Molecular cloning and characterization of a group of novel RNAs localized to the vegetal pole of Xenopus laevis oocytes

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)

First Committee Member

Mary Lou King - Committee Chair

Second Committee Member

Richard Voellmy - Committee Member


Using a differential screening procedure, I have isolated five novel vegetally localized RNAs in stage VI oocytes of Xenopus laevis. Their expression patterns in oocytes and early embryos were characterized. The RNAs localize to the vegetal cortex during oogenesis through two distinct pathways. One of the genes, VegT, was studied further. VegT was shown to be a new member of the T-box gene family which has been implicated in transcriptional regulation. VegT encodes a polypeptide of 437 animo acid residues with a putative nuclear localization signal. VegT polypeptide localized to nuclei after RNA injection. The carboxyl segment of VegT can act as a transcription activation domain in a yeast reporter assay. Whole mount in situ hybridization confirmed that VegT RNA is translocated to the vegetal half of oocytes during stage III/IV and mostly anchored in the cortical region at the vegetal pole. Zygotic VegT RNA is predominantly expressed in the Spemann organizer in early gastrula. Later in gastrulation, the expression is shifted to the ventral/lateral marginal zone. VegT is also expressed in a subset of Rohon-Beard neurons. When VegT was ectopically expressed on the ventral side of embryos by mRNA injection, secondary dorsal axes were formed. Immunostaining with a notochord marker showed that a significant number of the secondary axes possess organized notochords and otic vesicles. Lineage tracing experiments showed that the formation of the secondary axes is through an induction pathway. Animal cap explants injected with VegT RNA formed ventral/lateral mesoderm. Injection of VegT into the animal pole blocked completion of gastrulation and caused abnormal cell movement. These results suggest that the putative transcription factor VegT may have multiple functions in early embryogenesis, including dorsal/ventral patterning.


Biology, Molecular; Biology, Cell; Biology, Zoology

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