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Fig. 1. Expression analysis of BMP ligands and receptors from midgastrulation stage to hemogenic endothelium formation and the description of reagents to inhibit all BMP signaling in blood ontogeny. Primarily, expression in tissues involved in blood stem cell lineage is described. (A) Ligands: bmp2, bmp4, and bmp7 are the principal BMP ligands expressed during gastrulation and onward. At stage 10.5, midgastrulation, bmp2 is expressed in the dorsal mesendoderm. At stage 16, early neurula, bmp2 expression is localized to anterior ventral mesoderm, which encompasses cardiac progenitors and anterior hemangioblasts (AHB). At stage 20–23, bmp2 is expressed along the ventral mesoderm and in lateral plate mesoderm, with signal tapering toward the DLP mesoderm. At stage 26, bmp2 expression is localized along the DLP as well as ventral and cardiac mesoderm. At stages 34–39, bmp2 is expressed in the DA. At stage 10.5, bmp4 is expressed in mesendoderm, with expression diminishing toward dorsal mesendoderm. At stage 16–20, bmp4 is expressed extensively in ventral and lateral mesoderm. From stage 20 onward, bmp4 expression is localized to DLP, encompassing future hemangioblast. At stages 21–26, bmp4 expression is strong along the ventral and lateral plate mesoderm, specifically delineating the DLP tissue at the dorsal most expression domain. At stage 34, bmp4 is expressed in the DA. Bmp5 is not expressed in tissues related to blood lineages, except at stage 38–39, when it is expressed in the DA. Bmp6 is not expressed in HSC lineage. The only expression detectable is transiently in kidney tubules at stage 36. Bmp7 expression at stage 10.5 is localized to ventral most mesendoderm as well as a subset of dorsal mesendoderm. At stages 16–26, bmp7 is expressed along the ventral and lateral plate mesoderm, bordering the kidney field in the dorsal most extent. Bmp7 is strongly expressed in the lateral plate mesoderm for the rest of the developmental stages analyzed. From stage 34 onward, bmp7 is also expressed in the DA. Bmp8 is not expressed during Xenopus development. Bmp9 and bmp10 are expressed in the heart from stage 26 onward. Type I receptors: alk1 is not expressed in early time points; later alk1 expression is primarily restricted to the heart and at stage 38–39 to DA. Alk2 and alk3 are ubiquitously expressed at all stages analyzed. From stage 34 onward, their expression is also observed in the DA. Alk6 is not expressed in blood stem cell lineage but is widely expressed early in dorsal mesoderm and later in neural tissues, neural crest, somites, and notochord. Embryos at stages 10.5 and 34–39 are cleared to enable visualization of the staining of the deeper tissues. For stage 10.5 embryos, D is dorsal and V is for ventral side. For stages 16–20, embryos are visualized from anterior-dorsal (A-D) and anterior-ventral (A-V) angles, except stage 16 bmp4 staining, which is documented from anterior–posterior (A-P) lateral view. From stage 21 onward, the pictures of embryos are taken from lateral view, with anterior–posterior labeled, where it is relevant, on the figure. Expression profile was not determined (nd) for some stages. (Scale bars: 0.5 mm.) (B) BMP2 and BMP4 signal through type I receptors, Alk3 and Alk6. Noggin inhibits signaling by preventing ligands from binding to receptors. DMH1 blocks signaling downstream of Alk3 but not Alk6. (C) BMP5, -6, and -7 signal through type I receptors Alk2, Alk3, and Alk6. Noggin blocks binding of BMP5 and -7 to type I receptors. Noggin does not inhibit signaling downstream of BMP6. DMH1 inhibits Alk2 and Alk3 but not Alk6. (D) BMP9 and -10 signal through type I receptors Alk1 and Alk2. Noggin does not block BMP9 or -10 from binding to receptors. DMH1 blocks Alk1 and Alk2 receptor activity.
dorsal aorta head region lateral plate mesoderm dorsal lateral plate mesoderm spinal cord head mesenchyme head mesoderm anterior dorsal lateral plate region
dorsal aorta lateral plate mesoderm dorsal lateral plate mesoderm head region head mesenchyme head mesoderm cranial nerve anterior dorsal lateral plate region
head region head mesoderm head mesenchyme ventral mesoderm lateral plate mesoderm dorsal lateral plate mesoderm tail region tail bud anterior dorsal lateral plate region
Sometime during NF stage 33 and 34 to NF stage 35 and 36
dorsal aorta blood vessel intersomitic vessel heart head region head mesenchyme head mesoderm lateral plate mesoderm dorsal lateral plate mesoderm anterior dorsal lateral plate region
dorsal aorta blood vessel intersomitic vessel heart head region head mesenchyme head mesoderm lateral plate mesoderm dorsal lateral plate mesoderm anterior dorsal lateral plate region
Sometime during NF stage 33 and 34 to NF stage 35 and 36
dorsal aorta intersomitic vessel lateral plate mesoderm dorsal lateral plate mesoderm head mesoderm head mesenchyme head region anterior dorsal lateral plate region
