Differentiation of the mouse embryoid bodies grafted on the chorioallantoic membrane of the chick embryo.

In order to test the developmental potential of the mouse embryonic-stem-cell-derived embryoid bodies as chorioallantoic grafts, the embryoid bodies were transplanted to the chorioallantoic membrane (CAM) of the chick embryo. The graft implantation was achieved if the embryoid bodies were transferred to the CAM into the blood drop created by gentle laceration of a CAM blood vessel. The resulting tumors were recovered after 10 days, when they were rounded white elevations, up to 1 mm big. Histological analysis showed that they were made of groups of compacted epithelial-like cells and fibroblast-like spindle shaped cells divided by the CAM mesenchyme. The grafting caused angiogenic response of the CAM. Blood vessels converged toward the tumor and spread through the CAM mesenchyme among the groups of condensed cells. Although the embryonic bodies were able to implant to the CAM of the chick, their differentiation did not result in a wide variety of differentiated cell types or in the formation of complex structures resembling morphogenesis. Thus in comparison with in vitro differentiation of embryoid bodies on an adhesive substrate, or in vivo differentiation under the mouse kidney capsule, the differentiation potential of embryoid bodies as chorioallantoic grafts appeared restricted. However, we suggest that the accessibility of the chorioallantoic graft can be an advantage for future experiments.