In the fields of genetics and molecular biology, RNA hybridization refers to the binding of one strand of RNA to a second strand of RNA with an entirely or partially complementary sequence. This hybridization occurs via non-covalent interactions, predominantly hydrogen bonds and Van der Waals forces, between the nitrogenous bases (A, U, G, and C) of the two RNA strands. The result is the formation of an RNA duplex that can have profound biologal implications, and can be exploited for use as a molecular biology tool. 
Some RNAs, particularly microRNAs (miRNAs), can have a gene regulatory effect at the RNA level by binding to a messenger RNA (mRNA) and inhibiting it's transcription into a protein product. Furthermore, RNA in situ hybridization (or RNA ISH) is a type of molecular hybridization in which a strand of complementary RNA (cRNA) of known sequence is labeled (usually with a fluorophore, radioisotope, or an antigen for which exists a labeled antibody) and used to detect endogenous RNA in a cell or tissue culture. When the RNA strand that is being used as a probe is conjugated to a fluorophore, and thus a fluorescent signal will indicate to the observer the location of the target RNA being investigated, the technique is referred to as RNA FISH (fluorescent in situ hybridization). RNA hybridization is a molecular biology technique used to detect or identify a specific RNA molecule such as messenger RNA (mRNA) or microRNA (miRNA) in a biological sample. Cellular samples are fixed and permeabilized in order to facilitate riboprobe entry into target cells and subsequent attachment of the riboprobe to the RNA molecule of interest  . Tissue samples are typically fixed with formalin and embedded in paraffin  .
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