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Title: The regulation of derriere : a direct target of VegT
Author: White, Richard John
ISNI:       0000 0001 3567 0934
Awarding Body: University of London
Current Institution: University College London (University of London)
Date of Award: 2002
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The T-box transcription factor VegT, whose transcripts are restricted to the vegetal hemisphere of the Xenopus embryo, is required for both the specification of endoderm and also to regulate the production of mesoderm-inducing signals. Since VegT is a transcriptional activator, it is likely to exert its effects by regulating the expression of target genes. This thesis describes an analysis of the regulation of one such target gene, derriere. Derriere is a TGF-β superfamily member expressed in the vegetal pole and marginal zone of Xenopus laevis embryos. First, several candidate target genes, which exhibit mesoderm-inducing activity, were tested using a hormone-inducible version of VegT to identifying direct downstream effectors of VegT. These include the TGF-β superfamily members Xnrl-4 and derriere. In agreement with other groups it was found that Xnr1, Xnr2, Xnr4 and derriere are direct downstream targets of VegT, whereas Xnr3 (a neural inducer) is not. Second, a fragment of the derriere promoter was isolated and studied using reporter gene assays, electrophoretic mobility shift assays and transgenesis. The promoter contains two putative T-box binding sites, one of which binds VegT protein in vitro, that are required for expression of a reporter gene in oocytes, but are not required for expression in embryos. This is due to at least one positive feedback loop mediated by TGF-β signalling, through two Fast binding sites in the derriere promoter. This causes the rapid accumulation of transcripts in the marginal zone in the hour preceding gastrulation even in the absence of the T-box binding sites. Finally, the question of the function of derriere in the Xenopus embryo was addressed using animal cap recombination assays and the injection of an antisense morpholino oligonucleotide. These results demonstrate that derriere is subject to complex regulation and is a good candidate for one of the endogenous mesoderm-inducing signals activated by VegT.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Genetics