Preparation of RNA probes and in situ hybridization were carried out as previously described (17 (link)). Digoxigenin (DIG)- and fluorescein-labeled antisense and sense RNA probes for zebrafish parapinopsin and parietopsin mRNAs were synthesized by using the DIG RNA labeling kit and fluorescein RNA labeling kit (Roche), respectively. Sections were pretreated with proteinase K and hybridized with each RNA probe in ULTRAhyb Ultrasensitive Hybridization Buffer (Ambion). For double fluorescence labeling, sections hybridized with DIG-labeled probes were incubated with HRP-conjugated anti-DIG antibody (Roche) and subsequently treated with the TSA plus DNP (HRP) system (Perkin-Elmer), followed by incubation with Alexa 488-conjugated anti-DNP antibody. Fluorescein-labeled probes on the sections were detected by incubation with alkaline phosphatase-conjugated anti-fluorescein antibody (Roche) followed by a color reaction using the HNPP Fluorescent Detection Set (Roche).