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???displayArticle.abstract??? COUP-TFs (Chicken Ovalbumin Upstream Promoter Transcription Factors) have been proposed to be negative regulators of retinoid receptor-mediated transcriptional activation. In a previous paper we reported the cloning of a Xenopus (x) COUP-TF (Matharu, P.J. and Sweeney, G.E. (1992) Biochim. Biophys. Acta 1129, 331-334). Here we describe the cloning of a second xCOUP-TF. Amino acid sequence comparison between these two Xenopus COUP-TFs revealed a high level of similarity. Extensive amino acid sequence conservation was found among all Drosophila, Xenopus, zebrafish and mammalian COUP-TF genes examined. Phylogenetic tree analyses indicate that the vertebrate COUP-TFs fall into three classes. The two Xenopus COUP-TF genes show similar temporal expression patterns: both are expressed from the end of gastrulation. In situ hybridization studies reveal complex expression patterns in the developing central nervous system (CNS), besides expression in the eye and in some mesodermal tissues. Retinoic acid (RA) treatment enhances xCOUP-TF-A expression in neurula stage embryos, whereas the expression of xCOUP-TF-B is inhibited during the same developmental period. The strictly conserved amino acid sequences and the strong similarities between the expression patterns of the two different xCOUP-TFs on the one hand, and other vertebrate COUP-TF homologues on the other, make it likely that COUP-TFs have a conserved role in patterning the nervous system.
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Fig. 4. Whole mount in situ hybridization with an antisense xCOUP-TF-A RNA probe (A-D) and an antisense xCOUP-TF-B RNA probe (E-H). (A)
Lateral view of a stage 18 embryo; the arrow indicates the anterior border of the hindbrain expression domain. (B) Dorsal sideview of a stage 28 tailbud.
(C) Anterior part of a stage 31 embryo; an arrow indicates the mid-hindbrain border, rhombomeres are numbered. (D) Stage 26 embryo, stained
for a prolonged time to show the somite expression. (E) stage 18 embryo, arrow points to hindbrain expression. (F) stage 25 embryo, dorsal sideview.
(G) Anterior part of a stage 31 embryo, arrow indicates anterior border of hindbrain, rhombomeres are numbered. (H) Dorsal view of the head of a
stage 31 embryo. o in C, F, and G indicates the position of the otic vesicle. All embryos were cleared with Murray (benzyl alcohobbenzyl benzoate
1:2), except for B and F. Anterior is to the left.
Fig. 5. Transverse sections of embryos hybridized with an xCOUP-TF-A (A-C; stage 31) or an xCOUP-TF-B probe (D-l? stage 37). All sections are
slightly oblique, the dorsal side being more. posterior than the ventral side. (A,D) Section through the prosencephalic region. (B) Section at the eyelevel;
xCOUP-TF-A is expressed mainly in the branchial arches and ventrally in the eyes. (C) Section through the spinal cord. xCOUP-TF-A is expressed
in the ventral part of the spinal cord (arrows) and in the somites. (E) Section through the eyes and the hindbrain; neural staining is in rl . (F)
Section through the otic vesicle and r5. Abbreviations: ba, branchial arch; cg, cement gland; e, eye; nc, notochord; o, otic vesicle; p. prosencephalon; r,
rhombencephalon; s, somite; SC, spinal cord. Bars are 1OOpm (A,B) or 50pm (C-F).
Fig. 6. Effects of RA on xCOUP-TF-A and xCOUP-TF-B expression patterns. Left (A,C,E,F), control embryos; right (B,D,F.G), embryos treated with
10-6M RA from stage 10 onwards. Embryos in A-D were hybridized with an xCOUP-TF-A probe; E-H show xCOUP-tf-B expression in normal and
in RA-treated embryos. (A,B,E,F) Neurula stage (18) embryos. (CD) Stage 31 tailbuds. (G,H) Stage 27 tailbud embryos. The longer arrow in (A)
indicates xCOUP-TF-A expression in the anterior-most part of the neural tube; the shorter arrow points to eye anlagen. The arrow in (B) points to the
anterior part of the neural tube. Left arrow in (E) marks the anterior xCOUP-TF-B staining. whereas the right arrow points to the hindbrain expression.
nr2f5 (nuclear receptor subfamily 2, group F, member 5) gene expression in Xenopus laevis embryos, NF stage 31, as assayed by in situ hybridization, lateral view, anteriorleft, dorsal up.
