Fig. 5

Bilaterally symmetric development of larvae treated with Nodal signaling inhibitor. a Dorsal view showing pitx expression on left side (arrowhead) of untreated 24-hpf larva. b Lack of left-handed pitx expression and symmetrical arrangement of somitocoels (arrowheads) in treated larva. c Mouth opening shown with pou4 expression in control 72-hpf larva. d Disappearance of mouth-related expression of pou4 and complete lack of organs originating from left side and domed pharyngeal floor (arrowhead) in treated larva. e, f Transverse sections showing future oral regions of control larvae at 24 hpf. g, h Transverse sections of treated 24-hpf larva showing bilaterally symmetric internal structures with a pair of rostral coeloms. Levels are comparable between (e) and (g) and (f) and (h), respectively. No oral mesovesicle but somitocoel on left side almost identical to that on right side in treated larvae (compare arrowheads between f and h). i Ventral view of normal pharynx with mouth opening (arrowheads). j, k Ventral views of treated pharynx showing bilaterally symmetric endostyle and club-shaped gland (arrowheads). i–k are shown with background of BM purple to clarify morphological details. l, m Immunolabeling for ventral muscles and acetylated tubulin. Left lateral views showing untreated larvae (72 hpf) (l) and SB505124-treated larvae with lack of neurons and oral musculature (66 hpf) (m). anp, anterior neuropore; csg, club-shaped gland; ch, notochord; CNS, central nervous system; es, endostyle; lld, left lateral diverticulum; m, mouth; nt; nerve cord; om, oral muscle; omv, oral mesovesicle; ONR, oral nerve ring; ph, pharynx; pn, peripheral nerve; pp, preoral pit; rc, rostral coelom; 1sc/L or R, first left or right somitocoel. Scale bars 50 μm for (a–d), 20 μm for (e–h), 100 μm for the others