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Translational control of cyclin B1 mRNA during meiotic maturation: coordinated repression and cytoplasmic
A F Barkoff1, K S Dickson, N K Gray
1Department of Biochemistry, University of Wisconsin, 433 Babcock Drive, Madison, Wisconsin 53706, USA.
Abstract:
Translational control is prominent during meiotic maturation and early development. In this report, we investigate a mode of translational repression in Xenopus laevis oocytes, focusing on the mRNA encoding cyclin B1. Translation of cyclin B1 mRNA is relatively inactive in the oocyte and increases dramatically during meiotic maturation. We show, by injection of synthetic mRNAs, that the cis-acting sequences responsible for repression of cyclin B1 mRNA reside within its 3'UTR. Repression can be saturated by increasing the concentration of reporter mRNA injected, suggesting that the cyclin B1 3'UTR sequences provide a binding site for a trans-acting repressor. The sequences that direct repression overlap and include cytoplasmic polyadenylation elements (CPEs), sequences known to promote cytoplasmic polyadenylation. However, the presence of a CPE per se appears insufficient to cause repression, as other mRNAs that contain CPEs are not translationally repressed. We demonstrate that relief of repression and cytoplasmic polyadenylation are intimately linked. Repressing elements do not override the stimulatory effect of a long poly(A) tail, and polyadenylation of cyclin B1 mRNA is required for its translational recruitment. Our results suggest that translational recruitment of endogenous cyclin B1 mRNA is a collaborative effect of derepression and poly(A) addition. We discuss several molecular mechanisms that might underlie this collaboration.
Insights
Translational repression of cyclin B1 mRNA in Xenopus oocytes is mediated by its 3' untranslated region. Relief of this repression and polyadenylation are linked, enabling translation during meiotic maturation.
Area of Science:
- Molecular Biology
- Developmental Biology
- Xenopus oocyte maturation
Background:
- Translational control is crucial for meiotic maturation and early development.
- Cyclin B1 mRNA translation is repressed in Xenopus oocytes and activated during maturation.
Purpose of the Study:
- Investigate the mechanism of translational repression of cyclin B1 mRNA in Xenopus laevis oocytes.
- Identify cis-acting sequences and trans-acting factors involved in translational control.
Main Methods:
- Injection of synthetic reporter mRNAs into Xenopus oocytes.
- Analysis of translational repression and polyadenylation.
- Mapping of cis-acting regulatory sequences within the 3' untranslated region (3'UTR).
Main Results:
- Repression of cyclin B1 mRNA translation is mediated by sequences within its 3'UTR.
- These repressing sequences overlap with cytoplasmic polyadenylation elements (CPEs).
- Relief of repression and cytoplasmic polyadenylation are functionally linked and required for translational recruitment.
Conclusions:
- Translational recruitment of cyclin B1 mRNA during meiotic maturation is a collaborative process involving derepression and poly(A) addition.
- Specific sequences in the 3'UTR, including CPEs, are critical for regulating translation.
- The findings provide insights into the molecular mechanisms governing translational control in early development.