Observations of the marginal band system of nucleated erythrocytes.

Abstract

The marginal band (MB) of nucleated erythrocytes (those of nonmammalian vertebrates) is a continuous peripheral bundle of microtubules normally obscured by Hb. Treatment of these elliptical cells with modified microtubule polymerization media containing Triton X-100 yields a semilysed system in which MB, nucleus and trans-MB material (TBM) are visible under phase contrast. The TBM apparently interconnects structural components, passing around opposite sides of the nucleus and suspending it in native position. In uranyl acetate-stained whole mounts (goldfish) examined by transmission electron microscopy, the TBM appears as a network. MB of semilysed cells are relatively planar initially, but twist subsequently into a range of figure-8 shapes with 1 of the 2 possible mirror-image configurations predominant. Nuclei and MB can be released using proteolytic enzymes, to which the TBM seems most rapidly vulnerable. MB thus freed are birefringent, generally untwisted, and much more circular than they are in situ. The flattened, elliptical shape of nucleated erythrocytes may be a result of TBM tension applied asymmetrically across an otherwise more circular MB, and the figure-8 configuration may occur when there is extreme TBM shrinkage or contraction.