Xenopus VegT RNA is localized to the vegetal cortex during oogenesis and encodes a novel T-box transcription factor involved in mesodermal patterning.

@article{Zhang1996XenopusVR,
  title={Xenopus VegT RNA is localized to the vegetal cortex during oogenesis and encodes a novel T-box transcription factor involved in mesodermal patterning.},
  author={J Zhang and Mary Lou King},
  journal={Development},
  year={1996},
  volume={122 12},
  pages={
          4119-29
        }
}
An RNA localized to the vegetal cortex of Xenopus oocytes encodes a novel T-box protein (VegT) capable of inducing either dorsal or posterior ventral mesoderm at different times in development. VegT is a nuclear protein and its C-terminal domain can activate transcription in a yeast reporter assay, observations consistent with VegT functioning as a transcription factor. Zygotic expression is dynamic along the dorsoventral axis, with transcripts first expressed in the dorsal marginal zone. By… 

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A vegetally localized T-box transcription factor in Xenopus eggs specifies mesoderm and endoderm and is essential for embryonic mesoderm formation.

It is established that Brat plays a critical role in embryonic mesoderm formation and body patterning, by expressing a dominant-negative, transcriptional repressor form of Brat in embryos, and by isolated a new member of the T-box family of transcription factors.

Bix1, a direct target of Xenopus T-box genes, causes formation of ventral mesoderm and endoderm.

It is suggested that Bix1 acts downstream of both VegT and Xbra to induce formation of mesoderm and endoderm, which would suggest that Brachyury target genes have proved difficult to identify.

The Xenopus homologue of Bicaudal-C is a localized maternal mRNA that can induce endoderm formation.

Xenopus homologue of the Drosophila gene Bicaudal-C encodes a putative RNA-binding molecule expressed maternally and localized predominantly to the vegetal half of the egg, which leads to ectopic endoderm formation in the absence of mesoderm induction.

Repression of zygotic gene expression in the Xenopus germline

The findings suggest that PGCs are unable to respond to maternally inherited endoderm determinants because RNAPII activity is transiently blocked while these determinants are present.

The role of Mixer in patterning the early Xenopus embryo

Functional assays of Mixer-depleted vegetal cells showed that they have increased mesoderm-inducing activity, demonstrating that Mixer plays an essential role in controlling the amount of mesmoderm induction by the vegetal Cells.

Zygotic VegT is required for Xenopus paraxial mesoderm formation and is regulated by Nodal signaling and Eomesodermin.

It is demonstrated that zVegT is the orthologous gene of zebrafish Spadetail/Tbx16 and chick Tbx6L/T bx6, and has an essential role in paraxial mesodermal formation, and that it is regulated by a coherent feedforward loop of Nodal signaling via Eomes.

Mesoderm induction in Xenopus is a zygotic event regulated by maternal VegT via TGFbeta growth factors.

It is concluded that mesoderm induction in Xenopus depends on a maternal transcription factor regulating these zygotic growth factors, as measured by the expression of mesodermal markers MyoD, cardiac actin, Xbra, Xwnt8 and alphaT4 globin.

derrière: a TGF-beta family member required for posterior development in Xenopus.

The findings indicate that derrière plays a crucial role in mesodermal patterning and development of posterior regions in Xenopus, and constructed a dominant interfering Derrière protein (Cm-Derrière), which preferentially blocks Derriere activity relative to that of other TGFbeta family members.

Bix4 is activated directly by VegT and mediates endoderm formation in Xenopus development.

It is demonstrated that Bix4 acts directly downstream of VegT to specify endodermal differentiation in Xenopus embryos and that a single T-box binding site is able to act as a mesoderm-specific enhancer when placed upstream of a minimal promoter.
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