Fig. S1

Gross anatomy of the scale and different populations of scale-forming osteoblasts.

(A) The scale is divided into two fields (border defined by the white dashed line): the anterior (left) and the posterior (right) field. The anterior field is overlapped by the preceding and neighbouring scales and is characterized by a focus (f), representing the growth centre of the scale, and serrations (s), concentric thickenings of the bony surface disposed around the focus. The posterior field is exposed and covered on both sides by the epidermis. The radii (r), grooves along the scale surface, originate from the focus and reach the posterior margin perpendicularly. Circuli (c) are semi-circular undulations which parallel the posterior margin and mark growth stages. The red insets highlight the regions depicted in (B-D). (A′) Imbrication of two consecutive scales. (B-D) Maximum intensity projection (MIP) of DAPI and phalloidin stainings of scale. (B) Highly compacted osteoblasts stretched along the scale margin. (C) Osteoblasts along the serrations, covering the scale surface in the region of the anterior field. The nuclei are located along the ridges and the cell bodies have ‘closet’ structures filling the areas between neighbouring serrations. (D) Osteoblasts in the posterior field located along the grooves (arrow) and along the circuli (arrowhead). (E-E′ ′) Different populations of osteoblasts on scale of Tg(SA1-mCT2aC#HB;βactin: switch) fish where the recombination was induced between 16 and 48 hpf. (E) MIP of 2-photon stacks showing DsRed+ osteoblasts along the serrations (filled arrowhead), on the surface of the posterior field (arrow), along the grooves (empty arrowhead), and along the circuli depressions (asterisks). (E′) MIP of second harmonic generation (SHG) stacks showing the scale osseous layer. Groove of a radius (empty arrowhead) and circulus depression (asterisk). (E′ ′) Merge of (E-E′).