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Fig. 6. Analysis of mD2LIC–/– mutants at 8.5-9.0
dpc. (A,B) Expression of T is discontinuous and distorted in the notochord of
embryos lacking mD2LIC. (A) Wild-type embryo; (B)
mD2LIC–/– embryo. (C,D) Expression of
Shh is also discontinuous in null mutant embryos (data not shown) and
is absent in the ventral neural tube as seen in histological sections (black
arrowheads; sections shown here are from the head region). (C) Wild-type
embryo; (D) mD2LIC–/– embryo. (E,F)
mD2LIC-null embryos lack expression of Foxa2 in notochord and ventral
neural tube and expression is greatly reduced in definitive embryonic
endoderm. (E) Wild-type embryo (ventral view); (F) mutant embryo (ventral
view); Foxa2 expression is lacking in notochord and ventral neural
tube (arrowhead), and there is a reduction of expression in definitive
endoderm (arrow). (G-Q) Defective establishment and maintenance of the
left-right axis in mD2LIC–/– mutants.
Wild-type (G, distal view) asymmetric expression of nodal around the node is
not observed in null mutants (H, distal view). At the early somite stage,
left-lateral plate specific expression of nodal (I, posterior view) is either
expressed bilaterally (J, ventral view), on the right (K, dorsal view, white
arrowheads; black arrowhead indicates expression in the node), on the left or
absent (data not shown). Expression of Leftb in the left side of the
ventral neural tube (L, anterior view, arrowhead; broken white line indicates
the anterior edge of the head folds) is absent in null mutants (M, dorsal
view, arrowhead) and Ebaf expression is randomised (in this case
showing bilateral expression). Left lateral plate Pitx2 specific
expression (N, ventral view) is randomised in null mutants, appearing
bilaterally in class I and II mutants (O,P, ventral view, arrowheads) or on
the left (Q, left-hand embryo, ventral view, arrowhead) or on the right (Q,
right-hand embryo, ventral view, arrow) in class III mutants. White lines
indicate the boundary of the headfolds. (R,S) Lack of Fgf8 expression
in the anterior neural ridge (ANR) of
mD2LIC–/– embryos. (R) Wild-type embryo
(ventral view). Arrowhead shows expression of Fgf8 in the ANR. (S)
mD2LIC–/– mutant embryo (ventral view).
Fgf8 expression does not occur the in ANR (arrowhead). (T-Y) TUNEL
staining reveals altered apoptotic profiles during neural tube closure. Normal
apoptosis in the region of the hindbrain (arrowheads; T, lateral view; U,
dorsal view of trunk; V, dorsal view of head) is absent in mutant (arrowhead
in W, lateral view; X,Y, dorsal view). In addition, ectopic cell death is
observed along the dorsal midline in mutants (X, dorsal view of trunk,
arrowhead), but does not occur in wild-type littermates (U). Cell death is
also observed in the cephalic mesoderm surrounding the notochord in the region
of the head (arrowheads, Y).
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