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Fig. 2 Conserved features of juvenile bone front and adult suture mesenchyme. A Confocal image of juvenile frontal bones (Alizarin Red+) from animals receiving GFP+ neural crest precursor transplants. Dotted line indicates region for adjacent orthogonal projection. Brackets denote mesenchyme ahead of the growing frontal (F) bone. N = 3. B Confocal image of juvenile frontal bones. Mosaic recombination within Sox10:Cre; actab2:loxP-BFP-STOP-loxP-dsRed fish labels a neural crest clone in magenta, and RUNX2:GFP labels nascent osteoblasts. Dotted line indicates region for adjacent orthogonal projection. Brackets denote mesenchyme ahead of the bone front. N = 5. C Dot plot of mesenchyme-enriched genes. D, E In situ hybridization for six2a in the juvenile frontal bone and adult coronal suture. Dotted lines outline the frontal (F) and parietal (P) bones. Arrow marks the tip of the growing frontal bone. Orange boxed inset shows expression of six2a at suture edges and red boxed inset shows six2a expression in mid-suture region. In situs were performed in biological triplicate. F, G Confocal images show fli1a:GFP+ mesenchyme relative to Calcein Blue+ calvarial bones at juvenile and adult stages. Arrow denotes fli1a:GFP+ cells ahead of the growing frontal bone, and arrowheads suture mesenchyme expression. Note extensive labeling of vasculature by fli1a:GFP. N = 5 each stage. H, I Orthogonal sections of confocal images show fli1a:GFP+ cells at the juvenile frontal bone tip (H, arrow) and adult suture relative to sp7:mCherry+ osteoblasts. Asterisks mark fli1a:GFP+ endothelial cells. N = 3 each stage. Scalebars: 50 μM (A, B), 100 μM (D–I).