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Fig. 7. The signal from the neural tube is not sufficient to trigger lateral
rectus development. (A) Scheme of quail-chick neural tube grafting
at HH10; dorsal view, anterior to the top. (B-F) Lateral views of
operated embryos at HH19, stained for the lateral rectus marker Lbx1
in blue and the quail cell marker QCPN in brown; anterior to the top, dorsal
to the left. The anteroposterior orientation of the grafts is indicated. (B)
Orthotopic control grafting of rhombomere2; Lbx1 is expressed at the
normal location (green arrow). (C) When the neural tube from posterior
midbrain to rhombomere 2 levels was grafted in place of midbrain and posterior
diencephalon, the ectopic rhombomere 2 did not trigger ectopic Lbx1
expression (open arrowhead). (D) Similarly, no ectopic Lbx1
expression occurred when the graft was transplanted in place of rhombomeres
4-6 (open arrowhead). (E) When the posterior midbrain to rhombomere 2 was
replaced with neural tissues from anterior midbrain to diencephalic levels,
Lbx1 was expressed at the normal location dorsal to the mandibular
arch (green arrow). (F) Grafting of the posterior hindbrain, including parts
of the otic placode to midbrain-rhombomere 2 levels, led to the development of
an ectopic otic vesicle, and also permitted Lbx1 expression (green
arrow). Scale bar: 200 µm. d, diencephalon; hy, hyoid arch; lr, lateral
rectus EOM; m, midbrain; ma, mandibular arch; ov, otic vesicle; r,
rhombomere.
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