In situ hybridization with oligonucleotide probes

In situ hybridization (ISH) is an important method for tracing the regional and cellular sites of gene expression (mRNA distribution) within a tissue. This method comes into its own when applied to the intermingled cell types of the brain. ISH allows the particular cell type in which the mRNA is contained to be marked out from others. The technique is simple—a nucleic-acid probe, tagged with either radiolabeled nucleotides or molecules allowing calorimetric/light detection, is applied to a tissue section. The probe searches out and finds (hybridizes to) its corresponding mRNA in the cells and forms a probe-mRNA double helix. After the excess probe has been washed away, the section is either exposed for autoradiography or processed histochemically to reveal the sites on the section targeted by the probe. ISH with oligonucleotides needs less hands-on time than other ISH methods. Large numbers of oligonucleotides (e.g., up to 20 at one time) and sections (e.g., 100) can be handled at once. The method is well suited to large-scale studies that, for example, compare the expression of all members of a gene family or map the expression of novel gene sets.