A procedure for making simultaneous determinations of the relative levels of gene transcripts in tissues or cells

In this paper, we describe a method for making simultaneous determinations of the relative levels of selected resident gene transcripts in biological samples. The procedure consists of immobilizing a battery of cloned genes on a nitrocellulose or nylon filter and hybridizing the filter with radiolabeled cDNA synthesized from mRNA extracted from tissue or cell lines. The intensity of the autoradiographic signals obtained from the various genes on the filter is interpreted to be roughly proportional to the relative numbers of transcripts of the genes present in the original mRNA population. The reliability of the method was established by detecting the expression of c-N-ras and c-myc in human promyelocytic HL-60 cells, which are known to express these two oncogenes. The accuracy of the technique was further established by using a conventional method to hybridize filter-bound, cytoplasmic RNA with labeled probes synthesized from plasmid inserts of genes identified by the screening procedure. The utility of the procedure was demonstrated by our ability to simultaneously examine the relative levels of expression of 21 oncogenes in a radiation-induced canine lung carcinoma.