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Decrease in the levels of specific non-polysomal messenger ribonucleoproteins during the mouse sarcoma-180 ascites
Abstract:
A few mRNAs in S-180 ascites cells are found as non-polysomal messenger ribonucleoprotein particles, whose translation is restricted both in vivo and in vitro. To determine if these mRNPs remain untranslated throughout the cell cycle we obtained S-180 ascites cells enriched in cell cycle stages by centrifugation through ficoll gradients. The "inactive" mRNA species were clearly present in the pre-polysomal fraction from S and pre-S phase cells, however they were not detected in the mRNP fraction from post S phase cells. Hybridization of a cloned cDNA probe for one of these species (P-40) to polysomal RNA from pre- or post-S phase cells demonstrated it was present in substantially higher concentrations in polysomes from post-S phase cells, consistent with its translation after S phase. We also observed that a poly (A)-minus form of the mRNA coding for actin was restricted to post S phase cells.
Insights
Certain messenger RNAs (mRNAs) are translationally repressed in S-180 cells. These inactive mRNAs become active and translated specifically after the S phase of the cell cycle.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Non-polysomal messenger ribonucleoprotein particles (mRNPs) represent a pool of translationally restricted mRNAs.
- Understanding the cell cycle regulation of mRNA translation is crucial for comprehending gene expression control.
Purpose of the Study:
- To investigate whether specific untranslated mRNAs remain repressed throughout the entire cell cycle.
- To determine the cell cycle-specific translational regulation of certain mRNA species in S-180 ascites cells.
Main Methods:
- Enrichment of S-180 ascites cells in specific cell cycle stages using ficoll gradient centrifugation.
- Analysis of mRNA distribution in polysomal and non-polysomal fractions across different cell cycle phases.
- Hybridization of a cloned cDNA probe (P-40) to detect specific mRNA species in polysomal RNA.
Main Results:
- "Inactive" mRNA species were detected in the pre-polysomal fraction of S and pre-S phase cells but not in the post-S phase mRNP fraction.
- The P-40 mRNA species was found in significantly higher concentrations in polysomes from post-S phase cells, indicating translation after S phase.
- A poly (A)-minus form of actin mRNA was exclusively observed in post-S phase cells.
Conclusions:
- Specific mRNAs are translationally regulated in a cell cycle-dependent manner, becoming active after the S phase.
- The observed translational control mechanisms contribute to the precise temporal regulation of protein synthesis during the cell cycle.