MicroRNAs (miRNAs) are a class of small, single-stranded RNA molecules, typically consisting of about 19 to 24 nucleotides, that play important roles in the regulation of gene expression in cells. They are involved in post-transcriptional regulation, meaning they influence the translation of messenger RNA (mRNA) into proteins after the mRNA has been transcribed from DNA.
The process by which miRNAs regulate gene expression involves several steps:
Transcription: miRNA genes are transcribed from DNA by the enzyme RNA polymerase II into primary miRNA (pri-miRNA) transcripts.
Processing: The pri-miRNA transcripts are processed by a complex of enzymes, including the Drosha and Dicer proteins, to produce mature miRNAs. This processing involves cleavage of the pri-miRNA into a shorter hairpin structure, known as a precursor miRNA (pre-miRNA), followed by further cleavage to generate the mature miRNA.
Targeting: Mature miRNAs bind to specific sequences, typically located in the 3' untranslated region (UTR) of target mRNAs, through base pairing interactions. This binding leads to repression of gene expression through various mechanisms, including inhibition of translation and degradation of the target mRNA.
MicroRNAs have been found to regulate a wide range of biological processes, including development, differentiation, proliferation, apoptosis, and metabolism. Dysregulation of miRNA expression or function has been implicated in various diseases, including cancer, cardiovascular disease, neurodegenerative disorders, and autoimmune diseases.
Because of their roles in gene regulation and their potential as diagnostic and therapeutic targets, miRNAs have attracted considerable attention in biomedical research. Studies of miRNAs have led to insights into the molecular mechanisms underlying disease pathogenesis and have opened up new avenues for the development of miRNA-based therapeutics and diagnostic tools.