Concanavalin A receptor 'tipping' in Tetrahymena and its relationship to cell adhesion during conjugation

Shortly after mixing cells of complementary mating types of Tetrahymena, the cells develop the ability to pair, a process inhibited by ConA, and the region joining the cells becomes ringed with ConA receptors. This study examines the arrival of ConA receptors at the conjugation junction by looking at cells in the period between mixing and pairing. By brief incubations with F-ConA at intervals after mixing, it was ascertained that some cells had fluorescent tips as early as 15min. A kinetic analysis revealed that 'tipping' occurs in a manner that appears to be related to subsequent cell pairing. Cytoskeletal frameworks (CFs) were isolated under conditions in which ConA receptors remain attached. Western blot analysis of these structures revealed four major and several minor ConA-binding proteins. However, between mixing and the establishment of over 80% paired cells, changes occurring in the banding pattern were slight. This indicates that new populations of ConA receptors are not produced to any great extent after mixing. Head- on examination of CFs showed that it was possible to monitor simultaneously the process of tip transformation (widening of the nonciliated area of the tip) and ConA-receptor localization. ConA receptors originate posterior to the tip, begin to occupy the surface of the tip in clusters as the tip widens and eventually coat the transformed tip. Finally, as cells join pairs, the receptors relocate to a ring around the conjugation junction. These data suggest that ConA receptors accumulate at the anterior tips and then concentrate at the edge of the junction. This could provide a mechanism for controlling cell-cell adhesion.
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