CHROMOSOME PAINTING, A POWERFUL TOOL FOR CHROMOSOMAL ANALYSIS Fluorescent in situ hybridization (FISH) has been used to detect the location of specific genomic targets using probes that are labeled with specific fluorochromes. The limited number of available, spectrally non-overlapping fluorochromes, has prevented the simultaneous identification of multiple targets including different chromosomes. In the april issue of Nature Genetics, Speicher et al report a method that is called multiplex-fluorescence in situ hybridization (M-FISH). They developed, epifluorescence filter sets and computer software that allowed detection and discrimination of 27 different DNA probes hybridized simultaneously to human chromosomes. The technique allowed detection of simple and complex chromosomal rearrangements. In addition, complex chromosomal abnormalities could be identified that could not be detected by the conventional cytogenetic banding techniques. In the July 26, 1996 issue of Science, Schrock et al report of development of a similar technique that allows the multi-color detection of human chromosomes. The technique has been accomplished by allowing 24 cominatorially labeled chromosome painting probes to hybridize with the human chromosomes. Then, the emitted spectrally overlapping chromosome specific DNA probes were resolved by using computer separation (classification) of the spectra. This technique can be used for detection of chromosomal abnormalities. On the basis of the location of the probes used, the size of the alteration can be estimated. In addition, the developed technique provides information that complements the conventional banding analysis. With the use of this technique, the authors easily identified presence of numerous chromosomal translocations and unambiguously identified structural alterations including a giant marker chromosome (mar1) in the aneuploid breast cancer cell line, SKBR3. The cost of the equipments developed by Schrock et al and Speicher et al is estimated to be close to $80,000. The application of these techniques should facilitate analysis of chromosomal aberrations and genetic abnormalities in various human diseases including cancer. These new techniques would undoubetedly find wide clinical applications and specifically for the characterization of complex karyotypes will complement standard cytogenetic studies. REFERENCES: Michael R. Speicher, Stephen Gwyn Ballard & David C. Ward: Karyotyping human chromosomes by combinatorial multi-fluor FISH, Nature Genetics, 12, 368-376, 1996 E. Schröck, S. du Manoir, T. Veldman, B. Schoell, J. Wienberg, M. A. Ferguson-Smith, Y. Ning, D. H. Ledbetter, I. Bar-Am, D. Soenksen, Y. Garini, T. Ried :Multicolor Spectral Karyotyping of Human Chromosomes. Science, 494-497, 1996