Detailed genome-wide screening for inter- and intrachromosomal abnormalities by sequential G-banding and RxFISH color banding of the same metaphase cells

While the now-classic chromosome banding methods, such as G-banding, remain the techniques of choice for the initial screening for karyotypic abnormal ities, sometimes chromosomal rearrangements involve segments too small or t oo similarly banded to be detected or described adequately by these techniq ues. The necessity to use a genome-wide, fluorescence in situ hybridization (FISH)-based screening technique as a complement to G-banding is especiall y obvious in cases where the information obtained by the latter analysis do es not provide an adequate guide to the choice of probes for chromosome-spe cific FISH. Furthermore, the same metaphase cells should ideally be used fo r both G-banding and FISH analysis to overcome the scarcity of metaphases o bserved in many cases and to ensure the correct interpretation of chromosom al aberrations in cytogenetically unstable neoplasms with massive cell-to-c ell karyotypic variability. We describe a protocol which enables cross-spec ies color banding (RxFISH), a new FISH-based screening technique that simul taneously imparts specific color banding patterns on all chromosomes, of pr eparations that have been G-banded and mounted for up to several years, as well as a procedure allowing chromosome-specific painting of the same metap hase cells to resolve whatever doubts persist after the preceding G-banding and RxFISH analyses. This approach makes possible a detailed, genome-wide screening for inter- and intrachromosomal abnormalities including archival cases whose karyotypic rearrangements had been incompletely identified by G -banding. (C) 2000 Elsevier Science inc. All rights reserved.