ABSTRACT
Fluorescence in situ hybridization (FISH) is an approach that enables the mapping of DNA-probes in nuclei and/or on chromosomes. A major shortcut of FISH is that it normally can only be done on fixed, dead and in most cases heat denatured tissues. The Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR/Cas9) system is used for targeted genomic editing, and high success rates are reported for such experiments. However, far from all high expectations it was clear from the beginning that even rates of ~99.9% correct targeting of a gene defect in a patient is not specific enough to justify a responsible use in gene therapy. Furthermore, recent research showed that CRISPR/Cas9 is able to induce chromothripsis, an effect which is definitely unwanted, deleterious and/or a starting point of malignification of cells. CRISPR-FISH is done in fixed cells. Here a ribonucleoprotein (RNP) consisting of a target-specific CRISPR RNA (crRNA), a fluorescent-labelled transactivating crRNA (tracrRNA), and Cas9 endonuclease are used.
