epsilonglobin

Epsilonglobin, also known as epsilon globin, is a globin chain that is expressed during early embryonic development in humans and other vertebrates. It is encoded by the HBE1 gene and contributes to the composition of embryonic hemoglobins, forming tetrameric proteins that help transport oxygen in the developing embryo.

In humans, the HBE1 gene lies within the beta-like globin gene cluster on chromosome 11. Epsilon globin is predominantly produced in the yolk sac during early gestation and is progressively downregulated as fetal and adult globin genes become active. By late fetal life and after birth, epsilon-globin expression is minimal or absent in healthy individuals, though trace production can persist in some contexts.

Biochemically, epsilon globin partners with other globin chains to form embryonic hemoglobins. Notable combinations include alpha2epsilon2 in Hb Gower I and zeta2epsilon2 in Hb Portland, which contribute to the oxygen-transport capabilities of the embryonic circulatory system before fetal and adult hemoglobins predominate.

Regulation of epsilon-globin expression involves the global regulatory architecture of the beta-globin cluster, including locus control region elements and stage-specific transcription factors that orchestrate the switch from embryonic to fetal and adult globin gene expression. The epsilon gene is considered among the earliest beta-like globin genes to be expressed in development, with its activity largely silenced as part of normal maturation.

Clinical relevance is limited but not negligible; epsilon-thalassemia and related disruptions of HBE1 are rare and usually have mild or variable hematologic effects compared with other globin disorders. Epsilon-globins are also of interest in comparative genomics and evolutionary studies of hemoglobin gene clusters.