Fig. 2

Early iridosomes contain several crystal leaflets that later coalesce into a single plate-like crystal. (A) An illustration of the zebrafish larva eye showing the iridophore (blue) and melanophore layers (purple), next to the lens. The anatomical location of the sections and areas that were taken for cryo-SEM (B-D) and cryo-FIB-SEM (E-G) are marked by a black rectangle and a black box, respectively. (B-D) Cryo-SEM images of freeze-fractured surfaces of a zebrafish larva eye and the iridophores within it. (B) A low magnification of the eye surface. Iridophore and melanophore layers are pseudocolored in blue and purple, respectively. (C) A close-up view of an iridophore next to a melanophore. (D) Iridosomes at different maturation stages. (E-G) Cryo-FIB-SEM images and 3D representations of segmented milled sections from a freeze-fractured zebrafish larva eye. (E) An illustration showing the stack of images of consecutive volumetric sections, with pseudocolored iridophore and melanophore layers. (F) An eye iridophore 3D representation of the area marked by a dashed rectangle in E. Mature elongated iridosomes and round developing iridosomes are marked in blue, nucleus is marked in gray. The early 200–300-nm-long iridosomes shown in (G_i-G_iii) are marked with white arrows. (G_i-G_iii) Cryo-FIB-SEM micrographs of different planes within the iridophore shown in (F). White arrows mark the iridosomes whose 3D reconstructions are shown in the insets.