Simultaneous identification and banding of human chromosome material in somatic cell hybrids

We have developed a method that identifies human chromosomes in human x hamster somatic cell hybrids and simultaneously bands these same metaphases. Other methods generally require separate slides for banding and detection of human chromosome material, making the precise characterization of human material difficult. Our procedure involves denaturing metaphase chromosomes, followed by in situ hybridization of biotinylated whole human DNA. Fluoresceinated avidin is then bound to the biotinylated DNA, staining the human chromosomes yellow-green when excited with UV light. Chromosome banding is achieved by staining the slides with DAPI and actinomycin D. The fluorescein and DAPI excite maximally at 488 and 355 nm and emit at 520 and 450 nm, respectively. This permits identification of the human material at one excitation wavelength and visualization of the banding patterns at another wavelength. With this procedure, we have successfully identified both intact and broken human chromosomes, as well as human material involved in human x hamster translocations. The results indicate that this procedure is more accurate and considerably more rapid than previous methods and can be routinely employed for the cytogenetic analysis of human x rodent hybrids.