Localization of Gene Expression in Human Atherosclerotic Lesions by In SituHybridization

The technique of in situ hybridization was developed in the late 1960s (1 ) and is based on the ability of a single-stranded sequence of nucleotides to hybridize specifically to a complementary sequence to form stable double-stranded duplexes or hybrids. Incorporating a readily detectable label into the nucleotide sequence permits it to be used as a probe to identify specific complementary target sequences within cells or tissues and thereby derive useful information on the site(s) of expression of a particular gene. Although this technique can be adapted to detect any nucleotide sequence, this chapter is concerned with the detection of mRNA. The advantage of in situ hybridization for detecting mRNA over other methods such as Northern blotting is that this technique allows morphological identification of a specific mRNA species in a particular cell or a subpopulation of cells within a tissue. This can yield useful information on sites of synthesis, turnover, and, when combined with a method such as immunocytochemistry, storage of the transcribed protein.