Fig. 2

SIX1 expression pattern in the head of HH15 (25ss) chicken embryo. a Schematic representation of a HH15 chicken embryo; red dotted lines indicate the position and orientation of sections shown in b-g, h-j and k-m images. b and h SIX1 transcripts expression in the lateral mesenchyme of the anterior head, and, in a more caudal section (h), in the periocular mesenchyme, foregut (f), branchial arch (ba) mesenchyme and superficial ectoderm and otic vesicles (ov) (e, eye). c-g Horizontal section (D-V dorso-ventral orientation); SIX1, SOX10 and TUJ1 immunostainings (the box area is magnified in c’-g’): SIX1 is expressed in the mesenchyme surrounding the trigeminal ganglion (tg) and in the trigeminal ganglion and nerves, where it labels a subset of TUJ1-positive neurons, not SOX10-positive non-neuronal cells (c’-g’); arrow in g’ indicates a SIX1-positive neuron. i, j section at the level of the eye, showing SIX1 expression in the periocular cranial mesenchyme, the BA mesenchyme and the endoderm lining the pouch, k-m Section at the anterior somitic level; SIX1 is strongly expressed in the dermomyotome (l) while SOX10 labels the migratory NCC, indicated by an arrowhead (m). Scale bars, 100 μm