Fig. 1

SIX1 expression pattern in the head of HH11 (13ss) chicken embryo. a Schematic representation of a HH11 (13ss) chicken embryonic head; red dotted lines indicate the position and orientation of the sections shown in b-f (mesencephalic level) and g-k (rhombencephalic level). b and g SIX1 gene transcripts are detected in the foregut endoderm and in the cranial mesenchyme, located ventral to the mesencephalon (in b) and more laterally, at the rhombencephalic level (in g). c-f Transversal section, showing immunoreactivity to SIX1 (d) and SOX10 (e), with no apparent overlap (See merge staining in f). d and i Adjacent sections to b and g, respectively, after SIX1 immunostaining, show an expression pattern of SIX1 similar to that observed after in situ hybridization. e and j SOX10 antibody labels the NCC, which migrate from the mesencephalon dorsolaterally under the ectoderm in e and are starting to migrate from the rhombencephalon in j. f and k Merge of SIX1 and SOX10 stainings (arrows: migratory NCC; arrowheads: cranial paraxial mesodermal cells). D-V, dorso-ventral orientation; f, foregut; nt, neural tube; h, heart. Scale bars, 100 μm