Experimental production of siderocytes

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.

Ultrastructural study of the blood cells of the beluga whale, Delphinapterus leucas

General cytological and ultrastructural features of cells found in the peripheral blood of three captive beluga whales (Delphinapterus leucas) are described. We noted all major peripheral cell types common to the circulation of mammalian species, including polymorphonuclear neutrophils, eosinophils, basophils, lymphocytes, and monocytes, as well as myelocytes, erythroblasts, and plasma cells. Platelets and two populations (normal and hypochromic) of red blood corpuscles were observed.

A mathematical model of erythropoiesis in mice and rats. Part 1: Structure of the model

A mathematical model has been developed which describes the regulation of erythropoiesis in mice and rats. The main model assumptions are: (1) Regulation is mediated by erythropoietin (EPO). (2) The production of EPO depends exponentially on the tissue oxygen pressure (e.g. in the renal production sites). (3) There are sigmoidal dose-response curves relating the EPO concentration in the plasma to the mitotic activity of CFU-E and proliferative erythropoietic precursors. For maximum stimulation two to four additional mitoses may occur, while for an absent stimulus three to five mitoses may be omitted. (4) The normal precursor transit time of three to four days may be shortened by more than 50% during maximum stimulation. (5) The erythrocytes have a normal lifespan of 42-56 days, which may be reduced to 15-20 days under erythropoietic stimulation. Among these assumptions, the dose-response relationships between EPO and the mitotic activity of CFU-E and the proliferative erythropoietic precursors are the most important hypotheses of the model. This is the first of a series of three papers and gives a description of the mathematical formalism and the parameters used. In the subsequent papers computer simulations on erythropoietic stimulation and suppression are presented.

Pathologic Sideroblasts and Siderocytes Associated with Chloramphenicol Therapy in a Dog

Siderotic granules were recognized in blood erythrocytes from a male Boxer dog with suppurative prostatitis, cystitis and pyelonephritis that was being given high dosage chloramphenicol therapy. Siderotic inclusions were recognized in the cytoplasm of 96% of the rubricytes and metarubricytes in a bone marrow aspirate. Siderotic inclusions were numerous and in some cases formed a ring around the nucleus. This perinuclear location suggested that pathologic mitochondrial iron accumulation had occurred, resulting in the formation of "ringed" sideroblasts. The occurrence of pathologic sideroblasts was confirmed by electron microscopy. Blood siderocytes and bone marrow sideroblasts disappeared after cessation of chloramphenicol therapy.

Ferritin metabolism in reticulated-siderocytes

Reticulated-siderocytes (reticulocytes which contain siderotic granules), obtained from the circulation of pigs after vigorous phlebotomy, were incubated in vitro. A rapid disappearance of granules from the reticulocytes was observed over 24 hr. Simultaneously with the decrease in granules, soluble ferritin accumulated in the media and siderotic granules developed in monocytes. The disappearance of the granules from the reticulated-siderocytes was oxygen-dependent and the loss of granules and the accumulation of ferritin in the media were both prevented by the addition of cyanide or dinitrophenol. It is concluded that the ferritin aggregates in the granules of reticulated-siderocytes are dispersed intracellularly into soluble ferritin, that soluble ferritin is excreted from the cell, and that one or both of these steps is dependent upon oxidative metabolism. Blood monocytes are capable of taking up soluble ferritin from the media and converting this into siderotic granules. Thus, a reticulocyte to plasma to monocyte ferritin pathway has been described.