April 14, 2010 – Swedish scientists have developed a method to study genetic variation in individual cells and tissues, offering new insights into gene expression that could greatly improve diagnostic tests.

According to a new study from Uppsala U. published in Nature Methods, existing assays used in testing for genotoxic chemicals (they inhibit DNA repair and affect cancer risk) are not sensitive enough — molecules can escape detection, nor can it be positively determined which molecules came from which cells. New assays with single-molecule sensitivity are required, for example, in studying cancer tumors which are a jumble of both healthy and cancerous cells.

Working within two EU-funded projects — COMICS (‘Comet assay and cell array for fast and efficient genotoxicity testing’), to develop ways to test effects of chemicals on human genetic material without using animals, and READNA ("Revolutionary approaches and devices for nucleic acid analysis"), to revolutionize nucleic acid analysis methods — the researchers converted messenger RNA (mRNA) into a type of DNA molecule that can be detected by a type of fluorescent probes ("padlock probes"), enabling them to study DNA repair at the molecular level.

Results of typical assays represent an average number for many cells, within which signals of a small minority of cells can be drowned out. These "padlock probes," which lock onto DNA after hybridization, can amplify those signals, and thus enable detection and identification of just the mRNA levels in cells.

"Hitting the proverbial needle in the haystack should now be possible," stated Mats Nilsson of Uppsala U. "This should entail significantly more sensitive and precise diagnostic methods, improving the prospects that patients will receive the treatment they need."