Early encounters of the repetitive kind: a prelude to cell adhesion in conjugating Tetrahymena thermophila.
The relationship between direct cell contacts and subsequent cell-cell adhesion was studied in the ciliated protozoan, Tetrahymena thermophila. During sexual reproduction, adhesion into pairs begins at approximately 1 hr after mixing starved complementary mating types. However, direct contacts between cells prior to pairing are known to be required for the development of adhesion-readiness. We find here that the initial contact interactions are necessary but not sufficient to drive the cells to adhesion-readiness. Secondary interactions are needed. Two distinct experimental strategies were used. First, we examined the effects of a mutant that is unable to pair but which can stimulate two different wild-type mating type cells to pair when mixed. We showed that stimulation by the mutant is only partial; in response to mutant cells, wild-type cells ceased forming food vacuoles but did not undergo tip transformation or concanavalin A (Con A)-receptor tipping. Further, kinetic analysis shows that when mixed together, pair-formation among partially stimulated wild-type cells is slightly delayed, allowing time for these pre-pairing processes to occur. This indicates that, beyond the initial contact interaction, mutant-stimulated wild-type cells require a subsequent interaction which cannot be fulfilled by the mutants. Secondly, we found that by blocking contact interactions between wild-type mating types at various time intervals after they were mixed, additional increase in tip transformation and Con A receptor tipping was prevented. Further, both processes underwent a regression. This indicates that multiple contact interactions are required to drive the cells to adhesion readiness and to prevent developmental slip-back.
Brown
F
F
Biology Dept., Wesleyan University, Middletown, Connecticut 06459.
Tirone
S
S
Wolfe
J
J
D000818:Animals; D002448:Cell Adhesion / Q000502:physiology*; D002478:Cells, Cultured; D008856:Microscopy, Fluorescence; D009154:Mutation; D011952:Receptors, Concanavalin A / Q000032:analysis; D012098:Reproduction / Q000502:physiology; D016808:Tetrahymena thermophila / Q000166:cytology / Q000502:physiology* / Q000648:ultrastructure
D011952:Receptors, Concanavalin A