Figure 2. Mel1a, Mel1b, and Mel1c double-label immunocytochemistry of cryostat sections of Xenopus laevis corneal epithelium. A and C: Corneas obtained at 12:00 noon (12N) in the light. B and D: Corneas obtained at 12:00 midnight (12M) in the dark. Sections were immunolabeled with Mel1a and either Mel1b or Mel1c receptor antibodies. Mel1a labeling is represented in red, and Mel1b and Mel1c labeling is represented in green. Yellow indicates regions of co-localization of the red and green signal. Melatonin receptors are expressed in the surface epithelium, but their relative levels of expression and distribution change between 12N and 12M. Arrows indicate the immunolabeled plasma membranes of the surface epithelium. Nuclei are stained with DAPI. The magnification bar (D) represents 20 µm.