Fig. 3. Frequency of (A) osteogenic, (B) adipogenic and (C) chondrogenic progenitors in E11 AGM and its subregions, the dorsal aorta with its surrounding mesenchyme (AoM) and the urogenital ridges (UGRs). Osteogenic and adipogenic progenitor frequencies were determined based on the number of colonies displaying ALP activity and refractile, lipid-containing vesicles, respectively. Chondrogenic progenitor frequency was determined based on the number of cartilagenous foci after 21 days of aggregate culture. Data are expressed as mean±s.d. (n=3 to five independent experiments). Because the AGM region also contains primordial germ cells expressing ALP, the specificity of this marker with regard to osteogenic commitment was addressed. Oct4-GFP transgenic AGM cells were sorted and evaluated in osteogenic cultures for ALP-expressing colony frequency. The frequency of osteogenic progenitors in the primordial germ cell depleted (sorted Oct4-GFP negative) fraction was identical to unsorted AGM cells (1.32±0.41/10⁴ vs 1.30±0.14/10⁴, respectively). Thus, primordial germ cells are not contributing to the ALP-expressing colony frequency after culture in osteogenic-inductive conditions.