Fig. 1.

Fig. 1.

Crystal formation dynamics and development in zebrafish eye iridophores. (A) Brightfield image of a 5 d post fertilization (dpf) zebrafish larva showing the highly reflective iris produced by guanine-based crystals in the eye. Scale bar, 500 μm. (B) Schematic of the spatial arrangement of iridophores in the larval eye and the guanine-containing iridosomes within them. Bottom: cryo-TEM image of a single membrane-bound iridosome containing a guanine crystal. (C–E) Maximum intensity projections (MIPs) from confocal imaging of pnp4a:PALM-mCherry (pnp4a is an established iridophore marker) (61) transgenic larvae at 48, 60, and 96 hpf, revealing the progressive differentiation of iridophores and the accumulation of intracellular crystals during development. Iridophore membranes are labeled in red, while guanine crystal reflectance is shown in white. Insets highlight higher magnification views. Scale bar, 10 μm. (F–J) Time-lapse confocal images of a single iridophore in the developing larval eye over 5 h. Initially, only a few guanine deposits are visible. As development proceeds, crystal number increases rapidly, reflecting active biogenesis of iridosomes during this developmental window. Scale bar, 10 μm.