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The recruitment of membrane-bound mRNAs for translation in microinjected Xenopus oocytes
Abstract:
Xenopus oocytes were injected with several heterologous mRNAs to investigate specific message recruitment onto polysomes. When large amounts of mRNA such as ovalbumin, which is translated on membrane-bound polysomes, are injected, most of the stable message accumulates in a postpolysomal supernatant. Conversely, when similar amounts of nonmembrane-bound mRNAs such as those which code for adenovirus protein are injected, most of the messages are found in a polysome pellet. Nonpolysomal mRNAs such as zein, ovalbumin, and lysozyme can be recruited onto membrane-bound polysomes by injected rough endoplasmic reticulum (RER). Only RER, but not Golgi apparatus, plasma membrane, or salt-washed RER has such recruiting ability. In addition, the nontranslating messengers can be recruited by injecting the salt wash of the RER. Since most nontranslating mRNAs sediment to regions less than the 80 S monosome, the step at which translational regulation takes place is probably initiation rather than elongation. The mechanism by which recruitment might occur is discussed.
Insights
Messenger RNA (mRNA) recruitment to polysomes in Xenopus oocytes depends on mRNA type and the presence of rough endoplasmic reticulum (RER). Specific RER components facilitate the translation of non-polysomal mRNAs.
Area of Science:
- Molecular Biology
- Cell Biology
- Xenopus Oocyte Research
Background:
- Messenger RNA (mRNA) localization and translation are critical for protein synthesis.
- The role of cellular structures like the rough endoplasmic reticulum (RER) in mRNA recruitment is not fully understood.
Purpose of the Study:
- To investigate the specific recruitment of heterologous mRNAs onto polysomes in Xenopus oocytes.
- To determine the role of the rough endoplasmic reticulum (RER) in this mRNA recruitment process.
Main Methods:
- Injection of various heterologous mRNAs into Xenopus oocytes.
- Fractionation of oocyte extracts to isolate polysomes and post-polysomal supernatants.
- Assessing mRNA distribution in different cellular compartments.
Main Results:
- Membrane-bound polysomes preferentially recruit specific mRNAs (e.g., adenovirus protein mRNA), while non-membrane-bound mRNAs (e.g., ovalbumin mRNA) accumulate in the supernatant.
- Non-polysomal mRNAs can be recruited to membrane-bound polysomes by injected rough endoplasmic reticulum (RER).
- The RER, but not other organelles or salt-washed RER, possesses this mRNA recruitment ability, suggesting specific RER-associated factors are involved.
Conclusions:
- Translational regulation, likely at the initiation step, is influenced by mRNA type and RER interaction.
- Specific components of the RER are crucial for recruiting non-translating mRNAs to active polysomes.
- This study provides insights into the mechanisms of mRNA localization and translational control in eukaryotic cells.