Figure 1. Prostaglandin agonists and antagonists alter runx1/cmyb expression without affecting vascular development.

In situ hybridization for runx1/cmyb or flk1 at 36 h.p.f. Photomicrographs were taken with Nomarski optics at 10× (a-c, left panels) and 40× (a-c, right panels, and e-m) magnification. a-c, Representative examples of chemicals in the prostaglandin pathway discovered in the screen are shown; 10 μM linoleic acid increases, and 20 μM celecoxib reduces HSC numbers. runx1⁺/myb⁺ HSCs are indicated: endothelial cells (arrow); haematopoietic clusters (arrowhead). d, Quantitative PCR profile of endothelial and HSC-specific gene expression following exposure to long-acting dmPGE2 (10 μM, blue) or the nonspecific Cox inhibitor indomethacin (10 μM, green) versus control (red). Both treatments resulted in statistically significant differences compared with controls for each gene examined (ANOVA, *P < 0.05; mean, s.d. and n are listed in Supplementary Table 2). e-m, dmPGE2 and indomethacin exert opposing effects on runx1/cmyb expression by in situ hybridization (e, h, k); flk1 is used to assess the effects on vascular development (f, i, l). Confocal microscopy images of cmyb-gfp; lmo2-dsRed bigenic fish exposed to dmPGE2 and indomethacin showing an increase and decrease in HSC (yellow) number along the ventral wall (yellow arrowhead) of the aorta, respectively (g, j, m). Quantitative analysis of 10 embryos in each treatment group revealed significant differences in HSC numbers (Supplementary Fig. 1i).