XB-ART-2071Dev Cell 2005 Apr 01;84:599-610. doi: 10.1016/j.devcel.2005.03.001.
Show Gene links Show Anatomy links
Functional specificity of the Xenopus T-domain protein Brachyury is conferred by its ability to interact with Smad1.
Members of the T-box gene family play important and diverse roles in development and disease. Here, we study the functional specificities of the Xenopus T-domain proteins Xbra and VegT, which differ in their abilities to induce gene expression in prospective ectodermal tissue. In particular, VegT induces strong expression of goosecoid whereas Xbra cannot. Our results indicate that Xbra is unable to induce goosecoid because it directly activates expression of Xom, a repressor of goosecoid that acts downstream of BMP signaling. We show that the inability of Xbra to induce goosecoid is imposed by an N-terminal domain that interacts with the C-terminal MH2 domain of Smad1, a component of the BMP signal transduction pathway. Interference with this interaction causes ectopic activation of goosecoid and anteriorization of the embryo. These findings suggest a mechanism by which individual T-domain proteins may interact with different partners to elicit a specific response.
PubMed ID: 15809041
Article link: Dev Cell
Species referenced: Xenopus laevis
Genes referenced: ag1 agr2 gsc smad1 smad10 smad2 smad4 tbxt vegt ventx2.2
Morpholinos: ventx2.1 MO4
Article Images: [+] show captions
|Figure 6. Interference with the Interaction between Xbra and XSmad1 Allows Xbra to Activate goosecoid and Causes Anteriorization of the Developing Embryo (A) Coexpression of the N-terminal 47 amino acids of Xbra allows wt Xbra to induce expression of goosecoid. Xenopus embryos were injected with RNA encoding Xbra (400 pg) or Xbra(17) (1 ng) or both. Animal cap explants were isolated at late blastula stage 9 and cultured until sibling embryos reached early gastrula stage 10.5. RNA prepared from these animal caps was assayed by real-time RT-PCR. (B) The N-terminal region of Xbra elevates goosecoid expression in isolated ventral marginal zone tissue. Ventral marginal zone regions derived from control embryos or embryos injected ventrally at the four-cell stage with 4 ng RNA encoding wt (HLLSAVE) or mutated (AAASAVE or HLLSGAE) versions of Xbra(17) were collected at early gastrula stage 10.5 and assayed by real-time RT-PCR for expression of goosecoid. Note that wt Xbra(17), but not the mutated versions, causes upregulation of goosecoid. goosecoid expression in an isolated dorsal marginal zone is shown for comparison purposes. (C). Embryos injected ventrally with wt or mutated versions of Xbra(17), as described in (B), were subjected to in situ hybridization by using a probe specific for goosecoid. Note that wt Xbra(17), but not the mutated versions, causes upregulation of goosecoid (arrow), albeit in only three cases out of 20. (G) Wt Xbra(17) (H), but not the mutated versions (I and J), disrupts normal development (G). Embryos were injected ventrally with wt or mutated versions of Xbra(17), as described in (B), and photographed at stage 22. (K) Embryos injected ventrally with Xbra(17), but not the mutated versions, show elevated expression of the anterior and dorsal markers N-CAM and XAG2. Additional experiments revealed upregulation of Otx-2 by just 400 pg of Xbra(17) RNA, with even greater elevation by 4 ng RNA. At this higher concentration, however, some elevation of expression was also observed by using the two control constructs (data not shown).|