- Title
-
Chordin and dickkopf-1b are essential for the formation of head structures through activation of the FGF signaling pathway in zebrafish
- Authors
- Tanaka, S., Hosokawa, H., Weinberg, E.S., Maegawa, S.
- Source
- Full text @ Dev. Biol.
Chd acts downstream of the FGF signaling pathway to induce the anterior and posterior neuroectoderm. Each image represents the expression pattern of otx2 or hoxb1b in (A and B) wild-type embryos, (C and D) uninjected ichabod embryos, (E and F) FGF8 mRNA-injected ichabod embryos, and (G and H) FGF8 mRNA and MOdkk1b-injected ichabod embryos. All embryos are shown at 80% epiboly stage in lateral views. Scale bars represent 100 µm. EXPRESSION / LABELING:
PHENOTYPE:
|
Chd expression is not sufficient to induce the formation of complete head structures in ichabod embryos. (A–D) Phenotypic observation of ichabod embryos at 24 hpf. Embryos were classified using the phenotypic classification criteria reported by Kelly et al., 2000 ; Maegawa et al., 2006: Class 1 embryos show a severe ventralized phenotype; embryos develop neither a head nor a trunk. Class 1a embryos develop a partial trunk and spinal cord but no head structures; class 2 embryos develop a spinal cord and hindbrain but lack head structures anterior to the midbrain; class 3 embryos develop a defective forebrain and no eyes; class 4 embryos develop complete head structures but no notochord; class 5 embryos have no apparent deficiencies and survive until they are adults. (A) Uninjected ichabod embryos showed a ventralized phenotype, and were classified as a class 1 phenotype (22/22). (B) Upon injection with FGF8 mRNA, ichabod embryos showed a class 4 phenotype (14/20). (C) The majority of the ichabod embryos that were injected with chd mRNA were classified as a class 3 phenotype (14/20). (D) Ichabod embryos injected with β-catenin mRNA showed a class 5 phenotype (18/22). Scale bar represents 100 µm. PHENOTYPE:
|
Dkk1b is a downstream component of the FGF signaling pathway. Expression of dkk1b in (A) a wild-type embryo, (B) an uninjected ichabod embryo, (C) an FGF8 mRNA-injected ichabod embryo, and (D) a β-catenin mRNA-injected ichabod embryo. Embryos are at the shield stage, shown in animal pole views. Scale bar represents 100 µm. |
Dkk1b acts downstream of the FGFsignaling pathway to induce the formation of complete head structures and neuroectoderm patterning. Phenotypic representation of (A) uninjected (50/52), (B) FGF8 mRNA-injected (35/52), and (C) FGF8 mRNA and MOdkk1b-injected ichabod embryos at 24 hpf (38/43). Each image represents the expression pattern of otx2 or hoxb1b in (D and E) wild-type embryos, (F and G) uninjected ichabod embryos, (H and I) FGF8 mRNA-injected ichabod embryos, and (J and K) FGF8 mRNA and MOdkk1b-injected ichabod embryos. (D–K) All embryos are shown at 80% epiboly stage in lateral views. Scale bars represent 100 µm. EXPRESSION / LABELING:
PHENOTYPE:
|
Synergistic activities of chd and dkk1b mRNA induce the formation of a dorsal axis with a complete head structure in ichabod embryos. Phenotypic representation of (A) uninjected (63/63), (B and C) dkk1b mRNA-injected (48/64), (D and E) chd mRNA-injected (55/64), (F and G) chd and dkk1b mRNA-injected (47/58), and (H and I) β-catenin mRNA-injected ichabod embryos (48/62). (C, E, G, and I) Magnified images of the head region of B, D, F, and H. All embryos are shown at 24 hpf. Scale bars represent 100 µm. (J) Phenotypic classes obtained for each treatment. PHENOTYPE:
|
Dkk1b is a downstream factor of chd. Expression of dkk1b in (A) wild-type embryos, (B) uninjected ichabod embryos, and (C) chd mRNA-injected ichabod embryos. Expression of chd in (D) wild-type embryos, (E) uninjected ichabod embryos, and (F) dkk1b mRNA-injected ichabod embryos. All embryos are shown at the shield stage in animal pole views. Scale bars represent 100 µm. PHENOTYPE:
|
FGF-induced dkk1b expression is dependent on chd. Expression of dkk1b in (A) wild-type embryos, (B) uninjected ichabod embryos, (C) FGF8 mRNA-injected ichabod embryos, and (D) FGF8 mRNA and MOchd-injected ichabod embryos. Expression of chd in (E) wild-type embryos, (F) uninjected ichabod embryos, (G) FGF8 mRNA-injected ichabod embryos, and (H) FGF8 mRNA and MOdkk1b-injected ichabod embryos. All embryos are shown at the shield stage in animal pole views. Scale bars represent 100 µm. PHENOTYPE:
|
Activation of the FGF signaling pathway maintains dkk1b expression levels from mid-gastrulation to early somitogenesis, whereas chd fails to maintain dkk1b expression levels after mid-gastrula stage. Expression of dkk1b in (A–C) wild-type embryos, (D–F, P and Q) uninjected ichabod embryos, (G–I) FGF8 mRNA-injected ichabod embryos, (J–L) chd mRNA-injected ichabod embryos, (M–O, R and S) β-catenin mRNA-injected ichabod embryos, (T and U) β-catenin and XFD mRNA-injected ichabod embryos, and (V and W) β-catenin and d50 mRNA-injected ichabod embryos. Embryos are shown at the shield stage (P, R, T and V, dorsal views), 65% epiboly (A, D, G, J, M, Q, S, U and W, dorsal views), 90% epiboly (B, E, H, K and N, animal views), and 5-somite stage (C, F, I, L and O, lateral views). Scale bars represent 100 µm. EXPRESSION / LABELING:
PHENOTYPE:
|
Reprinted from Developmental Biology, 424(2), Tanaka, S., Hosokawa, H., Weinberg, E.S., Maegawa, S., Chordin and dickkopf-1b are essential for the formation of head structures through activation of the FGF signaling pathway in zebrafish, 189-197, Copyright (2017) with permission from Elsevier. Full text @ Dev. Biol.