The Journal of Cell Biology, Vol 79, 235-251, Copyright © 1978 by The Rockefeller University Press
Nonuniform distribution of concanavalin-A receptors and surface antigens on uropod-forming thymocytes
S de Petris
Uropods can form spontaneously in a variable fraction of mouse thymocytes
incubated for 30--60 min in vitro at temperatures between about 8 degrees
and 37 degrees C. The majority of the cells with a typical uropod are
medium and large thymocytes. The "normal" distribution of concanavalin-A
receptors and antigens recognized by a rabbit anti-mouse thymocyte serum
was studied on these cells by electron microscopy using ferritin-conjugated
lectin or antibodies. The cells were fixed with glutaraldehyde or
formaldehyde before labeling. The distribution was essentially uniform on
spherical cells. On the contrary, on cells which had formed a uropod the
labeled receptors and antigens appeared to be preferentially concentrated
around the nucleus, and depleted over the uropod, and especially over the
constriction at the base of the uropod. Uropod formation and inhomogeneous
distribution were inhibited or reversed by cytochalasin B, but not by
vinblastine or colchicine. When the same ligands were applied to unfixed
cells, the labeled and cross-linked components capped normally towards the
cytoplasmic pole of the cell. These observations are described in relation
to the ability of receptors and antigens to interact with an intracellular
mechanical structure, and to the mechanism of capping.
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