Some factors associated with a developmental change in hemoglobin components in early fetal mice

Lethal alpha-thalassaemia created by gene targeting in mice and its genetic rescue

Mutations at the alpha-globin locus are the most common class of mutations in humans, with deletion of all four adult alpha-globin genes resulting in the perinatal lethal condition haemoglobin Barts hydrops fetalis. Using gene targeting in mice, we have deleted a 16 kilobase region encompassing both adult alpha-globin genes. Animals homozygous for this deletion become hydropic and die late in gestation mimicking humans with hydrops fetalis. Introduction of a human alpha-globin transgene rescued these animals from perinatal death thus demonstrating the utility of this murine model in the development of cellular and gene based approaches for treating this human genetic disease.

Abelson virus drives the differentiation of Harvey virus-infected erythroid cells

Abelson murine leukemia virus (A-MuLV) and Harvey murine sarcoma virus (Ha-MSV) are retroviruses carrying unrelated onc genes. However, both of these viruses are capable of stimulating the growth and differentiation of erythroid precursor cells; the target cells for both appear at the same time during fetal development and follow a similar pattern throughout ontogeny. In addition, the colonies induced by each virus are morphologically similar and synthesize the adult form of hemoglobin. However, A-MuLV-infected cells are Epo-independent, whereas Ha-MSV-infected cells are Epo-dependent. Superinfection of Ha-MSV-infected cells with A-MuLV overrides their Epo-dependency. Thus, the consequences of the infection are determined by the interaction of the different onc gene products with identical or similar erythroid cells.

Proportion of fetal hemoglobin synthesis decreases during erythroid cell maturation

Peripheral blood mononuclear cells from pregnant and postpartum women were cultured in vitro with erythropoietin. Burst-forming unit (BFU-E)-derived erythroid colonies composed of immature erythroblasts with low hemoglobin contents were observed by day 8 of culture. By day 12 of culture, numerous BFU-E-derived erythroid colonies with high hemoglobin contents were present. The gamma/(gamma + beta) globin synthetic ratio was approximately 12% in the early cultures and 6% in the late cultures, indicating that the proportion of fetal hemoglobin synthesis decreases during erythroid cell maturation. These studies also reveal that the capacity fof fetal hemoglobin production by peripheral blood BFU-E in vitro is not altered during pregnancy.

Fetal hemoglobin variants in mice

Two strains of mice, DBA and C3H, have a fetal globin polypeptide chain which differs in electrophoretic mobility from the corresponding fetal chain of the C57B1 strain. Mice of the DBA and C3H strains also differ from those of the C57B1 in adult hemoglobin type. Results of backcrossing the (DBA x C57B1) hybrid to the C57B1 suggest that the fetal chain locus and the adult beta-chain locus are closely linked.