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Differential gene expression in wild-type and X-ray-sensitive mutants of Chinese hamster ovary cell lines
1Department of Radiation Oncology, University of Rochester Medical Center, NY 14642.
Abstract:
Complementary DNA cloning, differential screening and Northern hybridization techniques were used to study differential gene expression in the wild-type Chinese hamster ovary (CHO) K1 cell line and its two X-ray sensitive mutants, xrs-5 and xrs-6. 11 species of mRNAs were found underexpressed in the two independently isolated mutants. The steady-state levels of those mRNAs are 3-26-fold less in the two mutants, depending on the particular species. 6 of the underexpressed mRNAs have been identified by comparing the sequences of the cloned cDNAs to the known sequences in GenBank. 4 of them code for the structural proteins of ferritin heavy chain, nonmuscle myosin light chain 3nm, ribosomal protein S17 and L7, respectively. The other two have strong homology with mouse B2 or retroviral sequences. The remaining 5 mRNAs did not show significant homology with any of the known sequences and apparently represent newly isolated species. The effect of 137Cs gamma-rays on the expression of the 11 mRNAs has been studied. Radiation inhibited the expression of the B2-like gene in the mutants but not in the wild-type CHO cells. The levels of the other 10 mRNAs were not affected by radiation. The underexpression of this group of genes in both xrs-5 and xrs-6 mutants seems to be related to their radiation-sensitive phenotype, although the specific gene responsible has not been identified. Two models are proposed to explain the mechanism of underexpression. It is suggested that a cellular factor or/and chromosome structural changes are involved.
Insights
Researchers identified 11 underexpressed mRNAs in X-ray sensitive Chinese hamster ovary (CHO) K1 cell mutants (xrs-5, xrs-6). Radiation affected B2-like gene expression, suggesting a link between gene underexpression and radiation sensitivity.
Area of Science:
- Molecular Biology
- Genetics
- Cell Biology
Background:
- Chinese hamster ovary (CHO) K1 cell lines are widely used models for studying DNA repair and radiation sensitivity.
- X-ray sensitive mutants (xrs-5, xrs-6) provide valuable tools for investigating the genetic basis of radiation response.
- Differential gene expression analysis is crucial for identifying genes involved in cellular responses to DNA damage.
Purpose of the Study:
- To identify differentially expressed genes in X-ray sensitive CHO K1 mutants compared to wild-type cells.
- To investigate the impact of gamma radiation on the expression of these identified genes.
- To explore potential mechanisms underlying the radiation-sensitive phenotype in the mutants.
Main Methods:
- Complementary DNA (cDNA) cloning and differential screening were employed to identify underexpressed mRNAs.
- Northern hybridization was used to validate and quantify the expression levels of selected mRNAs.
- Sequence homology searches in GenBank were performed to identify known genes among the cloned cDNAs.
- The effect of 137Cs gamma-rays on mRNA expression was assessed in both mutant and wild-type cell lines.
Main Results:
- Eleven mRNA species were found to be underexpressed (3-26 fold) in both xrs-5 and xrs-6 mutants compared to wild-type CHO K1 cells.
- Six of these underexpressed mRNAs were identified, including those coding for ferritin heavy chain, nonmuscle myosin light chain 3nm, ribosomal protein S17 and L7, and sequences homologous to mouse B2 or retroviral elements.
- Gamma radiation from 137Cs inhibited the expression of the B2-like gene specifically in the mutants, while other identified mRNAs remained unaffected.
- The underexpression of these genes in the mutants appears to correlate with their radiation-sensitive phenotype.
Conclusions:
- The study identified a set of underexpressed genes in X-ray sensitive CHO K1 mutants, suggesting their potential involvement in radiation response pathways.
- Radiation-induced modulation of a B2-like gene in the mutants highlights a specific molecular difference compared to wild-type cells.
- The findings support the hypothesis that altered gene expression, potentially due to cellular factors or chromosomal structural changes, contributes to the radiation-sensitive phenotype of xrs-5 and xrs-6 mutants.
- Further research is needed to pinpoint the specific genes responsible and elucidate the precise mechanisms of underexpression.