mikrorNAt

MikroRNAt, commonly referred to as microRNA (miRNA), are small non-coding RNAs typically about 22 nucleotides long. They regulate gene expression at the post-transcriptional level in a wide range of organisms, including animals and plants.

Biogenesis: miRNAs are transcribed as primary transcripts (pri-miRNA) by RNA polymerase II, processed in the nucleus by Drosha-DGCR8 into precursor hairpins (pre-miRNA), exported to cytoplasm by Exportin-5, then processed by Dicer into a mature miRNA duplex. One strand is incorporated into the RNA-induced silencing complex (RISC), predominantly with an Argonaute protein, guiding the complex to target mRNAs.

Targeting mechanism and effects: miRNA typically bind to complementary sequences in the 3' untranslated region of target mRNAs, often via a seed sequence (nucleotides 2–8). Binding can repress translation or promote mRNA degradation, reducing protein output. A single miRNA can regulate multiple targets, and a single mRNA can be regulated by multiple miRNAs, forming complex regulatory networks.

Biological roles and clinical relevance: miRNAs participate in development, differentiation, cell proliferation, and apoptosis, and are implicated in numerous diseases, including cancer, cardiovascular disorders, and neurological diseases. Dysregulation can contribute to disease; miRNAs can serve as biomarkers and potential therapeutic targets, using mimics to restore deficient activity or inhibitors (antagomirs) to suppress overactive miRNAs.

Detection and research: miRNA discovery and profiling rely on sequencing, microarrays, and quantitative PCR, with resources in miRNA databases and conservation across species. The study of miRNA biology continues to reveal complex gene-regulatory circuits controlling cellular physiology.