Zygote arrest (Zar) proteins, Zar1 and Zar2, are required for successful fertilization and embryogenesis. Synthesis of developmentally important proteins is crucial to embryogenesis and is regulated by translation of mRNA. Zar proteins bind the mRNA of developmentally important proteins via a specific sequence found in the RNA called the Translational Control Sequence (TCS). It is already known that RNAs containing a TCS are translationally repressed in immature oocytes and activated in mature oocytes. It is also known that the N-termini of both Zar1 and Zar2 repress translation when tethered to reporter mRNA. The purpose of this study was to show Zar proteins are bona fide translation factors and are candidates for mediating translational regulation by the TCS.
In a dual luciferase tethered assay, both Zar proteins repressed translation up to 50% in immature Xenopus oocytes and repression was relieved during oocyte maturation, consistent with translational regulation of developmentally important mRNAs. Interestingly, Zar1 required the reporter mRNA have a poly(A) tail to repress translation, whereas Zar2 did not. Furthermore, Zar1 and Zar2 interacted with overlapping but distinct sets of proteins. Proteins recovered from GST affinity purifications included many known translation factors, such as CPEB, 4E-T and embryonic poly(A)-binding protein. In particular, eukaryotic initiation factors were identified such as eIF4E-1b. These interactions changed during maturation, coincident with change in Zar function.
Together, these data suggest Zar proteins do have roles as translation regulators and may mediate repression by the TCS. They also suggest mechanistic differences between Zar1 and Zar2.
|Commitee:||Johnson, Aaron, Stith, Bradley|
|School:||University of Colorado at Denver|
|School Location:||United States -- Colorado|
|Source:||MAI 54/04M(E), Masters Abstracts International|
|Subjects:||Molecular biology, Biochemistry, Developmental biology|
|Keywords:||Gene expression, Maternal factor, Oocyte maturation, RNA-binding proteins, Translational repression, mRNA translation|
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