Zebrafish crlr is expressed in somites, endothelial cells, and their precursors. Crlr expression was analyzed in zebrafish embryos by ISH at the indicated developmental stages. Embryos are anterior to the left and lateral to the top, except in panels A-C and L that represent dorsal views. (E,K,N) The transverse sections through the trunk are highlighted as vertical black bars in panels D, J, and M, respectively. At 4-ss (A) and 13-ss (B) crlr is expressed within the somites (white arrowheads). At 15-ss, white arrowhead points to crlr expression along a midline through the trunk (C). At 18-ss (D,E) crlr is expressed in the midline under the notochord (black arrowhead). At this stage, double ISH (F) shows the expression of crlr (blue) by kdra⁺ angioblasts (red). Confocal laser microscopy shows a detail of the tail region of 18-ss embryo after double fluorescence ISH for kdra (red in panel G) and crlr (green in panel H); the area in white boxes are merged in panel I, where white arrowheads point to the layer of crlr⁺/kdra⁺ DA angioblasts close to the notochord (merged signal in white). (J) At 26 hpf, crlr is expressed by blood vessels of the head, in the heart tube (white arrow), and in DA of the trunk (black arrowhead). (K) Cross-section of a 26-hpf embryo, confirming crlr expression in DA (black arrowhead). At this stage, crlr is expressed also by the right- and left-lateral DA (panel L; white arrowheads). At 48 hpf, lateral view (M) and cross-section (N, black arrowheads) demonstrate crlr expression in both DA and PCV.