Disturbed haem and globin synthesis in reticulocytes of prenatal flexed-tailed (f-f) anaemic mice

Deep coverage mouse red blood cell proteome: a first comparison with the human red blood cell

Mice have close genetic/physiological relationships to humans, breed rapidly, and can be genetically modified, making them the most used mammal in biomedical research. Because the red blood cell (RBC) is the sole gas transporter in vertebrates, diseases of the RBC are frequently severe; much research has therefore focused on RBC and cardiovascular disorders of mouse and humans. RBCs also host malaria parasites. Recently we presented an in-depth proteome for the human RBC. Here we present directly comparable data for the mouse RBC as membrane-only, soluble-only, and combined membrane-bound/soluble proteomes (comprising, respectively, 247, 232, and 165 proteins). All proteins were identified, validated, and categorized in terms of subcellular localization, protein family, and function, and in comparison with the human RBC, were classified as orthologs, family-related, or unique. Splice isoforms were identified, and polypeptides migrating with anomalous apparent molecular weights were grouped into putatively ubiquitinated or partially degraded complexes. Overall there was close concordance between mouse and human proteomes, confirming the unexpected RBC complexity. Several novel findings in the human proteome have been confirmed here. This comparison sheds light on several open issues in RBC biology and provides a departure point for more comprehensive understanding of RBC function.

A mutation in a mitochondrial transmembrane protein is responsible for the pleiotropic hematological and skeletal phenotype of flexed-tail (f/f) mice

We have studied the flexed-tail (f) mouse to gain insight into mammalian mitochondrial iron metabolism. Flexed-tail animals have axial skeletal abnormalities and a transient embryonic and neonatal anemia characterized by pathologic intramitochondrial iron deposits in erythrocytes. Mitochondrial iron accumulation is the hallmark of sideroblastic anemias, which typically result from defects in heme biosynthesis or other pathways that lead to abnormal erythroid mitochondrial iron utilization. To clone the f gene, we used positional cloning techniques, and identified a frameshift mutation in a mitochondrial transmembrane protein. The mutated gene, Sfxn1, is the prototype of a novel family of evolutionarily conserved proteins present in eukaryotes.

Unequal alpha and beta globin mRNA in reticulocytes of normal and mutant f/f fetal mice

Messenger RNA (mRNA) was isolated from adult as well as normal and mutant f/f fetal mouse reticulocytes by poly-U affinity chromatography. mRNA from normal adult reticulocytes directed equal synthesis of alpha and beta globin chains in wheat germ cell free translational system. mRNA from either normal or mutant f/f fetal reticulocytes directed 40% more alpha globin synthesis than beta globin synthesis. These observations are suggestive that there is significantly more alpha mRNA than beta mRNA in normal and mutant f/f fetal mouse reticulocytes.

Haemopoietic progenitor cells in prenatal congenitally anaemic 'flexed-tailed' (f/f) mice

The incidences of erythroid colony forming cells (CFUe) and granulocyte-macrophage colony forming cells (CFUc) have been measured in 11-18 d prenatal livers of mice of genotype f/f and nearly congenic +/+ controls. In normal fetal livers numbers of CFUe (cells able to form colonies of 16 or more cells after 72 h in vitro) rise to a maximum on day 14 of gestation and represent c 1% of total fetal liver cells. In f/f fetal livers, peak values for numbers and proportions of CFUe are 50% of normal. The f/f lesion does not reduce the numbers of CFUc in fetal liver. Since this deficiency in CFUe parallels deficiencies of similar magnitude in spleen-colony forming units (CFUs) and erythroblasts in the liver, and erythrocytes in the blood, of f/f fetuses it is concluded that the f/f lesion is expressed at an early stage of haemopoietic development in prenatal life. The possibility that restricted haem synthesis is the primary effect of the f/f genotype and responsible for disturbances of both haemopoietic cellular proliferation and haemoglobin synthesis is examined.