Fig. 2

a–d Optical sections at the level of the forebrain of WT embryos at the 2–3 som (a), 5 som (b), 7 som (c), and 10 som (d) stages. e–l Transverse sections through the ANP of 2–3 som (e, i), 5 som (f, j), 7 som (g, k) and 10 som (h, l) embryos. e–h Tg[emx3:YFP] embryos labeled with anti-GFP (green), phalloidin (F-actin, magenta), and DAPI (nuclei, blue). i–l WT embryos labeled with phalloidin (F-actin, green), anti-Sox3 (magenta), and anti-p63 (nuclear label, green). m Higher magnification image of j, gray scaled to reveal F-actin and p63 and pseudo-colored - color code: light blue: superficial eye field cells, dark blue: deep layer eye field cells that apically constrict to form the optic vesicles, green: neural component of the neural fold, orange: olfactory placode (Sox3/p63-negative cells), yellow: non-neural component of the neural fold. n Measurements of neural fold convergence, scored as the distance between the medial-most p63-positive cells on either side of the midline at different developmental stages. Notches depict the 95% confidence interval around the median and the green triangle depicts the distribution mean. 2 som: 48 measurements from 14 embryos, mean = 136; 5 som: 144 measurements from 16 embryos, mean = 73.0; 7 som: 87 measurements from 10 embryos, mean = 36.0; 10 som: p63 domain is fused, no measurements. Statistical analysis: Mann–Whitney U tests, two-sided; 2 som vs 5 som: P = 1.18e⁻²¹, AUC = 0.961; 2 som vs 7 som: P = 8.35e⁻²², AUC = 1.00; 5 som vs 7 som: P = 2.14e⁻³¹, AUC = 0.958. o Side view of a 4 som Tg[emx3:YFP] embryo. s superficial layer, d deep layer, NF neural fold, NG neural groove, hyp hypothalamus, tel telencephalon, ov optic vesicle, DL dorso-lateral hingepoints; M medial hingepoint, NE neural ectoderm, NG neural groove, NNE non-neural ectoderm, OP olfactory placode. Annotations: black arrowhead = median groove, white open arrowhead = elevated neural fold-like structure, dashed line = separation of the deep and superficial layers; brackets = hingepoints; dotted line = A-P range of the neural folds; white arrowhead = medial-most epidermis; red asterisk = neural groove. Scale bars: a and o = 100 μm, e = 25 μm.