Secretory organelle biogenesis: Trichocyst formation in a ciliated protozoan

Abstract

By classical electron microscopy and immunoelectron microscopy, the biogenesis of trichocyst secretory granules has been followed in the ciliated protozoan Pseudomicrothorax dubius. The very early pre-trichocysts form by fusion of bristle-coated, electron-dense vesicles (dense vesicles) with electron-translucent vesicles (clear vesicles), both of which originate in a well-developed trans-Golgi network (TGN). The pre-trichocyst grows by further fusion with dense and clear vesicles as well as with other pre-trichocysts until it reaches its maximum diameter of about 2 μm. Dense and clear vesicle formation from the TGN has been followed, and the fusion sequence of dense vesicles with the pre-trichocyst has been documented. The contents of the dense vesicles are the precursors of the trichocyst tip, which is composed of four arm-like rods, whereas the shaft precursors are supplied by the clear vesicles. The first evidence of trichocyst shaft formation is the appearance of a paracrystalline, dense core condensation center in the pre-trichocyst. Following shaft formation, the trichocyst tip forms by fusion and condensation of the dense arm precursors along each of the four sides of the shaft. Docking of the fully formed trichocyst in the cell cortex is described. Pre-trichocyst biogenesis in cells grown with and without Se is compared

Trichocysts—Paramecium's Projectile‐like Secretory Organelles

“…Again, similar observations are reported from P. dubius (Peck et al. ) and, thus, may be a general rule. That crystallization fails in docking‐defective Paramecium mutants underscores its relevance for biogenesis and maturation to docking‐competence (Pouphile et al.…”

“…Similar details have been reported for Pseudomicrothorax dubius (Peck et al. ). In a transcriptome analysis after depleting Paramecium cells of trichocysts by AED stimulation (Fig.…”

“…Their involvement in pretrichocyst formation is supported by ultrastructural evidence from P. dubius where vesicles with clear and dense contents fuse to finally form mature trichocysts (Peck et al. ). Whether bristle‐coated vesicles would also transport lysosome‐like constituents to trichocysts (as outlined below) remains unclear.…”

Tetrahymena thermophila: A divergent perspective on membrane traffic

“…Our recent data, combined with insights from studies in Paramecium (de Loubresse, ; Vayssié et al, ) and another Ciliate, Pseudomicrothorax dubius (Peck et al, ), suggest that the two classes of mucocyst proteins are transported by different mechanisms. The first depends on the aggregation of core components, and is responsible for delivery of Grl proteins, while the second depends on classical receptor‐mediated sorting of Grt proteins.…”

Secretory proteins in a ciliate cell: Identification of epitopes common to numerous polypeptides

“…Ejectable trichocysts are synthesized only when P dubius is grown with the trace element selenium [32]. Grown without selenium, cells may have pretrichocysts and non-ejectable trichocysts, but never ejectable trichocysts [11,35]. The trichocyst of P dubius is characterized by a shaft and four arms [15,31] and contains more than 40 proteins and glycoproteins [9].…”