Expression profiling of nos2b in zebrafish embryos by reverse transcription-polymerase chain reaction (RT-PCR) and whole-mount in situ hybridization (WISH). A: Chromosomal mapping of nos2b. Linkage map showing the localization of nos2b (=unp2188) to LG15 (obtained from http://wwwmap.tuebingen.mpg.de/). The distances between markers on the main map (left) are given in centimorgans (cM) and in centirays (cR) for the expanded region (right). B: Detection of nos2b transcripts by RT-PCR revealed a lower maternal expression in contrast to a higher expression after 16 hours postfertilization (hpf). An internal control using the house-keeping gene, elongation factor 1 alpha (ef1α) is also shown. C-E: nos2b transcripts were first detected at 14 hpf in the prospective ventral diencephalon. Expression of nos2b (arrowheads in C,D,E,F and G) is confined to the anterior part of the forebrain as shown in the frontal view (D), lateral view and the flat mount ventral view (E) of the 14 hpf embryo double stained with nos2b and catL1b. The gray dotted line in E outlined the optic primordium (op). F: By 20 hpf nos2b remained in the ventral floor of the forebrain. G: However, nos2b is excluded from the lim3-positive anterior pituitary. H-J: In addition, nos2b expression domain is ventrad to the nk2.1-positive hypothalamus (H,I) and colocalizes with fgf3 (J). d, diencephalon; e, eye; hg, hatching gland; ht, hypothalamus; pit, pituitary; t, telencephalon.