Differential display is a technique which relies on the polymerase chain reaction to identify messenger RNA differences between related tissue samples. We have employed an improved differential display technique, called fluorescent differential display (FDD), to identify the genes that are differentially expressed in normal and malignant mammary tissues. From FDD fingerprints, we identified changes in intensity of approximately 3% (185 bands) of a total of 5, 837 bands. Each of these 185 bands represented a differentially expressed gene, and we focused our attention on the expression of the gene for caltractin, a member of the calcium-binding EF-hand protein superfamily. Northern blot analysis revealed that the level of mRNA for caltractin was higher in breast carcinoma than in corresponding normal tissue in all cases tested (5/5). Moreover, high-level expression of the gene for caltractin was also recognized in other malignant tumors, such as hepatocellular carcinoma (HCC), gastric cancer and leiomyosarcoma. The results of in situ hybridization showed strong stainings for caltractin mRNA in tumor-infiltrating lymphocytes (TIL), but not in malignant tumor cells. Our data suggests that the caltractin gene might be associated with the function of TIL.

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