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Figure 2. Hh/Gli Signaling Is Required for Respiratory Wnt-Mediated Specification in Xenopus
(A) Schematic of a section through the lung field showing a model of Hh/Gli regulation of Wnt/BMP-mediated respiratory induction.
(B) In situ hybridization and immunostaining of foregut sections from NF34 stage control and Hh/Gli-deficient Xenopus embryos generated by either Gli2+Gli3-MO injection or cyclopamine treatment from NF20–34. Expression of the lung-inducing wnt2/2b and bmp4 ligands and Nkx2-1+ respiratory specification requires Hh/Gli signaling, which can be rescued by injection of a human Gli2 mRNA. Foxf1+ lpm and nuclear pSmad1/5/8 are also reduced in Hh-deficient embryos. The scale bar represents 50 μM.
(C) Expression of ptch1 and wnt2b are activated in mesoderm explants treated with the Hh-pathway agonist SAG from NF20–34.
(D) Activation of β-catenin by Bio treatment from NF28–34 rescued and expanded (bracket) the nkx2-1 respiratory domain in Gli2+3 MO-injected embryos, indicating that Hh signaling acts upstream of Wnt. The red arrow indicated absent nkx2-1 expression. See also Figure S2. |
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Display additional annotations [+]
Gene |
Clone |
Species |
Stages |
Anatomy |
gli2
|
|
laevis
|
NF stage 35 and 36
|
head region
,
splanchnic layer of lateral plate mesoderm
,
pronephric kidney
,
neural tube
,
pharyngeal region
|
gli1
|
|
laevis
|
NF stage 35 and 36
|
head region
,
splanchnic layer of lateral plate mesoderm
,
neural tube
,
pharyngeal region
|
gli3
|
|
laevis
|
NF stage 35 and 36
|
head region
,
splanchnic layer of lateral plate mesoderm
,
pronephric kidney
,
neural tube
,
pharyngeal region
|
nkx2-1
|
|
laevis
|
NF stage 35 and 36
|
forebrain
,
endoderm
,
foregut
,
thyroid primordium
,
lung primordium
|
wnt2
|
|
laevis
|
NF stage 35 and 36
|
midbrain-hindbrain boundary
,
head region
,
splanchnic layer of lateral plate mesoderm
|
shh
|
|
laevis
|
NF stage 35 and 36
|
head region
,
endoderm
,
foregut
,
neural tube
,
pharyngeal region
|
sftpc
|
|
laevis
|
NF stage 35 and 36
|
endoderm
,
foregut
,
lung primordium
|
wnt2b
|
|
laevis
|
NF stage 35 and 36
|
lens
,
midbrain-hindbrain boundary
,
splanchnic layer of lateral plate mesoderm
|
|
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Figure 1. Bidirectional Endoderm-Mesoderm Signaling Is Required for Respiratory Specification in the Xenopus Foregut.
(A) Model of mesoderm-endoderm paracrine signaling during foregut organogenesis.
(B) Schematic of the Xenopus organ induction assay. The foregut endoderm (yellow) and mesoderm (orange) were isolated at NF20 and cultured together or separately until NF36–38.
(C) In situ hybridization using the indicated probes reveals that induction of nkx2-1/sftpc+ respiratory progenitors requires the mesoderm, whereas wnt2, wnt2b, and gli1 expression in the mesoderm requires the endoderm (outlines in yellow dashed line in embryo sections). The number of explants expressing the marker is indicated in the lower right of each image.
See also Figure S1. |