The eyes were enucleated and frozen in isopentane. For immunocytochemical staining, frozen sections were air dried on glass slides coated with 0.05% poly-l-lysine. Sections were incubated in 1% goat serum in 0.05 M PBS (pH 7.4) for 15 minutes. After three washes with PBS, the sections were incubated in 0.3% H2O2 in methanol for 30 minutes and washed with PBS. Subsequently, the sections were incubated at 4°C overnight with a polyclonal antiserum against GFP from rabbit (Dianova) diluted 1:200 in PBS. After three washes with PBS, the sections were covered with goat serum for 15 minutes. The secondary antibody (anti-rabbit IgG coupled to Cy3) was diluted 1:800 in PBS, and the sections were incubated for 1 hour at room temperature. After three washes with PBS, the sections were dehydrated, embedded in Entellan (EM Science, Darmstadt, Germany) and investigated under a fluorescence microscope (Axioplan; Carl Zeiss, Oberkochen, Germany), using Cy3 (excitation 550 nm, emission 570 nm)-specific or EGFP (excitation 471 nm, emission 503 nm)-specific filter sets. Photographs from the same area were taken with a digital camera (Orca; Hamamatsu) with both filter sets separately. Overlays were made with image-aquisition software (Openlab; Improvision). As a control, the anti-GFP antibody was omitted.