Figure 10. Mel1a and Mel1c immunocytochemistry of whole-mounted Xenopus laevis surface corneal epithelium obtained at 4-h intervals during a 24-h light–dark cycle. Frogs were housed under a 12 h:12 h light–dark cycle (6:00 AM: lights on; 6:00 PM: lights off). All tissues in this figure were obtained in the dark. Mel1c labeling is represented in green (A, D, and G) and Mel1a labeling is represented in red (B, E, and H). The yellow labeling in the merged images (C, F, and I) indicates regions of co-localization of the red and green signal. A-C: Corneas obtained at 8:00 PM (2 h after lights off). Mel1c immunolabeling is almost exclusively located in the cytoplasm, but there is intense Mel1a immunoreactivity present in the lateral membranes, and also in the cytoplasm. The cytoplasmic immunolabeling of Mel1a and Mel1c is not co-localized. D-F: Corneas obtained at 12:00 M (mid-dark). Most of the Mel1c immunoreactivity is in the cytoplasm, although some lateral membrane labeling is also detected. Mel1a immunoreactivity is predominant in the lateral membranes, but there are many irregular-appearing cytoplasmic compartments that express Mel1a immunoreactivity, and they do not co-localize with the Mel1c cytoplasmic labeling. Essentially, all Mel1c lateral membrane labeling is co-localized with Mel1a membrane labeling. G-I: Corneas obtained at 4:00 AM (2 h before lights on). Most of the Mel1c immunoreactivity is located in the cytoplasm, with very little membrane labeling detected. Most of the Mel1a immunoreactivity is located on the lateral membranes, with some immunoreactivity also appearing in irregular cytoplasmic compartments. The Mel1a and Mel1c cytoplasmic labeling is not co-localized. Nuclei are stained with DAPI. The confocal images in all panels are comprised of three optical slices of 400 nm each in the z-series. The magnification bar (I) represents 20 µm.