MicroRNSeknek

MicroRNSeknek, often referred to as microRNAs (miRNAs), are a class of endogenous small non-coding RNA molecules that regulate gene expression at the post-transcriptional level in eukaryotes. They are typically 21 to 24 nucleotides long and function as part of the RNA-induced silencing complex (RISC). miRNAs originate from longer primary transcripts and guide gene silencing by pairing with target mRNAs, usually at sites in the 3' untranslated region (3' UTR).

Biogenesis of miRNAs begins with transcription by RNA polymerase II to produce a pri-miRNA, which is cleaved in the nucleus by the Microprocessor complex (Drosha-DGCR8) to form a ~70-nucleotide pre-miRNA hairpin. The pre-miRNA is exported to the cytoplasm by Exportin-5, where Dicer processes it into a short miRNA duplex. One strand (the guide strand) is incorporated into RISC with an Argonaute protein, while the passenger strand is degraded.

The mature miRNA within RISC binds to complementary sequences on target mRNAs, typically through imperfect base pairing in the seed region (positions 2–8). This interaction usually results in translational repression and/or accelerated mRNA decay. A single miRNA can regulate multiple targets, and a single mRNA can be controlled by multiple miRNAs, enabling broad and nuanced regulation of gene networks.

Functions and significance of miRNAs span development, cell differentiation, metabolism, and immune responses. Dysregulation is associated with various diseases, notably cancer, cardiovascular, and neurological disorders. miRNAs hold potential as biomarkers in body fluids and as therapeutic targets, though challenges remain in delivery, specificity, and off-target effects.

History notes include the discovery of lin-4 and let-7 in Caenorhabditis elegans, which revealed a new class of gene regulators later found to be widespread across organisms.