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Mech Dev
2000 Mar 01;911-2:119-29. doi: 10.1016/s0925-4773(99)00280-4.
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XTIF2, a Xenopus homologue of the human transcription intermediary factor, is required for a nuclear receptor pathway that also interacts with CBP to suppress Brachyury and XMyoD.
de la Calle-Mustienes E
,
Gómez-Skarmeta JL
.
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Ligand-bound nuclear receptors (NRs) recruit cofactors such as members of the p160 family and CREB-binding protein (CBP) to activate transcription. We have cloned the Xenopus homologue of the human transcription intermediary factor 2 (TIF2), a member of the p160 family of cofactors. Xenopus TIF2 (XTIF2) mRNA is expressed homogeneously during late blastula-early gastrula stages and later becomes highly expressed in the notochord. To study the function of XTIF2 during development, we have used two dominant negative constructs, one encompassing the NR-binding domain and the other the CBP interacting region of XTIF2. Overexpression of the XTIF2 dominant negative mRNAs causes ectopic expression of Xenopus Brachyury (Xbra) and MyoD in all tissue layers. Moreover, ectopic expression of the dominant negative construct that contains the CBP-binding region produces strong phenotypes at hatching stage such as loss of head structures, shortened trunks and open blastopores, which can be rescued by XTIF2 coexpression. These observed defects are due, at least in part, to repression of dorsal mesoderm and endoderm genes. Our data suggest the existence of a NR pathway that requires XTIF2 and CBP to repress Xbra and XMyoD.
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10704837
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Fig. 2. Expression pattern of XTIF2 mRNA at different developmental stages. (A) Lateral view of a stage 9 embryo. Note the XTIF2 expression in the animal region. (B) Vegetal view of a stage 10 embryo; note the dorsal to ventral gradient of XTIF2 expression in the mesoderm and ectoderm. (C) Sagittal section of a stage 10 embryo viewed from the inside. Note the expression of XTIF2 in the prospective notochord and headmesoderm (arrow and arrowhead, respectively). (D) Dorsal view of a late gastrula (stage 12.5), XTIF2 is clearly expressed in the notochord (arrowhead). (E–G) Stage 16 embryos. (E) Lateral view; XTIF2 can be detected weakly in the anterior region of the embryo and in the epidermis. (F) Sagittal section; XTIF2 mRNA can be detected in the prechordal mesoderm (arrowhead). (G) Transverse section showing strong expression of XTIF2 in the notochord (arrowhead) and weak expression in the lateralmesoderm (white arrow) and neuroectoderm (black arrow). (H–J) Stage 20 embryos. (H) Lateral view; XTIF2 expression becomes stronger in the head region (arrowhead). (I) Sagittal section of a stage 20 embryo showing expression in the notochord and prechordal mesoderm (arrowhead and arrow, respectively). (J) Transverse section of a stage 20 embryo. The expression domains of XTIF2 seen at stage 16 are maintained at this stage. Note the strong expression in the notochord (black arrowhead), and the weak expression in the neural tube (white arrowhead) and somites (white arrow). Higher levels of expression are also detected at the boundary between the neural tube and somites (black arrow). (K–L) Hatching embryos (stage 35). (K) XTIF2 expression is stronger in the head with higher levels in the eyelens (arrowheads). XTIF2 mRNA is also detected in the pronephros (white arrow) and in the ventral region of the embryo (black arrow). Inset shows ventral view of this embryo. XTIF2 is expressed in a V-shaped domain (arrow). (L) Section across the eye level of the head showing strong XTIF2 expression in the eyelens (arrowheads). an, animal; vg, vegetal; b, blastopore; d, dorsal; v, ventral; a, anterior; p, posterior.
