Fig. 4. In vitro endothelial and haematopoietic differentiation potential of E11.5 AGM fractions sorted according to VE-cadherin (VEcad) and CD45 expression. (A) The frequency of clonogenic myeloid progenitors is 14-fold higher within the DP fraction compared with the haematopoietic (VE-cadherin^-CD45⁺) population. Tight (B) and diffuse colonies (C) are predominantly derived from VE-cadherin⁺CD45⁺ cells. (D) Clonal analysis of sorted VE-cadherin⁺CD45⁺ cells using OP9 assay reveals that haematopoietic progenitors are present at a frequency of 7.6%. (E) Cobble-stone areas (arrow) were frequently observed beneath the stoma and floating haematopoietic cells (asterisk), shown at higher magnification in F. (G) In vitro endothelial network formation was largely restricted to the VE-cadherin⁺CD45^- population. After 4 days of co-culture with OP9 stromal cells, 60 PECAM1⁺ tubules (blue staining) were produced from 5000 endothelial cells (H) and extensive network formation was seen from 20,000 cells (I). All data were collected from a minimum of three replicate experiments.