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Fig. 2. Neural crest cells are dispensable for early head muscle differentiation
and specification. (A) Scheme of dorsal neural tube/neural fold
ablation at HH8 to remove neural crest cells. Dorsal view, anterior to the
top, ablated area in turquoise. (B,F,J,N,R)
Heads of unoperated embryos; (C,G,K,O,S)
higher magnification of the lateral rectus/MAM region corresponding to boxed
area in B,F,J,N,R. (D,H,L,P,T) Operated
embryos (E,I,M,Q,U) higher magnification of
lateral rectus/MAM region as indicated in D,H,L,P,T. Embryos are at HH19;
lateral views, anterior is to the top, dorsal to the left. Embryos are double
stained with the RM0270 antibody to trace the nervous system (brown). (B-E)
Dlx5 expression. (B,C) In wild-type embryos, Dlx5 is
predominantly expressed in the neural crest cells filling the branchial
arches. (D,E) Operated embryo. While Dlx5 expression in the
derivatives of the nasal and otic placodes and expression in the maxillary and
mandibular ectoderm remained, the neural-crest-associated expression is absent
(open arrowheads). Moreover, the ophthalmic and the mandibulomaxillary aspect
of the trigeminal ganglion are separate. This indicates that the surgical
procedure was successful. (F-I) Paraxis expression. Both in the wild
type (F,G) and in the operated embryo (H,I), Paraxis labels the
developing lateral rectus EOM. (J-M) En2 expression. En2 is
expressed in the mandibular arch muscles of both the unoperated (J,K) and the
operated (L,M) embryo. (N-Q) Myf5 expression. In the wild type (N,O),
muscle anlagen for the mandibular and hyoid arch muscles and the lateral
rectus, dorsal oblique, dorsal rectus and ventral retcus EOM are
differentiating and express Myf5. This is also the case for neural
crest ablated embryos (P,Q). (R-U) MyoR expression. MyoR
expression associated with the ventral/branchiomeric muscle anlagen is present
in the wild type (R,S) and operated (T,U) embryo. Note that in the absence of
neural crest cells, the MyoR expression domains remained proximally
unsegregated (small arrows). Scale bars: 400 µm in B,F,J,N,R; 200 µm in
C,G,K,O,S; 400 µm in D,H,L,P,T; 200 µm in E,I,M,Q,U. d, diencephalon;
do, dorsal oblique EOM; dr, dorsal rectus EOM; hy, hyoid arch; ma, mandibular
arch; mmx, mandibulomaxillary aspect of the trigeminal; oph, ophthalmic aspect
of the trigeminal (Vth) nerve; ov, otic vesicle; r, rhombomere; VII, facial
nerve; vr, ventral rectus EOM.
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