XB-ART-38417
Dev Dyn
October 1, 2008;
237
(10):
2862-73.
Maternal Tgif1 regulates nodal gene expression in Xenopus.
Abstract
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
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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.
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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.
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