Frequency and absolute number of MSCs in the human AoM subregion. Three thousand primary AoM cells are incubated for 10 days, and on average 9.6 well-circumscribed CFU-F colonies emerge in the culture (A and left part of B). The total numbers of CFU-Fs are 164.2 and 200 in the AoM of embryos at CS 12 and CS 13, respectively (B right). Clonally amplified cells display homogenous surface markers (C). All of the individually plucked CFU-F colonies (n = 4) are capable of differentiating to adipocytes, osteocytes, and chondrocytes manifested by Oil-red-O, von Kossa, and Alcian blue staining, respectively (D). Noninduced cells stained by Oil-red-O and von Kossa are shown in the left (adipo and osteo in panel D). One representative of 2 individually expanded MSCs for 6 passages retains a cloning efficiency of 29.3% (E). CS indicates Carnegie stage. Original magnification: (A top) ×40; (A bottom) ×200; (D adipo and osteo) ×100; (D chondro) ×200.