Expression of zebrafish ECSCR. (A) qPCR measurement of ecscr transcript levels, normalized to beta-actin transcripts, during various stages of zebrafish development. Primer design is indicated in supplemental Figure 1. (B) Normalized qPCR of kdrl transcripts. (C) Dorsal view, with posterior up, of a 10-som embryo processed for ISH for the ets transcription factor etsrp¹⁶  showing the distribution of angioblasts in the posterior LPM. Scale bars for panels C through E, G, and I represent 200 μm. (D-I) Whole-mount ISH for ecscr message in zebrafish of the indicated stages. (D) 10-som, showing expression on premigratory angioblasts similar to etsrp⁺ cells. (E) Lateral view at 16 som. (F) Oblique view near the tail at 16 som, showing faint hybridization to migrating angioblasts (). (G) Lateral view at 18 som. (H) Dorsal view at 18 som. Hybridization is detected at the midline vascular cord. (I) Lateral view at 24 hpf. (J-K) Methacrylate sections of whole-mount in situs showing ecscr transcripts localized to midline vascular structures. (J) 18 som. (K) Higher magnification view of a 24-hpf section. point to DA and PCV. Scale bar represents 10 μm.