Single-cell expression profiling is a means to take a ‘snapshot’ of the gene activity of a specimen at the individual cell level. The active sites of  transcription are detected for many genes in their native cellular context using  in situ hybridization. This technique preserves each cell's characteristic repertoire of expressed alleles and the location of expressed alleles in the sub-cellular and tissue-level organization. The reaction is performed in situ, at the proper location of the gene activation events, to yield a visual analysis of complex expression patterns. Hybridization detection of transcription sites measures new transcription specifically, without considering total cell levels of transcripts,  translationto protein and all the other levels of post-transcriptional expression regulation. This allows detection of small incremental changes in transcript levels and direct analysis of causes and effects upstream of transcription. To date, the assay has been used...