Immunocytochemical analysis of trichocyst structure and development inParamecium

The structure and development ofParamecium multimicronucleatum trichocysts have been analyzed using a trichocyst core-specific monoclonal antibody (MAb) and indirect immunogold labeling on LR-Gold-embedded as well as on fixed, frozen, and cryosectioned material. The resting trichocyst body consistently shows a stain-free 150-nm-wide cortical region and a positively reacting core. Neither the cap nor the paracrystalline core of the tip is labeled. During trichocyst morphogenesis small immunogold-positive vesicles fuse to form larger vacuoles. A paracrystalline core forms within the vacuole matrix. The label becomes progressively concentrated within this core and, ultimately, is restricted entirely to the core. The trichocyst mutants ofParamecium tetraurelia, st A, tam 8, pt A¹, andft A³, show an almost unaltered trichocyst body with the same staining properties as wild-type trichocysts. These mutations affect mainly the structure and location of the trichocyst tip. In the trichlesstl mutant the contents of small cytoplasmic vesicles crossreact with the MAb.