Gene expression screening for specific genes associated with mouse mammary tumor development.

The preneoplastic hyperplastic alveolar nodule is a frequent and well-characterized precursor to mammary tumors in the mouse. Although the biological characteristics of the preneoplastic state have been understood for many years, the molecular alterations associated with preneoplasia and tumorigenicity are unknown. We applied the technique of differential display of mRNA to two closely matched cell populations of mammary preneoplasias that differed only in their tumorigenic potential. Two mRNAs were isolated that were overexpressed only in tumorigenic preneoplasias and in tumors and not in normal pregnant mammary gland or in nontumorigenic preneoplasias. Partial nucleotide sequencing indicated that one of the mRNAs had not yet been described, whereas the second mRNA was highly homologous to a relatively uncharacteristic gene termed pT-2. These results illustrate the utility of the differential display method for isolating and identifying uniquely expressed genes from tissues maintained in the microenvironment where tumors arise naturally.