Borday C et al. (2018), An atlas of Wnt activity during embryogenesis i...

XB-ART-54818

PLoS One 2018 Jan 01;134:e0193606. doi: 10.1371/journal.pone.0193606.

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An atlas of Wnt activity during embryogenesis in Xenopus tropicalis.

Borday C , Parain K , Thi Tran H , Vleminckx K , Perron M , Monsoro-Burq AH .

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Wnt proteins form a family of highly conserved secreted molecules that are critical mediators of cell-cell signaling during embryogenesis. Partial data on Wnt activity in different tissues and at different stages have been reported in frog embryos. Our objective here is to provide a coherent and detailed description of Wnt activity throughout embryo development. Using a transgenic Xenopus tropicalis line carrying a Wnt-responsive reporter sequence, we depict the spatial and temporal dynamics of canonical Wnt activity during embryogenesis. We provide a comprehensive series of in situ hybridization in whole-mount embryos and in cross-sections, from gastrula to tadpole stages, with special focus on neural tube, retina and neural crest cell development. This collection of patterns will thus constitute a valuable resource for developmental biologists to picture the dynamics of Wnt activity during development.

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Species referenced: Xenopus tropicalis
Genes referenced: egr2 en2 fezf2 otx2 pax3 rpe snai2 sox2 wnt1

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	Fig 1.Whole-mount gfp in situ hybridization on Tg(pbin7Lef-dGFP) embryos from stage 11 to stage 20. For each stage, anterior, dorsal, posterior and lateral views are shown. White dotted lines on anterior views delineate the prospective central nervous system during neurulation. NC: migrating neural crest cells, PSM: posterior presomitic mesoderm.
	Fig 2. Wnt activity during gastrulation and neurulation in cross-sections. Embryo transverse (or cross-)sections following whole-mount gfp in situ hybridization on Tg(pbin7Lef-dGFP) embryos, from stage 12.5 to stage 20. For each stage, 7 serial sections are shown. White dotted lines delineate the somites. e: nonneural ectoderm; np: neural plate: brackets indicate the approximate width of the neural plate.
	Fig 3. Wnt activity during organogenesis in whole embryos. Whole-mount gfp in situ hybridization on Tg(pbin7Lef-dGFP) embryos from stage 21 to stage 40. For each stage, lateral (side) and dorsal views are shown afb: anterior part of the forebrain; bi: blood islands; cns: central nervous system; ey: eye; f: fins; h-myo: hypaxial myoblast; NC: migrating neural crest cells; ot: otic vesicle; ov: optic vesicle; PSM: posterior presomitic mesoderm.
	Fig 4. Wnt activity at stages 24–25 and 40. Whole-mount gfp in situ hybridization (Aa, and Ba, lateral views) of Tg(pbin7Lef-dGFP) embryos at stage 24–25 (A) and stage 40 (B). For each stage, transverse sections are shown (Ab-n and Bb-p). The different levels of sections are indicated in panels a. bi: blood islands; ot: otic vesicle. PSM: posterior presomitic mesoderm.
	Fig 5. Wnt activity during neural tube development. (A) Anterior views of Tg(pbin7Lef-dGFP) embryos at stage 17 hybridized with probes against gfp alone (a) or gfp and krox20 or gfp (b) or gfp and wnt1(c). Dotted lines delineated the gfp staining. (B) Anterior views of Tg(pbin7Lef-dGFP) embryos at stage 18 hybridized with probes against gfp alone revealed with NBT/BCIP (a) or Fast Red (b) substrates or gfp and wnt1 (c). The same embryo is shown in b and c. Dotted lines delineate the gfp staining. (C) Dorsal views of embryos hybridized with probe against gfp at stage 25, 30 and 35. (D) Lateral views of the anterior part of embryos hybridized with probes against gfp, fezf2 or enr2 at stage 35. afb: anterior forebrain; ch: cortical hem; fb: forebrain; hb: hindbrain; mb: midbrain; MHB: Midbrain Hindbrain Boundary; pmb: posterior midbrain; r3 and r5: rhombomeres 3 and 5; rl: rhombic lip.
	Fig 6. Wnt activity during neural crest formation. (A) Dorsal view of a stage 12 Tg(pbin7Lef-dGFP) embryo hybridized with pax3 or gfp probes (posterior side is up). Dotted shapes delineate the presumptive neural border on both sides. Anterior view of a stage 12 Tg(pbin7Lef-dGFP) embryo hybridized with otx2 probe alone or otx2 and gfp probes together (dorsal side is up). (B) Dorsal view of a stage 14 Tg(pbin7Lef-dGFP) embryo hybridized with sox2 or gfp or both probes. Dotted shapes delineate the neural plate. The a and b dotted lines indicate the level of shown transverses sections. (C) Anterior views of a stage 18 Tg(pbin7Lef-dGFP) embryo first hybridized with probe against gfp and secondarily with probe against snai2. Dotted lines delineate gfp staining. (D) In situ hybridization against gfp on stage 21–22, 24–25, 26 and 29–30 Tg(pbin7Lef-dGFP) embryos (lateral views). For each stage, the dotted line indicates the level of the shown transverse section (a’-d’). ma: mandibular arch; nb: neural border; NC: migrating neural crest cells; np: neural plate; PSM: posterior presomitic mesoderm.
	Fig 7. Wnt activity during retinogenesis. (A) Whole-mount gfp in situ hybridization on Tg(pbin7Lef-dGFP) embryos from stage 14 to stage 20. Anterior views with the eye fields (dotted lines) are shown. (B) In situ hybridization against gfp on stage 21 to stage 40 Tg(pbin7Lef-dGFP) embryos. Whole-mount (lateral views of the head, anterior to the left) and transverse retinal sections are shown. Arrowhead points to surface ectoderm, black arrows to the Retinal Pigmented Epithelium (RPE) and presumptive RPE (pRPE), white arrows to the Ciliary Marginal Zone (CMZ). Black dotted lines delineate the optic vesicle. White dotted lines delineate the boundary between neural versus non-neural territories in the retina. (C) Schematic of a CMZ showing its spatial organisation with stem cells closest to the periphery (region 1), proliferative retinoblasts in the middle (region 2) and postmitotic cells at the central edge (region 3). On the bottom, an enlargement of the region delineated with black dotted lines in the stage 40 retinal section image shows the gfp signal in the peripheral half of the CMZ. White dotted lines delineate the 3 zones depicted in the schema. A strong staining is observed in zone 1, a fainter staining is detected in zone 2 and barely no staining is observed in zone 3. CMZ: Ciliary Marginal Zone; L: lens; NC: migrating neural crest cells; ov: optic vesicle; pNR: presumptive Neural Retina, pRPE: presumptive Retinal Pigmented Epithelium.
	Focus on selected structures. (A) Schematic of the Wnt reporter construct containing chicken β-globin insulators [20]. (B, C) Embryo transverse sections following whole-mount gfp in situ hybridization on Tg(pbin7Lef-dGFP) embryos, at stage 12.5 (B) and 22 (C). Right panels are enlargement of blue squares. Black dotted lines delineate the somites. (D) Whole-mount gfp in situ hybridization of Tg(pbin7Lef-dGFP) embryos at stages 29–30 and transversal sections at indicated level showing gfp staining in the dorsal and ventral fins. (E) Dorsal views of a stage 13 Tg(pbin7Lef-dGFP) embryo first hybridized with probe against gfp and secondarily with probe against sox2. Black dotted lines delineate the gfp-expressing domain. (F) Embryo transverse sections following whole-mount gfp in situ hybridization on Tg(pbin7Lef-dGFP) embryos, at stage 18 and 24–25. The squared regions delineated with the dotted line were enlarged. White dotted lines delineate the neural tube. (G) Dorsal view of a stage 12 Tg(pbin7Lef-dGFP) embryo hybridized with gfp and pax3 probes or gfp and otx2 probes (posterior side is up). Dotted lines delineate gfp staining. d-f: dorsal fins; ectod.: ectoderm; ins: fp: floorplate; insulator; mesod.: mesoderm; n: notochord; np: neural plate; NT: neural tube; v-f: ventral fins.

References [+] :

Al Alam, Contrasting expression of canonical Wnt signaling reporters TOPGAL, BATGAL and Axin2(LacZ) during murine lung development and repair. 2011, Pubmed