Expression of opn4-related genes in extraocular tissues prior to retinogenesis. (A) opn4xa is weakly expressed in bilateral domains the dorsal diencephalon as early as 1 dpf. (B) At 2 dpf, the opn4xa-expressing cells (blue) are located in close proximity to the orthodenticle homolog 5 (otx5) expressing presumptive pineal gland (C) and medial to the dorsal habenular nuclei that express the Ca2+-dependent activator protein (cadps2) at 4 dpf . (D–F) From 1–3 dpf, opn4a positive cells are found in the forebrain where (G) they coexpress the orthopedia (otp) gene, a marker of the preoptic area. (H) At 1dpf, opn4b expression is found in the ventral forebrain and (I) at 4dpf is expressed in the dorsal thalamus (J–K) opn4.1 is expressed in small subset of cells in the caudal hindbrain at 4dpf. opn4b is the only gene that is also expressed in the body, as shown in (L) a whole-mount embryo and in (M) a section through the tail region at 1dpf.