Golgi Information and Courses from MediaLab, Inc.

Although the nucleus has been extruded, the reticulocyte is still considered immature because it retains numerous organelles needed for hemoglobin production, such as ribosomes, mitochondria, and fragments of the Golgi apparatus. The reticulocyte is slightly larger (10 microns) than the mature erythrocyte. A reticulocyte normally remains in the bone marrow for one or two days before entering the circulation and its final 24 hours of maturation. The red cell is mature when hemoglobin production is complete and the organelles have disintegrated. Reticulocytes normally make up 0.5 - 1.5% of the peripheral blood red cells. They appear blue/gray on the Wright's stained smear. The residual RNA in the cytoplasm causes the blue/gray color. The terms, polychromasia or polychromatophilic, are used to describe these cells on a Wright's stained preparation. A supravital stain such as new methylene blue N or brilliant cresyl blue is used to stain reticulocytes for an actual count.

Several mutations of the HFE gene have been described. In the C282Y mutation, a base substitution leads to a change in the amino acid in position 282 from cysteine (C) to tyrosine (Y). The loss of the sulfhydryl-containing amino acid disrupts the tertiary structure of HFE so that it no longer binds to beta-2 microglobulin. Beta-2 microglobulin appears to act along with other proteins to chaperone the newly synthesized HFE out of the Golgi apparatus and to the cell surface where it can then bind to TfR. In the C282Y mutation, HFE remains in the Golgi, never making it to the cell surface. The result is that transferrin binding to TfR is enhanced and excessive amounts of iron enter the cells of the small intestine, liver, and other tissues. A second mutation, H63D, causes a histidine (H) residue in position 63 to be replaced by aspartic acid (D). The mechanism by which this mutation leads to increased iron uptake is less well understood when compared to the C282Y mutation. Unlike the C282Y mutation, the H63D mutation does not seem to affect the binding of beta-2 microglobulin and intracellular movement, since detectable concentrations of the mutated protein are found on cell membranes. Some researchers speculate that the H63D mutation affects the binding of proteins involved in iron regulation and uptake at the cell surface.A third mutation, S65C, leads to a serine-to-cysteine substitution in its associated protein. This mutation has been been found in some compound heterozygotes for C282Y or H63D, but is rarely associated with iron overload in HH.Additional mutations of HFE have been identified, but their clinical significance is unclear. Most laboratories performing molecular assays test for only the C282Y, H63D, and S65C mutations.