FROM COLORS TO KIDNEY STONES: THE CELLULAR REGULATION OF CRYSTAL-FORMING CELLS

Chameleons, spiders, planktonic crustaceans, fish, and many other animals use molecular crystals for an astonishing variety of optical functions, from white light scattering in spiders to tunable reflecting colors in the copepods. These crystals are formed by specialized cells called iridophores, in which remarkable control over crystal shape, size, and assembly is obtained using strategies that are beyond state of the art in materials science and solid-state chemistry. While these cells were identified many years ago, almost nothing is known about the processes which enable this tremendous control over bio- molecular crystals. We used the zebrafish skin iridophores as a model system to investigate: 1. How cells with different architectures and different optical properties are obtained? and 2. What is the cellular machinery which drives structural color change? Using diverse tools, we found that distinct iridophore types with different crystal morphologies, architectures, and optical properties were obtained by differentiation based on their microenvironments. We further found that only one type of iridophores was capable of changing its colors and that this color change was facilitated by motor proteins actively pulling the membrane-bound crystals.