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Figure 1. Restricted migration of branchial neural crest cells in Xenopus. (a) The initial segmentation and (b,c) migration of streams of neural crest into specific branchial arches (1–4). The third and fourth arch neural crest streams segment during migration. Adapted from [15]. (d) Expression pattern of AP-2 plus Krox-20 in a stage 25 Xenopus embryo revealed by whole-mount in situ hybridisation. AP-2 is expressed in all branchial neural crest (n1–n4: neural crest streams migrating into branchial arches 1–4), whereas Krox-20 expression is restricted to third arch neural crest (see also Figure 2f), which therefore is stained more intensely. (e) Section through dorsal region of migrating neural crest after detection of AP-2 plus Krox-20 expression. The neural crest destined for the second, third and fourth arches are adjacent. (f) Section through a more ventral region of the embryo shown in (d). After migration deep into the branchial arches, the streams of second, third and fourth arch crest are now separated by the pharyngeal pouches of the endoderm. |
