Genetic aspects of intracellular motility: cortical localization and insertion of trichocysts in Paramecium tetraurelia.

Wild-type and selected mutants of Paramecium tetraurelia were subjected to detailed analysis of the trichocyst phenotype. The characteristics of morphology, saltatory motility, and cortical insertion of trichocysts were found to be genetically distinguishable. In mutants with defective trichocyst saltatory motility, other intracellular motility systems (i.e. mitochondrial saltatory motility, and cyclosis) appeared to be unaffected. Saltatory motility appears to be an essential intermediate step in the functional development of the trichocyst, since it serves to transport the trichocyst from its site of assembly, deep in the cytoplasm, to the cortex, where it is inserted and becomes discharge-competent. If trichocyst saltatory motility is lost, as in the mutants ndA and tam8, then trichocysts are not transported to the cortex and are therefore not inserted. However, the successful transport of a trichocyst to the cortex does not guarantee the proper insertion of that trichocyst, as in the case of the mutant am. Apparently there are independent steps involved specifically with trichocyst insertion. The gross morphology of the trichocyst appears to be independent of its saltatory motility, and to a degree, independent of cortical insertion.