XB-ART-38417Dev Dyn October 1, 2008; 237 (10): 2862-73.
In Xenopus, the maternal transcription factor VegT is necessary and sufficient to initiate the expression of nodal-related genes, which are central to many aspects of early development. However, little is known about regulation of VegT activity. Using maternal loss-of-function experiments, we show that the maternal homeoprotein, Tgif1, antagonizes VegT and plays a central role in anteroposterior patterning by negatively regulating a subset of nodal-related genes. Depletion of Tgif1 causes the anteriorization of embryos and the up-regulation of nodal paralogues nr5 and nr6. Furthermore, Tgif1 inhibits activation of nr5 by VegT in a manner that requires a C-terminal Sin3 corepressor-interacting domain. Tgif1 has been implicated in the transcriptional corepression of transforming growth factor-beta (TGFbeta) and retinoid signaling. However, we show that Tgif1 does not inhibit these pathways in early development. These results identify an essential role for Tgif1 in the control of nodal expression and provide insight into Tgif1 function and mechanisms controlling VegT activity.
PubMed ID: 18816846
Article link: Dev Dyn
Species referenced: Xenopus laevis
Genes referenced: ctbp2 mapk1 nodal nodal1 nodal5 nodal5.2 nodal6 odc1 sin3a tgfb1 tgif1 tgif2 vegt
Article Images: [+] show captions
|Figure 1. Sequence and expression of Xenopus tgif1. A: Alignment of human (TGIF1), mouse (Tgif1), Xenopus tropicalis (xtr Tgif1), and Xenopus laevis (xla Tgif1) translated amino acid sequences. Identical residues are in black, similar residues are in grey. Boxes above the sequences mark the locations of a CtBP-binding motif, a nuclear-localization sequence, a Tgif-specific motif and an ERK phosphorylation site. The homeodomain is underlined with a dashed line. Arrowheads mark the sites of HPE mutations. Amino acid (a.a.) numbers are indicated for the X. laevis protein. B: Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis of tgif1 and tgif2 expression in animal (An) and vegetal (Vg) oocyte halves, compared with whole oocytes (Oo) and stage 10.5 embryos (10.5). The -RT indicates a stage 10.5 sample processed in the absence of reverse transcriptase. C: Quantitative real-time PCR (QPCR) analysis of tgif1 and tgif2 expression during early development. Samples were normalized to odc and values displayed as a percentage relative to an uninjected oocyte sample (relative expression %). D-I: in situ hybridization of tgif1. D: Stage 10.5 (top row) and stage 13 (bottom row) embryos. Both rows show an animal pole view. In the bottom row, anterior is to the left. E: Stage 18, anterior to the left. F,G: Stage 24 (F) and stage 36 (G). H,I: Sections through stage 30 embryos, hindbrain level section (H), spinal cord level section (I). Anterior is to the left. no, notochord.|
|Figure 5. Tgif represses nr5/6 expression in vegetal cells. A: Quantitative real-time polymerase chain reaction (QPCR) analysis of nr5 expression in embryos depleted of tgif1, VegT, or both. Relative expression values; samples were normalized to odc and values expressed as a percentage of uninjected control stage 10.5 embryos. tgif1-, embryos injected with 3.0 ng of tgif1-as2mp as oocytes, VegT-, embryos injected with 18.0 ng of vegt-MO as oocytes. B: Reverse transcriptase-polymerase chain reaction (RT-PCR) of mesendodermal markers in uninjected and tgif1-depleted explants. Cap, animal caps; Eq, equatorial/marginal zone region; Vg, vegetal mass/endodermal mass. Explants were cut at stage 9, and cultured to stage 11. Each sample contained five explants or two intact embryos. C-D prime : In situ hybridization of nr5/6 expression in control uninjected (B, Un) and tgif1-depleted embryos (C,D) at stage 10, obtained by fertilization of tgif1-as2mp-injected oocytes (3.0 ng) by the host-transfer method. Dorsal is toward the top.|