The pluripotency of the extraembryonic mesodermal cells of the early chick blastoderm: effects of the AP and AOV environments.

This study investigates the developmental potential of the extraembryonic mesodermal cells of the early chick blastoderm. [3H]Thymidine-labeled mesodermal fragments from the extraembryonic area pellucida (AP) and area opaca vasculosa (AOV) were transplanted into the AP or AOV of nonlabeled host blastoderms in culture, and their fate followed autoradiographically. All the homotopically transplanted mesodermal cells differentiated in accordance with their normal fates. However, not all the heterotopically transplanted mesodermal cells did so, for some of the stage 8 AP extraembryonic mesodermal cells (normally nonerythropoietic) gave rise to blood cells when transplanted into the AOV. We also observed that the stage 4-5 AOV mesoderm continues to migrate peripherally when heterotopically transplanted into the AP, at a time when the AP mesodermal cells are nonmigratory. In support of our premise that the stage 8-9 AP extraembryonic mesoderm has the potential to form blood, we observed a clear-cut production of hemoglobin when the latter mesoderm was co-cultured on coverslips with stage 4 AOV endoderm.