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Cloning of sequences expressed specifically in tumors of rat
Abstract:
The sequences specifically transcribed in tumor cells are believed to be closely related to transformed phenotypes. For the isolation of such sequences, a cDNA clone library was constructed by using poly(A)+ RNAs from azo-dye-induced rat ascites hepatomas. Thirty-one tumor RNA-responsive clones were isolated by screening 4,000 clones of this library with conventional techniques, differential colony hybridization, and RNA blot hybridization. These clones were categorized into two groups with respect to their size distribution of mRNAs from which clones were derived. The first group was complementary to a single distinct species, either about 1.5 or 0.6 kilobases in length, of poly(A)+ RNA, and the second showed no distinct bands but a smear on a RNA blot. Semiquantitative RNA dot blot assays revealed that the sequences of these clones were expressed very little, if at all, in normal and regenerating livers, while generally high in ascites hepatomas. This specificity was also true for other solid lines of tumors, such as Morris hepatoma 5123D of Buffalo rat and Walker 256 carcinosarcoma of Wistar rat. The smear class sequences were transcribed from middle-repetitive sequences of DNA, indicating that a class of middle-repetitive sequences is specifically transcribed in tumor cells.
Insights
Researchers identified specific RNA sequences transcribed in tumor cells, distinct from normal liver cells. These findings highlight unique gene expression patterns in cancer, including middle-repetitive DNA sequences.
Area of Science:
- Molecular Biology
- Cancer Research
- Genomics
Background:
- Tumor cells exhibit unique gene expression profiles related to their transformed state.
- Identifying these specific transcripts is crucial for understanding cancer biology.
Purpose of the Study:
- To isolate and characterize RNA sequences specifically transcribed in tumor cells.
- To investigate the expression patterns of these sequences in different liver conditions and tumor types.
Main Methods:
- Construction of a cDNA library from azo-dye-induced rat ascites hepatoma poly(A)+ RNAs.
- Screening of 4,000 clones using differential colony hybridization and RNA blot hybridization.
- Semiquantitative RNA dot blot assays to determine expression levels.
Main Results:
- Thirty-one tumor RNA-responsive clones were isolated.
- Clones were grouped based on mRNA size: single distinct species (1.5 or 0.6 kb) or a smear.
- These sequences showed minimal expression in normal/regenerating livers but high expression in ascites hepatomas and other solid tumors.
- Smear class sequences were derived from middle-repetitive DNA sequences.
Conclusions:
- Specific RNA sequences are highly expressed in tumor cells compared to normal or regenerating liver tissues.
- Middle-repetitive DNA sequences can be specifically transcribed in tumor cells.
- These findings contribute to understanding tumor-specific gene expression.