How do microRNAs regulate gene expression?

MicroRNAs regulate gene expression by binding to messenger RNAs (mRNAs) and preventing them from being translated into proteins.

MicroRNAs, or miRNAs, are small non-coding RNA molecules that play a crucial role in the regulation of gene expression. They are part of the RNA interference (RNAi) pathway, a biological process where RNA molecules inhibit gene expression or translation by neutralising targeted mRNA molecules.

The process begins with the transcription of a miRNA gene, which results in a primary miRNA (pri-miRNA). This pri-miRNA is processed into a precursor miRNA (pre-miRNA) and then into a mature miRNA. The mature miRNA is incorporated into a protein complex called the RNA-induced silencing complex (RISC). The miRNA within the RISC serves as a guide, leading the complex to a specific mRNA molecule.

The miRNA binds to the mRNA molecule by base pairing with a specific sequence on the mRNA. This binding can result in one of two outcomes, depending on the degree of complementarity between the miRNA and mRNA. If the miRNA and mRNA are fully complementary, the RISC will cleave the mRNA, leading to its degradation and preventing it from being translated into a protein. If the miRNA and mRNA are only partially complementary, the RISC will not cleave the mRNA, but will still prevent it from being translated into a protein. This is achieved by blocking the ribosome, the cellular machinery that translates mRNA into protein.

In this way, miRNAs can control the levels of proteins that are produced in a cell, allowing them to regulate a wide range of biological processes, including cell growth, differentiation, and apoptosis. They can also play a role in disease, with changes in miRNA expression levels being linked to various types of cancer and other diseases. Understanding the role of miRNAs in gene regulation is therefore an important area of research in molecular biology.