Characterization of a cDNA clone for a rare mRNA modulated by ovariectomy in mammary carcinomas

A complementary DNA (cDNA) clone (p13) for a rare mRNA was isolated from a cDNA library generated from total polyA+ RNA of 14-day lactating rat mammary gland. In vitro translation of the positively selected mRNA from p13 cDNA revealed on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) a polypeptide of 24 kDa. The p13 cDNA clone hybridized on northern blots predominantly to approximately 1100 base size RNA and weakly to approximately 3800 base size RNA from lactating mammary gland. It hybridized only to approximately 3800 base size RNA from rat liver. Southern blot analysis of genomic DNA showed differences in gene organization in mammary gland and liver. The mRNA level for the 24 kDa polypeptide was higher in 7-12 DMBA-induced tumor and lower in the MTW9 carcinoma as compared to lactating mammary gland. After ovariectomy, the mRNA level in mid pregnant gland increased but was reduced in the 7-12 DMBA tumors.