||Figure 5. XHoxb2 expression is precociously down-
regulated in second arch NCCs. A–D: Whole mount
in situ hybridizations with XHoxa2 (A,C) and XHoxb2
(B,D) antisense probes on stage-18 (A,B; dorsal views)
and stage-30 (C,D; lateral views) embryos. Anterior is
to the right. A,B: At stage 18, both XHoxa2 and
XHoxb2 are expressed in the neural plate and
premigratory NCCs of the hyoid (hcs) and branchial
crest (bcs) segments, albeit with distinct intensities.
C,D: At stage 30, the anterior limits of expression in the rhombencephalon are at the r1/r2 and r2/r3 borders for
XHoxa2 and XHoxb2, respectively (ov, otic vesicle). In
the NCCs, Xhoxa2 is strongly expressed in BA2 and at
lower levels in BA3-BA4, while Xhoxb2 expression is
no longer present in BA2 and BA3 and only persists in BA4.