Studies on the translation products of germ plasm RNAs of Xenopus laevis

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)


Molecular Cell and Developmental Biology

First Committee Member

Mary Lou King - Committee Chair


The protein expression pattern of Xcat2 RNA, a vegetally localized RNA which colocalizes with germ plasm in Xenopus laevis oocytes and embryos, was characterized. No endogenous Xcat2 protein was detected in any of the developmental stages assayed. However, it was possible to predict that Xcat2 RNA is translated just prior to or at the onset of gastrulation at St. 10 of embryogenesis. The large numbers of early stage oocytes screened without detecting endogenous protein eliminated the possibility of translation during oogenesis. The predicted Xcat2 protein sequence shares a region of similarity with the Drosophila protein Nanos. While Nanos functions in both anterior-posterior patterning of the Drosophila embryo and in maternal control of oogenesis, Xcat2 protein is proposed to have a single function in Xenopus. It is likely that Xcat2 protein is translated when the germ plasm becomes perinuclear prior to the onset of mitosis of the primordial germ cells. A model is proposed where Xcat2 protein inhibits the translation of another RNA whose product inhibits mitosis. After translation, Xcat2 RNA is degraded, resulting in the disappearance of the RNA by neurula.The absence of Xcat2 RNA translation during oogenesis indicated that translation is not activated by localization. This contrasts Xcat2 RNA from both nanos RNA and Vg1 RNA. Both of these RNAs are translationally repressed during localization; translation is activated only upon the completion of localization. Both localization and translational repression of nanos and Vg1 are mediated by elements in the 3$\sp\prime$UTR. Experiments; with chimeric Xcat2 RNA indicated that although Xcat2 localization is mediated through the 3$\sp\prime$UTR, translational repression in the oocyte is not. For Xcat2 RNA, therefore, translational activation is not as tightly linked to localization as it is for Vg1 or nanos RNAs.Sequence analysis of DeadSouth, previously identified as Xcat3, indicated that it encoded another kind of RNA binding protein, an RNA-dependent DEAD Box helicase. A DeadSouth type of DEAD Box protein has not been previously demonstrated to function in development.


Biology, Molecular; Biology, Cell

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