title: Regulation of flt-1 expression during mouse embryogenesis suggests a role in the establishment of vascular endothelium.
abstract: Flt-1 is a high affinity binding receptor for the vascular endothelial cell growth factor (VEGF) and is primarily expressed in endothelial cells. In this study we have investigated the temporal and spatial regulation of its expression by establishing mouse lines containing the lacZ gene targeted into the flt-1 locus through homologous recombination in embryonic stem (ES) cells. In the yolk sac as well as in the embryo proper, lacZ expression faithfully reflected the endogenous expression pattern of the flt-1 gene. LacZ staining of heterozygous embryos led to the following observations: (1) the onset of flt-1 expression is detected at the early primitive streak stage in the extraembryonic mesoderm, and is strongly up-regulated thereafter, reaching a maximum by early to midsomite stages and declining subsequently; (2) while flt-1 is widely expressed within the developing vascular endothelium, its expression level is differentially regulated both spatially and temporally. The pattern of flt-1 expression suggests that it may play an important role in the initiation of endothelium development; and (3) flt-1 is expressed in essentially all the cells in early blood islands, but later its expression is gradually restricted to the endothelial lineage. Our results indicate that flt-1 is a marker for hemangioblasts, the presumed progenitor for both hematopoietic and angioblastic lineage. The flt-1 expression pattern also suggests that it may play important roles in both vasculogenesis and angiogenesis.
authors.affiliation: Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada.
authors.forename: G H
authors.initials: GH
authors.lastname: Fong
authors.forename: J
authors.initials: J
authors.lastname: Klingensmith
authors.forename: C R
authors.initials: CR
authors.lastname: Wood
authors.forename: J
authors.initials: J
authors.lastname: Rossant
authors.forename: M L
authors.initials: ML
authors.lastname: Breitman
mesh_terms: D000818:Animals; D002874:Chromosome Mapping; D004730:Endothelium, Vascular / Q000196:embryology*; D005260:Female; D017403:In Situ Hybridization; D007763:Lac Operon; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis*; D020794:Receptor Protein-Tyrosine Kinases / Q000096:biosynthesis*; D017978:Receptors, Growth Factor / Q000096:biosynthesis*; D040281:Vascular Endothelial Growth Factor Receptor-1
chemical_list: D011518:Proto-Oncogene Proteins; D017978:Receptors, Growth Factor; D020794:Receptor Protein-Tyrosine Kinases; D040281:Vascular Endothelial Growth Factor Receptor-1