How do zebrafish stripes disappear?

Many animals, including chameleons and certain species of fish, tune their crystalline-based structural colors to facilitate camouflage, kin recognition, and mate choice. In such systems, remarkable colors are produced by constructive interference of light reflected from stacks of intracellular crystals. The machinery that enables this robust cellular reorganization is unknown. We have used iridophore cells of the zebrafish to reveal the cellular basis of structural color change. Using a combination of super-resolution fluorescence light microscopy, genetic manipulations, and micro-focused X-ray diffraction, we found that zebrafish iridophores are capable of changing their colors in response to stimuli and that this change occurs due to the tilting of the intracellular crystals. We discovered that crystal tilting is facilitated by microtubule motor proteins, which actively pull upon the intracellular crystals. More specifically, we showed that the microtubule minus-end directed motility of dynein is responsible for the red-shift in the iridophore reflected color, while the plus-end directed motility of kinesin is responsible for the blue-shift of the reflected color. Intriguingly, only a subpopulation of iridophores change their color upon stimulation, which results in the disappearance of the animal`s famous stripe pattern.