Detection of human Ha-ras transcripts in tumor cells by in situ hybridization

We demonstrate the development of a method for identification of human Ha-ras transcripts in cytological and histological preparations of rodent fibroblasts by RNA-RNA in situ hybridization. Fibroblasts, expressing human Ha- ras at high or a very low level, provide a biological model system to optimize in situ hybridization. For rapid detection we used the radiographic signal from cell smears, in directly overlaid x-ray film. Certain pretreatments of slides are shown to increase nonspecific probe binding. The methods described can be used for rapid detection of oncogene expression in small numbers of cultured cells, without prior extraction and purification of their RNA.