A new method for detecting pericentric inversions using COD-FISH

A new approach for detecting chromosomal inversions, based on the recently developed technique of chromosome orientation and direction fluorescence in situ hybridization (COD-FISH), is presented. COD-FISH is a strand-specific modification of standard FISH technology which allows the hybridization of single-stranded probes to one, and only one, chromatid of a metaphase chromosome. It can be used to determine the absolute 5’-to-3’ direction of DNA target sequences with respect to the short-to-long arm direction of a given chromosome. Since an inversion reverses the orientation of DNA sequences within the inverted region, an inversion becomes detectable as a “switch” in probesignal from one chromatid to the other, when compared to a reference probe outside of the inverted region. Pericentric inversions in chromosomes 1, 8, 10, and X, which had previously been identified by chromosome banding, were analyzed by theCOD-FISH technique. The results presented here demonstrate that COD-FISH can be used for the detection of pericentric inversionsand that, insome instances, it provides additional information not obtainable by more conventional methods of cytogenetic analysis. Practical limitations of the COD-FISH technique are also discussed.