Regulatory Mechanisms of Erythrocyte Differentiation in the Early Embryonic Yolk Sac

Abstract

Regulatory mechanisms of primitive erythroid cell differenti-ation are discussed. Chick or quail yolk sac cells at the definitive primitive streak stage were the main experimental materials. An intact endodermal layer was required for formation of well developed blood islands. Yolk sac cells were dissociated into single cells then reaggregated by centrifugation or on a gyratory shaker. Vigorous blood island formation was observed in the reconstructed yolk sac tissue. In this system, erythroid precursors have been proved to be sorted out first and then to differentiate into blood islands. Dissociation of embryos before formation of the primitive streak interfered with the formation of blood islands. Yolk sac erythropoietic presursor cells are much more radioresistant than are adult hemopoietic cells. Formation of erythroblasts and hemoglobin synthesis were much enhanced after treatment with dimethylsulfoxide and other murine leukemia cell inducers. These experi-mental results are compared with results of recent studies from other labora-tories on erythroid colony formation and on the induction of definitive erythro-cytes in yolk sac cells in organ culture.