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Fig. 6. Phenotypic defects and abnormal Nodal expression in
Gdf3 mutants. (A,B) Foxa2 is normally
expressed in the anterior primitive streak (ps) (A), but is often absent or
greatly reduced in Gdf3 homozygotes (B, arrow). (C,D)
Lhx1 is expressed in the primitive streak, nascent mesoderm and
anterior visceral endoderm (ave) (C), but is frequently absent (D, arrow) or
greatly reduced (D, arrowhead) in Gdf3 mutants. (E,F)
Expression of Otx2 in the anterior neuroectoderm (ane) is unaffected
in Gdf3 homozygotes. (G,H) Expression of Cerl
marks the AVE and definitive endoderm (de), but the definitive endoderm is
often absent in Gdf3 homozygotes (H, arrow). (I,J)
Hesx1 expression in the AVE is sometimes reduced or absent in
Gdf3-/- embryos (J, arrow). (K-M)
Hex expression in the AVE is sometimes completely absent (L) or is
misplaced distally (M, arrow). (N,O) Asymmetric expression of
Nodal in the left lateral plate mesoderm (lpm) is observed in
Gdf3-/- embryos with normal morphology at 8.0 dpc (N); a
few abnormal mutants lack Nodal expression in the lateral plate, but
retain expression around the node (nd) (O, arrow). (P,Q)
Expression of T (brachyury) marks the tailbud (tb) and notochord
(not) at 8.0 dpc (P), but is absent or greatly reduced in abnormal
Gdf3-/- embryos (Q, arrow). (R,S) In rare
Gdf3 homozygotes, expression of T reveals a partial axis
duplication (R, arrows), corresponding to formation of twinned notochords (S,
arrows) and multiple somites (arrowheads). (T-D')
Expression of Nodal is found in the proximal-posterior epiblast (ep)
at 6.0 dpc (T,Z), but is downregulated in some Gdf3 mutants (U) while
upregulated in others (V,A'). At 6.75 dpc, Nodal is expressed
in the posterior epiblast and in the visceral endoderm (ve) overlying the
primitive streak (W,B'), but some Gdf3-/- embryos
show an expansion of the primitive streak (X,C', double-headed arrow)
that is accompanied by increased expression in the visceral endoderm
(C', arrow). Abnormal Gdf3-/- embryos with the
`conical' morphology (Y) show high-level Nodal expression
circumferentially in the visceral endoderm surrounding a thick mesodermal
layer (mes) (D', arrow). (E',F') Expression of
Cripto in the proximal-posterior epiblast at 6.75 dpc is unaffected
in most Gdf3 homozygotes, but is upregulated in `conical' mutants
(F'). (G',H') Bmp4 expression in the
extra-embryonic ectoderm (exe) at 6.5 dpc is unaffected in Gdf3
mutants. (I',J') Expression of Gdf1 in the
pre-gastrulation epiblast is unaffected in Gdf3 homozygotes. Scale
bars: 100 µm for A-Y,E'-J'; 50 µm for Z-D'.
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