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Fig. 2. Early Nodal signaling is required for normal epithelialization of the
epiblast and to prevent ectopic expression of extra-embryonic VE markers and
Furin in distal regions. (A-D) Whole-mount in-situ hybridization
(ISH) of an antisense probe directed against the deleted exon 2 identifies
NodallacZ/lacZ null mutants
(B) and reveals specific expression of Nodal mRNA in the epiblast and
EmVE of wild-type embryos (A). Nodal expression is also detected by
ß-galactosidase staining of
Nodal+/lacZ heterozygotes (C). In
E5.25 NodallacZ/lacZ
homozygotes, Nodal expression independent of Nodal activity is
detected only in the epiblast (D). (E-H) Immunostaining of E-cadherin
(E,F) and laminin (G,H) reveals irregularities in the epithelial organization
of mutant epiblasts (F), and detachment of distal embryonic visceral endoderm
cells from the laminin-positive basement membrane (arrowhead in H).
(I-P) In wild-type and Nodal+/lacZ
heterozygous embryos (control), Gata4, Hnf4, Ttr and Furin adopt a
restricted expression in the ExVE around E5.5 (I,K,M,O). In sharp contrast,
ectopic distal expression of these markers is observed in
NodallacZ/lacZ null mutants
(J,L,N,P).
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