Trichocyst
From Palaeos
A type of ejectosome organelle producing hair like fibers for offensive and defensive purposes in Alveolata. A trichocyst is assembled as an elongate, spindle-shaped body which differentiates into an electron-dense cortex and a crystalline core. Vayssié et al. (2000). The trichocyst then docks with one of many specific sites on the cell membrane which show a characteristic double ring of 8 nm particles. When the trichocyst has docked (via a fibrous tube) with the double ring structure, a rosette of additional particles appears at the center of the double circle (in FFE preparations). Froissard et al. (2002). When an appropriate release stimulus is detected, the cell releases sequestered calcium ions into the cytoplasm which trigger rapid release of the trichocyst contents into the medium. Erxleben & Plattner (1994). The mechanism in Alveolata shares many important molecular details and protein homologies with the formation of secretory granules in Metazoa. Burgoyne & Morgan (2003).
[edit] References
Burgoyne, RD & A Morgan (2003), Secretory granule exocytosis. Physiol. Rev. 83: 581–632.
Erxleben, C & H Plattner (1994), Ca2+ release from subplasmalemmal stores as a primary event during exocytosis in Paramecium cells. J. Cell Biol. 127: 935-945.
Froissard, M, R Kissmehl, J-C Dedieu, T Gulik-Krzywicki, H Plattner, & J Cohen (2002), N-ethylmaleimide-sensitive factor is required to organize functional exocytotic microdomains in Paramecium. Genetics 161: 643-650.
Vayssié, L, N Garreau de Loubresse & L Sperling (2000), Growth and form of secretory granules involves stepwise assembly but not differential sorting of a family of secretory proteins in Paramecium. J. Cell Sci. 114: 875-886.
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