Promotion of osteogenesis by extra-embryonic epithelial in maxillary mesenchyme of the embryonic chick

Maxillary mesenchyme (HH stages 19-21), separated from its epithelium and grown as a graft on the chorioallantoic membranes of host chick embryos, did not form membrane bone. However, when isolated maxillary mesenchyme was recombined directly with chorioallantoic endoderm or chorioallantoic ectoderm and then grafted, it did form membrane bone in 87.5 and 70% of cases, respectively. This novel finding of extra-embryonic epithelia eliciting an osteogenic response from membrane bone-forming mesenchyme indicates that the germ-layer origin of an epithelium does not necessarily restrict its potential to promote membrane bone formation.