Fig. 1.

In contrast to pigmented WT larvae (A), casper larvae are highly transparent due to a lack of melanocytes and iridophores (B). Thyroid marker expression in casper embryos indicate normal progression of thyroid morphogenesis (C–E). WISH of casper embryos with riboprobes for nkx2.1a (C), tg (D), and slc5a5 (E) label the thyroid primordium at 26 hpf (C), demonstrate formation of a first follicle at 55 hpf (D) and stain the dispersed thyroid tissue along the pharyngeal midline at 100 hpf (E), respectively. Inset in D shows a magnified view of the thyroid region. Arrows point to the thyroid. Lateral (A–D) and ventral views (E) are shown with all embryos being oriented with anterior to the left.