BLOOD-BORNE SEEDING BY HEMATOPOIETIC AND ENDOTHELIAL PRECURSORS FROM THE ALLANTOIS

Until now the allantois has not been considered as a hematopoietic org an. Here we report experimental evidence demonstrating the in situ eme rgence of both hematopoietic and endothelial precursors in the avian a llantoic bud. When the prevascularized allantoic bud from a quail embr yo was grafted in the coelom of a chicken host, hematopoietic and endo thelial cells later were found in the bone marrow of the host. Because the graft was located at a distance from the limb bud, these cells co uld reach the bone marrow only by the circulatory pathway. This blood- borne seeding may be accomplished by distinct hematopoietic and endoth elial precursors, or by hemangioblasts, the postulated common precurso rs of these two lineages; we consider the latter interpretation more l ikely. We also show by reverse transcription-PCR that the allantois re gion expresses very early tile GATA genes involved in hematopoiesis an d some beta-globin chain genes.