Riou JF et al. (1996), Early regionalized expression of a novel Xenopu...

XB-ART-18666

Biochem Biophys Res Commun 1996 Jan 05;2181:198-204. doi: 10.1006/bbrc.1996.0035.

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Early regionalized expression of a novel Xenopus fibroblast growth factor receptor in neuroepithelium.

Riou JF , Clavilier L , Boucaut JC .

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A cDNA encoding a novel Xenopus fibroblast growth factor receptor, XFGFR4B, has been cloned. XFGFR4B mRNA is detected throughout embryogenesis. However, from the late gastrula stage on, XFGFR4B transcripts are expressed in two defined areas of the anterior neural plate. Interestingly, these two regions are fated to become parts of the retina, midbrain, hindbrain, and otic vesicle, all of which continue to express XFGFR4B mRNA in tailbud stage embryos and early tadpoles. Expression of XFGFR4B mRNA can be maintained at neurula stage in isolated blastula ectoderm in response to mesodermal induction by activin or neural induction by noggin, suggesting that XFGFR4B expression might be regulated by early cell interactions. Distribution of XFGFR4B mRNA suggests that XFGFR4B might serve an important function during patterning of neuroepithelium.

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Species referenced: Xenopus
Genes referenced: fgf2 fgfr1 fgfr4 nog

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	FIG. 1. Comparison of predicted amino acid sequences from XFGFR4B and XFGFR4. Dashes represent gaps in the sequences. Underlined sequences correspond to putative signal peptides. Ig-I, II and III are immunoglobulin-like domains I, II and III, respectively. AD, acidic domain; TM, transmembrane domain; TK, tyrosine kinase domain. Kinase inserts sequences are shadowed.
	FIG. 2. Temporal expression of XFGFR4B transcripts during embryogenesis. RNase protection analysis. XFGFR4B mRNA expression was compared with that of XFGFR1. EF-1a was used as internal control. XFGF4B mRNA is detected at all stages. Although expression of XFGFR1 transcripts is constant, XFGFR4B mRNA expression diminishes at late blastula stage to reach a maximum during gastrulation.
	FIG. 3. Spatial expression of XFGFR4B mRNA in early gastrulae. A) Diagram of an early gastrula stage embryo (sagital section) showing the position of the various dissected tissues. Thick lines indicate the position of cuts. Animal ectoderm (Ecto), supraequatorial (Supra), subequatorial (Sub) and vegetal endoderm (Endo) were dissected. Marginal zone explants were subsequently divided into dorsal, lateral and ventral parts. B) RNase protection analysis in dissected tissues. XFGFR4B, XFGFR1 and EF-1a transcripts expressions were simultaneously analyzed as in Fig. 2. XFGFR4B transcripts are expressed in every tissue. A high level of XFGFR4B expression was detected in the endoderm. A, Animal Pole; D, Dorsal; DMZ, Dorsal Marginal Zone; LMZ, Lateral Marginal Zone; V, Ventral; Vg, Vegetal Pole; VMZ, Ventral Marginal Zone.
	FIG. 4. In situ hybridization analysis of XFGFR4B during embryogenesis. A–C) Dorsal views. A) Late gastrula stage. B) Early neurula stage. C) Early tailbud stage. Arrowheads indicate the patches of XFGFR4B expression in the neural plate (A, B) and the corresponding regions at tailbud stage (C) including retina, midbrain and hindbrain. XFGFR4B transcripts are detected in more posterior regions of the neural tube at a lower level. Note the staining of the developing pronephros (p). D–F) Lateral views. D) Late tailbud stage. E) Early tadpole. F) Controls with a sense probe (lower magnification). Besides neural expression, XFGFR4B mRNA is detected in pronephros (p) heart (h) and myotomes (m) (D,E). Developing head part expresses high levels of XFGFR4B mRNA at the tadpole stage (E).
	FIG. 5. Expression of XFGFR4B mRNA in response to mesodermal and neural inductions. RNase protection analyses in blastula ectoderm were treated with 20 U/ml of activin, 20 ng/ml of bFGF or expressing noggin and cultured until midgastrula or late neurula stages. XFGFR4B, XFGFR1 and EF-1a transcript expressions were simultaneously analyzed as in Fig. 2. Explants cultured until the midgastrula stage expressed high levels of XFGFR4B and XFGFR1 mRNA whether they were treated with activin, bFGF or were uninduced controls. When cultured until the late neurula stage, only explants treated with activin or expressing noggin continue to express XFGFR4B and XFGFR1 at a similar level while their expressions dropped in bFGF-treated and uninduced explants. Embryo lanes correspond to midgastrula and late neurula stage whole embryo samples used as positive controls.