Studies on globin chain synthesis during hamster development.

Erythroid cells derived from the yolk-sac of the hamster embryos replicate in the embryonic circulation, actively synthesize hemoglobin, and are the dominant circulating erythroid cell through day 14 of gestation. Until day 11, at which time fetal liver rudiments appear, they are the only erythroid tissue present in the embryo. Because of their size (Fig. 1 and Table 1) they can be separated from erythrocytes produced by ontogenically later hemopoietic tissue (liver, spleen, bone marrow). The embryonic (three) and adult (three) globin chains of hamster hemoglobins separate cleanly by electrophoresis in polyacrylamide gel, (Fig. 2). This provides an advantage over mouse, whose x and z chains tend to co-migrate. During hamster embryonic development, yolk-sac erythroid cells first become available on day 7. Nine days later (birth), globin-chain ontogeny in the circulating blood is nearly complete (Fig. 3). When yolk-sac-derived erythroid cells are isolated at day 10 in gestation (prior to the appearance of fetal liver) and grown in culture for 3 days, changes in types of globin chains synthesized are identical to globin-chain ontogenic changes in vivo during gestational days 10 through 13 (Fig. 5). We conclude that the ontogenic "switch" of globin-gene expression in these erythroid cells is pre-programmed, and that the program is capable of full function despite a drastic change in cell environment from circulating blood to culture medium. The ability to study these primitive erythroid cells under the tightly controllable conditions of culture might facilitate acquisition of information on mechanisms of globin-gene ontogeny.