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. 2021 Sep 16;10:e68920. doi: 10.7554/eLife.68920

Figure 1. Ionic silver stains reproduce three-dimensional (3D) pigmentation patterns in X-ray microtomography (micro-CT) images.

(A) Schematic overview of staining procedure. Ammoniacal silver solution reacts with endogenous melanin to deposit solid silver, which attenuates X-rays in micro-CT imaging. (B) A representative cropped and rotated slice of a micro-CT reconstruction of a 5 days post-fertilization (dpf) wild-type zebrafish stained with silver. RPE = retinal pigment epithelium, P = body pigment, L = lens, r = resin, it = inner wall of sample tube, ot = outer wall of sample tube, b = air bubble. (C) 3D rendering of a 5 dpf wild-type zebrafish stained with silver with a heatmap to illustrate pigment density throughout the fish. (D) Corresponding light microscopy (left) and micro-CT (right) images exhibit the same pigmentation patterns. In the micro-CT image, a top-down 3D rendering of stained melanin is shown in grayscale with the dorsal-most melanin digitally colored red to aid comparison with the light micrograph. Some distinguishing shared features are highlighted with colored arrowheads. White arrows indicate deeper melanin obscured by soft tissue in the light micrograph that can be visualized by targeted 3D re-rendering. Scale bars = 200 µm. Unstained samples do not exhibit melanin-related attenuation (Figure 1—figure supplement 1).

Figure 1.

Figure 1—figure supplement 1. Unstained zebrafish larvae do not exhibit pigment pattern intensity in X-ray microtomography (micro-CT) reconstructions.

Figure 1—figure supplement 1.

A pigmented 5 days post-fertilization (dpf) wild-type larva (A) was prepared for micro-CT imaging without silver staining. (B) The sample (black arrowhead), embedded in resin within a polyimide tube, was surrounded by electrical tape to ensure proper positioning in the X-ray beam. (C) A 200-slice average intensity projection of the normalized micro-CT reconstruction from this unstained sample shows faint attenuation in the lenses (L) and at the edges of the eyes (white arrowheads), indicating that the sample was scanned. A 900-pixel × 25-pixel selection (yellow box) transecting the eyes was used to calculate an intensity profile for a single reconstructed slice of the unstained fish (D) showing virtually no intensity peaks above background. A similar selection (blue box) through a single reconstructed slice of a silver-stained 5 dpf wild-type larva (E) demonstrates intense melanin staining in the intensity profile (black arrows).