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Translational control of activin in Xenopus laevis embryos
1Department of Biochemistry and Molecular Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
Abstract:
Activin is a potent mesoderm inducing factor present in embryos of Xenopus laevis. Recent evidence has implicated activin in the inhibition of neural development in addition to the well-established induction of mesoderm in ectodermal explants. These diverse effects are critically dependent on the concentration of activin yet little is known about the mechanisms regulating the level of activin in the embryo. We report that the 3' untranslated region (3' UTR) of activin beta B mRNA inhibits the translation of activin in embryos. Micro-injection of activin mRNA from which the 3' UTR has been deleted is 8-10-fold more potent in inducing mesoderm than mRNA containing the 3' UTR. Truncation of the 3' UTR also leads to a marked enhancement of activin protein levels in embryos but has no effect when the truncated mRNA is translated in vitro. The 3' UTR also confers translational inhibition on a heterologous mRNA. These data show that a maternal factor(s) present in X. laevis regulates the translation of injected activin beta B mRNA. This factor(s) could be responsible for regulating the levels of endogenous activin beta B protein during mesoderm induction and the specification of ectodermal derivatives such as neural and epidermal tissues.
Insights
The 3' untranslated region (UTR) of activin beta B mRNA inhibits activin protein production in Xenopus embryos. This regulation by maternal factors is crucial for controlling mesoderm induction and ectodermal development.
Area of Science:
- Developmental Biology
- Molecular Biology
- Xenopus laevis Embryology
Background:
- Activin is a key signaling molecule in embryonic development, inducing mesoderm and inhibiting neural development in Xenopus laevis.
- The concentration-dependent effects of activin highlight the need to understand mechanisms regulating its levels during embryogenesis.
Purpose of the Study:
- To investigate the role of the 3' untranslated region (UTR) of activin beta B mRNA in regulating activin protein translation.
- To identify potential maternal factors controlling activin beta B mRNA translation in Xenopus embryos.
Main Methods:
- Micro-injection of modified activin beta B mRNA (with and without 3' UTR) into Xenopus embryos.
- In vitro translation assays.
- Quantification of mesoderm induction and protein levels.
Main Results:
- Deletion of the 3' UTR of activin beta B mRNA increased mesoderm induction potency by 8-10 fold.
- Truncation of the 3' UTR significantly enhanced activin protein levels in embryos, but not in vitro.
- The 3' UTR conferred translational inhibition on a heterologous mRNA, indicating a conserved regulatory mechanism.
Conclusions:
- The 3' UTR of activin beta B mRNA acts as a translational repressor in Xenopus embryos.
- Maternal factors in Xenopus laevis embryos regulate the translation of injected activin beta B mRNA.
- This translational control mechanism is likely essential for regulating endogenous activin beta B protein levels during key developmental events like mesoderm induction and ectodermal patterning.