Conserved activity of gnathostome Hoxa2 neural crest (NC) enhancers in zebrafish and lamprey. a Sequence alignment of gnathostome Hoxa2-Hoxa3 and lamprey hox2-hox3 gene loci against the human locus. Conserved non-coding sequences (pink), untranslated regions (UTRs) (cyan) and coding sequences (blue) are highlighted. The relative locations of the mouse hindbrain and NC cis-elements (top) are shown. Gnathostome Hoxa2 enhancers used for cross-species reporter analysis are detailed below the alignment. Letters within parenthesis indicate species of origin of the enhancer: zf, zebrafish; f, fugu; m, mouse. b, c Green fluorescent protein (GFP) reporter expression in zebrafish and lamprey embryos (lateral views), mediated by wild-type (b) and mutated (c) gnathostome NC enhancers. For zebrafish, the otic vesicle is circled and GFP expression in rhombomeres (r) and pharyngeal arches (2–5) indicated. Lamprey pharyngeal arches are labelled (2–4). GFP-expressing embryos shown are representative of the expression potential of the reporter construct in each case, as inferred from screening many (typically more than 100) injected embryos. Supplementary Table 2 provides the number of embryos and details of specific expression for all constructs in lamprey. Injection statistics for the transient transgenic zebrafish embryos shown in c are given in Supplementary Table 3. d Frontal sections through the transient transgenic lamprey embryos shown in Fig. 3b, with GFP transcripts detected by in situ hybridisation, revealing expression in NC-derived mesenchyme (arrowheads) in the pharyngeal arches (numbered). Scale bars: 100 µm
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