Fig. 4

Expression of the Radar gene during zebrafish embryogenesis. Whole-mount in situ hybridisation of embryos of different developmental stages. (Anterior is to the left, by convention). (A and B) Dorsal views from embryos at the 90% epiboly (9 hpf) and tailbud (11 hpf) stages. In (A), Radar is expressed in the anterior third of the embryo, at the edges of the neural plate, in two parallel lines of cells starting approximately distal to the future forebrain region. Later (B), the domain of expression has expanded both rostrally and caudally to surround the entire edge of the neural plate. The strongest staining is observed in the future mid- and hindbrain regions. The posterior midline of the embryo is also stained. (C and D) In the 16-somite-stage embryo (14 hpf), Radar is expressed as a salt and pepper pattern along the dorsal side of the embryo with stronger expression in a region posterior to the eye. Staining is also observed in a thin region at the level of the dorsal midline of the embryo and in the posterior part of the spinal cord in a rostro-caudal gradient with higher expression in the tailbud. Fainter staining is detectable in the hatching gland and the hypochord. (C) Left lateral view. A part of the yolk was lost during washing steps. (D) Dorsal view. (E-G) Expression of Radar in the 26-somite-stage embryo (22 hpf). (E) Left lateral view of an entire embryo. Expression persists in the dorsal midline of the embryo. starting rostrally on the sides of the fourth ventricle (tulip-like structure. dorsal view in (G)), continuing just behind the otic vesicle as the roof plate and caudally finishing as the roof plate and the future dorsal and ventral fins. Expression also persists in the hypochord and the hatching gland. New sites of expression include the dorsal quadrant of the eye, exactly opposite to the choroid fissure, the lateral line primordia (see (F). detail of the head region in (E)) and the posterior ventral mesenchyme. In (F), the position of the otic vesicle is indicated by an arrowhead. (H and I) Expression of Radar in posterior mesodermal tissues in wild-type (H) and ntl (I) embryos. The domain of expression in the ntl ventral posterior mesenchyme is smaller than in wild-type embryos. No detection in the region corresponding to the hypochord (above the mesenchyme region) is observed in ntl embryos. Dorsal expression of Radar is maintained in ntl embryos but out of focus because the tail is kinked. Arrowheads in (A), (C) and (E) indicated the level of the sections depicted subsequently.