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Fig. 2. Neural induction by inhibitors of Smad1 and Smad2 signaling occurs in the absence of the mesoderm in Xenopus. Double in situ hybridizations showed that neural marker induction in embryos injected with tActRIIB, Smad7 or Ski occurred in the absence of the mesodermal markers Chordin and MyoD. The red speckled staining is from the injected lineage tracer. |
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Fig. 7. Activation of Smad2 signaling converts neural tissue to neural crest and mesodermal tissues in Xenopus. (A) In the absence of DEX, leaky GR-Smad2 activity was sufficient for neural crest induction, but not sufficient for inhibition of neural markers or induction of mesodermal genes. Activation of GR-Smad2 by DEX (2 μM) at mid-gastrula stages led to inhibition of Sox2 and Sox3 and simultaneous induction of the mesodermal markers MyoD and Chordin in the neural plate (seen more clearly in Fig. 7B and Fig. 8). GR-Smad2 RNA (0.1-0.2 ng) was used. The embryos were orientated with the head toward the left and viewed from the dorsal side. (B) Induction of mesodermal markers by activated GR-Smad2 occurred in the neural plate, as shown in transversely bisected (top) or sectioned (bottom) embryos. |
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Display additional annotations [+]
| Gene |
Clone |
Species |
Stages |
Anatomy |
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twist1
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xenopus
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NF stage 28
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neural crest
,
branchial arch
,
head
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sox2
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xenopus
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NF stage 28
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olfactory placode
,
brain
,
eye
,
lens placode
,
epibranchial placode
,
[+]
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otx2
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xenopus
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NF stage 28
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olfactory placode
,
brain
,
eye
,
lens placode
,
head
|
|
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Fig. 10. Activation of Smad2 at gastrula stages in the neural plate leads to defective neural development in Xenopus. (A) Activation of GR-Smad2 (0.2-0.5 ng) at mid-gastrula stages (stage 11) in the neural tissue induced neural defects in frog tadpoles. Embryos showed reduced head structures and malformed or missing eyes. Embryos without DEX treatment developed normally. (B) Histological analyses indicated that neural development at both anterior (upper panels) and posterior (lower panels) trunk levels was defective when Smad2 signaling was activated. The neural tube was disrupted and ectopic notochord (yellow arrowhead) and mesenchyme (red arrowhead) were observed in the neural derivatives. (C) In situ hybridization demonstrated that Sox2 was reduced and split from the midline and Otx2 was reduced, but the neural crest marker Twist and the muscle marker MyoD were unaffected. All embryos were viewed from the lateral side with the anterior to the left, except the second column of Sox2 in panel C, which was viewed from the dorsal direction. |
