title: Common and distinct signals specify the distribution of blood and vascular cell lineages in Xenopus laevis embryos.
abstract: In an effort to elucidate the regulatory mechanisms that determine the fate of blood cells and vascular cells in the ventral blood island mesoderm, the embryonic expression of Xtie-2, a Xenopus homolog of the tie-2 receptor tyrosine kinase, was examined. Whole-mount in situ hybridization analysis revealed that Xtie-2 mRNA is expressed at the late tailbud stage within the regions where endothelial precursor cells exist. On the ventral side of embryos, Xtie-2-positive cells are predominantly present just outside the boundary of alpha-globin-positive cells, thus the expression pattern of these two markers seems mutually exclusive. Further experiments revealed that there is a consistent and strong correlation between the induction of Xtie-2 and alpha-globin expression in embryos and explant tissues. First, these two markers displayed overlapping expression in embryos ventralized by the removal of a "dorsal determinant" from the vegetal cytoplasm at the 1-cell stage. Second, expression of both Xtie-2 and alpha-globin were markedly induced in ectodermal explants (animal caps) from embryos co-injected with activin and bone morphogenetic protein (BMP)-4 RNA. Furthermore, both Xtie-2 and alpha-globin messages were strongly positive in dorsal marginal zone explants that had been injected with BMP-4 RNA. In contrast, however, there was a clear distinction in the localization of these two transcripts in embryos dorsalized by LiCl treatment. Distinct localization was also found in the ventral marginal zone (VMZ) explants. Using the VMZ explant system, we demonstrate a role of fibroblast growth factor (FGF) signaling in enhancing the vascular cell marker and reducing the blood cell marker. The present study suggests that the early steps of blood and vascular cell differentiation are regulated by a common BMP-4-dependent signaling; however, distinct factor(s) such as FGF are involved in different distribution of these two cell lineages.
authors.affiliation: Graduate School of Science and Technology, Niigata University, 8050 Ikarashi-2, Niigata 950-2181, Japan.
authors.forename: Fumie
authors.initials: F
authors.lastname: Iraha
authors.forename: Yoshinari
authors.initials: Y
authors.lastname: Saito
authors.forename: Keiko
authors.initials: K
authors.lastname: Yoshida
authors.forename: Masatoki
authors.initials: M
authors.lastname: Kawakami
authors.forename: Yumi
authors.initials: Y
authors.lastname: Izutsu
authors.forename: Ira Owen
authors.initials: IO
authors.lastname: Daar
authors.forename: Mitsugu
authors.initials: M
authors.lastname: Maéno
mesh_terms: D000818:Animals; D015415:Biomarkers; D001773:Blood Cells / Q000166:cytology / Q000502:physiology*; D001808:Blood Vessels / Q000166:cytology / Q000196:embryology* / Q000502:physiology; D002454:Cell Differentiation / Q000502:physiology*; D019070:Cell Lineage / Q000502:physiology*; D004625:Embryo, Nonmammalian / Q000502:physiology*; D005346:Fibroblast Growth Factors / Q000502:physiology; D005914:Globins / Q000235:genetics; D017403:In Situ Hybridization; D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics; D042787:Receptor, TIE-2; D015398:Signal Transduction / Q000502:physiology; D014982:Xenopus laevis
chemical_list: D015415:Biomarkers; D005346:Fibroblast Growth Factors; D005914:Globins; D020794:Receptor Protein-Tyrosine Kinases; D042787:Receptor, TIE-2