Embryonic hemoglobins are expressed in definitive cells

Area of Science:

• Hematology
• Developmental Biology
• Molecular Genetics

Background:

• Human embryonic globin chains, zeta and epsilon, are primarily synthesized in primitive erythroid cells derived from the yolk sac.
• These embryonic globins typically decrease rapidly during the transition to definitive erythropoiesis.

Purpose of the Study:

• To investigate the cellular expression of embryonic zeta and epsilon globin chains in definitive erythroid cells.
• To determine if embryonic globin synthesis persists in definitive erythropoiesis and how its expression changes with developmental age.

Main Methods:

• Dual-color immunofluorescence staining using specific monoclonal antibodies to detect zeta and epsilon globin proteins.
• Analysis of globin expression in erythrocytes and erythroblasts from fetal, newborn, and adult humans.
• In vitro liquid culture of erythroblasts to assess embryonic globin content during ontogeny.

Main Results:

• Embryonic globin proteins (zeta and epsilon) were detected in definitive erythroid cells.
• Over 50% of fetal erythrocytes were positive for zeta globin, and about 5% for epsilon globin.
• Approximately one-third of newborn red blood cells showed zeta-positive staining, with less than 1% for epsilon globin; adult erythrocytes lacked embryonic globins.
• Embryonic globin levels in cultured erythroblasts declined with ontogenic age, and in vitro expression was lower than in vivo.

Conclusions:

• Embryonic globin chains are synthesized within definitive erythroid cells, not exclusively in primitive ones.
• The decrease in embryonic globin expression during development is a gradual process that extends beyond the switch from primitive to definitive erythropoiesis.
• Modulation of embryonic globin gene expression involves regulatory mechanisms beyond a simple switch in erythropoiesis lineage.