MOUSE CHICK CHIMERA - A NEW MODEL TO STUDY THE IN OVO DEVELOPMENTAL POTENTIALITIES OF MAMMALIAN SOMITES

Chimeras were prepared by transplanting somites from 9-day post-coitum mouse embryos or semitic dermomyotomes from 10-day post-coltum mouse embryos into 2-day-old chick embryos at different axial levels. Mouse semitic cells then differentiated in ovo in dermis, cartilage and skel etal muscle as they normally do in the course of development and were able to migrate into chick host limb. To trace the behavior of semitic myogenic stem cells more closely, somites arising from mice bearing a transgene of the desmin gene linked to a reporter gene coding for Esc herichia coli beta-galactosidase (lacZ) were grafted in ovo. Interesti ngly, the transgene was rapidly expressed in myotomal muscles derived from implants. In the limb muscle mass, positive cells were found seve ral days after implantation. Activation of desmin nls lacZ also occurr ed in in vitro cultures of somite-derived cells. Our experimental meth od facilitates investigation of the mechanisms of mammalian developmen t, allowing the normal fate of implanted mouse cells to be studied and providing suitable conditions for identification of descendants of ge netically modified cells.