Hemosomegenesis and hemoglobin biosynthesis in vertebrates

Immunocytochemical mapping of the hemoglobin biosynthesis site in amphibian erythroid cells

During the past 25 years, several studies have attempted to determine the site of integration of the heme and the four globin chains in vertebrate erythroid cells that is important in the formation of the hemoglobin molecule. Mitochondrion-like organelles or hemosomes were pointed out as responsible for this task. We performed several experiments to investigate this hypothesis. The intracellular distribution of hemoglobin in amphibian erythroid cells was detected by post-embedding immuno-electron microscopy, using a polyclonal anti-human hemoglobin-proteinA-gold complex. Hemoglobin mapping showed an intense labeling in the cell cytoplasm, but none in cytoplasmic structures such as endoplasmic reticulum, mitochondria, mitochondrion-like organelles, Golgi complex, ribosomes or ferruginous inclusions. The mitochondrial fraction obtained according to the protocol described for some authors, showed by ultrastructural examination that this fraction has a heterogeneous content, also composed by microvesicles rich in cytoplasmic hemoglobin, an artifact generated by mechanical action during cell fractionation. Thus, when this fraction is lysed and its content submitted to electrophoresis, hemoglobin bands would be found inevitably, causing false-positive results, erroneously attributed to hemoglobin content of mitochondrion-like organelles. Our data do not confirm the hypothesis that the final hemoglobin biosynthesis occurs inside mitochondrion-like organelles. They suggest that the hemoglobin molecule be assembled in the erythrocyte cytoplasm outside of mitochondria or hemosomes.

Hematological response in fish: pronephric and splenic involvements in the goldfish,Carassius auratus L

Pronephric and splenic involvements in erythropoiesis and in stress-induced hematological response by goldfish,Carassius auratus, were examined under conditions of minimal stress and following transient (3h) temperature-induced elevation of O2 demand and transient (3h) exposure to hypoxia. Although hemoglobin content and red cell numbers were little affected, the ontogenic composition of the circulating erythrocyte population was significantly altered by both types of respiratory challenge and also by the stresses associated with capture, air exposure during transfer and intraperitoneal administration of label. Juvenile cell numbers increased sharply while mature erythrocyte abundances declined. Consistent with this, [(3)H] methylthymidine-labeled cell numbers rose in both spleen and pronephros following imposition of stress. Splenic erythropoietic activity was modest relative to that of the pronephros. Our observations point to a readily triggered response involving: [1] release of cells reservoired in the spleen and pronephros, [2] increased erythropoiesis and [3] karyorrhexis. We suggest that while the magnitude of response may depend on the quality and magnitude of the imposed stress, its central features are essentially constant.

The nature of hematological response in fish : Studies on rainbow troutOncorhynchus mykiss exposed to simulated winter, spring and summer conditions

Hematological status was examined in rainbow trout,Oncorhynchus mykiss, held for 3-4 weeks under temperature, photoperiod and PO 2 conditions approximating those of their winter, spring and summer habitats. The most striking change observed was in red cell population composition. In 'winter' fish mature cells were predominant; juvenile and developing erythrocytes characterized 'spring' and 'summer' animals. Hemoglobin, hematocrit and both mean erythrocytic volume and hemoglobin were modestly lower in 'spring' and 'summer' than in 'winter' fish. Red cell numbers were not significantly affected. These observations suggest that avoidance of viscosity-based increases in circulatory work cost is more advantageous than elevation of blood O2-carrying capacity. Although hemoglobin isomorph profiles were significantly altered, there is little evidence that such changes are of critical adaptive importance. Given presumed age-based reduction in gas transport effectiveness, the replacement of mature and senescent cells by more metabolically-competent juvenile cells appears to be the pivotal event in hematological response. Leucocyte counts were significantly elevated in 'spring' and 'summer' as compared to 'winter' fish. Lymphocyte/heterophil ratios declined from 8.27 in 'winter' fish to 3.13 in 'summer' trout. Thrombocyte, monocyte, eosinophil and basophil abundances were little changed.