequences in target mRNAs, thereby repressing translation. Beyond mRNAs, miRNAs also modulate the expression of other ncRNA, such as lncRNAs and circRNAs. Furthermore, ceRNAs can affect RNA transcript levels by sequestering shared miRNAs, thereby influencing gene regulatory networks