The globin gene expression program in the hamster embryo.

Molecular mechanisms involved in control of globin gene expression are a prominent target in current basic biologic research. A better understanding of these mechanisms might also impinge on a clinical goal: amelioration of the human hemoglobinopathies. Recent reports have established the coexistence of embryonic and adult globins in rodent yolk-sac erythroid cells, raising the possibility that globin ontogeny takes place in these cells. The present study was undertaken to define the extent of this putative ontogenic process. We measured daily rates of synthesis of individual globins in hamster yolk-sac erythroid cells from the earliest day in gestation that these cells are available (day 7) until the day they cease to replicate (day 13). Converted to a per-cell basis, the rates demonstrate an ontogenic progression in globin synthesis, from embryonic globins to adult globins, that encompasses nearly entirely the total globin ontogeny of this mammal. Synthesis of adult alpha globin is already detectable on day 7, whereas synthesis of the two adult beta globins does not appear until day 9. Synthesis of embryonic y globin stands in contrast to that of the other two embryonic globins (x and z), rising as they fall, a phenomenon reminiscent of the gamma globin of primates and certain ruminants. This physiologic primitive erythroid cell appears to be an unusually appropriate target for studies directed at globin ontogeny.