Journal of Cell Science, Vol 92, 205-215, Copyright © 1989 by Company of Biologists

Submitted on July 19, 1988
Accepted on October 28, 1988

Uneven Distribution of Surface Antigens During Antigenic Variation in Paramecium Primaurelia

¹ Centre de Génétique Moléculaire, CNRS, F-91190 Gif-sur-Yvette, France; European Molecular Biology Laboratory, Postfach 10.2209, D6900 Heidelberg, FRG
² Centre de Génétique Moléculaire, CNRS, F-91190 Gif-sur-Yvette, France

In Paramecium primaurelia surface antigen (SAg) expression can be experimentally controlled by temperature-shift-induced antigenic variation. As only one SAg is usually expressed at the cell surface under stable environmental conditions, we used the temperature-shift-induced change in SAg to follow the newly expressed antigen and the disappearing one, by both immunofluorescence and immunogold electron microscopy. The new SAg initially appeared scattered at the cell surface, over the ciliary and interciliary membrane domains, without any readily identifiable specific site of insertion into the plasma membrane. The concentration of the newly incorporated molecules then increased gradually on the plasma membrane. In contrast, the surface of the previously expressed SAg was not complementary to the pattern of the appearing SAg. The loss of the old SAg is delayed after the temperature shift and seems to occur more suddenly the appearance of new SAg. This loss is characterized by a subpopulation of cilia bearing old SAg coexisting with other cilia and a pellicle almost devoid of the old SAg molecules. The topological distribution of the new and old SAgs is discussed in relation to the lipidic nature of the SAg anchor and to a possible role of an Paramecium phosphatidylinositol phospholipase C.

Key words: surface antigen, Paramecium, antigenic variation, membranes, immunoelectron microscopy

Submitted on July 19, 1988
Accepted on October 28, 1988