13-P012 FGF8 morphogen gradient is formed by a source–sink mechanism with freely-diffusing molecules

(Kdr), suggesting that they are hemangioblast precursors of the blood and vascular endothelial lineages. However, the preferential differentiation of PECAM positive vascular endothelial cells suggests that Pofut2 is essential for differentiation of the hematopoietic lineage. Many POFUT2 target proteins are constitutive components of ECM or associate with ECM. Among these, CCN, TSP, and ADAMTS family members are involved in ECM synthesis and remodeling. The ability of Pofut2 mutant embryos to form teratomas comprised of tissues from all three germ layer origins, suggests that defects in Pofut2 mutant embryos result from abnormalities in the remodeling or turnover of extracellular matrix, cell-matrix interaction, and/or regulation of signal pathways. Notably, Nodal, BMP4, Fgf8, and Wnt3 expression is markedly elevated and expanded in Pofut2 mutants, providing evidence that O-fucose modification of TSRs is essential for modulation of growth factor signaling during gastrulation.