title: Spry1 is expressed in hemangioblasts and negatively regulates primitive hematopoiesis and endothelial cell function.
abstract: BACKGROUND
  Development of the hematopoietic and endothelial lineages derives from a common mesodermal precursor, the Flk1(+) hemangioblast. However, the signaling pathways that regulate the development of hematopoietic and endothelial cells from this common progenitor cell remains incompletely understood. Using mouse models with a conditional Spry1 transgene, and a Spry1 knockout mouse, we investigated the role of Spry1 in the development of the endothelial and hematopoietic lineages during development.
  
  
  RESULTS
  Quantitative RT-PCR analysis demonstrates that Spry1, Spry2, and Spry4 are expressed in Flk1(+) hemangioblasts in vivo, and decline significantly in c-Kit(+) and CD41(+) hematopoietic progenitors, while expression is maintained in developing endothelial cells. Tie2-Cre-mediated over-expression of Spry1 results in embryonic lethality. At E9.5 Spry1;Tie2-Cre embryos show near normal endothelial cell development and vessel patterning but have reduced hematopoiesis. FACS analysis shows a reduction of primitive hematopoietic progenitors and erythroblastic cells in Spry1;Tie2-Cre embryos compared to controls. Colony forming assays confirm the hematopoietic defects in Spry1;Tie2-Cre transgenic embryos. Immunostaining shows a significant reduction of CD41 or CD71 and dpERK co-stained cells in Spry1;Tie2-Cre embryos compared to controls, whereas the number of VEC(+) and dpERK co-stained cells is comparable. Compared to controls, Spry1;Tie2-Cre embryos also show a decrease in proliferation and an increase in apoptosis. Furthermore, loss of Spry1 results in an increase of CD41(+) and CD71(+) cells at E9.5 compared with controls.
  
  
  CONCLUSIONS
  These data indicate that primitive hematopoietic cells derive from Tie2-expressing hemangioblasts and that Spry1 over expression inhibits primitive hematopoietic progenitor and erythroblastic cell development and expansion while having no obvious effect on endothelial cell development.
authors.affiliation: Center for Molecular Medicine, Maine Medical Center Research Institute, Scarborough, Maine, United States of America.
authors.forename: Xuehui
authors.initials: X
authors.lastname: Yang
authors.forename: Yan
authors.initials: Y
authors.lastname: Gong
authors.forename: Robert
authors.initials: R
authors.lastname: Friesel
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D015703:Antigens, CD / Q000378:metabolism; D017209:Apoptosis / Q000235:genetics; D001789:Blood Group Antigens / Q000378:metabolism; D049109:Cell Proliferation; D004622:Embryo, Mammalian / Q000166:cytology / Q000378:metabolism; D004900:Erythroblasts / Q000166:cytology / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005260:Female; D005786:Gene Expression Regulation; D055018:Hemangioblasts / Q000166:cytology* / Q000378:metabolism*; D006410:Hematopoiesis / Q000235:genetics*; D008297:Male; D008565:Membrane Proteins / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D010750:Phosphoproteins / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism*; D010766:Phosphorylation / Q000235:genetics; D040201:Platelet Membrane Glycoprotein IIb / Q000378:metabolism; D019009:Proto-Oncogene Proteins c-kit / Q000378:metabolism; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism; D042787:Receptor, TIE-2; D011990:Receptors, Transferrin / Q000378:metabolism; D013234:Stem Cells / Q000166:cytology / Q000378:metabolism; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D015703:Antigens, CD; D001789:Blood Group Antigens; C068126:CD71 antigen; D008565:Membrane Proteins; D010750:Phosphoproteins; D040201:Platelet Membrane Glycoprotein IIb; D011990:Receptors, Transferrin; C425468:Spry1 protein, mouse; C489122:TER-119 antigen, mouse; D019009:Proto-Oncogene Proteins c-kit; D020794:Receptor Protein-Tyrosine Kinases; D042787:Receptor, TIE-2; C079086:Tek protein, mouse; D040301:Vascular Endothelial Growth Factor Receptor-2; D048049:Extracellular Signal-Regulated MAP Kinases