SRCT reveals subtle bone morphological abnormalities and alterations in mineral density distribution. a 3D volumetric rendering from μCT images showing fine endplate abnormalities. 1: normal IVD; 2: endplate sclerosis (blue arrow) and IVD calcification (pink arrow); 3: sclerosis (blue arrow), uneven edges and AF calcification (pink arrow); 4: sclerosis (blue arrow), AF calcification (pink arrow); osteophyte (dashed blue arrow). Scale bars = 50 μm. b 3D volumetric rendering from μCT images showing IVD internal changes in aged and sp7−/− zebrafish. Calcification depicted by pink arrow (SRCT 3D rendering). Note, young zebrafish with IVD and disc misalignment shows points of IVD calcification. Virtual sections (orthoslices) color coded for bone density (SRCT orthoslice). Dashed box regions are magnified and displayed on the right. Scale bars = 50 μm. c Quantification of mineralization robustness (%) in wt young (1 y), wt aged (3 y), and sp7−/− 1 y zebrafish (n = 3 per group, average from 4 sections per fish). One-way ANOVA and post hoc Holm–Sidak’s multiple comparisons test were used; data are the mean and SD. P values are indicated. d Paraffin sections stained with picrosirius red showing the thickness of collagen fibers (thin = blue/green and thick= red/orange). Scale bars = 50 μm. e Quantification of collagen fiber thickness from picrosirius red staining (blue = thin, green = medium, red = thick) (1 y, n = 8; 3 y, n = 8; 3 months, n = 7; sp7−/− 1 y, n = 6; we analyzed three sections per fish). One-way ANOVA, post hoc Tukey’s multiple comparisons test; data are the mean and SD. P values are indicated
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