Fig. 6

SIX1 expression in the nasal and periocular regions in E7 chicken. a Schematic representation of an E7 (HH30) chick embryo; the red line indicates the position and orientation of the section in b-m and o-q; adjacent sections are shown in n, r and s. (b-e) At the level of the eyes (e in b), SIX1 immunoreactivity (c) is widely detected in the periocular mesenchyme, nasal septum (* in b), maxillary bud (ma), and in extraocular muscles, positive for anti-myosin MF20 (d, e). f (Magnification of the area boxed in b) SIX1 expression pattern is dense in the periocular mesenchyme adjacent to the nasal septum positive for the chondrocytic marker CS. g-g” Highlights of the region boxed in f, showing SIX1 expression in the CS-positive scleral cartilage. h and i Magnifications of the areas boxed in e, showing SIX1 expression in medial rectus (h-h”) and inferior oblique (i-i”) extraocular muscles marked by MF20. j-n SIX1-positive nuclei are densely packed in the nasal mesenchyme and perichondrium while present at a lower density in the nasal septum (* in j), which is immunoreactive to CS (l, m) and SOX9 (n). o, p, q (magnifications of areas boxed in k, l, m) SIX1 is expressed in the CS-expressing nasal cartilage and, more strongly in its perichondrium; the latter tissues express the transcription factors SOX9 (r) and RUNX2 (s), respectively. D-V, dorso-ventral orientation; optic nerve (op). Scale bars, 100 μm, except for b-e, 300 μm and g - g”, 50 μm