Fig. 3. Marker gene expression in the zebrafish thyroid primordium. (A,D,G) hhex (A,G) or hhex plus nk2.1a (D) expression in the thyroid (arrows). (B,E,H) pax8 (B, H) or pax8 plus hhex (E) expression in the thyroid (arrows). (C,F,I) pax2.1 (C,I) or pax2.1 plus pax8 (F) expression in the thyroid (arrows). (J) Lower jaw area of 4 dpf wild-type larva, lateral view. Arrows indicate the nk2.1a expression in patches along the ventral aorta (arrowheads). (K) Cryosection of a 7 dpf wild-type larva, showing pax8 (arrow) expression in the area of a thyroid follicle. (L) Cryosection of a 7 dpf wild-type larva, showing pax2.1 expression (arrow) in the area of a thyroid follicle. The position of the sections in K,L corresponds roughly to the right arrow in J. e, Pax gene expression in the eye; h, heart, H, cartilage of the hyoid arch (second branchial arch); M, cartilage of the mandibular arch (first branchial arch); m, Pax gene expression in the midbrain-hindbrain boundary; mo, mouth cavity/pharynx.