Cloning and Screening of Sequences Expressed in a Mouse Colon Tumor

Polyadenylic acid-containing cytoplasmic RNA was isolated from a dimethylhydrazine-induced mouse transplantable colon carcinoma. Double-stranded complementary DNA synthesized using these molecules was inserted into the Hindlll site of pBR322 using Hindlll linkers, and the recombinant molecules were cloned in Escherichia coli. Clones were screened with labeled complementary DNA synthesized from the polyadenylic acid-containing cytoplasmic RNA of the tumor or normal mouse colon, liver, or kidney. Of 378 clones screened with the normal colon and tumor probes, seven showed major increases in abundance in the tumor tissue as compared to normal, and one showed a major decrease. Twenty-five other sequences were found which showed smaller increases and 22 showed smaller decreases. Of 373 clones screened with tumor, colon, liver, and kidney probes, 79% exhibited little evidence of tissue specificity in expression. The data for those sequences which do show tissue-specific regulation of expression suggest that the tumor continues to express sequences characteristic of the colon but also shows a loss, or decrease, in other gene products, most of which (19 of 25) are characteristic of the colon. Finally, nine of 10 sequences which increase from low abundance in the normal colon to high abundance in the tumor are found at a moderate to high level in the liver and kidney. On the other hand, 23 of 36 sequences which show more modest increases in the tumor as compared to normal are scarce or absent in the liver and kidney.