Figure 7. No Epistasis between ETO2, ETV6, and Hedgehog Signaling(A–C) Expression analysis by WMISH of Etv6, Eto2, Ptc1, Vegfa, and Dll4 in Eto2 (A) and Etv6 (B) morphants as well as in embryos treated with cyclopamine (C). Efficiency of Eto2 and Etv6 morpholinos is controlled by Runx1 staining at stage 39, and that of cyclopamine is controlled by Ptc1 staining. Red arrowheads, DA; orange arrowheads, Etv6 staining in the somites; blue arrowheads, notochord; yellow arrowheads, neural tube; white arrowheads, DLP. Numbers at the bottom of the panels indicate the number of embryos with the given phenotype out of the total number examined. Whole mounts are shown with anterior to the left and dorsal to the top.(D) Uncoupling the requirement for VEGFA isoforms during HSC development in Xenopus. Schematic diagram depicting the requirements for VEGFA isoforms in the succession of events leading to HSC formation. Stages 20–23: ETV6 regulates production of VegfA in the somites, VegfA short isoform is critical for correct programming of the adult hemangioblasts in the DLP (green arrows). Stages 24–26: the adult hemangioblasts (or DA precursors) express both endothelial (Flk1) and hematopoietic (Scl) markers and Vegfa in an autocrine manner. The hypochord secretes VegfA short isoform that guides migration of hemangioblasts to the midline (green arrows). Stages 27–30: ETO2 regulates production of VegfA long/medium isoforms (VegfA M/L) in the somites. These isoforms instruct the hematopoietic program of the DA precursors as they migrate along the somites (red arrowheads). Stages 36–41: the DA has formed and is specified as an artery. Cells in the hemogenic endothelium express NOTCH1; this will trigger expression of the HSC transcriptional program. n, notochord.
Image published in: Leung A et al. (2013)
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