Embryonic hemoglobin
Embryonic hemoglobins are the first protein complexes of the red blood pigment hemoglobin that appear in an early ontogenetic development phase during the embryonic period . They are formed in nucleated large blood-forming cells ( erythroblasts ) within the blood islands of the yolk sac or mesoblast , located in the part of the germ that supplies and surrounds the embryo .
| ζ chains | α chains | |
| ε chains | Hb Gower-1 | Hb Gower-2 |
| γ chains | Hb Portland-1 | HbF |
| β chains | Hb Portland-2 | HbA |
| δ chains | HbA 2 |
The embryonic hemoglobins are also tetrameric and consist of two pairs of subunits. Their globins differ in their protein content through episolon (ε) and zeta (ζ) chains, however, from later-formed fetal hemoglobin (HbF: α 2 γ 2 ) and adult hemoglobins (HbA (1) : α 2 β 2 or HbA 2 : α 2 δ 2 ). The embryonic hemoglobin formed primarily contains two zeta and two epsilon chains and is called Hb Gower-1 (ζ 2 ε 2 ) in humans . In addition, there are also variants in which zeta chains are replaced by alpha- or epsilon by gamma- or beta-chains: Hb Gower-2 (α 2 ε 2 ), Hb Portland-1 (ζ 2 γ 2 ) and Hb Portland-2 (ζ 2 β 2 ).
Embryonic hemoglobins characterize the (mesoblastic) phase of erythropoiesis in extraembryonic blood islands. Towards the end of the embryonic period, red blood cells are also formed intraembryonically, while blood formation predominates in the liver and spleen during the fetal period . The fetal hemoglobin (HbF) is characteristic of this (hepatolienal) phase and its amount increases accordingly. Therefore, the percentage of embryonic hemoglobins drops rapidly to a low level; this can be delayed in the case of chromosomal defects. Before birth, the (medullary) phase of blood formation in the bone marrow begins , with which adult hemoglobins (such as HbA) are made available.
Occasionally the abbreviation “HbE” is used for an embryonic hemoglobin. But HbE is also the abbreviation for hemoglobin E - a mutant of adult hemoglobin with two alpha and two beta chains in which one amino acid is exchanged for another - or the associated form of hemoglobinopathy .
Individual evidence
- ↑ He Z, Russell JE: Expression, purification, and characterization of human hemoglobins Gower-1 (zeta (2) epsilon (2)), Gower-2 (alpha (2) epsilon (2)), and Portland-2 (zeta (2) beta (2)) assembled in complex transgenic-knockout mice . In: Blood . 97, No. 4, February 2001, pp. 1099-105. doi : 10.1182 / blood.V97.4.1099 . PMID 11159543 .
- ↑ Al-Mufti R, Hambley H, Farzaneh F, Nicolaides KH: Fetal and embryonic hemoglobins in erythroblasts of chromosomally normal and abnormal fetuses at 10-40 weeks of gestation . In: Haematologica . 85, No. 7, July 2000, pp. 690-3. PMID 10897119 .