Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2024 Jun 4;121(23):e2308531121.
doi: 10.1073/pnas.2308531121. Epub 2024 May 28.

The physical and cellular mechanism of structural color change in zebrafish

Dvir Gur  1 , Andrew S Moore  2 , Rachael Deis  1 , Pang Song  2 , Xufeng Wu  3 , Iddo Pinkas  4 , Claire Deo  2 , Nirmala Iyer  2 , Harald F Hess  2 , John A Hammer  3 , Jennifer Lippincott-Schwartz  2
Affiliations

The physical and cellular mechanism of structural color change in zebrafish

Dvir Gur et al. Proc Natl Acad Sci U S A. .

Abstract

Many animals exhibit remarkable colors that are produced by the constructive interference of light reflected from arrays of intracellular guanine crystals. These animals can fine-tune their crystal-based structural colors to communicate with each other, regulate body temperature, and create camouflage. While it is known that these changes in color are caused by changes in the angle of the crystal arrays relative to incident light, the cellular machinery that drives color change is not understood. Here, using a combination of 3D focused ion beam scanning electron microscopy (FIB-SEM), micro-focused X-ray diffraction, superresolution fluorescence light microscopy, and pharmacological perturbations, we characterized the dynamics and 3D cellular reorganization of crystal arrays within zebrafish iridophores during norepinephrine (NE)-induced color change. We found that color change results from a coordinated 20° tilting of the intracellular crystals, which alters both crystal packing and the angle at which impinging light hits the crystals. Importantly, addition of the dynein inhibitor dynapyrazole-a completely blocked this NE-induced red shift by hindering crystal dynamics upon NE addition. FIB-SEM and microtubule organizing center (MTOC) mapping showed that microtubules arise from two MTOCs located near the poles of the iridophore and run parallel to, and in between, individual crystals. This suggests that dynein drives crystal angle change in response to NE by binding to the limiting membrane surrounding individual crystals and walking toward microtubule minus ends. Finally, we found that intracellular cAMP regulates the color change process. Together, our results provide mechanistic insight into the cellular machinery that drives structural color change.

Keywords: color change; guanine crystals; motor proteins; structural colors; zebrafish.

PubMed Disclaimer

Conflict of interest statement

Competing interests statement:The authors declare no competing interest.

Figures

Fig. 1.
Fig. 1.
Anatomy, crystal properties, and color change capabilities of the zebrafish scale iridophores. (A) The flank of an adult zebrafish. The Top Inset shows a closeup of the reflectance of individual scale iridophores (marked with black arrows). (B and C) Schematic illustration of a zebrafish scale and tissue showing a Top view of an isolated scale in which iridophores are located adjacent to the scale on its posterior side (B), and a side view (cross-section) showing the scales within the fish dermis in which iridophores are located adjacent to the scales (C). (D) Scale iridophores before (Top) and after (Bottom) NE-treatment display violet-blue and yellow reflectance, respectively. (E) 3D rendering of FIB-SEM serial-sectioning of a scale iridophore showing an array of thin intracellular crystals arranged in parallel (highlighted by pseudocoloring in blue and gray; the cell’s nucleus is pseudocolored red). The Bottom Left Inset shows a higher magnification view of the parallel crystal arrays, while the Top Right Inset shows a perpendicular view of the crystal arrays. (F) Detected reflectance (blue) under the light microscope from scale iridophores. The Top Inset shows a single crystal isolated from a scale iridophore (G) In situ micro-Raman spectra obtained from scale iridophores (red spectrum), together with a reference spectrum for anhydrous β guanine (blue spectrum). (H) The low-wavenumber region of the samples examined in (G). (Scale bars, (A) 3 mm, (D) 80 µm, (F) 40 µm.)
Fig. 2.
Fig. 2.
NE-induced changes in crystal tilt, crystal spacing, and cellular optical properties. (A) Top panel: representative FIB-SEM section (XZ plane) of an untreated iridophore. Bottom panel; representative FIB-SEM section (XZ plane) of a NE-treated iridophore. (B) Optical properties of untreated (blue curve) and NE-treated iridophores (yellow curve) compared to the corresponding Monte Carlo simulations (dotted for untreated, dashed for NE treated). (Scale bar, (A) 500 µm.)
Fig. 3.
Fig. 3.
Color change in scale iridophores is driven by the tilting of crystals. (A) Iridophores are typically blue before NE treatment (Left), red 4 min after NE addition (Middle), and finally yellow 7 min after NE addition (Right) (these two shifts were seen in 6 out of 10 scales from three different fish). Insets show representative colors for each time point. (B) A schematic showing the X-ray diffraction experimental setup, where a change in the tilt orientation of crystals results in a change in the (Δω) of the diffraction spot. (C) Pseudotemporal colored representation of 32 diffraction spots over a 7-min period following NE addition. (Scale bar, (A) 10 µm.)
Fig. 4.
Fig. 4.
Microtubules and the microtubule minus end-directed motor protein dynein drive NE-induced color change. (A) JF549-labeled iridophores (Left) and corresponding kymographs of untreated (Top), nocodazole-treated (Middle), and NE-treated cells (Bottom). Kymograph Insets are contrasted for clarity. (B) Microtubule distribution visualized using an anti-α-tubulin antibody in an iridophore (arrow) and an adjacent dermal cell (arrowhead). (C) Iridophore in a scale after 10 min of recovery from nocodazole treatment (anti-α-tubulin, cyan; crystals autofluorescence, magenta). (D) TEM image of an iridophore showing ~25 nm tubes running parallel to the crystals. (E–H) Graphs showing the blue-to-red channel ratio (the deconvoluted components of an RGB movie) of iridophores treated with NE (E), nocodazole + NE (F), dynapyrazole-a + NE (G) and adenosine (H). (Scale bars, (A, Left) 4 µm, (A, Right) 10 µm, (B) 8 µm, (C) 5 µm, (D) 400 nm.)
See this image and copyright information in PMC

Similar articles

See all similar articles

References

    1. Hooke R., Micrographia: Or Some Physiological Descriptions of Minute Bodies Made by Magnifying Glasses, with Observations and Inquiries Thereupon (Dover Publications, 1665), vol. 20.
    1. Darwin C., The Descent of Man and Selection in Relation to Sex (D. Appleton and Company, 1896), vol. 1.
    1. Poulton E. B., The Colours of Animals: Their Meaning and Use, Especially Considered in the Case of Insects (D. Appleton and Company, 1890), vol. 67.
    1. Figon F., Casas J., “Morphological and physiological colour changes in the animalkingdom” in eLS, John Wiley & Sons Ltd., Ed. (John Wiley & Sons, Ltd., 2018), pp. 1–11.
    1. Lythgoe J. N., Shand J., The structural basis for iridescent colour changes in dermal and corneal irddophores in fish. J. Exp. Biol. 141, 313–325 (1989).

LinkOut - more resources

-